Biology of Hemiptarsenus varicornis (Hymenoptera: Eulophidae), a parasitoid wasp of the leafminer Liriomyza trifolii (Diptera: Agromyzidae)

Dipteran leafminers belonging to the family Agromyzidae are serious insect pests for many vegetable and ornamental crops in Asia including Vietnam and Japan. The parasitoid wasp Hemiptarsenus varicornis (Girault) has recently been recognized as an effective biological control agent of such leafminers including Liriomyza trifolii (Burgess) and L. bryoniae (Kaktenbach). However, the biology of H. varicornis is not fully understood. In this paper, we investigated development time, adult longevity, egg production and parasitism of H. varicornis in the laboratory, examining basic life history characteristics of this parasitoid. At a constant 25°C condition, females survived significantly longer than males when fed on honey solution in the absence of hosts. The mean longevity were 7 and 12 days for males and females, respectively. Development time from egg to adult emergence of males was significantly shorter than that of females (adv. 10.4 vs. 10.9 days at 25°C). Dissection experiments showed that females emerged with no or only a few mature and immature eggs. Fecundity of females remained steady when no hosts were provided (2-4 mature eggs), suggesting that H. varicornis have to feed on hosts to enhance egg production. Cage experiments were conducted to evaluate reproductive capacity of females. The results demonstrated that female H. varicornis killed on average 31 leafminer larvae by parasitism during 5 consecutive days since emergence. The female showed destructive host-feeding, and killed on average 11 leafminer larvae by host-feeding in addition to by parasitism. There was a positive relationship between numbers of hosts fed upon and those parasitized, suggesting again that host-feeding related to enhancement of egg production.