I. Why give a lecture on insects in BLD18? II. What are insects? III. Why are insects so diverse? IV. How many species of insects? V. Insect conservation:

I. Why give a lecture on insects in BLD18?

II. What are insects?

III. Why are insects so diverse?

IV. How many species of insects?

V. Insect conservation: causes of imperilment

VI. Insects & the endangered species act (esa)

Why give a lecture on insects in BLD18?

(1) Insects are extremely important in natural systems

“The little things that run the world” (E.O. Wilson)

central role of insects in most terrestrial ecosystems

Insects perform numerous ecosystem services:

scavengers, predators, detritivores & herbivores

prey for many vertebrates & other invertebrates

pollinators, seed dispersal, plant protection

(2) Insects are beneficial to humans

biological control (predators & parasites)

pollination (honeybees)

- 1 out of 3 bites of food people eat

silk production (silk moth - Bombyx mori)

food (non-western cuisines)

aesthetics (bees & butterflies)


(3) Insects are harmful to humans: agricultural pests

herbivores that use the same resources as humans

“pest” is an anthropocentric designation

crop losses to insects have remained constant or have increased with advent of pesticides


(4) Insects are harmful to humans: vectors of diseases

Vector = insect that carries a disease from one host to another

human diseases vectored by insects: malaria, sleeping sickness, plague, encephalitis, dengue, Chagas’ disease,

west nile virus

plant diseases vectored by insects: Pierce’s disease, Dutch Elm disease


From Gullan & Cranston (Insects: an outline of

entomology)

(5) Insects are fantastically diverse

perhaps 64% or more of estimated number of all species

over 106 described species* of insects

56% of all described species are insects

Insect conservation now seen as imperative to preserving biodiversity

* a species to which a binomial Latin name (e.g., Drosophila melanogaster) has been assigned by a taxonomist in a scientific publication



entomology)


Insects are in the phylum Arthropoda

OK, but what are arthropods?

(1) Trilobites – wholly marine and extinct; 4000 described species

(2) Crustaceans – mostly marine & freshwater; 30,000+ described spp.

(3) Chelicerates – a few marine, many terrestrial; 65,000+ described spp.

(4) Pycnogonids – all marine; 4,000 described spp.

(5) Myriapods – terrestrial; centipedes & millipedes; 13000 described spp.

(6) Hexapods – mostly terrestrial, a few freshwater

c. 1,000,000 described species!


Shared, derived features* of the Class Insecta:

(1) compound eyes

(2) gas exchange is predominantly tracheal

(4) three body segments: head, thorax, abdomen

(5) most have wings

* relative to other hexapods

Hemimetabolous Holometabolous



entomology)

Coleoptera (beetles) – c. 350,000 described species

Diptera (flies) – c. 125,000 described species

Lepidoptera (butterflies & moths) – c. 160,000 described species

Hymenoptera (ants, bees & wasps) – c. 100,000 described species


(1) Small size (0.2 – 300 mm)

insects divide the environment finely

(2) Old age (most extant groups 250-300 million years old)

insects have had time to fill & explore environment

(3) Associations with other organisms

especially with plants & other insects

herbivores, parasites, parasitoids, hyper-parasitoids

Does diversity beget diversity?

Female lays singleegg in host

Larva developsIn head capsule

New adult emergesfrom head capsule

Female attractedto healthy host

Larva pupariatesIn head capsule

Larva eventuallydecapitates host

Life cycle of ant-decapitating flies

Sanford Porter Photo


(4) Short generation time

insects capable of rapid population growth

(5) Winged flight

only other extant flying animals are birds and bats

avoid predators and high temperatures

seek out mates, colonize new areas, migrate & disperse


(6) Metamorphosis

life history divided into two separate stages

(1) larval: feeding & growth

(2) adult: reproduction & dispersal

(7) Diapause

period of arrested development

permits survival in seasonally inhospitable environments



Biologists have long realized the great diversity of insects

1758 Systema Naturae Carl Linnaeus listed 2000 insect species

1883 Ray (British entomologist) 20,000 species

2000 >1,000,000 described insect species


Biologists have long realized the great diversity of insects

described insects an unknown fraction of total

no central, organized database for the life on earth

unclear how many described species exist

- synonyms, narrow regional surveys

biologists still can’t estimate to the nearest order of magnitude how many insects exist

estimates range from 3-30 X 106


How is diversity estimated in the absence of described taxa?

(1) estimate tropical diversity by extrapolating from patterns

found in well-studied faunas of temperate regions

on average, there are 2 tropical mammal species for every temperate mammal species

2X as many topical insects than temperate ones?

such extrapolations assume that tropical: temperate species

ratios hold constant across phylogenetic groups

little evidence for this: groups often have idiosyncratic latitudinal

diversity relationships


How is diversity estimated in the absence of described taxa?

(2) estimate tropical diversity by extrapolating from patterns

found in well-studied faunas of tropical regions

In the 1980s, British entomologist Terry Irwin drew attention to the potential for tropical insect diversity to far outstrip previous estimates

Erwin used insecticidal fog

to knock down beetles from 19

Luehea seemannii trees in the

Amazonian rainforest of Peru


Erwin found > 1100 species of beetles - Remarkable!

