Accuracy of Lygus hesperus Knight (Hemiptera: Miridae) egg counts improves with egg development

Authors: SPURGEON, DALE; VAN EKERT, EVELIEN; ELHOFF, LEANNE

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2017
Publication Date: 3/15/2017
Citation: Spurgeon, D.W., Van Ekert, E., Elhoff, L.K. 2017. Accuracy of Lygus hesperus Knight (Hemiptera: Miridae) egg counts improves with egg development. Journal of Cotton Science. 21:1-7.

Interpretive Summary: Improvements in the management of the western tarnished plant bug on cotton may be attainable by non-insecticidal methods if the ecology of this pest is sufficiently understood. Of particular interest in this regard are the influences of environment, such as high temperatures, on plant bug reproduction. A key measure of plant bug reproduction is oviposition, which is usually estimated by visually counting eggs inserted within plant tissues. However, the accuracy of these sampling methods has been questioned. ARS scientists at Maricopa, AZ showed that delaying sampling until the eggs were partially developed improved sample accuracy. When egg counts were delayed until three days after oviposition, 94-96% of the eggs were detected compared with 76-89% when eggs were newly laid. Also, counts of newly laid eggs exactly matched total egg numbers 36% of the time, whereas counts of 3-d-old eggs matched total egg numbers 54% of the time. Even when the samplers counting eggs had no previous experience, a single repetition of the experiment followed by feedback and knowledge of the sample results improved sampler effectiveness, and those improvements were maintained through the remainder of the experiment. These findings can be used to obtain improved estimates of plant bug oviposition, and can reduce cost or improve accuracy of future studies of plant bug reproduction.

Technical Abstract: The western tarnished plant bug, Lygus hesperus Knight, is a key cotton (Gossypium spp.) pest managed primarily by application of insecticides according to nominal thresholds. Efforts to reduce reliance on insecticide-based tactics will require a more astute understanding of the physiological ecology of L. hesperus than is currently available. A key biological parameter that may be manipulated through cultural or genetic means is reproduction. Estimates of L. hesperus oviposition are commonly obtained by visual inspection, but the accuracy of those estimates has been questioned. Because the eggs swell during development, we hypothesized that delaying counts of eggs to permit some development might improve sampling accuracy. Estimates of L. hesperus egg numbers were obtained immediately after oviposition and again at 3 days after oviposition, and counts at both times were regressed with total eggs determined by the sum of either hatched eggs or the number of nymphs, and unhatched eggs. Sampler experience was a major factor influencing fidelity of egg counts with total eggs, but a single repetition of the experiment accompanied by knowledge of the results was sufficient to optimize sampler effectiveness. Regressions relating total eggs to counts, whether the counts were taken immediately after oviposition or after 3 days, were significant. However, compared with counts of newly-laid eggs, the regression relating egg counts at 3 days with total eggs was more stable and showed better agreement. These results can be used to maximize statistical power and minimize sampling errors in future examinations of L. hesperus oviposition.