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Evaluation ofEntomopathogenicNematodes for the Controlof Mediterranean Fruit Fly(Diptera: Tephritidae)Yoav Gazit , Yoram Rossler & Itamar GlazerPublished online: 28 Jun 2010.

To cite this article: Yoav Gazit , Yoram Rossler & Itamar Glazer (2000) Evaluationof Entomopathogenic Nematodes for the Control of Mediterranean Fruit Fly(Diptera: Tephritidae), Biocontrol Science and Technology, 10:2, 157-164, DOI:10.1080/09583150029297

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Biocontrol Science and Technology (2000) 10, 157 ± 164

Evaluation of Entomopathogenic Nematodes for the Controlof Mediterranean Fruit Fly (Diptera: Tephritidae)

YOAV GAZIT,É YORAM ROÈ SSLERÉ and ITAMAR GLAZER2

1 The `Israel Cohen’ Institute for Biological Control, Citrus Marketing Board ofIsrael, Bet-Dagan 50250, Israel; 2 Department of Nematology, Agricultural

Research Organization, The Volcani Center, Bet-Dagan 50250, Israel

(Received for publication 19 April 1999; revised manuscript accepted 11 December 1999)

The virulence of various entomopathogenic nematode (EPN) strains was evaluated against theMediterranean fruit Xy, C. capitata . The selected nematodes were assessed for their infectivityfor the Wnal larval stage of the insect host and under varying environmental conditions. Among12 EPN strains tested, Steinernema riobrave Texas (Sr TX) and Heterorhabditis sp. IS-5(H IS-5), showed high activity and induced > 80% mortality. Six EPN strains showed limitedactivity (> 30% mortality), and four strains had no eVect (< 20% mortality). Sr TX wasmore eVective than H IS-5. Mature C. capitata larvae were most susceptible to nematodeinfection during the Wrst 4 h after they began to emerge from their diet to pupate. Activity ofthe two nematode strains at a constant inoculation rate was dependent on insect larval density.The highest activity was recorded at 1.88 larvae cm 2 2 and decreased at higher larval densities.EPN activity was also directly related to nematode density. Maximal activity was shown at adensity of 150 infective juveniles cm 2 2. A similar activity pattern was also recorded with SrTX in four diVerent soil types. The persistence of this EPN in the soil extended over 5 daysbut there was no activity after 14 days. Except for a lower activity under cool conditions(17ë C), temperatures ranging between 22 and 41ë C, or moisture levels in the treated soilranging between 3 and 20%, had no signiWcant eVect on nematode activity. Our results suggestthat application of Sr TX against C. capitata may have potential for controlling C. capitata .

Keywords: Steinernema sp. Ceratitis capitata, entomopathogeni c nematodes, biological control

INTRODUCTION

Pesticide-bait application s have been used for many years to control the Mediterranean fruit¯ y, Ceratitis capitata (Wiedemann). The ecological drawbacks have prompted a search forother, environmentally-friendl y methods to control this pest. Mature C. capitata larvaeemerge from the host fruit and pupate in the ground, where they are exposed to potentialsoil-borne predators and parasites, such as entomopathogeni c nematodes (EPN) from thegenera Steinernema and Heterorhabditis.

Correspondence to: Y. Gazit. Tel: 972 3 9683 803; Fax: 972 3 9683 838; E-mail: yogazit@netvision.net.il

ISSN 0958-3157 (print)/ISSN 1360-0478 (online)/00/020157-08 � 2000 Taylor & Francis Ltd

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158 Y. GAZIT ET AL.

EPNs are already used for the control of arthropod pests (Georgis & Manweiler, 1994;Martin, 1997) which spend at least part of their life cycle in, or in close contact with, the soil(Martin, 1997). Since EPNs are active foragers and capable of actively penetrating the host’shaemocoel (Kaya & Gaugler, 1993), they are applied to the soil as a type of c̀over-spray’.

The susceptibility of adult C. capitata to Steinernema carpocapsae Filipjev ( 5Neoaplectana carpocapsae (Weiser)) and Heterorhabditis bacteriophora Poinar, was ® rstdemonstrated by Poinar and Hislop (1981) who proposed using EPNs as control agents.Lindegren and Vail (1986) studied the susceptibility of late third instar larvae of C. capitatato S. carpocapsae and Lindegren et al. (1990) examined infectivity under ® eld conditions.

In our study we compared the eYcacy of 12 available EPN strains for C. capitata andtested the most eVective strain under various conditions of the host larva’s biology andunder several environmental conditions.

