Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2012
Publication Date: 6/1/2012
Publication URL: http://www.bioone.org/doi/full/10.1603/EC11431
Citation: Duan, J.J., Oppel, C.B. 2012. Critical rearing parameters of Tetrastichus planipennisi (Hymenoptera: Eulophidae) as affected by host-plant substrate and host-parasitoid group structure. Journal of Economic Entomology. 105:792-801.
Interpretive Summary: Tetrastichus planipennisi is a parasitic wasp that were recently introduced to the United States of America (USA) from China for biological control of the emerald ash borer (EAB), which is a devastating forest pest in North America, killing hundreds of millions of native North American ash (Fraxinus spp.) trees since its discovery in Michigan, USA in 2002. We conducted laboratory studies to improve the method for rearing this parasitic wasp for biocontrol releases against EAB. Our study demonstrated that offspring production, body size and sex ratio of this beneficial wasp are significantly influenced by EAB larvae’s food plant type, EAB larva and wasp density, and/or EAB larva to wasp ratio used for rearing. EAB larvae inserted into tropical ash (F. uhdei) sticks produced significantly greater numbers of the parasitic wasp offspring than those larvae inserted into green ash (F. pennsylvanica) sticks. When maintained at the same number of EAB larvae and wasps (i.e., 1:1 host to wasp ratio) in the rearing arena, tests with multiple EAB larvae and wasps produced significantly great numbers of both male and female wasp offspring when compared to those with the single EAB larva and wasp treatment. As the EAB larva to wasp ratio decreased from 1:1 to 1:8 in the rearing arena, the average number of offspring produced per parasitized EAB larva increased significantly, whereas the wasp offspring sex ratio (female to male) changed from being female-biased (6:1) to male-biased (1:2) and the body size of female wasp offspring was also reduced significantly. Based on these findings, we suggest that the current method of rearing this beneficial wasp with artificially infested-EAB larvae use the tropical ash logs for EAB insertion, maintain multiple EAB larvae and wasps in a rearing arena and keep higher EAB larvae to wasp ratio for the primary wasp exposure assays.
Technical Abstract: Laboratory studies were conducted to evaluate the potential impact of host-plant substrate types, host-parasitoid group size and host to parasitoid ratios on select fitness parameters of the larval parasitoid Tetrastichus planipennisi Yang, newly introduced for biological control of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire, in the USA. Results from our laboratory assays showed that offspring production and critical fitness parameters (body size and sex ratio) of T. planipennisi from parasitized EAB larvae are significantly influenced by host plant substrate type, host-parasitoid group size (density), and/or host to parasitoid ratio used for parasitoid rearing. EAB larvae inserted into tropical ash (F. uhdei) logs appeared to have produced significantly greater numbers of T. planipennisi offspring than those larvae inserted into green ash logs. When maintained at a constant 1:1 host to parasitoid ratio, assays with larger host-parasitoid group sizes (3:3 to 12:12) produced significantly great numbers of both male and female offspring when compared to those with the single host-parasitoid (1:1) group treatment. As the host to parasitoid ratio decreased from 1:1 to 1:8 in parasitoid exposure assays, the average brood size (number of offspring per parasitized EAB larva) increased significantly, whereas the average brood sex ratio changed from being female-biased (6:1) to being male-biased (1:2) and the body size of female offspring as measured by the length of ovipositor and left-hind tibia was also reduced significantly. Based on these findings, we suggest that the current method of rearing T. planipennisi with artificially infested-EAB larvae use the tropical ash logs for EAB insertion. In addition, we suggest that the primary parasitoid exposure assays maintain both a larger (>1:1) host-parasitoid group size and higher (>1:2) host to parasitoid ratio.