Overwintering of Piezodorus guildinii (Heteroptera, Pentatomidae) Populations

Piezodorus guildinii (Westwood) is a soybean pest that causes significant economic losses in the Americas. The variability of overwintering (diapause) traits was evaluated in populations of the Southwest (SW) (33°55'-34°17'S, 57°13'-57°46'W) during 2-year period (2011-2013) and of the Northwest (NW) (32°01'-33°02'S, 57°50'-57°24'W) during 1-year period (2014-2015) Regions of Uruguay. Samples were taken from different plant species (cultivated legumes, wild shrubs, and trees) and from overwintering sites (leaf litter and bark). Alfalfa, Medicago sativa L. was the main host, with a collection period of 10-11 months in the SW and 12 months in the NW. Cluster analysis for each sex was carried out to group the months according to the similarity in diapause traits of populations (body size, body lipid content, immature reproductive organs, and clear type of pronotum band and connexivum in females). Female diapause in the SW was longer (beginning of autumn to end of winter) than that in the NW (mid-autumn to mid-winter). Male diapause was longer (mid-autumn to mid-winter) in SW1 (1st year) than in SW2 (2nd year) and NW (late-autumn to mid-winter). In both regions, male diapause was shorter than female. Differences were associated with maximum temperature at daylight hours ≤ 12.1, being necessary maximum temperatures below 23.8 °C for females and 19.2 °C for males to initiate diapause.