Circadian and seasonal flight activity differences between the sexes of the biocontrol agent Eadya daenerys (Hymenoptera: Braconidae) and the impact of host size on adult emergence

Abstract

Since its accidental introduction into New Zealand in 1916, the invasive eucalypt leaf beetle Paropsis charybdis remains a pest of economic significance to Eucalyptus forestry. For this reason, the braconid parasitoid Eadya daenerys has been approved for release as a classical biological control agent. To aid in field monitoring using hand netting of biocontrol releases and laboratory rearing protocols, the flight activity over 6 a year field research program of E. daenerys and the relationships between the parasitoid and the size of its beetle hosts were evaluated in the country of origin. Wasps were observed flying over 32 days from mid-November to mid-December in Tasmania. E. daenerys was found to exhibit a morning-based scramble competition mating system. Females flying in the early morning had lower mature egg loads (134.2 ± 27.6) than at other times of the day. In the first half of the season, male flight was most often seen in the early morning, whereas in the second half of the season, there was a 4.5-fold decrease in any wasps flying. Female flight activity significantly increased to 70% female in the evening hours from 5:00 pm to 8:00 pm, which by the second half of the season was almost exclusively female. Wasps were caught flying across a wide range of air temperatures (10.7–23.8°C), humidity and light levels, but even light winds reduced flight when average wind speed exceeded 0.27 m/s for males and 0.73 m/s for females. Beetle prepupal weight was a predictor of E. daenerys parasitism success with mean beetle prepupal weights significantly higher for stung but unsuccessfully parasitised larva (62.09 mg) than those successfully parasitised (52.94 mg). The chance of an emerged wasp larva spinning a pupal cocoon was found to increase by 5% with every 1-mg increase in its beetle prepupal weight. Heavier beetle prepupae produced bigger parasitoids. Field-collected adult E. daenerys had larger (12%) head capsule widths (mean of 1.42 mm) than those reared in the laboratory (mean of 1.27 mm), suggesting that improving host nutrition and laboratory rearing conditions for increasing host size may help optimise E. daenerys rearing success.