Plant influences on silverleaf whitefly oviposition and development and the potential for enemy‐free space

The silverleaf whitefly Bemisia argentifolii Bellows & Perring (also known as B. tabaci, biotype B) attacks several agricultural crops grown in the southern and western U.S. (Perring et al., 1993). Management of this pest is being promoted through importation and augmentation of biological control agents, development of resistant plant cultivars, and the introduction of alternative crops (Henneberry et al., 1998). One potential source of plant resistance is the reduction or elimination of trichomes from pubescent-leafed varieties. Plants that vary with respect to leaf pubescence have been tested for resistance, and these include soybean (McAuslane et al., 1995), cotton (Flint & Parks, 1990) and tomato (Heinz & Zalom, 1995). In general, more glabrous-leafed plants offer greater levels of resistance. However, the impacts of non-glandular trichomes on cantaloupe melon (Cucurbita melo L.), and more generally, of wild plants with trichomes, have not been investigated for their effects on B. argentifolii performance. Host plant resistance to herbivores can interact with biological control (Bergman & Tingey, 1979), with several possible outcomes (see Price et al., 1980; Hare, 1992). Polyphagous herbivores have access to several hosts, and therefore may select hosts so as to minimize the negative impacts from plant resistance and their natural enemies, alone, or in combination. In the Imperial Valley of California, agricultural habitats provide suitable host plants for the silverleaf whitefly throughout the year, and weeds and ornamental plants also are utilized (T. M. Perring, unpublished data). A survey of whitefly populations in the Imperial Valley identified parasitoid species on these herbivores. Most of the parasitism was attributed to Eretmocerus sp. nr. californicus, recently described as E. eremicus Rose & Zolnerowich (Headrick et al., 1999), yet the proportion of whiteflies parasitized varied seasonally and among a suite of crop and weedy whitefly host plants (T. S. Bellows & T. M. Perring, unpublished data). The purpose of this study was to determine performance of silverleaf whiteflies on glabrousand pubescent-leafed plant species on which parasitism by the natural enemy varied. Results are discussed in relation to the concept of enemy-free space (EFS; Jeffries & Lawton, 1984; Berdegue et al., 1996).