Session 6 Abstracts

Interaction of host plants on predation of a prospective biological control agent, Aceria salsolae, of Russian thistle, Salsola tragus Lincoln Smith USDA, Agricultural Research Service, 800 Buchanan Street, Albany, CA 94710, USA. [email protected]

Eriophyid mites have been proposed as a useful source of biological control agents of weeds because they are generally thought to be highly host-specific. However, under laboratory conditions some species have been able to reproduce on plants that are not known to be hosts in the field. Furthermore, these small herbivores may be susceptible to predation which could greatly reduce their efficacy. Eriophyids often use plant structures to help provide physical protection against predators. Thus it is possible that the effect of predators may depend on the species of plant, and that the herbivore may be best protected on its preferred host plant. This would both increase mite efficacy and narrow its effective host range. We conducted laboratory experiments to measure the effect of a generalist predatory mite, Neoseiulus californicus (Acari: Phytoseiidae), on the eriophyid mite, Aceria salsolae (Acari: Eriophyidae), a prospective agent for Russian thistle (Salsola tragus (Chenopodiaceae)) on a variety of target and non-target host plants. The mite reproduced faster on S. tragus than on Salsola paulsenii or Salsola australis, and populations were able to persist or increase on four non-target species in the genera Suaeda and Atriplex (both Amaranthaceae). The phytoseiid drastically reduced eriophyid mite populations on all target and non-target species tested. When predators were present, A. salsolae numbers were highest on S. tragus and dropped to very low levels on the non-target species tested. This predator appears to be capable of protecting the non-target species, but may also reduce impact on the target weed.

Melon fly interference with a weed biocontrol agent of ivy gourd, Mohsen M. Ramadan*1 and Thomas W. Culliney2 1State of Hawaii Department of Agriculture, Division of Plant Industry, Plant Pest Control Branch, 1428 South King Street, Honolulu, Hawaii 96814, USA. [email protected] 2USDA-APHIS, PPQ, Center for Plant Health Science and Technology, Plant Epidemiology and Risk Analysis Laboratory 1730 Varsity Drive, Suite 300, Raleigh, NC 27606, USA.

Acythopeus burkhartorum (Coleoptera: Curculionidae) is a petiole- and tendril-galling weevil introduced from for the biological control of ivy gourd, Coccinia grandis (Cucurbitaceae), an invasive weed in Hawaii, Guam and the Northern Mariana Islands. Ivy gourd is a perennial cucurbit vine native to East , south-eastern Asia and Arabia. In Hawaii, it forms thick mats that overgrow vegetation, walls, fences, telephone lines, and cultivated fields in coastal and lowland areas. Classical biological control programs in Hawaii, Guam, and Saipan were achieved by the introduction and release of three Kenyan species: the stem-boring , oedipus (: ), in 1996, the leaf-mining weevil, Acythopeus coccinea (Coleoptera: Curculionidae), and the gall weevil, A. burkhartorum, in 1999. The moth and the leaf-mining weevil became well- established and are still exerting control of this noxious weed. A total of 5 289 adult A. burkhartorum were released throughout the infested areas on Oahu, Hawaii, Guam, and Saipan, from 1999-2005. The incidences of galling by A. burkhartorum were limited to shady areas, and recent surveys (June-December 2013 and January-March 2014) showed that the weevil had not become permanently established on any of the release sites. Bird- and ant-predation on galling larvae was assumed to be the cause for this failure. We report that one of the reasons for the early disappearance of A. burkhartorum was melon fly, Bactrocera cucurbitae (Diptera: Tephritidae), interference by deposition of its eggs in the galls, causing decay as the eggs hatch. In a no- choice experiment, melon fly recognized 23% of the larger exposed galls as potential oviposition sites. Mean melon fly egg- load per gall was 9.0±2.1 eggs. Acythopeus burkhartorum larvae died in 40% of the infested galls that harbored 5.3±2.1 melon fly larvae per gall. Eventually, all galls with melon fly eggs rot as hatching fly larvae feed and promote decay of the galls before the weevil larvae complete development. The melon fly parasitoid, Psyttalia fletcheri (Hymenoptera: Braconidae), may probe the galls, but did not induce mortality. Future field monitoring of A. burkhartorum populations should take these factors into account.

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