Effects of neem on Nezara viridula (L.) (Hemiptera: Pentatomidae) and its major parasitoid, Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae), in cowpea

The commercial neem (Azadirachta indica A. Juss) formulation Neemix 4.5 EC (Certis LLC, Columbia, MD) was evaluated for control of the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), a cosmopolitan pest of cowpea (Vigna unguiculata [L] Walpers) and several food and fiber crops worldwide. Also, the nontarget effects of neem on Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae), a major egg parasitoid of N. viridula, were investigated. In addition, effects of neem on predation on N. viridula eggs in the field were assessed.; The antifeedant activity of neem was tested against adult N. viridula using a cowpea pod-dip method and a laboratory toxicity assay was conducted by dipping 4th instars. Feeding on neem-treated pods was significantly reduced compared with water-treated controls, based on counts of salivary sheath deposits on pod surfaces, inside pod walls and on seeds. The antifeedant effect of neem was significantly greater on pods treated with 5% aqueous neem solution than on those treated with 0.5%, indicating that the antifeedant activity was related to concentration. Bugs showed an initial negative feeding response before feeding on neem-treated pods; males and females did not differ in their response to the treatments. The LC₅₀ for nymphs was ≥61% (≥27450 ppm azadirachtin) at 2 d and ranged from 1.8–6.2% (810–2790 ppm) at 5 d post-treatment, which indicated that neem was slow acting. Sublethal treatments of nymphs affected molting and caused morphological defects in adults. Development time to adulthood also was prolonged and longevity of females was negatively affected by neem treatments.; Applications of 0.5% aqueous neem solution (225 ppm azadirachtin) to cowpea were used to evaluate neem against N. viridula (L.) in the field from 1999 to 2001. Neem was applied to each crop beginning at pod formation. Densities of N. viridula declined in treated cowpea plots, but significant differences between treated and controls were detected only before the third spray application in 1999 and 2001. Deformed adults were observed in neem-treated plots after the second spray application. Pod and seed damage was significantly reduced in neem-treated plots compared with controls in 2000 and 2001. Neem treatments reduced seed damage in 1999 and significantly increased total seed yield in 2001 compared with controls.; Field tests were carried out to determine the effects of neem treatments on the egg parasitoid, T. basalis and predators of N. viridula during 2000 and 2001. In laboratory choice and no-choice tests, treatment of N. viridula eggs with neem had no effect on parasitization by T. basalis. Parasitoid development and emergence from host eggs treated before or after parasitization also were not affected by neem compared with controls. Additionally, neem did not affect longevity of adult parasitoids from neem-treated eggs nor the reproductive activity of females compared with controls. In the field, parasitization was similar in neem-treated and water-treated control eggs. Similarly, neem treatments applied to cowpea did not affect parasitism of N. viridula eggs. No differences in predation on N. viridula neem-treated eggs or in neem-treated plots were detected compared with controls. Main predators of eggs were fire ants, Solenopsis invicta Buren, the coccinellids, Coccinella septempraactata L., Coleomegilla maculata lengi (DeGeer) and coccinellid larvae, and the orthopterans, Oecanthus fultoni Walker and Gryllus sp.