Global Climate Change: A Threat to Aphid Populations

Contents Foreword Preface About the Editors About the Contributors

Part I Insects and Climate Change

1 Integrated Crop and Pest Management Practices in Relation to

Global Climate Change

D. Prasad and C. Chattopadhyay

2 Impact of Climate Change on Insect Pests Management in Fruit Crops

Kuldeep Srivastava, Alok Kumar Gupta and Devinder Sharma

3 Global Climate Change: A Threat to Aphids Population

Navodita G. Maurice, P.W. Ramteke, Pradeep K. Shukla and Suchit A. John

4 Host Plant Responses to Tetranychus urticae Koch Mediated Biotic Stress and Management Strategies

Kanika, Rachna Gulati and Monika Geroh

5 Insect Pest Management in Climate Change

Subhash Chander, Mazhar Husain and Vishwa Pal

6 Comprehensive Impact of Climate Change on Insects and Insect Plant Interaction

G. K. Sujayanand, T. V. Prasad, Zakaullah Khan and S. Sheelamary

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7 Climate Change and Dynamics of Insect Pests: Management Options in Tobacco

U. Sreedhar

8 Pest Scenario, Plant Protection Approaches in the Current Context of Changing Climate

H. R. Sardana and M.N. Bhat

9 Climate Change: Pest Incidence in Agricultural Crops

Someshwar Bhagat, Ajanta Birah, N. Chattopadhyay and C. Chattopadhyay

Part II Plant Diseases and Climate Change

10 Climate Change Impact on Tropical Plant Diseases and Its

Management Strategies

A. Kandan, Jameel Akhtar, Baleshwar Singh, Zakaullah Khan, Anitha Pedapati and P. C. Agarwal

11 Hortipasture Ecosystem: Diseases and Management Strategies under Climate Change Scenario in Semi-arid Condition

H. V. Singh, Ritu Mawar, Sunil Kumar and R.V. Kumar

12 Occurrence of Mycotoxins under Changing Climatic Conditions

K. Kannan

13 Exploitation of Plant Genetic Resources for Crop Protection: On Climate Change Basis

Anitha Pedapati, Vandana Tyagi, Nidhi Verma, Satish Kumar Yadav and Prathiba Brahmi

14 Complex Interactions of Begomoviruses, Satellite Molecules and Whitefly Vector Associated With Cotton Leaf Curl Disease (CLCuD) Epidemic in Northwest India

Kajal K Biswas, Shruti Godara, Utpal K Bhattacharyya and Pranjib K. Chakraborty

15 Physiological Bases of Crop Response to Changing Climate

S. Jidhu Vaishnavi, M. Djanaguiraman and P. Jeyakumar

16 Ecofriendly Management of Tea Diseases in Current Scenario of Climate Change

Pranab Dutta, Himadri Kaushik, K.C. Puzari and R.P. Bhuyan

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Part III Nematodes and Climate Change

17 Influence of Climate Change on Predatory Soil Nematodes in

Management of Plant Parasitic Nematodes

Zakaullah Khan, Bharat Gawade, A. Kandan, Jameel Akhtar and T.V. Prasad

18 Impact of Climate Change on Nematode Population

Archana U Singh and D. Prasad

19 Multitropic Interaction with Nematodes and Climate Change

Anju Kamra and B.K. Vinay

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Index

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C. Chattopadhyay and D. Prasad (eds), Dynamics of Crop Protection and Climate Change © Studera Press 2016

Global Climate Change: A Threat to Aphids Population

Navodita G. Maurice, P.W. Ramteke, Pradeep K. Shukla

and Suchit A. John Global Climate Change We are now threatened by self-inflicted, swiftly moving environmental shifts whose long-term biological and ecological consequences result in the depletion of the protective ozone layer, global warming observed in the last 150 years, obliteration of an acre of forest every second, rapid-fire extinction of species and the prospect of a global nuclear war, which can threaten the survival of both plants and animals. There may be other such risks we are not aware of at present. Individually and cumulatively, these dangers designate the presence of a trap being set for human species. However, principled and lofty, the justifications may have been for the activities that brought forth these dangers, separately and taken together, they now imperil our species and many others. We are actually committing, what in religious language is sometimes called ‘Crimes against Creation’ (Drinkwater et al. 2009).

These assaults on the environment were not caused by any one generation but intrinsically, they are transnational, transgenerational and transideological, and escape from this global problem necessitates a perspective embracing all the peoples of the planet and all the generations yet to come. Problems of such magnitude and solutions must be recognized in context of both religious as well as a scientific dimension. Many scientists have been long engrossed in combating environmental crisis in order to preserve the environment of the earth. The short-term mitigations to these dangers include greater energy efficiency, rapid banning of chlorofluorocarbons or modest reductions in nuclear arsenals. The conversion from fossil fuels to a non-polluting energy economy, a continuing swift reversal of the nuclear arms race, and a voluntary halt to world population growth can help in renovation of earth’s environment. As with the issues of peace, human rights and social justice, religious institutions can be a

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strong force here, too, in encouraging national and international initiatives in both the private and public sectors, and in the diverse worlds of commerce, education, culture and mass communications (Dalrymple 1991) (Figure 3.1).

Figure 3.1 Effect of Climate Change on Environment.

The environmental crisis requires radical changes not only in public policy, but also in individual behaviour. The historical record makes clear that religious teaching, example and leadership are able to influence personal conduct and commitment powerfully. The efforts to safeguard and cherish the environment need to be infused with a vision of the sacred. The atmospheric concentration of CO2 is increasing at the alarming rates (1.9 ppm per year) in the recent years. The earth has warmed by 0.76°C (0.56 to 0.92) during last 100 years (1906 – 2005). Eleven of the last twelve years (1995 -2006) rank among the 12 warmest years recorded in the past 100 years. A lot more intense and longer droughts observed over wider areas since the 1970s, in the tropics and subtropics. The frequency of heavy precipitation events has increased over most of the land surface. Significantly increased rainfall has been observed in the Eastern parts of North and South America, Northern Europe and Northern and Central Asia. Drying has been observed in the Sahel, the Mediterranean, Southern Africa and parts of the Southern Asia. Average Arctic temperatures increased at almost twice the Global average rate in the past 100 years (Dalrymple 1991; Harrison et al. 2002).

