Induction and termination of reproductive diapause in Chrysoptharta agricola

Helen F Nahrung

Chrysoptharta agricola (Chapuis) (Coleoptera: Chrysomelidae: Paropsini) spends 6 - 7 months of its lifecycle as an adult in reproductive diapause sheltering in leaf litter. Beetles emerge in October - November to feed, mate and oviposit. We examined the effects of photoperiod and temperature on the induction and termination of reproductive diapause in the laboratory, and conducted field studies to validate results. Although usually univoltine, new adults may oviposit in summer before overwintering, with bivoltine years resulting in significantly more plantation damage. Laboratory experiments demonstrated that a critical photoperiod over 12 and under 16 hours of light was required to initiate diapause, although at 16 hours light 55% of beetles entered diapause in response to low temperature (9C) alone. High temperature subverted diapause in about 20% of adults at short photoperiods. Field observations and dissections of field-collected females indicated that the critical photoperiod is around 14 hours 40 minutes of daylight: adults emerging after this period entered diapause without producing eggs. Voltinism in C. agricola is thus a seasonally plastic trait that is dependent on emergence time of teneral adults. There was no difference in the length of time that males and females took to enter diapause in laboratory experiments, or in the field. Termination of diapause was primarily influenced by temperature, although photoperiod had an effect at low temperatures. The threshold temperature for time to initiate feeding was calculated as 5.4C (83.6DD), while the threshold for oviposition was 7.4C (82.2 DD after feeding). Our understanding of the mechanisms underlying reproductive diapause will aid management by enabling temporal prediction of beetle activity and attack in commercial plantations.

Induction and termination of reproductive diapause in Chrysoptharta agricola

Related links

Abstract

Details

Metrics