Marked Insects Released in Recapture Studies May Influence Population Estimates of Native Insects

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 the native insects so long as the released insects do not influence their behavior.  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.  Exploratory analyses indicated that, in both Acala and Pima cotton, captures of native males were significantly higher where reproductive females were released, compared with areas receiving pre-reproductive females or males, or reproductive males.  We presume the native males were attracted to pheromone produced by the marked reproductive females.  These results suggest caution should be exercised in interpreting captures of native insects collected in conjunction with mark-release-recapture studies.