COMPARATIVE TOXICITY OF SEVEN INSECTICIDES TO ADULT SPALANGIA CAMERONI PERKINS'

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1 COMPARATIVE TOXICITY OF SEVEN INSECTICIDES TO ADULT SPALANGIA CAMERONI PERKINS' Jeffrey G. Scott, Donald A. Rutz, and Jane Walcott Insect Toxicology Laboratory and Schwardt Insects Affecting Man and Animal Lab Department of Entomology Comstock Hall Cornell University Ithaca, New York Abstract: The toxicity of seven insecticides used for control of muscoid flics on dairies was evaluated against adult. male and female Spa/angia camero"i Perkins, an important biological control agent of fly pests. The toxicil)' of the insecticides decreased in the order of dimethoate > croloxyphos > permethrin dichloi'vos ::l:: Pyrenone > fenvalerate. Male S. camerolli were morc sensitive than females to crotoxyphos. permethrin, and fenvaleratc. Females were more sensitive than moles to dichlorvos. while there was no significant difference between the LCooS of dimethoate and Pyrenone for eflch sex. The tctfflchlorvinphos bioassay revealed a distinct plateau at ca. 55% mortality, suggesting that resistant. indi\'iduals were present in (his population. Comparison of S. cameroni and Musca c/omestica L. toxicity data (ljg/vial) revealed that fenvalerate, pennethrin, and dimethoale were more toxic 10 M. domestica, dichlorvos and Pyrenone were more toxic to S. cumerolli, and crotoxyphos was equally toxic to both species. rnle significance of these fmdings (0 successful control of J1y pests on dairies is discussed, Key Words: [nseda, parasiloid, pyl'cthroid, organophosphate, resistance. J. Agl'ic. Enlomol. 5(2): (April 1988) The house fly, Musca. domestica L. and stable fly, Stomoxys calcit.rans (L.), are major pests in and around dairy farms in the USA. Lowered milk production, reduced feed conversion efficiency, exposure to disease-causing agents, blood loss, and public health llnd nuisance concerns all result from house fly and stable fly activity. These pests cause direct annual losses (losses plus control costs) estimated at over $120 million nationwide (Anon. 1979). Present control techniques rely principally on pesticide use, which has many potentially serious drawbacks including destruction of nonrorget biological control agents, development of insect.icide resistance in the target Oy population, harmful levels of insecticide residues, and environmental pollution. For these reasons, considerable interest has been generated in development of integrated pest management (rpm) pmgrams for nies on dairy farms, with emphasis on biological control using hymenopterous panlsitoids. For IPM to be successful, the pesticides used should be highly selective (i.e., toxic to the pest and non-toxic to the beneficial parasiloids). However, little is currently known ahout the toxicity of insecticides commonly used for fly control on dairy farms to the beneficial biological conb'ol agents. lndigenous hymenopterous pupal parasitoids (Family Pteromalidae) are impoitant biological control agents of house flies and stable nics on dairy farms (Peterson and Meyer 1983; Smith and Rutz 1985). A previous study comparing the selectivity of scven insecticides between 1\4. domestica and Urolepis nl{/pes (Ashmead) revealed I HY\'lENOPTER:\; f'tcrornalidae. Accepted for public8tcd 20 May