MATERIALS AND METHODS

FliesC. capitata were derived from a laboratory colony initiated from infested citrus fruitscollected from various orchards in Israel. The ¯ ies were reared at 24 6 1ë C on a diet ofwheat bran, sugar and yeast (RoÈ ssler, 1984). This colony was replenished every two to threeyears by ® eld collected males. The last replenishment was carried out in September 1997.For the present study we used late third instar larvae that, unless indicated otherwise, werecollected within 2 h after they had exited from the diet to pupate.

Entomopathogeni c NematodesTwelve strains of steinernematid and heterorhabditid nematodes were tested in the presentstudy for activity against C. capitata. The species name and origin of these nematodes arelisted in Table 1. These EPNs were reared at 25ë C in the last instar of Galleria mellonellalarvae according to the method of Kaya and Stock (1997). After storage in water suspensionsat 10ë C for 7± 14 days the infective juveniles (IJs) were allowed to acclimate for 24 h beforeuse at room temperature (21± 23ë C).

TestsThe virulence of nematodes to C. capitata was tested using two arenas: (1) a small volumearena consisting of 150 ml plastic cups, 6 cm diameter and a surface area of 28 cm2 ,containing 30 g of dry soil, was used to screen several EPN strains and to determine theoptimal conditions for the study; (2) a large volume arena consisting of 4 l plastic containers,11 3 20 3 20 cm with a surface area of 400 cm2 , containing 3 kg of dry soil, was used tocompare EPN strains, evaluate their infectivity at diVerent concentrations, and assess theiractivity in various soil types, temperature and humidity regimes.

The soil used in most tests was a clay loam type that was obtained from an orange groveat `Tsri® n’ experimental station located in the coastal region of Israel. The soil was air driedfor a week and then the moisture level was adjusted to 7% (w/w) by adding distilled water.Final moisture content reached 10% after the nematodes were added in water suspension.Unless indicated otherwise, 30 late third instar larvae of C. capitata were exposed in eachtest to the inoculated and the untreated control soil by placing the larvae on the soil surface,and allowing them to burrow naturally into it. After 10 days, the number of emerged adultsin each cup was recorded. Mortality level (%) was calculated by subtracting the number ofemerged adults from the initial number of larvae. The mortality was adjusted for controlmortality (< 10%) using Abbott’s formula (Abbott, 1925).

Test (a). Screening EPNs for activity against C. capitata. Several EPN strains weresuspended in water and applied in 0.9 ml of the suspension to the small volume arena at a

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EPN FOR BIOLOGICAL CONTROL OF MEDFLY 159

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160 Y. GAZIT ET AL.

rate of 100 IJs cm - 2 soil. Strains that showed activity were further applied in 90 ml of thesuspension to the large volume arena at the same rate of 100 IJs cm - 2 soil. The two mosteVective EPN strains were then selected for further studies.

Test (b). The length of susceptibility period of pupating larvae. Mature C. capitata larvaewere collected soon after they began to emerge from the diet to pupate and were introducedto the soil in the small volume arena using 30 larvae/cup. EPN suspension (1 ml) containing100 IJs cm - 2 was applied to the soil: immediately (0 h) and 1, 2, 4, 6.5 and 24 h thereafter.

Test (c). EVect of larval density and EPN density on the eYcacy of EPN. In the smallvolume arenas, inoculated with a constant rate of 100 IJs cm - 2 , 30, 60, 120 and 240C. capitata larvae were placed to obtain a density ranging from 1.88 to 15 larvae cm - 2 . Ina separate test, a variable density of EPNs ranging from 25 to 150 IJs cm2 was applied to aconstant density of 1.88 larvae cm - 2 . Both tests determined the optimal ratio of IJs tolarvae for further testing.

Test (d). Persistence of EPNs in soil. Nematodes were applied to the soil in the largevolume arena at a constant rate of 100 IJs cm - 2 . Thirty mature C. capitata larvae wereintroduced to the soil 0, 1, 5, 14 and 30 days following the inoculation .

Test (e). The eVect of soil type on the activity and persistence of EPNs. Four representativesoil types were collected from diVerent locations in Israel: the standard soilÐ clay loam fromTsri® n (coastal area); loess from Bssor river (northern desert); grumosol from Yesodot(inner hills); and sandy silty loam from Hazeva (Arava desert). The soils were inoculated inthe large volume arena with EPNs at a constant rate of 100 IJs cm - 2 . Mature larvae wereintroduced to the inoculated soils immediately or 10 days after the inoculation .

