SUSCEPTIBILITY OF PREDATORY STINK BUG Podisus nigrispinus (DALLAS) (HETEROPTERA: PENTATOMIDAE) TO GAMMA CYHALOTHRIN

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1 SUSCEPTIBILITY OF PREDATORY STINK BUG Podisus nigrispinus (DALLAS) (HETEROPTERA: PENTATOMIDAE) TO GAMMA CYHALOTHRIN R. R. Coelho 1, A.I.A. Pereira 1, F.S. Ramalho 1, J.C. Zanuncio 2. (1) Unidade de Controle Biológico da Embrapa Algodão, C. Postal, Campina Grande, Paraíba. Bolsistas do CNPq, (2) Universidade Federal de Viçosa, MG. ABSTRACT Cotton Integrated Pest Management (Cotton IPM) strategies are based mainly on the potential of predators, parasitoids, and pathogens to suppress pest populations, using insecticides only as needed. Based on this strategy, investigations on side-effects of insecticides and other pesticides play a crucial role in IPM programs, when a combination of chemical and biological measures is required against insect pests. Therefore, the susceptibility of the predatory stink bug P. nigrispinus to the new pyrethroid insecticide gamma cyhalothrin was studied in the laboratory. Fifth-instar nymphs, male and female adults were exposed to gamma cyhalothrin. The predatory stink bug P. nigrispinus was maintained in growth chambers at 26 C, relative humidity of 60 ± 10%, and with a photoperiod of 14L:10D. Newly moulted fifth-instar nymphs (<24 h old), male and female adults (<24 h old) of P. nigrispinus were collected from the Biological Control Unit of the Embrapa Algodão. Formulated material was used in all bio-assays. Gamma cyhalothrin suspension concentrate was supplied by Dow Agrosciences Industrial Ltda Brasil. There is indication that P. nigrispinus is more tolerant to gamma cyhalothrin after topical exposure compared with its prey cotton leafworm. However, nymphs, adult females and males of P. nigrispinus show a high sensitivity to gammacyhalothrin after ingestion through drinking water. INTRODUCTION Cotton Integrated Pest Management (Cotton IPM) strategies are based mainly on the potential of predators, parasitoids, and pathogens to suppress pest populations, using insecticides only as needed. Based on this strategy, investigations on side-effects of insecticides and other pesticides play a crucial role in IPM programs, when a combination of chemical and biological measures is required against insect pests (Mohaghegh et al. 2000). Insecticides and acaricides selectivity are one of the cornerstones for the use of pesticides within IPM systems, insecticides and acaricides should be effectives against pest insects and mites, but relatively safe to natural enemies. However, beneficial arthropod species have a greater susceptibility to insecticides than their host or prey species. According to Boyd (1998) both behavioral (e.g.: locomotion, searching capability, self cleaning) and pesticide processes (e.g.: deposition, redistribution and weathering) may contribute to differences in susceptibility of predaceous insects and their prey to insecticides. The spined soldier bug Podisus nigrispinus (Dallas)(Heteroptera: Pentatomidae) is used in the control of some defoliators pests of the cotton crops like the cotton leafworm (Alabama argillacea (Huebner)(Lepdoptera:Noctuidae) and also fruit feeders as fall armyworm (Spodoptera frugiperda (Smith & Abbot), and Heliothis virescens (Fabricius). But, in some situations, the biological control agents are not able to eliminate completely the pest population, being used an additional treatment with insecticides (Mohaghegh et al. 2000), increasing the probably of contamination for beneficial species. There are a lot works about the susceptibility of chemical products on Podisus maculiventris (Mestdagh et al. 1996; De Clercq et al and 1998; De Cock et al. 1996) but, only a few studies have reported on the side-effects of pesticides on the pentatomid predator P. nigrispinus. Therefore, the susceptibility of the predatory stink bug P. nigrispinus to the new pyrethroid insecticide gamma

