Comparative studies on the effects of Bt-transgenic and non-transgenic cotton on arthropod diversity, seedcotton yield and bollworms control.

The effectiveness of commercial Bt-cotton in pest management, influence on arthropod diversity, natural enemies, and toxin flow in the insect fauna under field conditions were studied keeping in view the need to assess bioefficacy and biosafety of Bt-transgenic cotton. There were no significant differences in oviposition by Helicoverpa armigera on Bt-transgenic and non-transgenic cottons (9.2 versus 9.6 eggs plants-100), while the numbers of H. armigera larvae were significantly more on non-transgenic than on Bt-transgenic (10.4 versus 4.0 larvae plants-100) cotton. The Bt-cotton had significantly more number of mature opened bolls (9.6 versus 4.4 bolls plant-1), lower bollworm damage (12.8 versus 40.2% bolls damaged), and higher seedcotton yield (667.7 versus 231.7 kg ha-1). Population of cotton leafhopper, Amrasca biguttula biguttula was lower (582.2 versus 732.2 leafhoppers plants-100), while that of whitefly, Bemisia tabaci was higher on Bt-transgenic (65.2 versus 45.6 whiteflies plants-100) than on non-transgenic cotton. There was no significant influence of Bt-transgenic cotton on abundance of natural enemies of crop pests – chrysopids (9.6 versus 8.4 chrysopids plants-100), ladybird beetles (16.0 versus 10.8 ladybirds plants-100), and spiders (128.4 versus 142.8 spiders plants-100). There were no significant differences in H. armigera egg (19.8 versus 20.9%), larval (7.4 versus 9.6%), and larval-pupal (1.3 versus 2.9%) parasitism on Bt-transgenic and non-transgenic cottons in the farmer’s fields. The parasitism in larvae of H. armigera was far lower than that of the eggs, which might be because of early mortality of H. armigera prior to parasitoid development in the host larvae. Although, Cry1Ac Bt toxin was detected in Cheilomenes sexmaculatus, chrysopids, A. bigutulla bigutulla, Thrips tabaci, Myllocerus sp., Oxycarenus laetus, Dysdercus koenigii, spiders, bugs, and grasshoppers, no significant differences were observed in their abundance on Bt-transgenic and non-transgenic cottons, suggesting that there were no adverse effects of Bt-cotton on the arthropod diversity under field conditions.

Effect of mating and parasitism regimes on progeny production and sex-ratio of Campoletis chlorideae Uchida.

The ichneumonid parasitoid, C. chlorideae is an important natural enemy of pod borer/bollworm, Helicoverpa armigera (Hubner) in different agro-ecosystems. The sex-ratio of parasitoids has an important bearing on the population build up of the natural enemies for biological control of insect pests. Therefore, the present studies were conducted to gain an understanding of the influence of mating behaviour and abundance of the insect host on fecundity and sex-ratio of the parasitoid, C. chlorideae. There was no significant influence of number of matings and abundance of the insect host on cocoon formation, adult emergence, and larval and pupal periods of C. chlorideae. However, fecundity and female longevity were significantly influenced by mating and abundance of the insect host. There was a significant and positive correlation (r = 0.84**) between longevity and fecundity of C. chlorideae females. The unmated C. chlorideae females produced only males. Nearly 20% of the females that had mated twice were able to parasitize the H. armigera larvae successfully. The sex-ratio of the progeny from females that had mated twice was male biased. Females mated with males from the unmated females produced significantly less numbers of females than those mated with males from the fertilized females, indicating genetic regulation of sex-ratio in C. chlorideae.

Host plant resistance to insects: an eco-friendly approach for pest management and environment conservation.

Host plant resistance (HPR) to insects is an effective, economical, and environment friendly method of pest control. The most attractive feature of HPR is that farmers virtually do not need any skill in application techniques, and there is no cash investment by the resource poor farmers. Considerable progress has been made in identification and development of crop cultivars with resistance to the major pests in different crops. There is a need to transfer resistance genes into high-yielding cultivars with adaptation to different agro-ecosystems. Resistance to insects should form one of the criteria to release varieties and hybrids for cultivation by the farmers. Genes from the wild relatives of crops, and novel genes, such as those from Bacillus thuringiensis can also be deployed in different crops to make HPR an effective weapon to minimize the losses due to insect pests. HPR will not only cause a major reduction in pesticide use and slowdown the rate of development of resistance to insecticides in insect populations, but also lead to increased activity of beneficial organisms and reduction in pesticide residues in food and food products.