Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2012
Publication Date: September 4, 2012
Citation: Cooper, W.R. 2012. External visibility of spermatophores as an indicator of mating status of Lygus hesperus (Hemiptera: Miridae) females. Journal of Entomological Science. 47(4):285-290. Interpretive Summary: The reproductive biology of the western tarnished plant bug is poorly known despite the status of this insect as a major crop pest in the western United States. During mating the male plant bug deposits within the female a discrete body of material called a spermatophore. Although this spermatophore can sometimes be seen through the underside of the abdomen, mating is normally verified by dissecting the female. If detection of mating based on external examination of the abdomen is reliable, this method would greatly facilitate laboratory studies that require mated insects. Laboratory studies indicated the presence of an externally visible spermatophore correctly identified 99 percent of recently mated female plant bugs, and no unmated females were incorrectly categorized as mated. Additional studies at different temperatures indicated the ability to detect the spermatophore by external examination decreased with time, and the rate of this decline increased with temperature. Furthermore, mated females continued to lay fertile eggs beyond the time during which the spermatophore could not be viewed externally. These results indicate that recently mated female western tarnished plant bugs can be reliably distinguished from unmated females based on the presence or absence of an externally visible spermatophore. This ability will facilitate future research on plant bug reproductive biology by allowing the researcher to know mating status at the outset of experiments. Because the spermatophore becomes less apparent with increasing time after mating, this method is not suitable for identifying mating status of field collected plant bugs of unknown history.
Technical Abstract: Mated females of the western tarnished plant bug, Lygus hesperus Knight, are distinguished from unmated females by the presence of one or more spermatophores. The presence of a spermatophore is normally determined by dissection. A simple and non-destructive method to distinguish mated L. hesperus females from unmated females would facilitate laboratory studies that require mated insects. Spermatophores are visible through the abdominal sternites of recently mated L. hesperus females, but the consistency and persistence with which spermatophores are externally visible has not been previously documented. The overall objective of this study was to evaluate whether examination for the presence of externally visible spermatophores is a reliable method to determine whether L. hesperus females have mated. The presence of externally visible spermatophores correctly discerned 99 percent of recently mated (less than 24 h) females from unmated females. None of the unmated females were misclassified as mated. The apparency of visible spermatophores decreased with increasing time after mating until the spermatophores were no longer visible. The period during which spermatophores were externally visible decreased linearly with increasing temperature from 15.6 to 29.4-degrees C. Females continued to oviposit fertile eggs after spermatophores were no longer externally visible. Results indicate that examination for the presence of externally visible spermatophores is a reliable method to discern mated female L. hesperus from unmated females in controlled laboratory studies. Because spermatophores become less apparent with increasing time after mating, this method is not suitable for the classification of mating states of field collected insects or others of unknown history.