Cold days, Cold nights and frost have become less frequent, while hot days, hot nights and heat waves have become more frequent. Mountain glaciers and snow cover

Maurice, Ramteke, Shukla and John | 63

have declined on average in both Southern and Northern Hemispheres. The maximum area covered by seasonally frozen ground has decreased by about 7% in the Northern Hemisphere since 1900, with a decrease in spring of up to 15%. Increase of intense tropical cyclone activity in the Northern Atlantic since 1970s; also in some other regions (because of reliability and quality of data) is greater. There is no clear trend in the annual numbers of tropical cyclones. The Fourth Assessment Report of Intergovernmental Panel on Climate Change, IPCC (2007) concluded “There is high confidence that the recent regional changes in temperature have had discernible impacts on many physical and biological systems”.

Within the next 25-30 years, the world’s population will increase to nearly 8 billion people. All of that increase will occur in the developing countries. The overwhelming majority of undernourished people live in Asia and Pacific. During seasonal food shortages and in times of famine and social unrest, the number of undernourished people increases. Nearly 13 million children under 5 years of age die every year from preventable diseases and infections such as measles, diarrhoea, malaria and pneumonia or from some combination of these. According to some estimate, malnutrition is a factor in one-third of these cases (UNICEF 1989) (Table 3.1, Figure 3.2). Climatic Changes Scenario for India Twenty five million more children will suffer from malnutrition by 2050 due to the effects of climate change, and India will be one of the worst affected in the Asian region, a report by International Food Policy Research Institute (IFPRI) claims. Table 3.1 Trends in the Use of Cereal as Animal Feed

(Million metric tons)

Region 1983 1993 1997 2020 (**) China 40-49 78-84 91-111 226 India 2 3 2 4 South East Asia 6 12 15 28 Latin America 40 55 58 101 Sub-Saharan Africa 2 3 4 8 Developing World 128 194 235 444 Developed World 465 442 425 511 WORLD 592 636 660 954

Source: Calculated from Data in FAO 2000 ** The 2020 projections are from the July 2002 version of the IMPACT model


Figure 3.2 Effect of Climate Change on Human Health Temperature An annual mean area averaged surface warming over the Indian subcontinent to range between 3.5°C and 5.5°C over the region by the 2080s (Ramakrishna et al. 2003). These projections showed more warming in winter season over summer monsoon. The spatial distribution of surface warming suggests a mean annual rise in temperatures in north India by 3°C or more by 2050. During winter, the surface mean air temperature could rise by 3°C in northern and central parts, while it would rise by 2°C in southern parts by 2050. Over the Indian region, the warming will be restricted to 1.4 +/- 0.3°C in the 2020s; 2.5±0.4°C in the 2050s and 3.8±0.5°C in the 2080s (Table 3.2). Table 3.2 Climate Change Scenario for India

Year Season Increase in temperature (°C) Change in Rainfall

Lowest Highest Lowest Highest

2020s Rabi 1.08 1.54 -1.95 4.36 Kharif 0.87 1.12 1.81 5.10

2050s Rabi 2.54 3.18 -9.22 3.82 Kharif 1.81 2.37 7.18 10.52

2080s Rabi 4.14 6.31 -24.83 -4.50 Kharif 2.91 4.62 10.10 15.18

Effect on Monsoon India will experience a declination in summer rainfall by the 2050s. Since summer rainfall


accounts for almost 70% of the total annual rainfall over India and is crucial for Indian agriculture, this could have a demoralizing effect on the Indian economy and on food security. Fall in rainfall by 5 to 25% in winter, while it would be 10 to 15% increase in summer monsoon rainfall over the country. It was also reported that the date of onset of summer monsoon over India could become more variable in future (Huntley 2007). Effect on Agricultural Production Recent Intergovernmental Panel on Climate Change (IPCC) report and a few other studies specify a probability of 10 to 40% loss in crop production in India with increase in temperature by the end of this century due to global warming. Higher temperatures reduce the total duration of a crop cycle by reducing early flowering, thus, shortening the ‘grain fill’ period. In north India, for instance, a temperature rise of 0.5°C could lessen wheat yield due to heat stress by about 10% if rainfall does not increase. The scientists predict that a temperature increase of 3°C will result in a 15 to 20% decrease in wheat yield, and also a decrease in rice yield. Wheat yield declined by 5% when temperature during March increased above normal by 10°C under Punjab conditions. According to studies conducted by IARI, New Delhi, a loss of 4 to 5 million tones in the overall wheat production will occur with every 1°C increase in temperature throughout the growing period of the crop.

Abrupt rise in temperature during September-October leads to off season flowering in peach and mango affecting its yield. In the recent past, temperature shift causes inappropriate flower bud differentiation and flowering in kinnnow and peach. North-Western plains of India have experienced repetitive warming in the month of February and March in 1996 and 2000 onwards during tillering and heading of wheat crop which resulted in more incidences of foliar blights. In Rajasthan, a 2°C rise was assessed to reduce production of pearl millet by 10 to 15%. The loss in farm-level net revenue is estimated to range between 9% and 25% for a temperature rise of 2°C-3.5°C. India could lose 40% fish population over the next 50 years. Every year of delay in our addressing the climate change situation, results in a loss of close to $ 500 billion (Pimm 2009) (Figures 3.3, 3.4, Table 3.3).

Climate change is related to human activity that alters the composition of global atmosphere. Some aspects of climate variability including increasing frequency and intensity of extreme weather events, such as droughts and floods are attributed to climate change. A predication of rise in environmental temperature in Indian subcontinent by 2-3.5°C may lead to increase in sea water level, erratic rains, natural disaster of variable gravity, and 9-25% reduction in agricultural and animal husbandry-based production. Diseases emergence and re-emergence converges are interrelated and surface in the form of a complex system. The major factors are microbial adoption and change, host susceptibility to climate and weather, changing ecosystems, demographics and population, economic development and land use, international trade and travel, technology and industry, reduction in animal and public health services or infrastructure, poverty and social inequality, war and dislocation, lack


of political will and the most important intent to do harm (Huntley 2007).

Figure 3.3 Projected Impact of Climate Change on Agricultural Yield. For Color Reference, See Page 389. Source: Cline 2007.

