Mesquite twig girdler, Oncideres rhodosticta: Should spillover during high population densities limit biological control potential?

Tuesday, November 15, 2022

10:00 AM – 10:12 AM PT

Location: Vancouver Convention Centre, Meeting Room 207

Presenting Author(s)

DT

David C. Thompson

Professor
New Mexico State University
Las Cruces, New Mexico

Co-Author(s)

IP

Ikju Park

Assistant Professor
Kyungpook National University
Daegu, Kyongsang-bukto, Republic of Korea
Kristen Bowers

Post Doctoral Fellow
New Mexico State University
Las Cruces, New Mexico

Honey mesquite (Prosopis glandulosa Torr.) is the most common woody plant on more than 28 million ha of semi-arid southwestern rangelands. Attempts to control mesquite using a variety of techniques have been implemented for the past century including mechanical removal (grubbing), adjusting stocking rates, and applying both stem and foliar herbicide either aerially or through individual plant treatments. Regardless of which control measures are used, numerous native insects feed on mesquite. Although native insects commonly cause considerable damage to weed species, their use as a management tool is often overlooked. Every few years, densities of the mesquite twig girdler, Oncideres rhodosticta, in the southwestern United States are substantial. This insect has potential as a biological control agent in other parts of the world, such as South Africa, where mesquite is an invasive plant; however, during these periods of high population densities, damage to congeneric and confamilial native and ornamental hosts is relatively common, so the insect has been rejected from consideration as a candidate biological control agent. We argue that these spillover events are an artifact of high insect densities rather than an ability to develop sustainable populations on a broader host range. The responses of adult beetles to volatile organic compounds from mesquite and other native trees and shrubs showing damage and the very limited survival of twig girdlers on the spillover hosts suggests the need for a reevaluation of host range testing techniques in weed biological control.