Regional assessment of Helicoverpa zea populations on cotton and non‐cotton crop hosts

Abstract

Selection pressure on bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by cotton, Gossypium hirsutum (L.) (Malvaceae), that produces one or more Bacillus thuringiensis Berliner (Bt) proteins is reduced by plantings of non‐Bt refuge cotton that produce non‐selected individuals. However, the contributions of non‐Bt, non‐cotton crop hosts to the overall effective refuge for H. zea on Bt cotton have not been estimated. A 2‐year, season‐long study was conducted in five US cotton‐producing states to assess the spatial and temporal population dynamics and host use of H. zea. Helicoverpa zea larval estimates in commercial crop fields demonstrated that non‐cotton crop hosts, such as maize, Zea mays L. (Poaceae), grain sorghum, Sorghum bicolor (L.) Moench (Poaceae), peanut, Arachis hypogaea L. (Fabaceae), and soybean, Glycine max (L.) Merrill (Fabaceae), collectively support much larger larval populations than cotton throughout the season. Larval populations were almost entirely restricted to maize in the middle part of the season (June and portions of July), and were observed in non‐cotton crop hosts more frequently and typically in larger numbers than in cotton during the period when production would be expected in cotton (July and August). Numbers of H. zea larvae produced in replicated strip trials containing various crop hosts paralleled production estimates from commercial fields. In contrast, the number of H. zea adults captured in pheromone traps at interfaces of fields of Bt cotton and various crop hosts rarely varied among interfaces, except in instances where maize was highly attractive. With the exception of this early season influence of maize, moth numbers were not related to local larval production. These data demonstrate that H. zea adults move extensively from their natal host origins. Therefore, non‐cotton crop hosts, and even relatively distant hosts, contribute significantly to effective refuge for H. zea on Bt cotton. The results presented here demonstrate that substantial natural refuge is present for Bt‐resistance management of H. zea throughout the mid‐South and Southeast portions of the US cotton belt.

Managing resistance to Bt crops in a genetically variable insect herbivore, Ostrinia nubilalis

“…Surveys of the major U.S. cotton pests, Heliothis virescens and Helicoverpa zea, indicate that both species utilize unstructured refuges at higher rates than we observed for ECB (Gould et al 2002, Gustafson et al 2006, Orth et al 2007, Jackson et al 2008. These data have played important roles in the 2007 approval by EPA to eliminate structured-refuge requirements in IRM plans for Bt cotton varieties pyramided with Cry1Ac and Cry2Ab2 genes in parts of the United States (EPA 2006a(EPA , 2008.…”

Seasonal Abundance, Species Composition, and Population Dynamics of Stink Bugs in Production Fields of Early and Late Soybean in South Arkansas

“…Data (Neunzig 1964). Average captures from pheromone traps in both areas indicated that Ͼ90% of the heliothines were H. zea (Allen 2007 (Allen 2007, Jackson et al 2008 was being conducted at the interface of Bt cotton to understand heliothine movement among crops. Sampling began in early June and continued weekly through the Þrst week of September with four sets of 25 sweeps taken at random locations with a 38-cm sweep net in each soybean and cotton Þeld.…”

Helicoverpa zea and Bt Cotton in the United States

“…The natural refuge for resistance management of dual-toxin cottons, 41 is based largely on the production of bollworm from non-cotton hosts during the period of cotton susceptibility to infestations. Jackson et al 39 and Head et al 40 reported that most of the insects colonizing cotton were from C 4 hosts, probably corn. The threat of elevated resistance because of expanding acreages of Bt corn in cotton-growing regions is the impetus for research projects in the USDA, ARS Southern Insect Management Research Unit on the ecology, dispersal and resistance mechanisms of bollworm in these changing cotton-corn production systems.…”

“…Efficient management of bollworm in cotton relies on Bt cotton, effective insecticides, and increasingly, a knowledge of landscape level information on pest population growth. 39,40 An important landscape level influence was the adoption of a natural refuge concept with the commercialization of pyramided-gene Bt multiple toxin cottons in 2002. 41 This change in EPA resistance management strategies for Bt previously controlled indirectly with broad spectrum insecticides targeted at boll weevil and tobacco budworm became more numerous and required control.…”

“…Bt cotton provides control of bollworm, but supplemental management with applications of insecticide has been required for control of this pest since the first commercial deployment of the transgenic plants in 1996. [23][24][25][26][27][28][29][30] Insecticide use for non-lepidoperan pests, especially Lygus lineolaris (Palisot de Beauvois) and a complex of stink bugs (Pentatomidae), have cotton was due to the documentation of non-cotton host plants as a dominant source of bollworm colonizing Bt cotton, 39,40 and a broader appreciation of landscape level influences on management of this polyphagous agricultural pest.…”