The Mating Systems of the Emerald Ash Borer and Related Buprestid Beetles
Open Access
- Author:
- Lelito, Jonathan Peter
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 18, 2008
- Committee Members:
- Thomas Charles Baker, Dissertation Advisor/Co-Advisor
Thomas Charles Baker, Committee Chair/Co-Chair
James Lewis Frazier, Committee Member
James Homer Tumlinson Iii, Committee Member
James Harold Marden, Committee Member - Keywords:
- invasive insect
mating system
Fraxinus
Agrilus
ash
Buprestidae - Abstract:
- The emerald ash borer, Agrilus planipennis (EAB), is a serious introduced invasive pest of North American ash trees in the genus Fraxinus. My research objectives were to study the behavior of this beetle and other members of the genus Agrilus also present in North America to find pre-mating behaviors that could be exploited to create a more species-specific and effective trap for EAB than is currently available in the toolkit for monitoring this invasive pest. The first series of experiments I conducted were designed to elucidate activity patterns and mate-finding behaviors of EAB in the field and laboratory. I conducted behavioral observations of virgin pairs of EAB of known ages and recorded behaviors that might be related to mate-finding or courtship, such as wing-fanning, ‘juddering’ or body-vibration, contact and mounting behavior by males. I also extensively observed EAB in the field, looking specifically for gender-specific behaviors and diurnal activity periods that might hint at how the beetles locate their mates in a natural setting. Males are more active during the day, and both sexes strongly prefer sunlit perches on the host plant. Male EAB perform pre-copulatory flights that end in rapid dives onto the backs of stationary conspecifics, and are attracted to both dead male and dead female beetles pinned to host plant leaves, suggesting the use of a visual cue to locate mates. My next step was to take my work to the field and used the knowledge I gained about the mating system of EAB to create a male-specific trap that may help to monitor the spread of this pest. My first method of trap construction was to attach a dead EAB to an ash leaflet and cover the leaflet in a spray-on adhesive; this simple strategy was effective at capturing adult male EAB. I then tested these simple traps at both high and low EAB population-density and at high and low heights in ash trees. As I had hypothesized based upon my earlier behavioral observations and experiments, traps captured more EAB at higher heights and higher population densities, and always captured a strongly male-biased sample of adult EAB. I then performed a series of trapping experiments to potentially improve the design of the trap, including using synthetic materials with and without dead EAB and chemical cues as lures for adult EAB. This series of experiments culminated in a broad comparison of my trap types against USDA APHIS monitoring traps. I have now shown that on a surface-area basis, my traps are more effective than a plastic purple prism trap for capturing adult EAB in the field. My research has also contributed to a change in APHIS’ monitoring regime from purple to green traps. I have also performed investigations into the chemical cues used by EAB to assess a contacted conspecific for gender. By examining the cuticular chemistry of newly emerged and mature adult EAB of both genders, I have shown, in collaboration with other researchers, that female EAB cuticular chemistry changes as the beetle matures. This change coincides with sexual activity in the laboratory. Further, use of a specific cuticular hydrocarbon, 3-methyltricosane, can increase the time spent investigating a dead beetle by live, adult male EAB. This is a first step toward identification of the contact sex pheromone used by adult (presumably male) EAB to assess a contacted conspecific for gender information, and has increased our understanding of the mating system of this insect. Though the focus of this work is Agrilus planipennis, I also performed comparative studies on the mating behaviors of two other species in the target genus Agrilus: A. subcinctus, a native ash-twig borer, and A. cyanescens, an introduced insect that feeds upon invasive plants in the genus Lonicera. My work on these insects shows that males of both species also appear to use visual cues to locate mates in a way similar to that of male EAB. Indeed, male A. cyanescens are even attracted to non-conspecific insects of similar color and can be induced to attempt to copulate with these non-conspecific lures, even off of the primary host plant. My experimental results strongly suggested that vision is the primary mode of mate location in my three target species. These comparative studies helped to further the depth of understanding we have about mating behaviors in both EAB and Buprestid beetles in general. In summary, my work has increased scientific understanding of the mating systems of three species of Agrilus beetles in the family Buprestidae. I have assessed the use of vision and contact chemistry in the mating systems of these beetles, and I have tested and improved a novel trap using a visual cue as a lure for a pest insect. This knowledge has allowed us to ask new questions regarding the roles of vision and cuticular chemistry in insects, and has added to the information available to researchers and regulatory officials concerned with slowing the spread of an invasive insect, the emerald ash borer.