Figure 3.4 Sources of Greenhouse Gases Emission


Table 3.3. Projected Effects of Climate Change on Agriculture

Climatic Element

Expected Changes By 2055s

Confidence in Prediction

Effects on Agriculture

Temperature

Rise by 1-2oC. Winters warmer more than summers. Increased frequency of heat waves

High

Faster, shorter , earlier growing seasons, range moving north and to higher altitudes, heat stress risk, increased evapotranspiration

Precipitation Seasonal changes by + 10%

Low Impacts on drought risk, water logging, irrigation supply, transpiration

CO2 Increase from 360 ppm to 450-600 ppm

Very high Good for crops, increased photosynthesis

Sea level rise

Rise by 10-15 cm increased in south and offset in north by natural subsistence/rebound

Very high

Loss of land, coastal erosion flooding, salinization of groundwater

Variability Increases across most climatic variables. Prediction uncertain

Very high

Changing risk of damaging events (heat, waves, droughts, floods, etc.) which effect crops and timing of forming operations.

It has been realized that emergence of new infection is influenced by socio-

economic, environmental and ecological factors causing significant threat to public health worldwide (Sahney et al., 2010). Aphids (Homoptera: Aphididae): Potential Agricultural Pests Nature may refer to the general realm of various types of living plants and animals inhabiting the planet earth. Of all the animals dwelling over earth, 80% is contributed by the members of the largest phylum of the Animal Kingdom, Arthropoda. Among arthropods, insects are amid the most assorted group of animals embracing more than a million depicted species, and are known to inhabit all available niches (Chapman 2006; Wilson 2009). About 850,000 to 1,000,000 species of insects are known which are placed in 30 or more orders, but four dominate in terms of numbers of described species, with an estimated 600,000 to 795,000 species include Coleoptera, Diptera, Hymenoptera and Lepidoptera. Many insects are beneficial to the environment and to humans. Some insects, like wasps, bees, butterflies, and ants pollinate flowering plants


(Novotny et al. 2002). In ecology, predation describes a biological interaction where a predator feeds on its prey (Begon et al. 1996). Predators may or may not kill their prey prior to feeding on them, but the act of predation often results in the death of its prey and the eventual absorption of the prey's tissue through consumption (Getz 2011). Parasitism is a type of non-mutual relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. The word parasite now also refers to microparasites, which are typically smaller, such as viruses and bacteria, and can be directly transmitted between hosts of the same species (Combes 2005). Unlike predators, parasites are generally much smaller than their hosts; both are special cases of consumer-resource interactions (Getz 2011) (Figure 3.5).

Figure 3.5 Global Distribution of Aphids Source: Mandrioli 2012

Agriculture in India has a significant history. Today, India ranks second worldwide in farm output. Agriculture and allied sectors like forestry and fisheries accounted for 16.6% of the GDP in 2009, about 50% of the total workforce (Sinha 2010). The economic contribution of agriculture to India's GDP is steadily declining with the country's broad-based economic growth. The agricultural yield is not safe from the grip of insects acting as pests. Many insects are considered pests by humans (Renuka, 2003). Overall yield losses due to insects in 2005 were up slightly from 2004, at 4.57%, completing a five-year trend toward lower losses. The bollworm/budworm complex retained its ranking as the No. 1 cotton pest, reducing yields by 1.5%, followed by Lygus, 0.95%, stink bugs, 0.64%, thrips, 0.426% and spider mites, 0.35%. Total cost and loss for insects in 2005 were $ 1.264 billion. Direct management costs for arthropods were $ 56.51 per acre. Cost plus loss came to $ 88.60 per acre. Insects commonly regarded as pests include those that are parasitic (mosquitoes, lice, bed bugs), transmit diseases (mosquitoes, flies), damage structures (termites), or destroy agricultural goods (locusts, weevils) (Adams et al. 2000).

Aphids are also under these pests causing tremendous losses to the agricultural yield. Different species of aphids are known to cause yield reduction differently for


example, 10-90% of losses were reported for the oilseed crops in India by the species of aphids viz., Brevicoryne brassicae and Lipaphis erysimi alone that reached 70-80% in Pakistan. However, 48% of soybean yield reduction was reported by the soybean aphid, Aphis glycines alone in the United States in the year 2008 (Catangui et al. 2009). Aphids, also known as plant lice are small sap-sucking insects, and members of the superfamily Aphidoidea (McGravin 1993). Aphids are among the most destructive insect pests on cultivated plants in temperate regions. The damage they do to plants has made them enemies of farmers and gardeners the world over, but from a zoological standpoint, they are a very successful group of organisms. Their success is in part due to the asexual reproduction capability of some species (Piper 2007) (Figure 3.6).

(a) Aphis nerii on oleander (b) Aphis glycines on soybean (Nerium spp.) (Glycine max)

(c) Lipaphis erysimi on mustard (d) Brevicoryne brassicae on cabbage (Raphanus sativus) (Brassica oleracea)


e. Aphis craccivora on cowpea f. Macrosiphum rosae on rose (Vicia faba) (Rosea spp.)

g. Rhopalosiphum maidis on corn leaf h. Hydraphis coriandri on coriander twig (Zea mays) (Coriandrum sativum)

i. Aphis gossypii on leaf of j. Hysteroneura setariae on common gourd common doob grass (Lagenaria vulgaris) (Cynodon dactylon)


k. Uroleucon compositae on twig of l. Myzus persicae on leaf of chilli (Carthemus tinctorius) (Capsicum annuum)

Figure 3.6 Different Species of Aphids Infesting Agricultural and Horticultural Crops. For Color, Reference, See Page 389-391. Morphology About 4,400 species of 10 families are known. Around 250 species are serious pests for agriculture and forestry as well as an annoyance for gardeners. They vary in length from 1 to 10 millimetres (0.04 to 0.39 inch). Aphids are distributed worldwide, but are most common in temperate zones (Courtney 2005). Most aphids have soft bodies, which may be green, black, brown, pink or almost colourless. Aphids have antennae with as many as six segments (Blackman and Eastop 1994). Aphids feed themselves through sucking mouthparts called stylets, enclosed in a sheath called a rostrum, which is formed from modifications of the mandible and maxilla of the insect mouthparts (Strovan 1997). They have long, thin legs and two-jointed, two-clawed tarsi. Most aphids have a pair of cornicles (or "siphunculi"), abdominal tubes through which they exude droplets of a quick-hardening defensive fluid containing triacylglycerols, called cornicle wax (Granett et al. 2001).

Aphids have a tail-like protrusion called a "cauda" above their rectal apertures. They have two compound eyes and a tubercle behind and above each eye, made up of three lenses (called triommatidia) (Dixon 1998; Mutti 2006). When host plant quality becomes poor or conditions become crowded, some aphid species produce winged offspring, "alates“ that can disperse to other food sources (Aphis glycines). The mouthparts or eyes are smaller or missing in some species and forms (Aphis pomi) (Fisher 2000). Many aphid species are monophagous (that is, they feed on only one plant species) (Brevicoryne brassicae). Others, like the green peach aphid Myzus persicae, feed on hundreds of plant species across many families (Dadd and Mittler 1965) (Figure 3.7).


Figure 3.7 General Morphology and Life Cycle of Aphids (Homoptera: Aphididae) Source: Singh 2007

Many aphid species are monophagous (feed on only one plant species). Others, like the green peach aphid (Myzus persicae) feed on hundreds of plant species across many families. Aphids passively feed on sap of phloem vessels in plants, just like their fellow members of Hemiptera (scale insects and cicadas). Once a phloem vessel is punctured, the sap, which is under high pressure, is forced into the aphid's food canal. Occasionally, aphids also ingest xylem sap, which is a more dilute diet than phloem sap as the concentration of sugars and amino acids are 1% of those in the phloem (Spiller et al. 1990; Fisher 2000). Xylem sap is under negative hydrostatic pressure and requires active sucking, suggesting an important role in aphid physiology (Malone et al. 1999). As xylem sap ingestion has been observed following a dehydration period, it was suspected that aphids consume xylem sap to replenish their water balance; the consumption of the dilute sap of xylem permitting aphids to rehydrate (Powell and Hardie 2002). However, recent data showed that aphids consume more xylem sap than expected and that they notably do so when they are not dehydrated and when their fecundity decreases (Pompon et al. 2010) suggesting that aphids, and potentially, all the phloem-sap feeding species of the order Hemiptera, consume xylem sap for another


reason than replenishing water balance. It was suggested that xylem sap consumption is related to osmoregulation. High

osmotic pressure in the stomach, caused by high sucrose concentration, can lead to water transfer from the hemolymph to the stomach, thus, resulting in hyperosmotic stress and eventually to the death of the insect. Aphids avoid this fate by osmoregulating through several processes. Sucrose concentration is directly reduced by assimilating sucrose toward metabolism and by synthesizing oligosaccharides from several sucrose molecules, thus reducing the solute concentration and consequently, the osmotic pressure (Ashford et al. 2000; Wilkinson et al. 1997). Oligosaccharides are then excreted through honeydew, explaining its high sugar concentrations, which can then be used by other animals such as ants. Furthermore, water is transferred from the hindgut, where omostic pressure has already been reduced, to the stomach to dilute stomach content (Shakesby et al. 2009). Eventually, aphids consume xylem sap to dilute the stomach osmotic pressure (Pompon et al. 2010). All these processes function synergetically, and enable aphids to feed on high sucrose concentration plant sap as well as to adapt to varying sucrose concentrations.

Plant sap is an unbalanced diet for aphids as it lacks essential amino acids, which aphids, like all animals, cannot synthesise, and possesses a high osmotic pressure due to its high sucrose concentration (Dadd and Mitler 1965; Fisher 2000). Essential amino acids are provided to aphids by bacterial endosymbionts, harboured in special cells, bacteriocytes (Buchner 1965). These symbionts recycle glutamate, a metabolic waste of their host, into essential amino acids (Whitehead and Douglas 1993). As they feed, aphids often transmit plant viruses to the plants, such as to potatoes, cereals, sugarbeets and citrus plants. These viruses can sometimes kill the plants (Febvay et al. 1995). Effect on Plants and Agricultural losses Plants exhibiting aphid damage can have a variety of symptoms, such as decreased growth rates, mottled leaves, yellowing, stunted growth, curled leaves, browning, wilting, low yields and death. The removal of sap creates a lack of vigour in the plant, and aphid saliva is toxic to plants. Aphids frequently transmit disease-causing organisms like plant viruses to their hosts. The green peach aphid, Myzus persicae, is a vector for more than 110 plant viruses. Cotton aphids (Aphis gossypii) often infect sugarcane, papaya and peanuts with viruses (McGavin 1993). Aphids contributed to the spread of late blight (Phytophthora infestans) among potatoes in the Irish potato famine of the 1840s (Nichols 2007). The cherry aphid or black cherry aphid, Myzus cerasi, is responsible for some leaf curl of cherry trees. This can easily be distinguished from 'leaf curl' caused by Taphrina fungus species due to the presence of aphids beneath the leaves. The coating of plants with honeydew can contribute to the spread of fungi which can damage plants (Gillman 2005; Reynolds and Volk 2007). Honeydew produced by aphids has been observed to reduce the effectiveness of fungicides as well


(Dik and Pelt 1992). The attack of Elatobium abietinum on the Sitka spruce needles resulted in falling of

the needles and the time taken for needle fall was found to be inversely related to the feeding time of aphids (Parry 1974). The Russian wheat aphid, Diuraphis noxia (Mordvilko) attacks the seedlings of 'TAM W-lOl' winter wheat (Triticum aestivum L.) resulting in water imbalances expressed as a loss of turgor and reduced growth followed by substantial reductions in biomass, carbon assimilation, reduction in leaf area ratio, stem weight ratio, leaf chlorosis, leaf rolling, and plant stunting (Burd and Burton 1992). D. noxia affects plant height, shoot weight, and number of spikes and the yield per plant significantly reduces by infestation through the heading stage governed by fall and spring infestations in 1987-1988 (Burd et al. 1993). Feeding of Schizaphis graminum (Rondani), Rhopalosiphum padi (L.), and Macrosiphum avenae (F.) caused yield losses in 'Rough Rider' winter wheat (Triticum aestivum L.), and 'Cougar' winter rye (Secale cereale L.) for 3 years continuously in South Dakota fields and 50% of the losses were caused when aphids attacked the plants at seedling stage further yield losses were recorded when aphids fed in spring during the boot stage (immature in florescence invested in leaf sheath), however, no losses were observed when aphids fed on mature (dough stage) plants (Kieckhefer and Kantack 1988).The bird cherry-oat aphid (Rhopalosiphum padi L.) was responsible for 52% yield losses in barely in ten commercial farms in central Sweden (Östmana et al. 2003). Data collected from studies of Tatchell (1989) indicate that the damage caused by aphids on major crops in Britain may give a potential economic loss of £ 70 × 106 where severe widespread infestations of wheat alone could result in losses of £ 120 × 106.

