Spatial and temporal variability in host use by Helicoverpa zea as measured by analyses of stable carbon isotope ratios and gossypol residues

Abstract

Summary 1.A high dose ⁄ refuge strategy has been adopted in the USA to manage the risk of Bacillus thuringiensis (Bt) resistance in target pests such as the cotton bollworm (CBW), Helicoverpa zea (Boddie) in transgenic Bt cotton Gossypium hirsutum L. Structured refuges, consisting of non-Bt cotton, have been a mandated part of this strategy to produce non-selected insects that are temporally and spatially synchronous with insects from the Bt crop, diluting Bt resistance alleles through mating. However, the bollworm is highly polyphagous and exploits a large number of crop and weedy hosts concurrently with Bt cotton. 2. A study was carried out in five major US cotton-producing states during 2002 and 2003 using the ratios of 13 C to 12 C in bollworm moths to estimate the proportions of the population originating from C 3 or C 4 plants. A separate study measured gossypol residues in moths from four states in 2005 and 2006, enabling the identification of moths whose natal hosts were cotton rather than other C 3 hosts. 3. C 4 hosts served as the principal source of bollworm moths from mid-to-late June to early September, depending on the state. Beginning in late August ⁄ early September and lasting 1-4 weeks, the majority of moths exhibited isotopic compositions characteristic of C 3 hosts. During this period, however, the minimum percentage of moths that developed as larvae on C 4 hosts was typically >25%. By mid-September and through October and November, the majority of the bollworm population exhibited C 4 isotopic compositions. 4. Between late June and early August, cotton-derived bollworm moths (moths with gossypol residues) comprised <1% of moths in all states, and remained below this level throughout the season in North Carolina. In other states, cotton-derived moths increased between early August and early September to peak at an average of 19AE1% of all moths. 5. Synthesis and applications. Data on 13 C ⁄ 12 C ratios and gossypol residues in CBW moths were used to assess the importance of structured non-Bt cotton refuges for the management of Bt resistance risk in H. zea. Weekly estimates of bollworm breeding on cotton, C 3 plants other than cotton and C 4 plants showed that, throughout the season, the majority of bollworm moths caught in pheromone traps adjacent to cotton fields did not develop as larvae on cotton. This result implies that management practices in cotton such as the use of structured cotton refuges will play a relatively minor role -particularly compared with maize Zea mays L. -in managing potential resistance to Bt cotton in populations of the CBW in the US Cotton Belt.

Landscape effects on the abundance and larval diet of the polyphagous pest Helicoverpa armigera in cotton fields in North Benin

“…41 All individual H. armigera moths were preserved in alcohol (ethanol 95%) for biochemical analyses. 17,42,43 Host plants with different photosynthetic pathways (C 3 versus C 4 plants) leave an isotopic signature, specific to the plants on which the larvae have fed, in the adult insect's inert tissues (wings and chitin). 16 The method involves analysing the ratio of carbon isotopes ( C) C12 and C13 ( 12 C/ 13 C).…”

“…To determine the use of cotton as a host plant, we analysed gossypol residues in moth extracts using a modified method (Appendix D) derived from the method presented in Head et al 17 Cotton has a C 3 photosynthetic pathway; thus, we analysed gossypol only in moths already identified as being in the C 3 group. A total of 1060 individual gossypol analyses were run (182 moths trapped in 2011 and 878 in 2012).…”

“…Stable isotopes have previously been used to identify natal origin in studies of insect migration 15 and natal host plant use. 16 Biochemical markers can also be used, 17 as the analysis of gossypol residues in adult H. zea tissues showed that the majority of bollworm moths caught in pheromone traps adjacent to cotton fields did not develop as larvae on cotton.…”

Heliothis virescens and Bt cotton in the United States

“…However, this is only a logical supposition since there was not an accurate way to differentiate the exact host plant or geographical origin of the males captured in traps until recently. 71 In contrast to this great body of information, a few reports of larval densities present in wild hosts and other crops importantly, the use of two or more Bt toxins with unique modes of action can be critical in diminishing the development of resistance to B. thuringiensis, [46][47][48][49][50] one of the greatest challenges for the future of this technology.…”

Cross-species amplification and polymorphism of microsatellite loci in Helicoverpa armigera and Helicoverpa zea (Lepidoptera: Noctuidae) in Brazilian cropping systems

“…Although the exact evolutionary relationship between H. armigera and H. zea is uncertain, they are considered "twin" or "sibling" species, and are able to mate and produce fertile offspring under laboratory conditions (Laster and Hardee, 1995;Laster and Sheng, 1995;Cho et al, 2008, Pogue, 2013. Both H. armigera and H. zea are highly polyphagous and have high reproductive and dispersal capacities that favor their rapid adaptation to various control tactics (e.g., insecticides and genetically modified plants) (Fitt, 1989;Head et al, 2010;Yang et al, 2013;Razmjou et al, 2014;Walsh et al, 2014). Due to the invasion of H. armigera, both species now coexist in Brazilian landscapes.…”