M. J. Sullivan

Treatment Thresholds for Stink Bugs (Hemiptera: Pentatomidae) in Cotton

Abstract The green stink bug, Acrosternum hilare (Say), the southern green stink bug, Nezara viridula (L.), and the brown stink bug, Euschistus servus (Say), were predominant phytophagous Pentatomidae detected during 1995–1997 in cotton in South Carolina. These species occurred in similar numbers in conventional and transgenic cotton ‘NuCOTN33B’, containing the gene for expression of CryIA(c) δ-endotoxin of Bacillus thuringiensis Berliner variety kurstaki. Adult stink bugs moved into cotton from wild and cultivated alternate hosts during July, and reproducing populations usually were detected in cotton from late July into September. Applications of either methyl parathion (0.56 kg [AI]/ha) directed for stink bugs or λ-cyhalothrin (0.037 kg [AI]/ha) or cyfluthrin (0.056 kg [AI]/ha) for control of cotton bollworm, Helicoverpa zea (Boddie), provided effective control of pentatomids in NuCOTN33B or conventional ‘DP5415’ and increased yields compared with untreated plots. Fiber quality did not differ among treated or untreated plots of NuCOTN33B. The ground-cloth technique was used to estimate populations of stink bugs, and data indicated that treatment at one bug per 2 m of row adequately protected cotton from yield loss due to stink bug damage. Observations on boll damage indicated that treatment might be necessary if >20–25% reveal internal symptoms of feeding injury during mid- to late season. More detailed damage thresholds should be developed to complement an approach based on population monitoring. This study validated current recommendations for management of pentatomids in cotton, demonstrated the necessity of threshold use for stink bugs in transgenic cultivars expressing endotoxin from B. thuringiensis, and provided insight into further development of management options for pentatomids in the crop.

Predaceous Arthropods and Lepidopteran Pests on Conventional, Bollgard, and Bollgard II Cotton Under Untreated and Disrupted Conditions

Abstract Field studies were conducted from 2000 through 2002 to determine whether the abundance of predaceous arthropods was negatively affected by Bollgard and Bollgard II transgenic cotton, Gossypium hirsutum (L.), that expresses one or two insecticidal proteins of Bacillus thuringiensis Berliner (Bt) for control of lepidopteran pests. During 2000, populations of predators and lepidopteran pests were monitored in small plots of DP50 (non-Bt), DP50B (Bollgard, expresses Cry1Ac), and DP50BII (Bollgard II, expresses Cry1Ac and Cry2Ab) under untreated conditions. In subsequent studies, plot sizes were increased and insect populations were monitored under conditions in which predators were either allowed to develop normally (untreated) or were disrupted with insecticides in early season. Populations of predators (Geocoris spp., Orius insidiosus [Say], Nabis spp., Solenopsis invicta Buren, spiders, coccinellids, and lacewings [Chrysopidae and Hemerobiidae]) were consistently as high or higher in Bollgard and Bollgard II compared with non-Bt. Under untreated and disrupted conditions, season-long populations of Helicoverpa zea (Boddie) were consistently but not significantly lower in DP50BII compared with DP50B. In this study and in previous studies, DP50BII provided excellent control of H. zea despite predator disruption. However, under high population pressure in 2002, H. zea numbers exceeded economic thresholds when predators were disrupted (five larvae >2/3 cm in length per 100 plants on 26 July) and would have required insecticidal intervention. Compared with DP50B, DP50BII provided significantly better control of Pseudoplusia includens (Walker) and Spodoptera frugiperda (J.E. Smith) under both disrupted and untreated conditions. Until experience is gained in wide scale commercial plantings, Bollgard II varieties should be monitored closely for lepidopteran pests that might survive the toxins, particularly where populations of predaceous arthropods have been disrupted.

