Author
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Spurgeon, Dale |
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Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings Publication Acceptance Date: 1/2/2015 Publication Date: 5/10/2015 Citation: Spurgeon, D.W. 2015. Critical photoperiod inducing diapause in Lygus hesperus. National Cotton Council Beltwide Cotton Conference. PP. 260-263. Interpretive Summary: The western tarnished plant bug (Lygus bug) is a major pest of crops in the western U.S. This pest survives the winter as an adult in a state of diapause characterized by large fat reserves and undeveloped reproductive organs. The diapause state in this bug may represent an ecological vulnerability that is amenable to cultural management if it is sufficiently understood, but much about diapause in this pest remains unknown. When Lygus were reared from eggs to adults under daylengths ranging from 10 to 13 hours, the incidence of diapause increased with decreased daylength from 13 to 11 hours. The incidence of diapause at daylengths of 10 and 11 hours was similar. The maximum incidence of diapause was greater for female bugs (80%) than for male bugs (51%). These maxima were lower than those previously reported for Lygus bugs in California. In addition, the diapause response was widely variable at but the longest daylength (13 hours) where the incidence of diapause was low. The critical daylengths that induced diapause at a rate that was half the estimated maximum were 11 hours 54 min for females and 12 hours 7 min for males. The low but variable incidence of diapause that we observed was probably caused by variation in the natural population of Lygus in central Arizona. This variability may be important in allowing this population of Lygus bugs to adapt to local conditions where climate and host availability often permit reproduction on fall and winter alfalfa and weed hosts. Such geographical variation in diapause response is known for some other insects. Our results provide baseline information for comparison in future studies of the influences of geographical location and environmental factors on the diapause response of Lygus bugs. Technical Abstract: The western tarnished plant bug, Lygus hesperus, is a key pest of western cotton. The pest status of L. hesperus has diminished in Arizona cotton because of improved management strategies and use of selective insecticides. Additional gains in Lygus management will require better understanding of its basic ecology, including the dynamics of diapause. The objective of the research was to quantify the relationship between daylength and diapause incidence under controlled temperature conditions. Lygus hesperus were reared under daylengths ranging from 10:14 to 13:11 (L:D) h at a constant temperature of 26.7 degrees C. The diapause response for each Lygus gender was described by a logistic function. Females entered diapause more frequently than did males. The diapause response was highly variable at all but the longest daylength, and no daylength resulted in more than 80% diapause for either gender. The logistic functions predicted critical photoperiods of 11:44 (h:m) for females and 11:21 (h:m) for males. Population-specific critical photoperiods (50% of the maximal diapause response) were 11:54 (h:m) for females and 12:07 (h:m) for males. Incidence of diapause increased only slightly at photoperiods shorter than 11 h. The L. hesperus population in central Arizona appears less responsive to short daylengths than is the population in the San Joaquin Valley of California. Both intra- and inter-populational heterogeneity in the diapause response may represent an ecological bet-hedging strategy to capitalize on frequent winter-time conditions conducive to reproduction in the southern portions of the L. hesperus geographical range. |
