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Termination of pupal diapause in the bollworm Helicoverpa armigera by an imidazole derivative KK‐42

The bollworm Helicoverpa armigera , an important pest of cotton and other agricultural crops, overwinters in pupal diapause. Short daylength and lower temperature experienced during larval development are the major environmental triggers responsible for the induction of diapause (Li & Xie, 1981). Diapause is not a graded response to the environmental conditions but an ‘all or none’ phenomenon. Temperature is the most important factor in determining the duration of diapause (Wang et al., 1999). Diapausing pupae are characterized by a virtual absence of the moulting hormone and diapause can be broken by the injection of 20-hydroxyecdysterone (Wang & Gong, 1997). In some insects, KK-42 was reported to act as an anti-juvenile hormone (JH) agent (Kuwano et al., 1985; Kiuchi et al., 1985; Gelman et al., 1995) or as ecdysteroid antagonist (Kadono-Okuda et al., 1987; Kiuchi & Akai, 1988; Gelman et al., 1995). KK-42 was also shown to induce a precocious termination of diapause in pharate first instar larvae of the wild silkmothAntheraea yamamai , and the gypsy moth Lymantria dispar japonica(Suzuki et al., 1990, 1993; Bell et al., 1994; Lee & Denlinger, 1996). The ability of KK-42 to disrupt pupal diapause has not been investigated. The bollworm H. armigera is one of the most serious pests in Asia, especially in China. Our preliminary investigations revealed that ecdysteroids are crucial factors in the control of induction and termination of pupal diapause in this pest. The aim of the present study was to examine whether KK-42 exerts anti-ecdysteroid effects or, to the contrary, induces a precocious diapause break. In the first case, bollworms cultured under non-diapause conditions and treated with KK-42 as prepupae should develop into diapausing pupae or, at least, the length of the pupal instar should be extended. If, on the other hand, KK-42 could break pupal diapause, the treatment of diapausing pupae with KK-42 should cause a precocious termination of diapause. In this paper, we describe the effects of KK-42 on non-diapausing and on diapause-bound H. armigera prepupae and pupae. In pilot experiments we found that KK-42 may cause a precocious termination of diapause, presumably by stimulating ecdysteroid production from the prothoracic glands.