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United States Department of Agriculture

Agricultural Research Service

Research Project: Sustainable Pest Management Strategies for Arid-land Crops

Location: Pest Management and Biocontrol Research

Title: Classification of Diapause Status by Color Phenotype in Lygus hesperus

Author
item Brent, Colin

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 2012
Publication Date: N/A

Interpretive Summary: Recent studies on the western tarnished plant bug, Lygus hesperus Knight, have highlighted the need to identify a reliable external marker for the internal changes that differentiate a normal animal from one that has delayed its reproductive development while overwintering, a condition known as diapause. To test the efficacy of a color based discrimination system, female and male L. hesperus were reared under short day length conditions until 10 d old adults. They were separated into three color groups (yellow, pale green, dark green) then dissected to determine internal development. Most yellow individuals were in diapause, dark green individuals were not, and pale green ones were mixed. A group of 25 assessors, naïve with regard to Lygus bug development, were then asked to use a simplified color criteria (yellow = diapause, green = non-diapause) to estimate the status of a mixture of diapausing and non-diapausing 2-7 d old adults. Assessor accuracy was found to be ineffective for assessing adults of both sexes younger than 4 days because color differences, which increased with age, were subtle or non-existent at this stage. For 4-7 d old bugs, 84% of females and 67% of males were correctly categorized, on average. Incorrect assessments in all but the youngest males over-identified diapause, but for females there was no trend in mis-categorizations. Overall, the results indicate that diapause status can be adequately discriminated by color assessment, with greatest accuracy when sampling older females.

Technical Abstract: Recent studies on adult diapause in the western tarnished plant bug, Lygus hesperus Knight (Heteroptera: Miridae), have highlighted the need to identify a reliable external marker for the internal changes that differentiate a normal animal from one that is overwintering. To test the efficacy of a color based discrimination system, L. hesperus of both genders were reared from egg through day 10 of adulthood under a 10 h photophase at a constant temperature. They were separated into three color groups (yellow, pale green, dark green) then dissected for diapause categorization based on internal development. Most yellow individuals were in diapause, dark green individuals were not, and pale green ones were mixed. A group of 25 assessors, naïve with regard to Lygus bug development, were then asked to use a simplified color criteria (yellow = diapause, green = non-diapause) to estimate the status of a mixture of diapausing and non-diapausing adults of both genders aged 2-7 d post-eclosion. After dissection to verify diapause status, assessor accuracy was found to be ineffective for assessing adults of both sexes younger than 4 days because color differences, which increased with age, were subtle or non-existent at this stage. For 4-7 d old bugs, 84% of females and 67% of males were correctly categorized, on average. Incorrect assessments in all but the youngest males over-identified diapause, but for females there was no trend in mis-categorizations. Overall, the results indicate that diapause status can be adequately discriminated by color assessment, with greatest accuracy when sampling older females. However, factors other than photoperiod appear to also influence coloration.

Last Modified: 7/28/2014
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