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Title: Effect of Parasitoid: Host Ratio and Parasitoid and Host Group Size on Fitness of Spathius galinae (Hymenoptera: Braconidae), a Parasitoid of Emerald Ash Borer (Coleoptera: Buprestidae): Implications for Mass-Rearing

item WATT, TIMOTHY - University Of Delaware
item Duan, Jian
item TALLAMY, DOUGLAS - University Of Delaware
item HOUGH-GOLDSTEIN, JUDY - University Of Delaware

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2015
Publication Date: 3/29/2015
Citation: Watt, T.J., Duan, J.J., Tallamy, D.W., Hough-Goldstein, J. 2015. Effect of Parasitoid: Host Ratio and Parasitoid and Host Group Size on Fitness of Spathius galinae (Hymenoptera: Braconidae), a Parasitoid of Emerald Ash Borer (Coleoptera: Buprestidae): Implications for Mass-Rearing. Journal of Economic Entomology. 108:951-956.

Interpretive Summary: The parasitic wasp (Spathius galinae) is a newly discovered natural enemy of the invasive emerald ash borer (Agrilus plannipennis) that has killed tens of millions of North American ash trees since it was discovered in 2002 in the US. This natural enemy has been recently imported to the US and is being considered for introduction to the US for biological control of the invasive emerald ash borer. To develop methods for mass production of this biocontrol agent, ARS researchers at the Beneficial Insects Introduction Research Unit (Newark, DE) and cooperators at the Department of Entomology and Wildlife Ecology, University of Delaware determined the optimal number of EAB larvae per cage relative to the number of the wasps used for effectively producing the offspring of the parasitic wasp. Findings from our study indicated that using 8 wasps and one EAB larvae per cage resulted in highest rate of EAB attack (parasitism) without negatively affecting the number, size and ratio of female to male wasp offspring. In addition, our findings showed that a group of 10 EAB larvae and 10 wasps per cage produced the greatest number of wasp offspring per parental wasp. These findings will significantly increase the efficiency in mass production of this natural enemy for biocontrol releases against EAB.

Technical Abstract: Producing insect natural enemies in laboratories or insectaries for biological pest control is often expensive, and developing cost-effective rearing techniques is a goal of many biological control programs. Spathius galinae Belokobylskij and Strazenac (Hymenoptera: Braconidae), a recently described ectoparasitoid specializing on emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), larvae, is expected to be released in the US to provide biological control of this invasive wood-borer. To improve rearing outcomes for S. galinae, we investigated the effects of parasitoid: host ratio and parasitoid and host group size (density) on parasitoid fitness. Our results showed that when 1 emerald ash borer host larva was exposed to 1, 2, 4, or 8 female parasitoids, parasitism rate was positively associated with increasing parasitoid: host ratios, and brood size, sex ratio, and fitness estimates of progeny were not affected. However when a constant 1:1 parasitoid: host ratio was used, but group size varied from 1 female parasitoid and 1 host, 5 parasitoids and 5 hosts, 10 of each and 20 of each in same size rearing cages, percent parasitism was much higher when at least 5 females were exposed to 5 hosts. Moreover, the number of progeny produced per female was greatest when group size was 10 parasitoids and 10 hosts. These findings demonstrate that S. galinae may be reared most efficiently in moderately high density groups (10 parasitoids and hosts) and with a 1:1 parasitoid: host ratio.