Extended Sentinel Monitoring of Helicoverpa zea Resistance to Cry and Vip3Aa Toxins in Bt Sweet Corn: Assessing Changes in Phenotypic and Allele Frequencies of Resistance.

Transgenic corn and cotton that produce Cry and Vip3Aa toxins derived from Bacillus thuringiensis (Bt) are widely planted in the United States to control lepidopteran pests. The sustainability of these Bt crops is threatened because the corn earworm/bollworm, Helicoverpa zea (Boddie), is evolving a resistance to these toxins. Using Bt sweet corn as a sentinel plant to monitor the evolution of resistance, collaborators established 146 trials in twenty-five states and five Canadian provinces during 2020-2022. The study evaluated overall changes in the phenotypic frequency of resistance (the ratio of larval densities in Bt ears relative to densities in non-Bt ears) in H. zea populations and the range of resistance allele frequencies for Cry1Ab and Vip3Aa. The results revealed a widespread resistance to Cry1Ab, Cry2Ab2, and Cry1A.105 Cry toxins, with higher numbers of larvae surviving in Bt ears than in non-Bt ears at many trial locations. Depending on assumptions about the inheritance of resistance, allele frequencies for Cry1Ab ranged from 0.465 (dominant resistance) to 0.995 (recessive resistance). Although Vip3Aa provided high control efficacy against H. zea, the results show a notable increase in ear damage and a number of surviving older larvae, particularly at southern locations. Assuming recessive resistance, the estimated resistance allele frequencies for Vip3Aa ranged from 0.115 in the Gulf states to 0.032 at more northern locations. These findings indicate that better resistance management practices are urgently needed to sustain efficacy the of corn and cotton that produce Vip3Aa.

Regional pest suppression associated with widespread Bt maize adoption benefits vegetable growers.

Transgenic crops containing the bacterium Bacillus thuringiensis (Bt) genes reduce pests and insecticide usage, promote biocontrol services, and economically benefit growers. Area-wide Bt adoption suppresses pests regionally, with declines expanding beyond the planted Bt crops into other non-Bt crop fields. However, the offsite benefits to growers of other crops from such regional suppression remain uncertain. With data spanning 1976-2016, we demonstrate that vegetable growers benefit via decreased crop damage and insecticide applications in relation to pest suppression in the Mid-Atlantic United States. We provide evidence for the regional suppression of Ostrinia nubilalis (Hübner), European corn borer, and Helicoverpa zea (Boddie), corn earworm, populations in association with widespread Bt maize adoption (1996-2016) and decreased economic levels for injury in vegetable crops [peppers (Capsicum annuum L.), green beans (Phaseolus vulgaris L.), and sweet corn (Zea mays L., convar. saccharata)] compared with the pre-Bt period (1976-1995). Moth populations of both species significantly declined in association with widespread Bt maize (field corn) adoption, even as increased temperatures buffered the population reduction. We show marked decreases in the number of recommended insecticidal applications, insecticides applied, and O. nubilalis damage in vegetable crops in association with widespread Bt maize adoption. These offsite benefits to vegetable growers in the agricultural landscape have not been previously documented, and the positive impacts identified here expand on the reported ecological effects of Bt adoption. Our results also underscore the need to account for offsite economic benefits of pest suppression, in addition to the direct economic benefits of Bt crops.

Use of black light traps to monitor the abundance, spread, and flight behavior of Halyomorpha halys (Hemiptera: Pentatomidae).

Monitoring the distribution and abundance of an invasive species is challenging, especially during the initial years of spread when population densities are low and basic biology and monitoring methods are being investigated. Brown marmorated stink bug (Halyomorpha halys (Stål)) is an invasive agricultural and urban pest that was first detected in the United States in the late 1990s. At the time of its detection, no method was available to effectively track H. halys populations, which are highly mobile and polyphagous. One possible solution was the utilization of black light traps, which are nonspecific traps attractive to night flying insects. To determine if black light traps are a reliable monitoring tool for H. halys, a state-wide network of 40-75 traps located on New Jersey farms were monitored from 2004 to 2011 for H. halys. This proved to be a highly effective method of monitoring H. halys populations and their spread at the landscape level. The total number of brown marmorated stink bug caught in New Jersey increased exponentially during this period at a rate of 75% per year. Logistic regression estimates that 2.84 new farms are invaded each year by H. halys. The results indicate that black light traps are attractive to early season populations as well as at low population densities. Weekly trap catch data are being used to generate state-wide population distribution maps made available to farmers in weekly newsletters and online. While no economic threshold currently exists for brown marmorated stink bug, the maps provide farmers with a tool to forecast pest pressure and plan management.