Capture probability of released males of two Bactrocera species (Diptera: Tephritidae) in detection traps in California.

The genus Bactrocera (Diptera: Tephritidae) includes approximately 70 polyphagous species that are major pests of fruit and vegetable crops. Most Bactrocera species have limited geographic distributions, but several species are invasive, and many countries operate continuous trapping programs to detect infestations. In the United States, California maintains approximately 25,000 traps (baited with male lures) specifically for Bactrocera detection distributed over an area of approximately 6,400 km2 (2,500 miles2) in the Los Angeles area. Although prior studies have used male lures to describe movement of Bactrocera males, they do not explicitly relate capture probability with fly distance from lure-baited traps; consequently, they do not address the relative effectiveness of male lures in detecting incipient populations of Bactrocera species. The objective of this study was to measure the distance-dependent capture probability of marked, released males of Bactrocera dorsalis (Hendel) and Bactrocera cucurbitae (Coquillett) (methyl eugenol- and cue lure-responding species, respectively) within the detection trapping grid operating in southern California. These data were then used to compute simple probability estimates for detecting populations of different sizes of the two species. Methyl eugenol was the more powerful attractant, and based on the mark-recapture data, we estimated that B. dorsalis populations with as few as approximately 50 males would always (>99.9%) be detected using the current trap density of five methyl eugenol-baited traps per 2.6 km2 (1 mile2). By contrast, we estimated that certain detection of B. cucurbitae populations would not occur until these contained approximately 350 males. The implications of the results for the California trapping system are discussed, and the findings are compared with mark-release-recapture data obtained for the same two species in Hawaii.