Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2006
Publication Date: 12/1/2006
Citation: Li, J., Coudron, T.A., Pan, W., Liu, X., Zhang, Q. 2006. Host age preference of Microplitis mediator (Hymenoptera: braconidae), an endoparasitoid of Mythimna separata (Lepidoptera: noctuidae). Biological Control. 39:257-261.
Interpretive Summary: The cotton bollworm, one of the most destructive pests of field crops throughout the world, has become resistant to nearly all types of chemical control which in turn has increased the importance of developing a biological component to control this pest. A beneficial wasp has been shown to be an effective biological control agent for the control of the bollworm. That discovery has elevated the importance of rearing large numbers of the wasp for release in field crops to control the bollworm. This paper reports an efficient method for rearing the wasp on a natural host insect by measuring preference for host age and completion of wasp development. Additionally, the same criteria used to successfully rear the wasp were found to be important for the successful application of the wasp in field crops. Consequently, these findings are valuable to researchers and commercial companies involved in rearing the wasp and also valuable to the commercial companies and farmers performing the release of the wasp in field crops.
Technical Abstract: Microplitis mediator (Haliday) is a solitary endoparasitoid of larvae of the cotton bollworm, Helicoverpa armigera (Hübner) and the oriental armyworm, Mythimna = Leucania separata (Walker). The preference and suitability of different instars of M. separata for M. mediator were determined under laboratory conditions. The select coefficient revealed that M. mediator parasitized 1st to 4th instars, but preferred 2nd and 3rd instars. Seventy-one percent of parasitism was achieved when the 2nd instars were used as hosts. Parasitoid emergence and pupation were dependent on the instar parasitized and occurred from both 5th and 6th instars. The mean developmental time from egg to prepupae of M. mediator parasitizing 1st to 4th instars of the host was 8.27, 8.30, 8.30 and 9.20 days, respectively. Cocoon weights were lower when 1st and 2nd instars served as hosts rather than 3rd and 4th instars. The percentage mortality of host larva that died before parasitoid emergence were 26.00, 11.33, 5.33, 3.33 and 2.00 when exposed as 1st to 5th instars, respectively. The results of this study suggest that 2nd and 3rd instars of M. separata would be the best host instar stage for mass rearing M. mediator in laboratory. When augmentative field releases of M. mediator are initiated for management of M. separata, parasitoids should be released when 2nd and 3rd instars are present in the field.