ARS | Publication request: Marked insects released in recapture studies may influence population estimates of native insects

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: January 3, 2013
Publication Date: N/A

Interpretive Summary: Naturally-occurring insect populations are often too low, too variable, or occur at the wrong times to facilitate some field studies. In those cases, it is often possible to rear insects in the laboratory and release them in the desired numbers into the study area. During such studies, inferences about the population of native insects may be made so long as they are not influenced by the released insects. In a recent study using released insects to evaluate sampling methods for the western tarnished plant bug in cotton, we observed unequal distribution of native plant bugs among the treatments. Analyses indicated numbers of native males were higher where we released older, reproductively mature females than where we released younger females or males of either age category. Because numbers of native females were not similarly affected, we presume the released females attracted the native males. Our observations are consistent with earlier contentions of a volatile, female released sex attractant in this bug, and suggest caution should be exercised in interpreting captures of native insects collected in conjunction with studies of released insects.

Technical Abstract: Recent studies of sweepnet collection efficiency for the western tarnished plant bug, Lygus hesperus Knight, in cotton have capitalized on the utility of mark-release-recapture methods. During such sampling studies, native lygus are commonly captured along with the insects that were marked and released. In some situations, it would be useful to draw inferences regarding the populations of native insects so long as their behavior is not influenced by the released insects. During a recent study of the influence of L. hesperus gender and age class on sweepnet sampling efficiency, we noted a bias in the distributions of captured native lygus adults. Exploratory analyses indicated that, in both Acala and Pima cotton, captures of native adult male lygus were significantly higher where reproductively mature females were released, compared with areas receiving pre-reproductive females, or males of either physiological age class. We presume the native males were attracted to pheromone released by the marked reproductive females, or to some other olfactory attractant associated with those females. These support earlier contentions of a volatile, female released sex attractant in L. hesperus, and suggest caution should be exercised in interpreting captures of native insects collected in conjunction with mark-release-recapture studies.