Interference of the insect growth regulator methoprene in the process of larval‐pupal differentiation

Abstract

Studies with epidermal cells of a number of insects showed that a sequence of physiological events takes place prior to and during the process of commitment of the epidermal cells from the larval to the pupal stage. At the onset of metamorphosis RNA synthesis, including that of RNA, was suppressed for about 30 h just prior to the wandering stage. At the completion of the wandering stage, pupally committed epidermal cells synthesize a new type of RNA termed hetero-disperse nuclear RNA (hnRNA). It is suggested that this RNA species could play a role in the permanent shutting-off of larval-specific genes. Methoprene, a juvenile hormone analogue (JHA), delayed the larval-pupal transformation and prevented these changes in RNA synthesis when applied prior to the appearance of the hnRNA, but had no effect when applied after this period. Treatment with the ]HA in the early last larval instar prevented not only the normal rise in ecdysteroid titer, but also the increase in the activity of chitinolytic enzymes. Treatment of young pupae had no effect on either the ecdysteroids titer or on enzyme activity. A causal relationship between molting hormone titer and the activity of chitinolytic enzymes is proposed. o 1993 WiIey-Liss, Inc.

Characterisation of juvenile hormone esterase in Drosophila melanogaster

“…P'TTH is released in response to very low JH titre and other physiological or environmental cues (critical weight or critical ratio of body dimensions in some Lepidoptera, Jones et al, 1981), causing a small pulse of ecdysone release (Watson et al, 1987). In both Lepidoptera and Diptera this is a major endocrine event with major changes in gene expression (Cherbas, 1993) and in the types of RNA synthesised (Shaaya, 1993). The ecdysteroids, together with low JH titre, cause commitment to the production of pupal rather than larval proteins at the next ecdysone pulse, as well as a behavioural change from feeding to wandering (Dominick and Truman, 1985).…”

“…These changes in endocrine status are associated with numerous changes in behaviour and gene expression in both dipterans and lepidopterans (Cherbas, 1993). Thus, the function of the prewandering ecdysone peak together with low JH titre appears to be induction of the first events in the onset of metamorphosis (Andres and Thummel, 1992;Shaaya, 1993). At the molecular level one of the first responses in insect epidermal cells is a brief cessation of RNA synthesis followed by the production of a novel RNA type (hetero-disperse nuclear RNA, hnRNA) (Shaaya, 1993).…”

“…Thus, the function of the prewandering ecdysone peak together with low JH titre appears to be induction of the first events in the onset of metamorphosis (Andres and Thummel, 1992;Shaaya, 1993). At the molecular level one of the first responses in insect epidermal cells is a brief cessation of RNA synthesis followed by the production of a novel RNA type (hetero-disperse nuclear RNA, hnRNA) (Shaaya, 1993). The hnRNA may have a role in the permanent repression of larval mRNA synthesis and/or the induction of pupal genes.…”

Effect of methoprene on the progeny production of Tribolium castaneum (Coleoptera: Tenebrionidae)

“…Juvenile hormone analogues are lethal to embryos when applied during blastokinesis,12, 13 or to larvae, which then produce malformed pupae 5, 14. Much of the research on JHAs has focused on mortality due to the disruption of development during metamorphosis 15–21…”