The potential for biological control of the invasive Asian longhorned beetle with native North American parasitoids
Date
2018
Authors
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Publisher
University of Delaware
Abstract
The invasive Asian longhorned beetle (ALB), Anoplophora glabripennis (Motschulsky), is a destructive xylophagous forest pest species originating from Asia. First discovered in New York in 1996, breeding populations have since spread to several U.S. states, and are also found in Canada and Europe. Currently, control of ALB is focused on its eradication; however, the rapid detection and removal of infested host trees is complicated by the cryptic nature of the wood boring larvae. Moreover, the removal and treatment of both infested and at-risk trees has led to tremendous ecological and economic impacts in infested regions. More sustainable options for the management of invasive ALB populations are greatly needed; therefore, my dissertation research focused on exploration for mortality factors of ALB in its endemic China as well as the potential for a new-association biological control approach using native North American parasitoids. ☐ Mortality factors affecting ALB eggs, larvae, pupae, and adults infesting Populus and Salix were investigated in several Chinese provinces. Results revealed that ALB density and mortality caused by various abiotic and biotic factors varied between host tree species as well as among different years and regions in China. Overall ALB density was the highest in Jilin province, and in Gansu province nearly four times the density of live larvae and pupae were found infesting Populus compared to Salix. In a survey across all provinces, ALB eggs were the life stage that was most susceptible to mortality factors, with the majority of eggs dying from undetermined factors, followed by parasitoids, and lastly from being removed by woodpeckers or other unknown predators. Larval and pupal stages were least susceptible to mortality factors throughout China, and the majority of those that died were either removed by woodpeckers or taken by unknown predators. We recovered the parasitoids Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) and Scleroderma guani Xiao et Wu (Hymenoptera: Bethylidae) from a small number of larvae and pupae in Gansu province and Beijing City. ☐ While foreign exploration has not resulted in the discovery of any host-specific co-evolved biocontrol agents, exploration for native North American natural enemies has revealed several native parasitoid taxa that can form new associations with ALB under laboratory conditions. One of the native parasitoid species, Ontsira mellipes Ashmead (Hymenoptera: Braconidae), has been continually reared on ALB larvae at the United States Department of Agriculture, Agricultural Research Service, Beneficial Insects Introduction Research Unit (USDA-ARS BIIRU) since 2010, and may be useful as a new-association biocontrol agent against ALB. Currently, little is known about this North American parasitoid species; therefore, several laboratory experiments were conducted to investigate its life history, thermal tolerances, host preference, and potential to adapt to ALB through continuous laboratory rearing. ☐ Life history studies indicated that adult O. mellipes parasitized approximately 21% of beetle larvae presented to them throughout their life, and that host paralysis occurred 1 – 2 d after oviposition. Adult female parasitoids produced around 26 offspring throughout their lifetime. Females that were provided access to a host, honey, and water survived 9 d longer, on average, then females denied access to these resources. Egg to adult development was completed in around 3 wk, during which larvae developed through five instars before pupating and emerging as adults. ☐ Thermal studies were carried out to determine the effect of temperature on immature development, phenology, and adult reproduction and survival. Development time from egg to pupa significantly decreased from 26.7 to 6.1 d as temperature increased from 10 to 30°C, and no pupae eclosed as adults at 10°C. Furthermore, increasing temperature from 15 to 30°C significantly decreased pupa to adult emergence from 39.7 to 12.2 d. Based on the linear regression equations obtained from immature development stages, we estimate a single generation of O. mellipes requires 342.9 degree days accumulated above a lower development threshold temperature of 11.1°C. Results of the lower developmental threshold and degree-day requirements for O. mellipes obtained from linear regression models were then combined with temperature data from ALB infested areas in the U.S. to estimate the phenology of this parasitoid. This reveled that nearly 1.2 to 3.7 generations per year may occur in ALB infested areas. Adults parasitoids attacked (parasitized) host larvae across all the tested temperatures; however, parasitism reached a maximum at 25°C. Additionally, increasing temperatures significantly reduced the pre-oviposition period and longevity of female O. mellipes. ☐ Host preference studies using ALB-reared parasitoids revealed that the most abundantly and frequently collected native cerambycid naturally infesting red maple trees, Neoclytus acuminatus ssp. acuminatus, is most likely not a host of O. mellipes as no larvae were parasitized during no-choice testing, while 70.4% of ALB larvae were parasitized. ☐ Laboratory adaptation experiments revealed that host attack rates (% parasitism) increased from 46.9% to 65.7% between the F1-2 to F68-71 generations of parasitoids reared on ALB, indicating a marginally significant increase in host attack rates by later generation parasitoids (F41-43, F68-71). Additionally, later generation parasitoids produced significantly more progeny, on average, than did early generation females (F1-2). ☐ The overall results of the laboratory studies indicate that the artificial selection process acting through current laboratory rearing conditions has enhanced this candidate biocontrol agent’s ability to attack and reproduce on ALB, and further demonstrates the potential of using O. mellipes as a new-association agent of the invasive ALB. While investigations in China did not reveal any co-evolved and host specific naturally enemies, we suggest that future investigation should examine the causal agents of mortality in the field that is currently categorized as undetermined.
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Keywords
Asian longhorned beetle, Biological control, Braconidae, Invasive species, Parasitoid