Development, survival and hatching periodicity of Lygus hesperus (Hemiptera: Miridae) eggs under constant and variable temperatures

Authors: Spurgeon, Dale; Brent, Colin

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2016
Publication Date: 12/6/2016
Publication URL: https://handle.nal.usda.gov/10113/63308
Citation: Spurgeon, D.W., Brent, C.S. 2016. Development, survival and hatching periodicity of Lygus hesperus (Hemiptera: Miridae) eggs under constant and variable temperatures. Journal of Entomological Science. 51(4):292-304.

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 and survival was similar under moderate variable temperatures (range from 57 to 86 F, daily average of 72 F) and a corresponding constant temperature. Under lower temperatures (daily average of 59 F) development was about 20% faster and survival was higher under variable temperatures (range from 45 to 73 F) compared with a constant temperature. In contrast, this pattern was reversed under higher temperatures (daily average of 84 F), and egg development under variable temperatures (range from 70 to 99 F) was about 20% 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 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 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 microclimate within western cotton (Gossypium spp.) seems favorable for the western tarnished plant bug (Lygus hesperus Knight) provided adequate soil moisture is available. Diminishing water supplies and increasing costs in the West will likely change irrigation practices and induce at least periodically unfavorable conditions for Lygus. Knowledge of L. hesperus thermal ecology has been limited to constant temperatures, whose relevance to variable temperature environments is unknown. Eggs of L. hesperus were reared under low (mean = 15 C), medium (mean = 22 C), or high (mean = 29 C) constant (+/- <0.5 C) or diurnally fluctuating (+/- 8 C) temperatures. Development time and survival were similar between constant and variable regimes at the medium temperature. In contrast, variable low temperatures hastened egg development and increased survival whereas variable high temperatures delayed development and reduced survival compared with constant regimes. Within the studied temperature range, the relationship between temperature and egg development rate was linear for constant temperatures, but a quadratic term was needed to describe this relationship under variable temperatures. Under medium variable temperatures egg hatch was disproportionately high during the warmest period of the day (1300–1900 h) compared with the constant regime. Differences between regimes were less pronounced at high temperatures except for the conspicuous absence of hatch between 1300–1900 h in the variable regime, when temperatures were always >32 degrees C. These results indicate the limited utility of constant temperature data for understanding L. hesperus thermal ecology, and provide baseline information to better plan and interpret applied studies of Lygus thermal ecology.