Test ( f ). EVect of soil moisture on EPN activity. Clay loam soil from Tsri® n was air driedfor a week and then wetted to reach a ® nal moisture content of 3, 6, 12 and 20% (w/w),including the water added with the nematode suspensions. Infective juveniles of Sr TX wereapplied in the large volume arena at a density of 100 IJs cm - 2 . Mature C. capitata larvaewere introduced to the treated soils immediately after the inoculation . The survival of ¯ iesin non-treated soil was used as a control.

Test (g). EVect of temperature on EPN activity. Infective juveniles of Sr TX were appliedin the large volume arena to clay loam soil, at a density of 100 IJs cm - 2 . Mature larvaewere introduced to the treated soils immediately after the inoculation . The soil was exposedto constant temperatures of 17, 22 and 27ë C or to a variable temperature regime in aglasshouse with no climatic regulation in which soil temperatures ranged between a maximumof 41ë C during the day and a minimum of 21ë C at night.

RESULTS

The Sr TX and H IS-5 strains showed the highest activity against Mediterranean fruit ¯ ylarvae (test a, Table 1). Six strains caused less than 80% mortality but more than 30%,whereas four strains induced less than 30% mortality. The Sr TX and H IS-5 strains werehence selected for further testing.

The highest eYcacy of the EPNs was on larvae within 2 h of the onset of pupation (test b,

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EPN FOR BIOLOGICAL CONTROL OF MEDFLY 161

Figure 1). Strain Sr TX was superior to H IS-5, and remained so even 4 h after the larvaebegan to pupate. Strain Sr TX induced 20% mortality even in young pupae, 24 h after thebeginning of pupation.

The activity of a constant concentration of the Sr TX and H IS-5 strains decreased withthe increase in larval density (test c, Figure 2). At the lowest larval density, the mortalityrates induced by Sr TX and H IS-5 were 95.5 6 3.6% and 85.2 6 4.2%, respectively. Nematode

FIGURE 1. Activity of S. riobrave TX ( s ) and Heterorhabditis sp. IS-5 ( d ) against mature C. capitatalarvae, as a function of the time since larvae began to pupate. Mortality (%) was calculatedwith regard to the control (< 10%) using Abbott’s formula (Abbott, 1925). Data representmean 6 SE. Asterisks indicate a signi® cant diVerence between S. riobrave TX and Heterorhabditissp. IS-5 (according to Two tail t-test; *P< 0.05, **P< 0.01 and ***P< 0.001).

FIGURE 2. Activity of S. riobrave TX ( s ) and Heterorhabditis sp. IS-5 ( d ) against mature C. capitatalarvae, as a function of larval density in the soil. Mortality (%) was calculated with regard tothe control (< 10%) using Abbott’s formula (Abbott, 1925). Data represent mean 6 SE (n 5 4).

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162 Y. GAZIT ET AL.

concentration also aVected activity (test c, Figure 3), and mortality in both strains washighest at 150 IJs cm - 2 .

The Sr TX strain was signi® cantly more eVective against C. capitata than the H IS-5strain. We therefore used it for further testing at a density of 100 IJs cm - 2 and < 1.88larvae cm - 2 .

The Sr TX strain lost 50% of its activity after 5 days in the standard soil (test d, Figure 4)and after 14 days there was no activity. In another test, the activity in all soil types remained

FIGURE 3. Activity of S. riobrave TX ( s ) and Heterorhabditis sp. IS-5 ( d ) against mature C. capitatalarvae, as a function of nematode density in the soil. Mortality (%) was calculated with regardto the control (< 10%) using Abbott’s formula (Abbott, 1925). Data represent mean 6 SE(n 5 4).

FIGURE 4. Activities of S. riobrave TX against mature C. capitata larvae as a function of the elapsed timefrom the inoculation of the soil with the nematodes to the exposure of the mature larvae.Mortality (%) was calculated with regard to the control (< 10%) using Abbott’s formula (Abbott,1925). Data represent mean 6 SE (n 5 4).