Sitobion avenae is one of the most harmful cereal aphids in Western Europe damaging winter wheat in Southern Sweden and aphid population varies greatly with years reaching peaks at different crop stages resulting in declination of volume weight and grain weight but protein percentage remains unharmed (Larsson 2005). S. avenae is also responsible for late-season virus transmission causing direct yield loss by feeding on heads and flag leaves of wheat (Chapin et al. 2001). Aphids and several mosaic viruses viz., cucumber mosaic cucumovirus, watermelon mosaic and zucchini yellow mosaic potyviruses work together resulting in major losses in cucurbitaceous crops grown in the inland valleys of California with 100% incidence of foliar symptoms followed by reduced cumulative, marketable melon yields characterized by decline in the number of fruit, fresh weight and size (Stapletona and Summersb, 2002). The 7 most common cereal aphid species, namely, Metopolophium dirhodum, Rhopalosiphum padi, Sitobion avenae, Diuraphis noxia, R. maidis, Schizaphis graminum and Sitobion miscanthi bring great reduction in the yield of cereals causing great economical losses (Dixon, 1987). The number of Aphis fabae Scop. per plant and per acre on field beans (Vicia faba L.) is inversely related to seeding rate (Way and Heathcote 1966).

Soybean aphid (Aphis glycines Matsumura) reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces became one of the most important pests of soybean throughout the North


Central region (Ragsdale et al. 2007). A. glycines can even reduce yields of soybean as much as 50% and is the vector of several viral diseases. The aphid removes phloem sap resulting in a reduction of chlorophyll content (Diaz-montano et al. 2007). Greenbug, Schizaphis graminum (Rondani), and rice root aphid, Rhopalosiphum rufiabdominalis (Sasaki), colonized seedling wheat immediately after crop emergence, with apterous colonies peak in December or January and then decline and caused economic loss of wheat in South Carolina. Bird cherry-oat aphid, Rhopalosiphum padi peaks in February or March. Based on transmission assays, R. padi is primarily responsible for vectoring the predominant virus serotype (PAV) in wheat (Chapin et al. 2001). A positive correlation occurs between spread of potato leaf roll virus (PLRV) and numbers of Myzus persicae (Sulzer) damaging the potato fields in Southern Idaho (Bryne and Bishop 1979).

Barley yellow dwarf virus (BYDV) damages winter cereals and population dynamics of aphid, R. padi in fields in the northern half of France. The curve of the percentage of plants infested by R. padi during autumn is highly related to BYDV yield losses (Fabre et al. 2003). Accurate prediction of yield loss caused by cereal aphids in small grains involves assessment of the aphid population density on plants, the duration of their feeding, and the growth stage of the crop at the time of feeding as observed in case of Diuraphis noxia and R. padi on the growth and yield of spring wheat, Triticum aestivum (Kieckhefer et al. 1995). Myzus persicae (Sulzer) infestations on potato foliage and tuber production cause reduction in tuber dry weight, moisture content of infested leaves, declination in leaf growth without harming stem growth (Petitt and Smilowitz 1982). M. persicae infested on the sugar-beet plants is also responsible for the spread of the yellowing viruses (beet yellows and beet mild yellowing viruses) during January, February and March when temperatures fall below – 0.3°C (31.5°F) (Watson et al. 1975). The lettuce aphid (Nasonovia ribisnigri (Mosley)) is the most serious pest of crisphead lettuce in the lower Fraser Valley of British Columbia infesting plants present near the margins in the fields (Mackenzie and Vernon 1988). Metopolophium dirhodum, R. padi and S. avenae were the commonest alatae trapped from April/May to August, with most in July and early August during 1970-1971, where the first alatae appeared in the Rothamsted survey suction trap. Most species occurred first near the sheltered edge of the crop, but M. dirhodum was widespread over the field. Alate M. dirhodum moved more often than apterae, but both morphs of S. avenae moved equally often and more frequently between larvipositions than did those of M. dirhodum (Dean 1973). Aphids under Attack Aphids are soft-bodied and have a wide variety of insect predators. Aphids also are often infected by bacteria, viruses and fungi. Insects attacking aphids include predatory coccinellidae (lady bugs or ladybirds), hoverfly larvae (Diptera: Syrphidae), parasitic wasps, aphid midge larvae, "aphid lions" (larvae of green lacewings), crab


spiders and lacewings (Neuroptera: Chrysopidae). Fungi attack aphids include Neozygites fresenii, Entomophthora, Beauveria bassiana, Metarhizium anisopliae and entomopathogenic fungi like Lecanicillium lecanii. Aphids brush against the microscopic spores. These spores stick to the aphid, germinate and penetrate aphid's skin. The fungus grows in the aphid hemolymph and after about 3 days, aphid dies and the fungus releases more spores into the air. Infected aphids are covered with a woolly mass that progressively grows thicker until the aphid is obscured. Often the visible fungus is not the type of fungus that killed the aphid, but a secondary fungus (Brust 2006) (Figure 3.8).

a. Predatory ladybird b. Hoverfly larva (Doros spp.) (Coccinella septempunctata) feeding on aphid

c. Parasitoid wasp (Peristenus digoneutis, d. Larva of Aphidoletes aphidimyz Ichneumonoidea: Braconidae feeding on aphids laying egg inside aphid


e. Green lacewing larve f. Green peach aphid, Myzus persicae, (Chrysoperla carnea) feeding killed by the fungus Pandora neoaphidis on aphid (Zygomycota: Entomophthorales)

Figure 3.8 Aphids under Attack. For Color Reference, See Page 391-392.