2 140 J. Agric. Entomol. Vol. 5, No.2 (1988) that fenvslerate and crotoxyphos were more toxic to the fly than the parasitoid; Pyrenone and dichlorvos were more toxic to the parasitoid, while permethrin, dimethoate and tetrachlolvinphos showed similar toxicity to both (Scott and Rutz 1988). However U. rufipes is only one of several important muscoid fly biological control agents. Because similar data are needed on other parasitoids we determined the toxicity of seven commonly used insecticides against Spalangia camerom Perkins, an important parasitoid of house nies and stable nies. MATERIALS AND METHODS Spalangia cameroni was collected from dairies in and around Tompkins, Schuyler, and Cayuga counties of New York in Parasitoids were collected by using the sentinel pupae parasitoid monitoring method (Rutz and Axtell 1979) and have been colonized in the lab since being collected. Insecticides tested were: crotoxyphos (Ciodrin) [dimethyl (E)-) methyl-2-(iphenylethoxycarbonyl)vinyl phosphatel, dichlorvos (Vspona) 12,2-dichloro-vinyl dimethyl phosphatel, dimethoate (Cygon) [O,O-dimethyl S-methylcarbomoylmethyl phophorodithioatel, fenvalerate i(rs)-oc-cyano-3-phenoxybenzyl (RS-2-(4 chlorophenyl)-3-methylbutyratej, permethrin 13-phenoxybenzyl(1 RS)-cis-trans 3-)2,2dichlorovinyl) 2,2 dimethylcyclopropanecarboxylate, Pyrenone jpyrethrins + piperonyl butoxidel, and tetrachlmvinphos (Rabon) 1(Z)-2-chloro-l-(2,4,&-trichlorophenyl) vinyl dimethyl phosphatel. Sources of the insecticides were given previously (Scott and Rutz 1988). The synergists piperonyl butoxide (PBO > 95%), diethyl maleate (OEM, Aldrich Chern. Co., 97%) and S,S,S-triburyl phosphorotrithioate (DE F) were also used. One- to six-day-old parasitoids were tested by a surface contact assay (Scott md Hutz 1988). This method involved covering the inside surface of a 37 cm 2 glass jar with insecticide (or insecticide plus synergist), aspirating the parasitoids, and transferring 20 parasitoids into the jar. The dosage of the synergists was 100 g/jar for OEM and 10 g/jal" for PBO and DEF. These doses gave no control mortality. Each jar was covered with a wire mesh top and the parasitoids were given a small drop of 10% sucrose on the lid as a food source. Males and females were tested separately. Susceptibility was assessed after holding the parasitoids at constant temperature (28 Q C) for 48 hours (LD 15:9). Twenty parasitoids were tested at each dose using at least four doses giving between 0% and 100% mortality. Each test was replicated a minimum of five times. Results were analyzed by the method of Finney (1952). 'Weights of S. cameron; were determined using freshly killed specimens. Batches of 20 male or female parasitoids (n = 30) were weighed. RESULTS Toxicity of the seven insecticides to S. cameroni decreased in the order of dimethoate > crotoxyphos > pennethrin dichlorvos Pyrenone fenvalerate. Overall, there was a 126-fold reduction in toxicity from dimethoate to fenvalerate based on female LC 50 values. There was substantial variation in the toxicity of compounds within classes of insedicides; however, the pyrethroids were generally less toxic than the organophosphates to S. cameroni. Male S. cameroni were significantly more sensitive than females to fenvalerate, pennethrin, and crotoxyphos (P ). For all insecticides except tetrachlorvinphos, the data points fit the log dose-probit tine (P "- 0.05, chi-squared tes P " for dichlolvos) and there was no

