Influence of photoperiod on the overwintering induction of Galerucella calmariensis L

Understanding the phenology of biological control agents is critical for developing effective rearing methods. In the case of Galerucella calmariensis L, a biological control agent introduced against purple loosestrife (Lythrum salicaria), the presence of an obligatory diapause affects successful rearing. G. calmariensis individuals were reared from egg to adult under four different combinations of long and short photoperiods. Two weeks after adult emergence, individuals from each treatment were dissected to check for ovary development and presence of developed eggs as indicators of overwintering induction. Individuals treated under short photoperiod throughout their lifetime were found to have smaller ovaries and few developed eggs, indicating an effective overwintering induction. The adult stage of G. calmariensis was determined to be the stage sensitive to photoperiod, as evidenced by reduction in ovary size, decreased overwintering mortality and increased post-overwintering fecundity in individuals treated as adults with short daylength. Increased post-overwintering fecundity when diapause was effectively induced can increase the efficiency of rearing programs for G. calmariensis and other weed biological control agents with a reproductive diapause.