Efficacy of Insecticides of Different Chemistries Against Helicoverpa zea (Lepidoptera: Noctuidae) in Transgenic Bacillus thuringiensis and Conventional Cotton

Abstract Six insecticides of different chemistries were evaluated against the cotton bollworm, Helicoverpa zea (Boddie), in non-B.t. (Deltapine ‘DP 5415’, Deltapine ‘DP 5415RR’) and transgenic Bacillus thuringiensis (Berliner) (B.t.) (Deltapine ‘NuCOTN 33B’, Deltapine ‘DP 458 B/RR’) cotton. In 1998, treatments consisted of three rates each of a pyrethroid (lambda-cyhalothrin), spinosyn (spinosad), carbamate (thiodicarb), pyrrole (chlorfenapyr), oxadiazine (indoxacarb), and avermectin (emamectin benzoate) in a nonirrigated field. In 1999, treatments consisted of three rates each of lambda-cyhalothrin, spinosad, thiodicarb, and indoxacarb in an irrigated and a nonirrigated (dryland) field. The highest rate of each insecticide corresponded to normal grower-use rates. Spinosad and thiodicarb controlled H. zea in non-B.t. cotton, whereas other materials were less effective. Even though H. zea is becoming increasingly resistant to pyrethroid insecticides, lambda-cyhalothrin was highly effective in dryland B. thuringiensis cotton. Spinosad and thiodicarb were equally effective. Data indicated that reduced rates of lambda-cyhalothrin, spinosad, and thiodicarb could be used for control of H. zea in dryland B.t. cotton systems. However, reduced rates of these insecticides in a heavily irrigated B.t. cotton system did not provide adequate control.

Activity of Selected Neonicotinoids and Dicrotophos on Nontarget Arthropods in Cotton: Implications in Insect Management

Abstract Certain neonicotinoids are used in cotton, Gossypium hirsutum (L.), to control various piercing–sucking pests. We conducted field studies using three neonicotinoids (acetamiprid, thiamethoxam, and imidacloprid) and an organophosphate (dicrotophos) to assess the activity of these insecticides against nontarget arthropods, particularly predators, and to determine the potential economic consequences of such activity. Mortality among populations of the big-eyed bug, Geocoris punctipes (Say), and the red imported fire ant, Solenopsis invicta Buren, was highest after thiamethoxam and dicrotophos treatments. Numbers of arachnids were consistently lower after dicrotophos treatments, whereas none of the neonicotinoids caused appreciable mortality. Total predators in pooled data from five separate studies revealed that numbers, compared with untreated plots, were reduced by ≈75% in dicrotophos, 55–60% in thiamethoxam, and only 30% in both acetamiprid and imidacloprid plots. Acetamiprid and thiamethoxam exhibited significant mortality against field-deposited eggs of bollworm, Helicoverpa zea (Boddie). Both thiamethoxam and dicrotophos plots exhibited bollworm numbers that were approximately three times higher than treatment thresholds (three per 100 plants), whereas numbers in untreated plots were below threshold levels. In one study on Bt cotton, a significant negative correlation was observed between numbers of predators and bollworm larvae. Results demonstrated that neonicotinoids differ in activity against predaceous arthropods and bollworm eggs and that high predator mortality can result in resurgence of bollworm larvae and additional insecticide costs.

Pyrethroid-resistant Helicoverpa zea and transgenic cotton in South Carolina

Abstract Failures to control Helicoverpa zea (Boddie) on cotton in South Carolina were associated with resistance to pyrethroid insecticides. Resistance to cyhalothrin, cypermethrin, and permethrin was observed in a colony collected as larvae from cotton in Estill, SC, in September 1996. Cyhalothrin resistance was expressed as an incompletely dominant trait. In 1997, resistance to cyhalothrin was observed in males captured in pheromone traps in Estill and nearby Ulmer. Resistance was also observed in Cameron and Holly Hill (Santee), SC, 150 km to the north, in adults reared from larvae collected from cotton. In contrast, all moths trapped in the Pee Dee River drainage 300 km to the north were susceptible. Putative mechanisms for resistance as related to improved monitoring of population genetics and implications for control of pests on transgenic insecticidal cotton are discussed.