Moisture is required for the termination of egg diapause in the chrysomelid beetle, Homichloda barkeri

Four factors (moisture, light regime, temperature, food type) were examined for their effects on the embryonic diapause of Homichloda (Weiseana) barke ri (Jacoby) (Coleoptera: Chrysomelidae), a biocontrol agent for prickly aca cia, Acacia nilotica (L.) Willdenew ex Delile (Mimosaceae). Moisture is cri tical for termination of diapause. A single wetting of eggs resulted in a l ow hatch rate while a sequence of wetting events followed by periods of dry ness produced a high hatch rate. A relatively constant proportion of embryo s within each batch initiated development at each wetting event, with hatch ing complete after the eighth wetting event in these trials. An extended in terval between wetting events, tested at up to 23 days, did not result in a decreased overall hatch rate. A threshold time of exposure to moisture of between 3 to 6 h is required before development proceeds. The response of e ggs to the moisture regime is seen as a strategy for taking advantage of av ailable food after rainfall by terminating diapause, rather than merely a q uiescent response to the absence of moisture. Temperature affected developm ent time and the proportion of eggs that developed. Experimental manipulati ons of photoperiod and host-plant availability showed no effect on embryoni c development.