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EPN FOR BIOLOGICAL CONTROL OF MEDFLY 163

TABLE 2. The persistence of S. riobrave TX in four types of soil as indicatedby the activity immediately after nematode inoculationa (0 d) and 10days later (10 d)

Mortality after soil inoculation(mean % 6 SE)b

Source Type of soil 0 d 10 d

Tsri® nc Clay loam 95.8 6 1.70 54.2 6 4.50Bssor Loess 91.9 6 1.65 53.5 6 8.49Yesodot Grumosol 91.4 6 3.69 74.3 6 5.95Hazeva Sandy silty loam 90.9 6 9.00 75.0 6 16.00

aEPN were applied at a rate of 100 IJs cm - 2 in the large volume arena.bMortality (%) was calculated with regard to the control (< 10%) using Abbott’s

formula (Abbott, 1925).cOur standard soil for the study.

above the 50% mortality level for 10 days (test e, Table 2). The persistence of nematodeactivity in grumosol and sandy silty loam was higher than in the clay loam and loess.

Temperatures between 22 and 41ë C and soil moisture levels between 3 and 20% had nosigni® cant eVect on the eYcacy of the Sr TX strain (tests f and g).

DISCUSSION

A biologica l pest control system based on EPNs requires not only an eVective strain ofnematode, but also one that can maintain its infectivity in the soil under the wide range ofenvironmental conditions that the pest inhabits. In this study we evaluated EPNs for controlof C. capitata. DiVerent entomopathogenic nematode strains varied in their ability to infect® nal instar larvae of C. capitata. Among several strains tested, twoÐ Sr Tx and H IS-5Ðwere found to be the most eVective. Between these two, Sr TX caused higher infectivity andhad better persistence in the variable environmental conditions tested.

A biologica l control system for C. capitata using EPNs requires the presence of infectivejuveniles in the soil, ready to encounter the pupating larvae as they reach the ground and,shortly after, when they are most susceptible to infection. We found that the Sr TX nematodewas able to infect the ® nal instar larvae within 4 h of emerging from the diet to pupate.

The infectivity of Sr TX depended on the EPN/larva ratio, probably due to the numberof nematodes that are required to infect an individua l larva. In the small and large volumearena tests the highest mortality obtained was at a rate of > 100 IJs cm - 2 .

We observed that the infectivity of Sr TX in the soil decreased within 10 days and wascompletely lost after 14 days. This indicated that in order to achieve an eVective rate ofnematodes in the soil, repeated application s would be required.

Our results indicate that the infectivity of the Sr TX strain to C. capitata larvae persistedin various moisture and temperature regimes. This characteristic makes this strain a potentialcandidate for EPN based biologica l control systems against the ¯ y, even in countries withvariable climatic conditions.

ACKNOWLEDGEMENTS

The authors thank Ruth Akiva (CMBI, Bet-Dagan, Israel) and Liora Salame (Departmentof Nematology, Volcani Center ARO, Bet-Dagan, Israel) for technical assistance.

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Georgis, R. & Manweiler, S.A. (1994) Entomopathogenic nematodes: A developing biocontrol technology,in Agricultural Zoology Reviews (Evans, K., Ed.), Intersept, Andover, pp. 63± 94.

Kaya, H. & Gaugler, R. (1993) Entomopathogenic nematodes. Annual Review of Entomology 38, 181± 206.Kaya, H.K. & Stock, S.P. (1997) Techniques in insect nematology, in Manual of Techniques in Insect

Pathology (Lacey, L., Ed.), Academic Press, San Diego, pp. 281± 324.Lindegren, J.E. & Vail, P.V. (1986) Susceptibility of Mediterranean fruit ¯ y, Melon ¯ y, and Oriental fruit

¯ y (Diptera: Tephritidae) to the entomogenous nematode Steinernema feltiae in laboratory tests.Environmental Entomology 15, 465± 468.

Lindegren, J.E., Wong, T.T. & McInnis, D.O. (1990) Response of Mediterranean fruit ¯ y (Diptera:Tephritidae) to the entomogenous nematode Steinernema feltiae in ® eld tests in Hawaii. EnvironmentalEntomology 19, 383± 386.

Martin, W.R. (1997) Using entomopathogenic nematodes to control insects during stand establishment.Hortscience 32, 196± 200.

Poinar, G.O., jr & Hislop, R.G. (1981) Mortality of Mediterranean fruit ¯ y adults Ceratitis capitata fromparasitic nematodes Neoaplectana and Heterorhabditis spp. Internationa l Research CommunicationsSystem, Medical Science: Microbiology, Parasitology and Infectious Diseases 9, 641.

Rossler, Y. (1984) Rearing unit for single-pair or small cultures of the Mediterranean fruit ¯ y (Diptera:Tephritidae). Journal of Economic Entomology 77, 556± 557.

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