Physiologically based demographics of Bt cotton–pest interactions

Deconstructing Indian cotton: weather, yields, and suicides

“…Short-season cotton was replaced by fertile Bt cotton despite no increases in yield because implementation requirements were less stringent, it gives excellent control of PBW [58], and in an industrial setting, the costs of the Bt technology are an acceptable cost-effective alternative to short-season cotton (see Additional file 1). Bt cotton is "softer" on natural enemies than insecticides [59,60] enabling reductions in insecticide use [61] that allows secondary pests (e.g., bollworms, budworms, whiteflies) to recede to prior low pest status [33]. Though not significantly different, mean natural enemy densities in Bt cotton are consistently lower than those in unsprayed non-Bt cotton [62], and the efficacy of some natural enemies is reduced when feeding on Bt-intoxicated prey [63,64].…”

“…Though not significantly different, mean natural enemy densities in Bt cotton are consistently lower than those in unsprayed non-Bt cotton [62], and the efficacy of some natural enemies is reduced when feeding on Bt-intoxicated prey [63,64]. For pests such as bollworms and defoliators having high reproductive capacities (500-1000 eggs/female/week) or pests with high tolerance to Bt toxins (e.g., plant bugs, whiteflies, and mealybugs), a small reduction in natural enemy density and efficacy may increase pest density and trigger insecticide use and ecological disruption [33]. Plant bugs have increased in Bt cotton in China and the USA, but this has been dismissed as due to reduced pesticide use [58,[65][66][67], despite strong evidence that insecticide use increases plant bug resurgence [33,55] (see Additional file 1).…”

“…For pests such as bollworms and defoliators having high reproductive capacities (500-1000 eggs/female/week) or pests with high tolerance to Bt toxins (e.g., plant bugs, whiteflies, and mealybugs), a small reduction in natural enemy density and efficacy may increase pest density and trigger insecticide use and ecological disruption [33]. Plant bugs have increased in Bt cotton in China and the USA, but this has been dismissed as due to reduced pesticide use [58,[65][66][67], despite strong evidence that insecticide use increases plant bug resurgence [33,55] (see Additional file 1). In India and Pakistan, sucking insect pests had been of minor concern in cotton but are now increasing in Bt cotton and contribute to yield losses and increased insecticide use [68,69].…”

“…2d). Several larvae may develop per mature fruit with the proportion reduction in lint yield being 0 ≤ ϕ = 0.061mean larvae/boll < 1 [30]. As occurs in other areas of the world, insecticide use to control PBW in India induces outbreaks of bollworms, defoliators, whiteflies, and other pests [29,[31][32][33][34].…”

Temporal allocation of metabolic tolerance to transgenic Bt cotton in beet armyworm, Spodoptera exigua (Hübner)

“…Guo et al [18] reported that significantly lower carboxylesterase (CarE) was observed in the larvae of Micromelalopha troglodyte fed on the leaves of transgenic poplars and revealed that these plants disturbed the insect metabolism mainly by restraining the activities of CarE in the midgut of larvae and subsequently caused larval death. Because the control efficacy of Bt cotton depends on the expression of Cry genes through synthesis of insecticidal protein [19], the temporal variation of efficacy may lead to insufficient control of herbivorous insects and the evolution of resistance or tolerance [20]. To date, there is limited information regarding the temporal variation of enzymes activities in the body of S. exigua in response to B. thuringiensis and further evaluation of these factors is necessary.…”