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Twospotted spider mite, Tetranychus urticae (Koch), has become a significant early season pest of cotton, Gossypium hirsutum L., in the midsouthern U.S. Sixteen experiments were conducted across the midsouthern U. S. to determine the impact of twospotted spider mite infestation timing on cotton injury, stunting, and yields. Twospotted spider mites from a greenhouse colony were used to initiate infestations at the three-leaf stage, at first flower, and at 200 heat unit intervals after first flower. Twospotted spider mite injury on a scale of zero to five (0 = no injury, 5 = severe injury), plant stunting, and final cotton yields were measured. In general, all infestation timings had higher injury ratings compared to the uninfested control. The highest injury ratings were observed for the three-leaf and first flower infestations. Additionally, infestations at the three-leaf stage caused more plant stunting than later infestation timings. In most of the experiments, the three-leaf infestation resulted in significant stunting of cotton plants. For cotton yields, early infestations caused the greatest yield losses. Significant yield losses compared to the untreated control were observed for infestations initiated up to first flower plus 800 heat units. These results suggest that cotton should be protected from twospotted spider mite infestations beyond that point in the growing season. Results from this experiment will be used to improve integrated pest management of twospotted spider mite in cotton. [ABSTRACT FROM AUTHOR]

Cotton, Gossypium hirsutum (L.), plants expressing insecticidal crystal (Cry) proteins from Bacillus thuringiensis Berliner (Bt) constitute the majority of cotton acreage planted across the southern region of the United States. Fall armyworm, Spodoptera frugiperda (J. E. Smith), can be a significant cotton pest in some years, but this species has not been a primary target of Bt cotton technologies. The objective of this study was to characterize fall armyworm oviposition sites on cotton plants expressing Bt proteins. Fall armyworm adults were released into isolation cages containing cotton plants expressing either single (Bollgard®, Cry1Ac) or pyramided proteins (Bollgard II®, Cry1Ac:Cry2Ab; WideStrike™, Cry1Ac:Cry1F) or a conventional non-Bt cotton line. Following an oviposition period of two-three days, cotton plants were destructively sampled to locate egg masses. The distribution of egg masses on Bt cotton plants was not significantly different from that on non-Bt plants. Most egg masses were recorded on leaves, predominately on the abaxial surface, regardless of cotton line. Significantly more egg masses (>68%) were deposited on leaves near or emerging directly from the main stem (sympodial branch nodes 0-2) than on leaves emerging from branch nodes farther from the main stem. Fall armyworm oviposition was not influenced by Bt proteins and sampling protocols for eggs and early instars should be similar in fields of Bt and non-Bt cotton plants. [ABSTRACT FROM AUTHOR]

Abstract: Field corn, Zea mays L., plants expressing Cry1Ab and Cry1F insecticidal crystal (Cry) proteins of Bacillus thuringiensis (Bt) Berliner are planted on considerable acreage across the Southern region of the United States. The fall armyworm, Spodoptera frugiperda (J.E. Smith), is an economically important pest during the mid-to-late season on non-Bt and some commercial Bt corn hybrids. The objective of this study was to quantify foliar injury and survivorship of fall armyworm on transgenic corn lines expressing Cry1Ab or Cry1F Bt proteins. Corn lines/hybrids expressing Cry1Ab, Cry1F, and a conventional non-Bt cultivar were evaluated against artificial infestations of fall armyworm in field trials. Larvae (second instars) of fall armyworm were placed on corn plants (V8-V10 stages). Leaf injury ratings were recorded 14 d after infestation. Hybrids expressing Cry1F had significantly lower feeding injury ratings than non-Bt corn plants. Development and survivorship of fall armyworm on Bt corn lines/hybrids were also evaluated in no-choice laboratory assays by offering freshly harvested corn leaf tissue to third instars. Transgenic corn hybrids expressing Cry1Ab or Cry1F significantly reduced growth, development, and survivorship of fall armyworm compared to those offered non-Bt corn tissue. However, 25–76% of third instars offered Bt corn leaf tissues successfully pupated and emerged as adults. These results suggest Cry1Ab has limited effects on fall armyworm; whereas Cry1F demonstrated significant reductions in foliar injury and lower survivorship compared to that on non-Bt corn tissues. Although fall armyworm is not considered a primary target for insect resistance management by the U.S. Environmental Protection Agency, these levels of survivorship could impact selection pressures across the farmscape, especially when considering that transgenic Bt cotton cultivars express similar Cry (Cry1Ac or Cry1F) proteins. [ABSTRACT FROM AUTHOR]

