|GOULD, JULI - Animal And Plant Health Inspection Service (APHIS)|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2020
Publication Date: 8/14/2020
Citation: Wang, X., Aparicio, E.M., Duan, J.J., Gould, J.R., Hoelmer, K.A. 2020. Optimizing parasitoid and host densities for efficient rearing of Ontsira mellipes (Hymenoptera: Braconidae) on Asian longhorned beetle (Coleoptera: Cerambycidae). Environmental Entomology. https://doi.org/10.1093/ee/nvaa086.
Interpretive Summary: The Asian longhorned beetle (ALB) is a high-risk invasive insect pest native to China and Korea that attacks various hardwood trees. First detected in the late 1990s in North America, it is the subject of extensive ongoing quarantine and eradication efforts. The beetles can be difficult to detect, especially in large forested areas, and new introductions are possible. Biological control is a valuable option for reducing established and incipient populations in areas where intensive management methods such as chemical control are prohibitively expensive and/or environmentally undesirable. Ontsira mellipes is a North American parasitoid wasp that attacks native longhorned beetles, but also readily attacks ALB. To develop an efficient rearing system for this parasitoid as a potential biocontrol agent for ALB, we investigated the effects of different densities of host and parasitoid on the parasitoid's efficiency and reproduction. An optimal combination of exposing three or four parasitoids to four hosts is proposed for efficient mass-rearing of this parasitoid.
Technical Abstract: Ontsira mellipes Ashmead (Hymenoptera: Braconidae) is a gregarious larval ectoparasitoid of woodboring cerambycids. It is native to North America but can readily attack the exotic Asian longhorned beetle Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae). This study aimed to develop an efficient rearing system for this parasitoid, as a potential novel association biocontrol agent for the beetle, by investigating the effects of different densities of host (two, three or four larvae) and parasitoid (one, two, three, four, five, six, seven and eight female wasps) on Ontsira’s parasitization efficiency and reproductive outcomes. Results showed that overall parasitism and total numbers of parasitized hosts or progeny produced increased with host and/or parasitoid densities, but the number of parasitized hosts or progeny produced per female parasitoid decreased with parasitoid density at each given host density. Nonlinear regression indicated a consistent pattern of mutual interference as parasitoid density increased. Additional experiments confirmed a complete absence of superparasitism (indirect interference), because the parasitoid detects hosts through vibration cues from host feeding, and attacked (thus paralyzed) hosts are no longer detectable. Thus, the interference likely results from direct or exploitative competition. Interestingly, female parasitoids responded to increased parasitoid density with a significant increase in clutch size. Overall, per capita parasitization efficiency or reproductive outcomes were optimized at a low parasitoid-host ratio but with large group size of hosts and parasitoids. Therefore, an optimal combination of exposing three or four parasitoids to four hosts is proposed for efficient mass-rearing of this parasitoid.