2 cyhalothrin was studied in the laboratory. Fifth-instar nymphs, male and female adults were exposed to gamma cyhalothrin. MATERIAL AND METHODS The predatory stink bug P. nigrispinus was maintained in growth chambers at 26 C, relative humidity of 60 ± 10%, and with a photoperiod of 14L:10D. Newly moulted fifth-instar nymphs (<24 h old), male and female adults (<24 h old) of P. nigrispinus were collected from the Biological Control Unit of the Embrapa Algodão. Formulated material was used in all bio-assays. Gamma cyhalothrin suspension concentrate was supplied by Dow Agrosciences Industrial Ltda Brasil. The exposure via topical contact was tested at seven concentrations of gamma cyhalothrin (nymphs: 11.7, 23.4, 46.9, 93.8, 187.5, 375.0, and ppm a.i, and adult females and males: 23.4, 46.9, 93.8, 187.5, 375.0, 750, and 1,500 ppm a.i). The exposure via ingestion of nymphs and adult females and males was conducted at concentrations: 0.47, 0.94, 1.88, 3.75, 7.50, 15.0, and 30.0 ppm a.i. For the exposure by topical contact, one microliter of different concentrations of the insecticide in water was applied on the thoracic dorsum of each predator. The controls were tested with 1µl of water. More than eighty insects were used for each treatment. They were placed individually in small plastic cups with 7.0 cm height and 7.0 cm diameter, with a hole in their cover. In the hole was inserted a plastic tube of 2.5 ml with distilled water and plugged with cotton in order to supply water to the predator and to maintain the humidity inside the cups. Immediately, after the treatment, Musca domestica (Diptera: Muscidae) larvae were provided as needed. Nymphs were checked for mortality every 24 hs until 8 days after moulting and survival of adults was monitored up to 8 days after emergence. Predators were exposed to the insecticide by ingestion through treated drinking water. The insecticide in solution was putted into the plastic tube that was inserted on the hole of each cup. An average of eighty nymphs and adult males and females were tested with a minimum of seven concentrations. Control groups were supplied with distilled water alone. During the first 24 hours, no food was supplied to stimulate the drinking behavior of the pentatomid. Afterwards, the insects were fed on M. domestica larvae (48 h old) as needed. Mortality, for nymphs, was counted 8 days after adult emergence and until 8 days old for adults. Mortality percentages included dead and those individuals could not move. The mortality of predator was evaluated applying probits analysis by probit procedure (SAS Institute Inc. 2003). RESULTS AND DISCUSSION In the Table 1, the toxicity effects of gamma cyhalothrin to 5th-instar nymphs, adult males and females of predatory stink bug P. nigrispinus are showed. Insects affected by gamma cyhalothrin showed some different symptoms of poisone like frequent falling, upturn its ventre (upside down), moving the legs slowly and those that moving just when were touched with a brush (The more commons). Wings deformed after moulting and dead imediatly after moulting were the less commons. For individuals exposure to gamma cyhalothrin via topical application, the LC 50 values were 103.9, 143.6, and ppm a.i for fifth-instar nymphs, and adult females and males, respectively. On the other hand, exposure to gamma cyhalothrin via ingestion yielded LC 50 values of 2.0, 2.0 and 1.9 ppm a.i for fifth-instar nymphs and adult females and males, respectively. In line with ours results, De Cock et al. (1996) found that nymphs of Podisus maculiventris (Say) were more susceptible to Imidacloprid (a nitroguanidine insecticide) after topical exposure than were

3 adults. This difference was suggested by Yu (1988) to explain the different cuticular penetration rate in topical toxicity in P.maculiventris. Therefore, although a cuticle of adults of P. nigrispinus is thicker and more rigid than that of nymphs, a reduced rate of penetration through the cuticle of adults may explain the differences in toxicity of gamma cyhalothrin to this predator. Gamma cyhalothrin is much more toxic to P.nigrispinus via ingestion than via topical contact. CONCLUSIONS There is indication that predatory stink bug P. nigrispinus is more tolerant to gamma cyhalothrin after topical exposure compared with its prey cotton leafworm. However, nymphs, adult females and males of P. nigrispinus show a high sensitivity to gamma cyhalothrin after ingestion through drinking water.

4 Table 1. Toxicity of gamma cyhalorhrin to fifth-instar nymphs and adult females and males of P. nigrispinus via topical exposure and ingestion. Application method Stage Slope ± SE LC 10 (95% FL) LC 50 (95% FL) LC 90 (95% FL) Topical exposure Fifth-instar nymph 1.62 ± ( ) ( ) ( ) Adult female 1.15 ± ( ) ( ) 1, (1, ,183.00) Adult male 1.13 ± ( ) ( ) 1,972 (1,065-5,502) Ingestion Fifth-instar nymph 1.28 ± ( ) 2.05 ( ) ( ) Adult female 1.32 ± ( ) 1.98 ( ) ( ) Adult male 1.94 ± ( ) 1.91 ( ) 8.73 ( ) Slope and LC values (in ppm a.i ) were estimated by probit procedure (SAS Institute Inc. 2003).

5 REFERENCES BIBLIOGRAPHY BOYD, M.L. & BOETHEL, D.J. Susceptibility of predaceous hemipteran species to selected insecticides on soybean in Louisiana. J. Econ. Entomol. v.91, p , DE CLERCQ, P.; COCK, A. DE; TIRRY, L.; VINUELA, E.; DEGHEELE, D. Toxicity of duflubenzuron and pyriproxyfen to the predatory bug Podisus maculiventris. Entomol. Exp. Appl. v.74, p.17-22, DE CLERCQ, P.; MESTDAGH, I.; DEGHEELE, D. Variation in susceptibility to pyriproxyfen in four laboratory strains of Podisus maculiventris (Say)(Het.: Pentatomidae). J. Appl. Entomol. v.122, p , DE COCK, A.; DE CLERCQ, P.; TIRRY, L.; DEGHEELE, D. Toxicity of diafenthiuron and imidacloprid to the predatory bug Podisus maculiventris (Heteroptera: Pentatomidae). Biol. Control v.25, p , MESTDAGH, I.; DE CLERCQ, P.; DEGHEELE, D. Susceptibility of the predatory bug Podisus maculiventris (Say)(Heteroptera: Pentatomidae) to pyriproxyfen residues on sweet pepper plants. Parasitica v.52, p , MOHAGHEGH, J.; DE CLERCQ, P.; TIRRY, L. Toxicity of selected insecticides to the spined soldier bug, Podisus maculiventris (Heteroptera: Pentatomidae). B. Sci. Technol. V.10, p.33-40, SAS INSTITUTE. SAS/STAT User s Guide. Cary, NC., p. YU, S. Selectivity of insecticides to the spined soldier bug (Heteroptera: Pentatomidae) and its lepidopterous prey. J. Econ. Entomol. v.81, p , 1988.

IMPORTANCE OF NATURAL ENEMIES FOR STINK BUG CONTROL. Introduction

IMPORTANCE OF NATURAL ENEMIES FOR STINK BUG CONTROL John R. Ruberson 1, Dawn M. Olson 2, Melissa D. Thompson 2, Russell J. Ottens 1, Michael D. Toews 1, Stan Jones 3 and William A. Mills 4 1 Department