Spatio-temporal variation in Helicoverpa egg parasitism by Trichogramma in a tropical Bt-transgenic cotton landscape

Abstract

1 Understanding the spatio-temporal dynamics of insects in agroecosystems is crucial when developing effective management strategies that emphasize the biological control of pests. 2 Wild populations of Trichogramma Westwood egg parasitoids are utilized for the biological suppression of the potentially resistant pest species Helicoverpa armigera (Hübner) in Bt-transgenic cotton Gossypium hirsutum L. crops in the Ord River Irrigation Area (ORIA), Western Australia, Australia. 3 Extensive, spatially-stratified sampling during a season of relatively high Trichogramma abundance found that spatial patterns of pest egg parasitism in the ORIA tend toward heterogeneity, and do not necessarily coincide with host spatiotemporal dynamics. Both patterns of host egg density and mean rates of parasitism are not good indicators of parasitoid spatio-temporal dynamics in ORIA cotton crops. 4 Parasitism rates can be significantly higher within the middle strata of the cotton plant canopy before complete canopy closure, despite a similar number of host eggs being available elsewhere in the plant. 5 Spatial variation in egg parasitism by Trichogramma in Bt-transgenic cotton is evident at the between-field, within-field and within-plant scale, and is not solely driven by host spatial dynamics. These factors should be considered when estimating Trichogramma impact on pest species during biological control and spatio-temporal studies of host-parasitoid interactions in general.

Dual Cry2Ab and Vip3A Resistant Strains of <I>Helicoverpa armigera</I> and <I>Helicoverpa punctigera</I> (Lepidoptera: Noctuidae); Testing Linkage Between Loci and Monitoring of Allele Frequencies

“…Collecting Helicoverpa spp. eggs in the Þeld is an expensive and laborious task, particularly as eggs often prove to be heavily parasitized (Davies et al 2011). Another major loss of material occurs when adults from the Þeld fail to mate under laboratory conditions.…”

Evaluation of spatial and temporal patterns of insect damage and aflatoxin level in the pre‐harvest corn fields to improve management tactics

“…The patterns were assessed using Spatial Analysis by Distance Indices (SADIE) or SADIEShell (version 2.0) (Conrad & Perry, 2008a). The software was developed for spatial analysis of ecological data in the form of spatially referenced counts (Perry, 1998;Perry et al, 1999Perry et al, , 2002Davies et al, 2011). All data were rounded to the nearest whole number for SADIE analysis, as required by the program.…”

“…The SADIE produces a number of indices that quantify the degree of non-randomness within the analyzed data set by testing the null-hypothesis that counts per sampling point are randomly arranged with respect to one another (Davies et al, 2011). Using this tool, the associations between each insect parameter and aflatoxin level, and spatio-temporal patterns in insect damage and aflatoxin level between the two sampling dates at each sampling site, were examined.…”

“…Patterns in association were thus graphically represented by mapping χ p . The mean comparison of χ p for all sites provides an overall measure of spatial association (χ ) between the two data sets (Davies et al, 2011).…”

Using Trichogramma Westwood (Hymenoptera: Trichogrammatidae) for insect pest biological control in cotton crops: an Australian perspective

“…Finally, we focus on cotton production in Australia and the shift away from the chemical paradigm towards more sustainable pest control approaches that use Trichogramma among other natural enemies, although similar basic work on predators is also required (see Furlong & Zalucki 2010). We especially cover future prospects in the northern tropics of Australia, such as the Ord River Irrigation Area (ORIA) (15°47′S, 128°44′E) in Western Australia, where Trichogramma have been effective at suppressing target insect pests and are considered crucial to the continued sustainability of Bt ‐transgenic cotton production in the region (Strickland & Lacey 1996; Davies et al . 2009, 2011).…”