Reproductive biology of Thrips tabaci from New York onion fields
Nault BA
Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456 USA.
Correspondence: ban6@cornell.edu
Knowledge of a pest＊s reproductive biology is important for developing effective management strategies. Onion thrips, Thrips tabaci Lindeman, is a serious pest of several field and vegetable crops and damaging populations can escalate quickly if not controlled. Thrips tabaci can reproduce sexually, but the most common mode of reproduction is thelytoky, a type of parthenogenesis in which unfertilized eggs develop into females. However, T. tabaci populations have been reported to reproduce via arrhenotoky (Kendall DM, Capinera JL. 1990. Southwestern Entomologist 15: 80每88), a type of parthenogenesis in which unfertilized eggs develop into males. Deuterotoky, a third type of parthenogenesis characterized by unfertilized eggs developing into either males or females, has been documented in the thrips species, Apterothrips apteris (Mound L. 1992. In: Cameron EA, et al., editors. Proceedings of the 1991 Conference on Thrips (Thysanoptera): Insect and Disease Considerations in Sugar Maple Management, 2每14), but not in T. tabaci. Male onion thrips are frequently encountered in New York and Ontario onion fields (MacIntyre-Allen JK. 2004. Population dynamics, insecticide resistance and management of onion thrips, Thrips tabaci Lindeman, in southwestern Ontario. Ph.D. dissertation, University of Guelph, Guelph, Ontario). Although arrhenotoky is assumed to be the principal mode of reproduction in these populations, it has not been empirically differentiated from deuterotoky. To identify the mode or modes of reproduction by T. tabaci populations in New York, the progeny of virgin females from these fields had to be identified. In 2002每2004, progeny of virgin females originating from 23 commercial onion fields were identified. About half of the populations were strictly thelytokous (n=13) whereas the other half included a combination of thelytokous, arrhenotokous and deuterotokous individuals (n=10). The factor(s) responsible for triggering the production of males is not known, but has been hypothesized to occur when temperature increases (Moritz G. 1997. In: Lewis T, editor. Thrips as Crop Pests, 2: 15每63. CAB International, Cambridge: University Press) or when populations develop resistance to insecticides (Kendall and Capinera 1990). Neither hypothesis has been examined. In 2002每2003, the level of susceptibility of T. tabaci populations to several commonly used insecticides was characterized using a laboratory bioassay (Shelton AM et al. 2003. Journal of Economic Entomology 96: 1843每1848). Concurrently, the modes of reproduction by the T. tabaci populations were identified and a correlation between resistance and reproductive mode examined. There was no relationship between susceptibility to insecticides and a particular mode of reproduction. The effect of temperature on production of males also was examined. A single population from western New York was separated into three sub-populations, each of which was maintained at 85∼, 75∼ or 65∼ F for three consecutive generations. Only females were produced, indicating that high temperature alone is not responsible for production of males. Other factors that may affect the mode of reproduction in Thrips tabaci populations are discussed.