Using an F1 screen, 352 feral individuals of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), were examined for the presence of Bacillus thuringiensis (Bt)-resistance alleles. These insects represented four geographical populations collected in central and northeastern Louisiana, USA, and one field population from the Gulf Coast area of Texas, USA, during 2006. The F1 screen used various crosses between field-collected insects and a laboratory strain of Cry1Ab-resistant D. saccharalis, including both reciprocal crosses and group mating. F1 neonates of the crosses were screened for Bt resistance on Bt maize leaf tissue. One field-collected individual of D. saccharalis was shown to have a Bt-resistance allele. Based on Bayesian analysis procedures, the Bt-resistance allele frequency in the five populations of D. saccharalis was 0.0028 with a 95% confidence interval of 0.0003–0.0079. The successful identification of a resistance allele in a field collection of insects suggests that the F1 screening technique could be an effective tool for detecting and monitoring rare Bt-resistance alleles in field populations of D. saccharalis. [ABSTRACT FROM AUTHOR]

Transgenic maize, Zea mays L., expressing the Bacillus thuringiensis (Bt) CrylAb toxin has been planted to extensive areas across the United States and several other countries, but no resistance has been documented in field populations of lepidopteran target pests. This article describes the first report of resistance alleles to commercially available CrylAb Bt maize in a Louisiana population of sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae) Two hundred thirteen two-parent isolines of D. saccharalis were screened for CrylAb resistance on Bt maize leaf tissue using an F2 screening technique. Larvae representing three isolines survived >15 d on Bt tissue in the F2 generation. The second generation backcross progeny (B1F2) derived from isoline 52 completed larval development on Bt maize in the greenhouse. Segregation and resistance frequency analysis associated with isoline 52 suggested that Bt resistance is probably determined by a nearly completely recessive allele at a single locus. With this assumption, the estimated resistance allele frequency in this population is 0.0023, within a 95% confidence interval of 0.0003-0.0064. [ABSTRACT FROM AUTHOR]

A lepidopterous pest complex of southwestern corn borer, Diatraea grandiosella Dyar, and sugarcane borer, Diatraea saccharalis (F.), causes economic damage to field maize, Zea mays L., in the southern United States. Management of natural infestations was evaluated in irrigated and non-irrigated plots of Bacillus thuringiensis (Bt) transgenic maize hybrid expressing the insecticidal Cry1A(b) protein associated with the MON810 transformation event. Bt maize significantly (P ≤ 0.05) reduced the number of adult borer exit holes per plant, frequency of plants with adult exit holes in stalks, and frequency of plants with ear shank and cob tunneling compared to non-Bt maize regardless of irrigation regime. Ear length and grain yields were not significantly (P > 0.05) improved in the Bt hybrid compared to those in the non-Bt hybrid but were either similar or significantly (P ≤ 0.05) greater in irrigated than in non-irrigated maize. As stalk borer infestation persisted, a significant (P ≤ 0.05) increase was observed in the number of adult borer exit holes per stalk and in the number of plants affected with exit holes, ear shank tunneling, and cob tunneling in the irrigated non-Bt maize than in the non-irrigated, non-Bt maize. This suggests that irrigated non-Bt maize fields may offer a favorable environment for increased maize stalk borer infestation and survival. During the two-year study, sugarcane borer abundance increased compared to southwestern corn borer. Larvae removed from plants near crop maturity revealed a three to one predominance of sugarcane borer over southwestern corn borer. This might signal greater selection pressure on sugarcane borer in Bt maize in the southern United States. Current Insecticide Resistance Management (IRM) plans need to consider stalk borer species composition in an area and the differences in Bt susceptibility between sugarcane borer and other maize stalk-borer species to meet the high-dose IRM strategy. [ABSTRACT FROM AUTHOR]