3 SCOTI et 01.: Toxicity of Insecticides to S. camenmi 141 indication of any plateaus. A plot of log dose tetrachlon!inphos vs. mortality (probit scale) shows the existence of a plateau that extends over a l6-fold dose range (Fig. 1) for both sexes. This indicated the existence of two distinct populations relative to their susceptibility to tetrachlorvinphos. The most likely explanation for this phenomenon was that 45% of the population was resistant to tetrachlorvinphos due to selection in the field. The similar response of males and females suggested that the resistance was not affected by the chromosomal ploidy in these psrssitoids , 7 ọ. 5 := J:l a male... female > := iii := - c CIl Ụ. CIl a Tetrachlorvinphos (1l9 per jar) Fig. 1. Toxicity of tetrachlorvinphos to male and female S. cameroni. In an efrort to determine the mechanism(s) responsible for the resistance to tetrachlorvinphos, we examined the effect of three synergists: piperonyl butoxide (PBO), DEF and DEM, inhibitors of oxidative, hydrolytic and glutathion S transferase mediated metabolism, respectively. In these tests the effect of the synergist was evaluated against both the susceptible (i.e., the approximately 55% of the individuals that die at the lower doses) and resistant (i.e., the approximately 45% of the individuals that die only at the higher doses) populations. DEM did not affect either population (Fig. 2). DEF showed a noticeable but erratic effect. DEF had no effect on the susceptible population, and its effect on the resistant population was inconclusive. PBO had a significant effect on both populations. There was an 8-fold increase in toxicity to the susceptible population, suggesting that mixed-function oxidases (MFOs) are important in the detoxification of tetrachlorvinphos in this species. There was also a significant effect on the resistant population(i.e., greater than seen for the susceptible strain), implying that the resistance may be due in part to elevated MFO activity. To investigate the basis of the differential susceptibility of males compared to females, we determined the average weight of each sex. Males were found to be

4 142 J. Agric. Entomol. Vol. 5, No.2 (1988) consistently smaller (P.s. 0.05) than females with average weights of 0.64 ± 0.02 mg (X ± SEM) and 0.74 ± 0.04, respectively. The generally greater tolerance to the insecticides exhibited by female S. cameroni was probably due to their larger size. The most notable exception was dichlorvos, to which females were more sensiti\'e than males. -: D _ +PBO... +DEF.. +DEM > 'I: 0 50 :::;; -l: 25 Gl u Gl 10 D Tetrachlorvlnphos (119 per jar) Fig. 2. Toxicity of tetl'8chlorvinphos to female S. cameroni in the presence of the synergists piperonyl butoxide (PBOl, DEF or diethyj maleate (OEM). Comparison of the parasitoid LC5(j-ny LCw ratio (Table 1) indicated that fenvalerate was much less t.oxic (41-fold) to the parasitoid than to M. domestica followed by permethrin (l7-fojd) and dimethoate (2-fold). Crotoxyphos and Pyrenone showed little selectivity while dichlorvos was more toxic to the parasitoids, having a parasitoid-oy ratio of It must be noted that the susceptibility strain of 1\1. domestica used for these comparisons may not necessarily be representative of A1. domestica populations on dairies that are often resistant to many pesticides (Meyer et al. 1987). DISCUSSION Our results indicate that fenvalerate, permethrin and dimethoate were more toxic to M. domeslica than to S. cameroni. It is likely that these insecticides would, therefore, offer a greater degree of control of fly populations due to their reduced toxicity to S. cameroni. It. should be realized that selective pesticides are only one of the alternatives for developing a successful IPM strategy. Selectivity may also be obtained by proper timing, application techniques, and other factors such as resistance. For example, if resistance to a given insecticide developed in the parasitoids, and not in the target flies, use of that insecticide would greatly improve the eficiency of an WM strategy. It appears resistance to tetrachlorvinphos has already developed to some extent in this strain of S. cameroni. It is noteworthy

5 SCOTT ct HI.: Toxicity of Insecticides to S. cwllcrolli 143 that the resistance has been maintained in this colony for over one year without any selection pressure, suggesting that the resistance mechanism(s) does not have a strong reproductive disadvantage. Our results suggest that a high level of resistance could be selected for in S. cameroni, and the resistant parasitoids released to supplement control of muscoid flies in an [PM system for daily farms. A similar system has been proposed for a predatory mite in apple orchards (Roush and Hoy 1981). Comparison of the t.oxicity between S. cameron; and J\4. domesnca after correcting for differences in weight (LC5(/mg body weight; ± SEM weight of female house flies was 11.9 mg ± 0.4, Scot.t and Rutz 1988) revealed that S. cameroni was more tolerant t.o all insecticides tested (range: fold, especially permethrin (280-fold) and fenvalerate (670-fold). This implies that M. domeslica is probably a better (i.e., more sensitive) animal for toxicity studies on pyrethroids or organophosphates. However, correcting toxicity data for dirferences in body weights may have little relevance to field situations in this case. Comparison of toxicity data between S. cameron and U. rufipes (Scott and Rutz 1988) shows thut dimethoate, pennethrin, Pyrenone and fenvalel'ate were more toxic to U. rufipes_ LC 50 values for dichlorvos and crotoxyphos were similar between both species. We now have data on two or the most common hymenopterous pupal parasitoids of nies on dairies. Fenvalerate is the only compound showing the desired chmacteristic of being highly toxic to M. domestica and much less toxic to S. cnmeroni and U. rufipes. However, more information is needed on the toxicity of these commonly used insecticides to other parasitoid species before adequate data will be available for whole-scale incorporation into an fpi\/1 program.

