Location: Beneficial Insects Introduction ResearchTitle: Effects of host plant and larval density on intraspecific competition in larvae of the Emerald Ash Borer (Coleoptera: Buprestidae)) Author
Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/15/2013
Publication Date: 12/1/2013
Citation: Duan, J.J., Larson, K., Watt, T., Gould, J., Lelito, J.P. 2013. Effects of host plant and larval density on intraspecific competition in larvae of the Emerald Ash Borer (Coleoptera: Buprestidae). Environmental Entomology. 42(6):1193D1200. Interpretive Summary: Emerald ash borer (EAB) is an insect pest that has killed millions of ash trees (Fraxinus spp.) in North America since being discovered in Michigan in 2002, and the management of EAB is projected to cost over $10 billion in the coming decade. Understanding the intraspecific competition is important in studying its population abundance or dynamics, and thus allows us to better predict how EAB will spread, and to develop sound control strategies. Using green ash and tropical ash logs infested with a series of EAB egg densities, we evaluated intraspecific competition in EAB larvae. Results from our study showed that as the EAB egg densities on each log increased, larval survivorship declined significantly. Accordingly, larval mortality, resulting from cannibalism and/or starvation, significantly increased as egg density increased, and the size of surviving larvae significantly decreased on both ash species. When larval density was adjusted to the same level, however, larval mortality from cannibalism and starvation was significantly higher and mean biomasses of surviving larvae was significantly lower in both ash logs. These findings suggest that when EAB density is high on a infested ash tree, larval competition is likely to regulate its population growth by causing higher mortality and smaller surviving larvae. In addition, this is also an important consideration for mass rearing EAB biological control agents (parasitoids) because the gregarious larval parasitoids can adjust clutch size and produce more progeny on larger hosts.
Technical Abstract: In many insects, competition for food, mate, and/or space among different individuals of the same species is a pervasive phenomenon with ecological consequences such as density-dependent regulation of insect abundance or population dynamics. The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a serious invasive pest of North American ash (Fraxinus spp.) trees, with its larvae feeding on the cambium tissue and making serpentine galleries between the interface of sapwood and phloem tissues of ash trees. Using artificial infestation of freshly cut logs of green ash (Fraxinus pensylvanica Marsh) and tropical ash [Fraxinus uhdei (Wenzig) Lingelsh] with a series of egg densities (200, 400, 800, and 1600 eggs/m2 of surface area of logs), we evaluated the mechanism and outcome of intraspecific competition in larvae of A. planipennis in relation to larval density and host plant species. Results from our study showed that as the egg densities on each log increased from 200 to 1600 eggs per m2 of surface area, larval survivorship declined from approximately 68% to 10% for the green ash logs, and 86% to 55% for tropical ash logs. Accordingly, larval mortality resulting from cannibalism and/or starvation significantly increased as egg density increased, and the biomass of surviving larvae significantly decreased on both ash species. When larval density was adjusted to the unit surface area (m2) of phloem in the linear regression model, however, larval mortality from intraspecific competition was significantly higher and mean biomasses of surviving larvae was significantly lower in green ash than in tropical ash. The role of intraspecific competition of A. planipennis larvae in density-dependent regulation of its natural population dynamics is discussed.