A seasonal relationship in abundance of greenbug, Schizaphis graminum (Rondani), and corn leaf aphid, Rhopalosiphum maidis (Fitch) on field planted sorghum, wheat, and volunteer johnsongrass has been known where with increase in aphid numbers the number of predators also increased suggesting that parasitism decreases aphid population levels (Lopez and Teetes 1976). A number of polyphagous predators namely dipterans, Philonthus sp., Tachyporus sp., staphylinid larvae and carabid beetles (Agonum dorsale) aggregate at concentrations of aphids either by direct attraction towards aphids as prey or aphids serve as alternative prey due to honeydew secretion indicating that aphids serve as food (Monsrud and Toft 1999). Carabid beetles (Agonum dorsale) are important aphid predators against the populations of cereal aphids and an inverse relationship between numbers of predators and aphids but positive relationships between aphids and aphid-specific predators and aphid parasites has been noticed responsible for population declination of cereal aphids (Edwards et al. 1979). Lacewing larvae (Chrysoperla carnea) are known as potential predators of aphids in many crops and adults prefer to release their eggs at places where aphid population is at peak so that the larvae can feed profitably (Rosenheim et al. 1993). Chrysoperla comanche and Chrysopa nigricornis predatory green lacewing species are abundant in pecan trees in Southern Arizona feeding on aphids viz., Monellia caryella and Melanocallis caryaefoliae. Females of both green lacewing species showed a significant preference for ovipositing on plants bearing aphids as both aphid species were suitable for larval development (Petersen and Hunter 2002).

Interactions among predators can a have substantial effect on the total impact of the predator complex. The interaction between foliar-foraging (Coccinella septempunctata) and ground-foraging (Harpalus pennsylvanicus) predators of the pea


aphid (Acyrthosiphon pisum) shows aphid “dropping” behaviour as elicited by C. septempunctata rendering the aphids susceptible to predation by H. pennsylvanicus on the ground. The strength of the synergistic interaction increases with increasing prey density (Losey and Denno 1998). The most active polyphagous predators of aphids on winter wheat in Belgium are the spiders, Erigone atra and Oedothorax apicatus, the staphylinids, Tachyporus hypnorum and Aloconota gregaria and the carabids, Pterostichus melanarius, Bembidion lampros, B. tetracolum and Platynus dorsalis [Agonum dorsale]. Among carabids, A. dorsale and Pterostichus melanarius have the highest predation indices followed by spiders, females of E. atra and Oedothorax whereas no important aphid predation was detected among staphylinids (Janssens and Clercq 1990).

Hippodamia convergens, Coleomegilla maculata lengi, Coccinella septempunctata, Scymnus spp., Chrysopa spp., Nabis spp., spiders and other coccinellid larvae are potential predators of aphids in the winter wheat fields (Maurice and Ramteke 2012; Rice and Wilde, 1991). The apple aphids (Dysaphis plantaginea and Aphis pomi) are attacked by aphidophagous predators including spiders, predaceous Heteroptera, Coccinellidae and Chrysopidae in Berne, Switzerland and during flowering of weeds these aphidophagous predators are observed more in number on the apple trees (Wyss 1995). Intraguild predation (IGP) is a common interaction in invertebrates and vertebrates, affecting the abundance and distribution of many species. Several parameters influence the magnitude and direction of IGP like, feeding specificity, size, mobility, and aggressiveness of the protagonists, as well as extraguild prey density. Aphid predators namely Aphidoletes aphidimyza (Diptera), Chrysoperla rufilabris (Neuroptera) and Coleomegilla maculata lengi (Coleoptera) attack potato aphid Macrosiphum euphorbiae and participates in Intraguild predation. The aphid specialist A. aphidimyza is more vulnerable to IGP than C. rufilabris and C. maculata. Sessile and low mobility stages of all species are extremely vulnerable to IGP and larger sized individual won confrontations (Maurice et al. 2011; Lucas et al. 1998). The parasites and predators of aphids occurring in northeast India and Bhutan include the parasite, Aphidius rosae, insect predators, Sphenoraia bicolor (Gallerucida bicolor), Monolepta signata, Chilocorus rubidus and Sphaerophoria scripta and spiders, Neoscona nautica and Thomisus spp. all attacking Macrosiphum rosae and in some cases also other aphids. Other natural enemies recorded for the first time from India include a species of Oenopia (O. quadripunctata) preying on Aphis fabae solanella on oak, and spiders Cyclosa insulana, Leucauge celebesiana and Theridion spp. preying on Aphis craccivora on broad bean (Vicia faba) and other plants (Raychaudhuri et al. 1979).

Cereal aphid populations in winter wheat are attacked by ground-dwelling generalist predators (mostly spiders, carabid and staphylinid beetles), flying predators (coccinellid beetles, syrphid flies, gall midges, etc.) and parasitoids (aphidiid wasps). Aphid populations are 18% higher at reduced densities of ground-dwelling predators, 70% higher when flying predators and parasitoids are removed, and 172% higher on the removal of both enemy groups. Parasitoid wasps probably have the strongest effect, as flying predators occur only in negligible densities (Maurice et al. 2012; Schmidt et al. 2003). The guts of Carabidae, Staphylinidae and earwig when dissected


shown remains of aphids indicating that they feed on aphids and the proportion containing aphid remains increases with aphid density (Sunderland and Vickerman 1980). Effect of Climate on Aphid Population Aphids can be easily killed by unfavourable weather, such as late spring freezes (Jones, 1979). Excessive heat kills the symbiotic bacteria that some aphids depend on, which makes the aphids infertile (Hughes 1963). Rain prevents winged aphids from dispersing, and knocks aphids off plants and thus, kills them from the impact or by starvation (Suwanbutr 1996). However, rain cannot be relied on for aphid control (Ostlie 2006). High Temperature The temperature requirements of some aphids differ from place to place for the same species and from species to species and the temperature requirements of the parasites and hyperparasites acquainted with these aphids differ in a similar manner but, as a rule, are higher than those of their hosts (Campbell et al. 1974). Asin and Pons (2001) studied the development, reproduction and longevity of corn aphids viz., R. padi, S. avenae and Metopolophium dirhodum at 18°C, 22°C, 25°C, 27.5°C and 30°C and reported that only nymphs of R. padi survived at 30°C, but the adult reproductive capacity was very low. R. padi performed better than M. dirhodum at all temperatures and better than S. avenae over the range of 22°C –27.5°C. They suggested that the better performance of R. padi was due to a lower nymphal mortality, lower developmental and pre-reproductive times and a higher intrinsic rate of increase (rm). Mccornack et al., (2004) determined the optimal temperature for soybean aphid (Aphis glycines) growth and reproduction on soybean under controlled conditions by constructing life tables at 20, 25, 30, and 35°C with a photoperiod of 16:8 (L:D) h and found that population growth rates were greatest at 25°C. As temperature increased, net fecundity, gross fecundity, generation time and life expectancy decreased. Nymphs exposed to 35°C failed to complete development, and all individuals died within 11 days.