6 Table 1. Toxicity of seven insecticides to male and female Spalangia cameroni and female Musca domestica. S. cameroni M. domestica + 95% Confidence Intervals Compound Sex LC 50 Lower Limit Upper Limit Slope (S.E.) n LC.. Ratio ;- Tetrachlorvinphos male t 1580 >.,. female t c Dichlorvos male (0.2) 900 female (0.2) '" "S Crotoxyphos 3 male (0.1) 680!2. female (0.6) Dimethoate male (0.5) 500 female (0.5) Q7 2.0,0' Permethrin male (0.2) 1040 z female (0.4) Pyrenone male female (0.3) 5.4 (0.6) Fenvalerate male (0.2) 700 female (0.3) In units of Ilg/jar. t Data did not fit a straight line. +From S<:ott and Rutz (1988) l '"

7 SCOTI et al.: Toxicity of Insecticides to S. r.;nmeroni 145 ACKNOWLEDGMENTS The authors wish to thank Barbara Schanbaker and Clare Stokes for technical assistance. This article is a publication of the Cornell University Agricultural Experiment Station, New York State College of Agriculture and Life Sciences, a statutory college of SUNY. This research was supported by Hatch projects and and a grant from the Northeast Pesticide Impact Assessment Project. REFERENCES CITED Anon Proceedings of a Workshop on LilJestock Pest Management: To Assess National Research Qnd Extension Needs for Integrated Pest Management of Insects. Ticks. and Mites Affecting LivestDcll. and Poultry. Kansas State University, Manhattan, Kansas. 322 pp. Finney, D. J I:Jrobit Analysis. Cambridge University Press, Cambridge. 2nd cd. 318 pp. Meyer, J. A., G. P. Georghiou, and M. K. Hawley I-louse fly (Diptera: Muscidae) resistance to pelmethlin on southern California dairies. J. Econ. EntomoL 80: Peterson, J. J., and J. A. Meyer Host preferences and seasonal distribution of pteromalid parasites (Hymenoptera: Pteromalidae) of stable nics and house flies (Diptera: l\.'luscidae) associated with confined livestock in eastern Nebraska. Environ. Entomol. 12: Roush, R. T., and M. A. Hoy Laboratory, greenhouse. and field studies of artificially selected carbaryl resistance in Metaseiulus occidentalis. Rutz, D. A., and R. C. AxtelL Sustained releases of Muscidifurax raptor (Hymenoptera: Pteromalidae) for house fly (Musca (/omcstica) control in two types of caged layer poultry houses. Environ. EntomoL 8: to. Scott, J. G., and D. A. Rutz Comparative toxicities of seven insecticides to Musca domestica (1...) (Diptera: Muscidae) and Urolepis rufipes (Ashmead) (Hymenoptera: Pteromalidae). J. Econ. Entomol. 81: Smith, L., and D. A. Rut.z The occun'cnce and biology of Urolepis rufipes (Hymenoptera: Pteromalidac), a parasit.oid of house nics in Nc\v York dairies. Environ. Eotomo!. 14: