Activity of Bacillus thuringiensis Berliner Against Different Ages and Stages of Helicoverpa zea (Lepidoptera: Noctuidae) on Cotton

Abstract

This study was done to compare the mortality of Helicoverpa zea (Boddie) eggs and larvae of different ages on cotton treated with Bacillus thuringiensis Berliner var. kurstaki. Mortality of H. zea neonates hatching from eggs collected from B. thuringiensis-treated cotton plots was significantly (P ≤ 0.01) higher for eggs 0 than 2 d in age at the highest (1.12kg/ha) rate, but did not differ at lower rates. However, across all rates the median lethal concentration (LC50) was 3.2-fold lower for larvae hatching from eggs that were 2 d in age than those from eggs 0 d in age. Mortality for larvae 1 d in age placed on B. thuringiensis-treated cotton terminals was significantly higher than for larvae 3 and 5 d in age at 4.48 and 8.96 kg/ha rates of B. thuringiensis. The LC50 for larvae 1 d in age (2.1 kg/ha) was 3 and 5.7-fold lower than for larvae 3 and 5 d in age, respectively (based on 95% confidence intervals). These data indicate that in cotton pest management systems, B. thuringiensis applications need to be directed at maximum oviposition and eclosion of H. zea neonates because control is very low against larger larvae.

Efficacy of Bacillus thuringiensis (Berliner) in controlling the tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

“…Another study performed with larvae from several Lepidopteran species showed that the variation in susceptibility during larval development depends on both the toxins tested as well as the species per se (Gilliland et al 2002). Nevertheless, in most cases, first instar larvae were the most susceptible to all toxins tested (Ali and Young 1996;Rausell et al 2000).…”

Variation in susceptibility of Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) (Lepidoptera: Noctuidae) in Australia to two Bacillus thuringiensis toxins

“…If H. punctigera have inherently lower levels of detoxifying enzymes in the neonate stage compared with H. armigera, then the negative eVect of proteinase inhibitors on gut function may be more pronounced, and the "knockdown" eVect more rapid especially when H. punctigera neonates are presented with a diet surface covered with Cry1Ac toxin. Susceptibility to Bt insecticides in Helicoverpa zea has been shown to decline as larvae develop (Herbert and Harper, 1985;Ali and Young, 1996). This was the case for Cry2Ab toxicity in both H. armigera and H. punctigera.…”

Toxicity of biocide GCSC-BtA on arthropod pests under different temperature conditions

“…kurstaki decreased with increasing age for the lepidopterous larvae, i.e. Helicoverpa zea Boddie (Lep., Noctuidae) (Ali and Young 1996) and Boarmia selenaria Schiff. (Lep., Geometridae) (Izhar et al 1979).…”

“…Besides, generally speaking, insects became more resistant to B.t. as larvae age (Ali and Young 1996). Therefore, it was important to test whether one or more specific variables significantly affected insect response to a pesticide (e.g.…”