Partitioned beetles into feeding categories:

(e.g., carnivore, scavenger, fungivore, and herbivore)

Guessed that 5%, 10%, 5% and 20% of the species in each feeding category were restricted to Luehea seemannii

Estimated that c. 160 species of beetles might be specialized on a typical tropical tree species


Erwin further speculated that …

400 species of unique canopy arthropod species per tree species

beetles are 40% of known arthropod species

600 species of arthropods per tree

2X as many arthropods occur in canopy compared to the number found on the forest floor

50,000 tropical tree species X 600 arthropods per tree = 30 X 106

Erwin’s provocative result greatly exceeded previous estimates


Erwin’s estimate high but illustrates:

The potential for insect diversity to far exceed that of other animals

Most diversity will be found in the big four insect orders: Coleoptera, Lepidoptera Hymenoptera, and Diptera

How little we know about diversity

Most taxonomists (those who name & classify organisms) work in the species poor north, whereas most insect species are tropical

Per taxon, far more scientists work on vertebrates than invertebrates.

Taxonomists are not being trained to replace those who retire.

(1) Introduced species

some intentionally introduced (e.g., biological control agents)

many others introduced by accident as a result of commerce

rate of introduction continues to increase with globalization

direct effects:

e.g., native ants displaced by Argentine ants

indirect effects:

e.g., host plants of an herbivore displaced by invasive plants

e.g., bio-control agents that share enemies with native species


(2) Habitat fragmentation

natural habitats surrounding areas occupied by people are often

fragmented

fragmentation compromises the biota:

altered hydrology

edge effects by invasive species

reduction in size of populations

increased isolation of populations

unlike like some vertebrates (top–order carnivores), insects may be

more likely to persist in small fragments


10

20

30

40

50

60

urban 0-25 26-50 51-100 >100

Distance (m) to nearest urban edge

urban matrixmesic fragmentsxeric fragments

Argentine ants / pitfall trap


0

0.4

0.8

1.2

1.6

0 0.5 1 1.5 2 2.5 3

log area (ha)

xeric fragmentsmesic fragmentsplots withinunfragmented areas

- 0.5

Log (number of native ant species)V. Insect conservation: causes of imperilment

(3) Habitat destruction

currently the leading cause of insect endangerment globally

lion’s share of insect biodiversity resides in tropical forests

preservation of these habitats will go a long ways to preserving not

only insect biodiversity but biodiversity generally

few comprehensive studies have been attempted to determine how

conversion of tropical forests will affect insect diversity



Lawton et al. 1997. Biodiversity inventories, indicator taxa and effects of habitat modification in tropical forest. Nature 391:72-76.

sampled 8 groups: birds, butterflies, ants (litter & canopy), beetles (flying

& canopy), termites & nematodes across a disturbance gradient in

Cameroon rain forest

disturbance gradient: primary forest, secondary forest, secondary forest

+ commercial plantation, fallow fields

plantation tree was a common native species


birds

beetles(flying)

canopy ants

termites

butterflies

beetles(canopy)

leaf-litterants

nematodes



Main points of Lawton et al. study:

all taxa (except nematodes) decreased sharply in species richness across

disturbance gradient

species turnover varied across taxonomic groups

no single group adequately predicted declines in any other group


(4) Climate change

insects are profoundly affected by subtle changes in climate

in the face of a changing climate insects may …

… tolerate

… adapt

… shift their ranges

… suffer extinction

potential effects of climate change currently an active area of research,

but one with many uncertainties


(4) Climate change

climate change is a natural phenomenon, but two important factors

distinguish anthropogenic climate change from past events

(1) it is occurring much more quickly

(2) in many areas natural habitats will exist primarily in a

fragmented state – lack of habitat connectivity may

hinder movement among fragments

Will climate change & fragmentation interact to increase extinctions?


(4) Climate change

Warren et al. 2001. Rapid response of British butterflies to opposing forces of climate and habitat change. Nature 414:65-67.

amateur lepidopterists compiled fine-scale distributional data for last

several decades, during which time UK climate has experienced warming

46 non-migratory butterflies all near N edge of their ranges in UK

many confined to warm micro-sites – might be expected to undergo range

expansions under global warming


(4) Climate change

instead most species declined over the past 30 years

89% sedentary habitat specialists (open symbols) shrank in distribution

50% of mobile, habitat generalists (closed symbols) increased in distribution


(4) Climate change

Changes in distribution correlated with changes in abundance

consistent with habitat loss interacting with climate change

- sedentary species differentially susceptible because they

can’t colonize isolated patches of habitat

- decline in abundance as a result


VI.Insects & the endangered species act (esa)

In US, insects obtain protection under the endangered species act (1973)

globally unique piece of legislation but not without its problem:

(1) species get listed too late: threatened & endangered

(2) political circumstances can affect particular listings

(3) historical focus has been on species preservation (as

opposed to habitat preservation)

listed vertebrates (e.g., California Condor) far outnumber listed insects

most listed insects are butterflies but this probably reflects …

… degree of knowledge about these conspicuous insects

… aesthetic considerations

non-butterflies listed as endangered frequently elicit controversy


Delhi sands flower-loving fly

sedentary, habitat specialist

formerly occupied 40 mile2 area

of dunes in SW SBD & NW RIV Cos.

98% of this habitat has been

converted either to agriculture or

urban developments

remaining 2% (vic. Fontana &

Colton) heavily fragmented


Delhi sands flower-loving fly

fly listed in 1993 as endangered

listing prevented some planned developments from being built

outcry of local politicians & some media sources

upside of listing: last fragments of a rare ecosystem preserved


Jobs versus flies?

NY Times (12/1/02)


Documents

I. Why give a lecture on insects in BLD18? II. What are insects? III. Why are insects so diverse? IV. How many species of insects? V. Insect conservation: