Cold Hardiness of Overwintering Larvae of Sphenoptera sp (Coleoptera: Buprestidae) in Western China

An undetermined species of Sphenoptera sp. is an important pest of Artemisia ordosica Krasch, and recently, an outbreak of this insect has spread throughout Ningxia, Inner Mongolia, Shanxi, and other regions in western China. The cold hardiness of overwintering larvae of Sphenoptera sp. was determined by measuring their supercooling point (SCP) and their mortality at sub-zero temperatures. Additionally, quantitative changes in sugars and low molecular weight sugar alcohols in larvae were determined following exposure of larvae to low temperatures. Mean SCP of overwintering larvae (i.e., collected in January) was -30.2 +/- 0.60 degrees C. The mortality rate of larvae approached 100% at -30 degrees C, whereas mortality rates of larvae in the higher temperature treatments were generally less than 25%. Five sugars and sugar alcohols (i.e., glycerol, fructose, glucose, inositol, and trehalose) were detected in larvae. When larvae were exposed to low temperatures for 4 h, inositol, trehalose and total content was generally higher at the highest incubation temperature (-10 degrees C) than at lower incubation temperatures. Following a longer exposure (30 d), content of fructose, glucose, trehalose and total content generally increased with decreasing temperature down to -25 degrees C. Thus it appears that Sphenoptera sp. larvae are freeze avoidant, and their cold hardiness may be achieved by accumulation low molecular weight sugars and sugar alcohols.