Western tarnished plant bug egg development and hatch under constant and variable temperatures

Authors: Spurgeon, Dale; Brent, Colin

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/24/2015
Publication Date: 5/19/2016
Citation: Spurgeon, D.W., Brent, C.S. Western tarnished plant bug egg development and hatch under constant and variable temperatures. National Cotton Council Beltwide Cotton Conference. p.p. 180-185. 2016.

Interpretive Summary: The western tarnished plant bug (Lygus bug) is presently the most important pest of Arizona cotton. As water supplies become limited in the arid West, water conservation techniques will likely result in at least periodically increased temperatures in the cotton crop. The Pest Management and Biocontrol Research Unit at Maricopa, AZ is studying temperature stress responses in Lygus in order to design management tactics to capitalize on these temperature changes. However, available information on Lygus thermal ecology is limited to results of studies conducted using constant temperatures. ARS scientists at Maricopa, AZ showed that Lygus egg development was slightly faster (about 0.4 day) under moderate variable temperatures (range from 57 to 86 F, daily average of 72 F) compared with a corresponding constant temperature. Under higher temperatures (daily average of 84 F), this pattern was reversed and egg development under variable temperatures (range from 70 to 99 F) was about 20% (almost 1 day) longer than under the constant temperature. The daily pattern of egg hatch was also changed by variable temperatures. Compared with the moderate constant temperature, egg hatch under variable moderate temperatures was increased during the warmest parts of the day and decreased during the cooler night. Under a high constant temperature hatch occurred at all times of the day, but no eggs hatched during the warmest period of the variable temperature treatment when temperatures were higher than 90 F. Our findings begin to uncover Lygus responses to temperatures like those occurring in the field, and suggest high temperatures represent an ecological limitation that might be exploited through transgenic or other molecular-based tactics.

Technical Abstract: The western tarnished plant bug (Lygus hesperus) is presently the most important pest of Arizona cotton. Cotton culture in the arid West is highly dependent on the availability of irrigation water. As water supplies become more limited, water conservation techniques such as deficit irrigation will likely result in at least periodically increased cotton canopy temperatures. The Pest Management and Biocontrol Research Unit at Maricopa, AZ is studying the molecular bases of thermal stress responses in Lygus in order to design molecular-based management tactics to capitalize on these microclimatic changes. However, currently available information on Lygus thermal ecology is limited to results of studies conducted using constant temperatures. We examined the development time and diel pattern of hatch of Lygus eggs at combinations of moderate and high temperatures, either held constant or exhibiting a variable thermoperiod. Development time was shorter under variable temperatures compared with constant temperatures in the moderate temperature treatment, but the difference was small. In contrast, development was faster at high constant temperatures compared with high variable temperatures. The diel pattern of egg hatch also differed between constant and variable regimes at both moderate and high temperatures. Results provide baseline information on the thermal ecology of Lygus eggs in response to a variable temperature environment, and suggests high temperatures represent an ecological vulnerability that may be exploited through transgenic or other molecular-based tactics.