Innate capacities for increase of Myzus persicae and Macrosiphum euphorbiae have been recorded by demographic analysis at constant temperatures between 5°C and 30°C. Both species show capacities for increase between 5°C and 25°C, where upper temperature threshold for growth of populations has been estimated between 25°C and 30°C and the lower temperature threshold lies below 5°C. Innate capacity for increase of M. persicae is generally higher than M. euphorbiae at temperatures between 15°C and 25°C because of more rapid development and earlier attainment of the maximum fecundity rate. Temperature also influences the innate capacity for increase by modifying developmental time, survival rate, and fecundity rate (Barlow 1962). The developmental periods of the immature stages of Aphis gossypii ranges from 12.0 days at 15°C to 4.5 days at 30°C and a constant temperature of 35°C is lethal to them. The


average longevity of adult females also reduces at 30-35°C. It is evident that temperatures over 30°C prolongs development, increases mortality of immature stages, shortens adult longevity, and reduces fecundity (Kersting 1999; Zamani et al. 2006). Plant growth stage and temperature exhibits a significant interaction on reproductive life span, total life span, and production of nymphs per female of wheat aphid, Diuraphis noxia (Girma et al. 1990). Viviparous, parthenogenetic populations of 1st instars and pre-reproductive or teneral pea aphids, Acyrthosiphon pisum Harris, when exposed to 39°C or -12°C for varying times, the intrinsic rates of increase for surviving populations (Gen 1) and their progeny (Gen 2) was observed. However, temporary exposure of populations to extreme temperature may decrease rates of growth of surviving populations and this effect may extend over subsequent generations and the age-structure of the population at the time of exposure may affect its subsequent growth rate (Harrison and Barlow 1973). Excessive Cold Hutchinson and Bale (1994) found that cold stress arising from a single exposure to subzero temperatures to R. padi affects key processes like development, reproduction and longevity exerting a dominant influence on aphid population dynamics, and these deleterious effects also act prenatally, predisposing some nymphs to die shortly after birth. Rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles lower the movement threshold of S. avenae (Powell and Bale 2006). The minimum temperatures of -7°C or lower noticeably reduces overwintering populations of the green spruce aphid, Elatobium abietinum, in north-east Scotland suggesting that at such temperatures, ice formation in the needles of the host Sitka spruce, causes attached aphids to freeze. Aphid mortality also occurs when maximum temperatures did not rise above +6°C for prolonged periods resulting in starvation following an extended chill coma (Powell and Harry 1976).

When the grain aphid S. avenae was low-temperature acclimated by rearing for three generations at 10°C, the discriminating temperatures of first instar nymphs and adult aphids were recorded as -11.5°C and -12°C, respectively. The maximum rapid cold-hardening was induced by cooling aphids at 0°C for 2 h (nymphs) or 30 min (adults), resulted in survival at the respective discriminating temperatures increasing from 26% to 96% (nymphs) and 22% to 70% (adults). Rapid cold-hardening ability is retained in aphids that have already undergone cold-acclimation, as it can be the case in overwintering aphids. Both rapid cold-hardening and subsequent exposure at previously lethal temperatures can enhance fitness in surviving individuals (Powell and Bale 2005). The eggs of R. insertum showed a seasonal increase in cold-hardiness under field conditions where their super cooling point fell from -35°C in November to below -40°C in January and then rising to -35°C or above by March indicating that eggs of R. inserturn are in diapause until mid-January, and hatching rate and cold-hardiness are actually governed by separate environmental factors (James and Luff 1982).

The mean super cooling points of first instar and adult M. persicae maintained at


20°C and cooled at 1°C were found to be -26.6°C and -25.0°C indicating extensive pre-freeze mortality under laboratory conditions. Acclimation at 10°C and 5°C did not affect super cooling both first instars and adult aphids. The level of cold in different winters can be expressed in terms of the total number of frost days and the frequency of abnormally cold days. Winter temperatures differ markedly in a vertical profile from the soil to the soil or grass surface, and then to the air (and foliage) above. Winter temperatures and the resultant aphid mortality is a primary determinant of the timing of the spring migration (Bale et al. 1988). The lethal temperature of first instar and adult stages of M. persicae when lowered following long term acclimation at low temperatures, the first instars consistently showed greater cold hardiness than adult stages at each acclimation temperature, with the differential increasing as the temperature was lowered. At -10°C mortality of adults approached 100% whereas more than 50% of nymphs were still alive at this temperature (Clough et al. 1990; Girma et al. 1990, 1993). Rain Population of spotted alfalfa aphid, Theriotiplris maculata (Buckton) starts peaking usually in April, July and October but rainfall is detrimental to the aphid population if a sufficient amount falls just prior to the expected build-up to initiate epizootic outbreaks of a fungus. Dates of population peaks were found to be dependent upon temperature and relative humidity (Neilson and Barnes, 1961). The effect of wind and rain on initiation of dispersal and subsequent distances moved by apterous S. avenae was quantified laboratory experiments by Mann et al. (1995). Wind duration and type (steady and gusting), rain duration and intensity, and a combination of wind and rain were the parameters investigated by them, after which they concluded that with increased duration of wind an increase in the average distance of the movements of aphids was observed but less movement was noticed when aphids were exposed to gentle gusting, than to steady wind or strong gusting. Increased duration of rain also increases the proportion of aphids lost from plants. Under heavy rain, the proportion of aphids off the release plant, the distance moved by them and the proportion of aphids lost, was found to be greater than for drizzle or light rain. When wind and rain were compared, rain had the greater impact on aphid dispersal. Leaf disturbances caused by strong gusts of wind or large rain droplets are of considerable importance in the initiation of aphid dispersal, but that wetness alone is not.

