Effects of elevated atmospheric CO 2 (double-ambient CO 2 ) on the growth and metabolism of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), fed on transgenic Bacillus thuringiensis (Berliner) (Bt) cotton [Cry1A(c)], grown in open-top chambers, were studied. Two levels of CO 2 (ambient and double-ambient) and two cotton cultivars (non-transgenic Simian-3 and transgenic GK-12) were deployed in a completely randomized design with four treatment combinations, and the cotton bollworm was reared on each treatment simultaneously. Plants of both cotton cultivars had lower nitrogen and higher total non-structural carbohydrates (TNC), TNC:Nitrogen ratio, condensed tannin, and gossypol under elevated CO 2 . Elevated CO 2 further resulted in a significant decrease in Bt toxin level in GK-12. The changes in chemical components in the host plants due to increased CO 2 significantly affected the growth parameters of H. armigera. Both transgenic Bt cotton and elevated CO 2 resulted in a reduced body mass, lower fecundity, decreased relative growth rate (RGR), and decreased mean relative growth rate in the bollworms. Larval life-span was significantly longer for H. armigera fed transgenic Bt cotton. Significantly reduced larval, pupal, and adult moth weights were observed in the bollworms fed elevated CO 2 -grown transgenic Bt cotton compared with those of bollworms reared on non-transgenic cotton, regardless of the CO 2 level. The efficiency of conversion of ingested food and of digested food of the bollworm were significantly reduced when fed transgenic Bt cotton, but there was no significant CO 2 or CO 2 × cotton cultivar interaction. Approximate digestibility of larvae reared on transgenic cotton grown in elevated CO 2 was higher compared to that of larvae fed non-transgenic cotton grown at ambient CO 2 . The damage inflicted by cotton bollworm on cotton, regardless of the presence or absence of insecticidal genes, is predicted to be more serious under elevated CO 2 conditions because of individual compensatory feeding on host plants caused by nitrogen deficiency.
The effects of three cotton cultivars with low ('ZMZ13'), medium ('HZ401'), and high ('M9101') gossypol contents on the development, reproduction, and survival of Aphis gossypii Glover and its predator Propylaea japonica (Thunberg) were investigated. Developmental duration and immature survivorship did not vary between aphids on the three cultivars, whereas A. gossypii feeding on M9101 (high gossypol cultivar) displayed significantly shorter adult longevity and lower fecundity than aphids fed on 'ZMS13' and 'HZ401'. Free fatty acid content in cotton aphids reared on 'M9101' was greater than in those reared on 'HZ401' and 'ZMS13'. No significant differences in survival and lifetime fecundity of P. japonica were observed between P. japonica fed cotton aphids reared on the three different cultivars. P. japonica fed aphids from 'M9101' showed a significantly shorter developmental period and greater adult weight than those fed aphids from the other two cultivars. The decreased larval developmental duration and increased adult weight of P. japonica fed cotton aphids reared on the high gossypol-containing cultivar might have been caused by the high fatty acid content of the prey aphids. Our results indicate that high gossypol in host cotton had an antibiotic effect on A. gossypii and showed a positive effect on growth and development of P. japonica at the third trophic level. This suggests compatibility between one form of host plant resistance and biological control by predators. The allelochemical contents should be taken into account in integrated pest management for their effects on both herbivores and entomophagous insects.
Host‐associated differentiation (HAD) is the occurrence of genetically distinct, host‐associated lineages. Most of the cases of HAD in phytophagous insects have been documented in specialist insects inhabiting feral ecosystems or in generalist parthenogens in agroecosystems. Herein we report HAD in the cotton fleahopper, Pseudatomoscelis seriatus (Reuter) (Hemiptera: Miridae), a native, generalist, non‐parthenogenetic insect feeding on native wild hosts [horsemint, Monarda punctata L. (Lamiaceae) and woolly croton, Croton capitatus Michx. (Euphorbiaceae)] and on cotton [Gossypium hirsutum L. (Malvaceae)] in the USA. Examination of genome‐wide genetic variation with AFLP markers and Bayesian analyses of P. seriatus associated with three different host plant species at five locations in Texas revealed a geographic pattern of HAD. The geographic pattern of HAD corresponded with differences in precipitation among the locations studied. In three locations, two distinct lineages of P. seriatus were found in association with horsemint and cotton/woolly croton, whereas in two other locations, populations associated with the different host plants studied were panmictic. We suggest that precipitation differences among locations translate into heterogeneity in vegetation distribution, composition, and phenology, which altogether may contribute to the observed geographic pattern of HAD.
The primary management tactic for lepidopteran pests of cotton in the United
States of America (USA) is the use of transgenic cotton that produces
Bacillus thuringiensis Berliner (Bt)
toxins. The primary target pests of this technology are Helicoverpa
zea (Boddie) and Heliothis virescens (F.) in the
eastern and central Cotton Belt of the USA. Concerns over the evolution of
resistance in H. zea to Bt
toxins and scrutiny of the necessity of Bt crops has escalated.
We reviewed published and unpublished data from field trials of
Bt cotton in the eastern and central Cotton Belt of the USA
through 2015 to evaluate the effectiveness of Bt cotton
(Bollgard, Bollgard II, WideStrike, WideStrike 3, and TwinLink).
Bt cotton reduced insecticide usage, reduced heliothine
pest numbers and damage, and provided a yield benefit, but Bollgard II and
WideStrike efficacy declined in the Midsouth over the period evaluated. In the
Southeastern region, heliothine damage remained constant through 2015, but yield
benefits declined from 2010 until 2015. Resistance of H.
zea to several Bt toxins is the most
plausible explanation for the observed changes in Bt cotton
efficacy. The introduction of new Bt toxins such as found in
Widestrike 3 and Twinlink may preserve the benefits of Bt
crops. However, while both Widestrike 3 and Twinlink had less damage than
Widestrike, damage levels of both were similar to Bollgard II.
The effects of elevated carbon dioxide (CO 2 ) on growth, metabolism, and performance of three generations of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), were studied. The insects were continuously fed transgenic Bacillus thuringiensis (Berliner) (Bt) cotton [ Cry1A (c) ] grown in open-top chambers. Two levels of CO 2 (ambient and 2 × ambient) and two cotton cultivars (non-transgenic Simian-3 and transgenic Bt GK-12) were used and bollworm larvae were reared on all four treatment combinations for three generations. CO 2 level and cotton variety significantly affected the growth and food digestibility parameters of H. armigera , with the exception of larval consumption rate for cotton variety. Overall, elevated CO 2 and transgenic Bt cotton both increased larval lifespan, food consumption rate, relative consumption rate, and approximate digestibility, while decreasing pupal weight, survival rate, fecundity, frass output, relative and mean relative growth rates (RGR/MRGR), and the efficiency of conversion of ingested and digested food (ECI/ECD). Moreover, there were significant CO 2 *variety interactions on pupal weight and ECD, and CO 2 *generation interactions on pupal weight, frass output, and MRGR. Furthermore, transgenic Bt cotton significantly decreased the population-trend index compared to non-transgenic cotton for the three successive bollworm generations, especially at elevated CO 2 . Damage inflicted by the cotton bollworm on cotton, irrespective of the presence of insecticidal genes, is predicted to be higher under elevated CO 2 conditions because of individual compensatory feeding on host plants. Conversely, population abundance is presumed to be lower under elevated CO 2 compared to that under ambient CO 2 , particularly in combination with transgenic technologies.
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