›› 2007, Vol. 50 ›› Issue (9): 920-926.

• RESEARCH PAPERS • Previous Articles     Next Articles

Parasitism and reproductive biology of Spathius agrili Yang (Hymenoptera: Braconidae)

  

  • Online:2007-09-20 Published:2007-10-10

Abstract:

Spathius agrili Yang (Hymenoptera: Braconidae) is an important natural enemy parasitizing larvae of the emerald ash borer (EAB), Agrilus planipennis Fairmaire (=A. marcopoli Obenberger) (Coleoptera: Buprestidae), in Tianjin, China. The survival time of S. agrili under different nutrimental conditions, egg productions of the parasitic wasp at different periods, influence of host size on the development of wasp offspring, and utilization of host beneath the bark of different thickness, were investigated in fields, combining with observations in the laboratory. The results showed that the survival days of the parasitoid differ significantly under different nutritional conditions. Wasps can live pronouncedly longer after feeding 20% honey dilution with the maximal survival time of 3 months, and under the same conditions females usually can survive a little longer than males. When supplied with nutrition, the maximum period for oviposition of the braconid is up to 8 weeks with the peak around the 2nd week. During the whole oviposition period, the mean egg production of 8-12 eggs per female per week is almost constantly maintained without high fluctuation. The newly hatched larvae of S. agrili may produce venoms and attack host initiatively, so help to improve the survival opportunities of parasitoid progeny. The number of successfully developed parasitoid offspring from host enhances with the increase of host larval weight, which indicates that the host nutrition capacity affects the development and survival of wasp progeny. S. agrili can utilize those hosts at right ages beneath the bark of 1-6.5 mm in thickness. Approximately 92% EAB larvae parasitized by Spathius are distributed at 1-4 mm thickness of the bark with the peak at 3 mm. Relationship between the number of wasps and bark thickness can be simulated with a quadratic parabola roughly, and the theoretical maximum number of the parasitoid would be expected at 3.97 mm thickness of the bark.