The effect of artificial acid rain on the reproduction and survival of the aphid Euceraphis betulae on silver birch was studied in Turku, southern Finland by Neuvonen and Lindgren (1987) and they found that in the bioassays aphids produced 40% to over 100% more progeny on birches watered with dilute sulphuric acid (pH 3.5) than on control trees. In four other cases the performance of aphids did not differ between the treatments. An index of aphid reproduction pooled was found to be significantly higher on acid-treated than on control birches. The reproduction of aphids on acid-treated birches was enhanced when precipitation was below long-term average,


suggesting an interaction between the stress caused by acid treatment and dry periods. Mechanical effect of heavy rains during the dry season in Puerto Rico is a factor in population suppression of Sipha flava (Forbes). If aphid populations were at least 5 or 6 per linear inch of leaf surface, the effect of heavy rains appeared to be density-dependent (Miskimen 1970). CO2 Levels

Experimental evidence regarding the responses of cereal aphids to rising atmospheric CO2 has been ambiguous. Some studies suggest increased population sizes under future CO2 levels, others suggest decreased population sizes, and still others suggest little or no difference. Newman et al. (2004) constructed a general mathematical model of the aphid-grass interaction to investigate a general aphid response to rising CO2 and concluded that aphid populations are likely to be larger under future CO2 concentrations if soil N levels are high, the aphid species' nitrogen requirement is low and the aphid species' density-dependent response in winged morph production is weak. In that model, and in field experiments, CO2 concentration influences aphid population dynamics through the effect it has on plant quality. However, future CO2 concentrations are also likely to be accompanied by higher ambient temperatures, a combination that has received little focus to date. It can be suggested that when both the factors are elevated, aphid population dynamics will be more similar to current ambient conditions than expected from the results of experiments.

In future, elevated CO2 environments can cast their effect on the chewing insects as they are likely to perform less well because of the effects of increased carbon fixation on their host plants. When the aphid, Aulacorthum solani was reared on bean (Vicia faba) and tansy (Tanacetum vulgare) plants under ambient and elevated CO2, performance was enhanced on both hosts at elevated CO2. The nature of the response was different on each plant species suggesting that feeding strategy may influence an insect’s response to elevated CO2. On bean, the daily rate of production of nymphs was increased by 16% but there was no difference in development time, whereas on tansy, development time was 10% shorter at elevated CO2 but the rate of production of nymphs was not affected. This increase in aphid performance could lead to larger populations of aphids in a future elevated CO2 environment (Awmack et al. 1997). The effects of elevated CO2 (ambient + 200 mol/mol) and temperature (ambient + 2.0°C) on plant chemistry, abundance of peach potato aphid M. persicae and on performance of one of its parasitoids Aphidius matricariae showed that total above-ground plant biomass, foliar nitrogen and carbon concentrations were not affected by elevated atmospheric CO2. Aphid abundance was enhanced by both CO2 and temperature treatment. Parasitism rates remained unchanged in elevated CO2, but showed an increasing trend in conditions of elevated temperature suggesting that M. persicae is an important pest of many crops, might increase its abundance under conditions of climate change (Bezemer et al. 1998).

Lesley and Bazzaz (2001) investigated interactions between five species of phloem-


feeding aphids and their host plants at elevated CO2: A. pisum on Vicia faba, Aphis nerii on Asclepias syriaca, Aphis oenotherae on Oenothera biennis, Aulacorthum solani on Nicotiana sylvestris, and Myzus persicae on Solanum dulcamara. Host plants grown at elevated CO2 had greater biomass, leaf area and C:N ratios than those grown at ambient CO2, while plants with aphids had lower biomass and leaf area than those without aphids. The responses of aphid populations to elevated CO2 were species-specific with one species increasing (M. persicae), one decreasing (A. pisum), and the other three being unaffected. CO2 treatment did not affect the proportion of a late individuals produced. In general, aphid abundance was not significantly related to foliar nitrogen concentration. In contrast to other insect groups, such as leaf chewers, populations of most phloem-feeders may not be negatively affected by increased CO2 concentrations in the future. The reasons for this difference include the possibility that aphids may be able to compensate for changes in host plant quality by altering feeding behaviour or by synthesizing amino acids. In addition, there is little evidence that aphid herbivory, even at high levels, will substantially modify the response of plants to elevated CO2. Air Pollution The population development of Aphis fabae on two main hosts, i.e., Viburnum opulus and Phaseolus vulgaris, in ambient air compared to filtered air was found to increase where the prevailing air pollutants, mainly constituted of nitric oxide (NO) and nitrous oxide (NO2). Strong increase in the content of organic nitrogen in foliage and total amino acids in phloem sap was noticed, due to which the plant-insect interaction was imbalanced when plants were submitted to ambient air on motorways due to changes in the nutritional quality for aphids (Bolsinger and Flückiger 1984, 1987). The effect of motorway air pollution on the infestation of Crataegus spp. by Aphis pomi in the chambers with ambient and filtered air showed a 4·4 times increase in the population of aphids in the ambient air. Analysis of phloem exudate showed a significant increase in glutamine relative to the sugar content in the plants grown in the polluted air. Some substantial changes in phenolic compounds were also recorded (Braun and Flückiger 1985).

Rose bushes (Rosa sp.) infected with aphid Macrosiphon rosae nymphs when fumigated with ambient Munich air or charcoal-filtered air showed 20% higher mean relative growth rate of confirming that air pollution enhances the pest potential of aphids (Dohmen 1986). Roadway emissions increased the abundance of the aphid Aphis fabae on two different host plants, Viburnum opulus and Phaseolus vulgaris. Phloem sap analysis of excised leaves revealed an increase in the amino acid due to ambient air pollution. The mean relative growth rates (MRGR) of larvae reared on ‘ambient air’ diets also increased significantly (Bolsinger and Flückiger 1989). Sitka spruce trees, with the aphid Elatobium abietinum when subjected to sulphur dioxide (SO2) exposure over a period of two months showed a three times abundance in aphid population (Warrington 1990). Development of spruce shoot aphid (Cinara pilicornis) populations


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Global Climate Change: A Threat to Aphid Populations