Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2001
Publication Date: 11/1/2001
Interpretive Summary: Tephritid fruit flies are among the most important threats to agriculture in the tropics and subtropics. In addition to species already established in the USA, there are a number of potentially dangerous species occurring throughout Latin America. Biological control has been proposed as a means of 1) regulating pest fly populations in the USA, and 2) suppressing pest numbers in neighboring countries in order to minimize the risks of their invasion into the USA. An important issue confronting biological control entomologists at the Center for Medical, Agricultural and Veterinary Entomology, ARS, is whether new parasitoid species should be introduced to address a particular problem, or whether the existing natural enemies should be augmented either through mass-rearing or conservation. The efficacy of these alternatives depends on whether or not there are "gaps" among the parasitoids in terms of host range and environmental preferences, ,and to what extent these can be filled by new introductions. One way of understanding how the various species of parasitoids that attack Anastrepha spp. fruit flies in Mexico interact is to examine their ovipositors (egg laying tubes). These exhibit considerable differences in length, and length affects where and how the various species can forage for hosts. Of the three hypotheses considered, it seems most likely that different ovipositor lengths are due to specializations needed to attack fly larvae in one or a few fruits unique to each parasitoid. However, it is difficult to predict what effect a new species would have on the efficacy of the parasitoid guild, and it may be better in the short term to conserve native natural enemies and forgo the importations of new species from elsewhere.
Technical Abstract: In southern Mexico, four native and one introduced species of Opiinae (Braconidae) attack larvae of Anastrepha spp. fruit flies. There is an overlap in the hosts of the parasitoids, but their ovipositors differ substantially in length. Three hypotheses are proposed to account for this variety of lengths: 1) Because of differences in the host stage attacked, there are differences in host vulnerability. 2) While longer ovipositors increase host range and thus have competitive advantages, they may be heavy, awkward, and expensive to move around. If so, species with longer ovipositors might invest more in locomotion (reflected in wing size and shape) and less in reproductive capacity (numbers of mature eggs held in the ovarial calyx). 3) While there are niche overlaps among the species, each has a "core environment" determined by factors such as temperature, humidity, seasonality, and host diversity. Ovipositor lengths have evolved to met the requirements of these specialized environments. Hypothesis #1 fails because all the species attack similar host stages. Neither was there support for hypothesis #2. There were no correlations between wing size and shape, or potential fecundity, and ovipositor length. The lack of correlation between species-pairs niche overlaps and differences in species-pairs relative ovipositor length is most consistent with hypothesis #3. Since it is difficult to predict the abilities of newly introduced species to integrate into the existing guild of natural enemies, it may be more prudent to forego the introduction of new species.