Geographic Variation of Diapause Induction Rates in Trichogramma drendrolimi (Hymenoptera: Trichogrammatidae) in China

Diapause variation is a key factor affecting the development and success of parasitoids employed as biological control agents. Trichogramma dendrolimi Matsumura is mass-reared for biocontrol purposes in several countries around the world. Here we investigated the rate of diapause induction in three populations of T. dendrolimi from different regions in China: Heilongjiang (44 degrees 55' N, 128 degrees 26' E; HLJ), Liaoning (40 degrees 18' N, 123 degrees 22' E; LN), and Jiangsu province (32 degrees 30' N, 120 degrees 09' E; JS). We measured the rates of diapause induction for populations from each region when exposed to temperatures of 8, 10, 12, and 14 degrees C, for periods ranging from 5 to 35 d. Results showed that both the temperature and exposure duration influenced diapause induction in the three populations of T. dendrolimi. The HLJ and LN populations showed the highest percentage of diapause under 12 and 10 degrees C, regardless of time period tested. After 20 d at 12 and 10 degrees C, 97.42% and 95.94% of individuals of HLJ and LN, respectively, entered diapause. After treatment for 20-35 d under 8 degrees C, or 15-25 d under 10 degrees C, the diapause rate of LN was higher than those of the other two populations. In contrast, the higher temperatures (1214 degrees C) induced diapause rapidly and steadily in HLJ. The diapause rate of JS was low for all temperatures and time periods. After 30 d at 12 degrees C, the JS population reached its highest diapause rate (29.56%). Our results showed significant variance in diapause rates among geographically distinct populations of T. dendrolimi in response to various abiotic conditions.