Temperature adaptability of two clades of Aphelinus mali (Hymenoptera: Aphelinidae) in China

Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae) is an effective natural enemy used in China to control the woolly apple aphid (Eriosoma lanigerum [Hausmann]) (WAA). Population of A. mali in China falls into two distinct genetic clades (Shandong clades and Liaoning clades). In the present results, the developmental threshold temperature of the Shandong clade (9.82 ± 1.44 °C) was lower than that of the Liaoning clade (10.72 ± 0.24 °C), while the effective accumulated temperature of the Shandong clade needed for development from oviposition to adult eclosion (126.45 ± 16.81 day-degree) was significantly higher than that of the Liaoning clade (107.99 ± 3.44 day-degree). The supercooling and freezing points of the Liaoning clade (− 27.66 °C, − 27.17 °C) were significantly lower than those of the Shandong clade (− 26.04 °C, − 25.54 °C). Some other differences between the two clades as well were the content of fat, trehalose, and protein of overwintering larvae of the Liaoning clade (60.8%, 7.57 μg/one insect, 10.11 μg/one insect) as these were significantly higher than those of the Shandong clade (45.5%, 5.73 μg/one insect, 8.05 μg/one insect). The occurrence of the first adult emergence of the Shandong clade of A. mali was earlier in the year than that of the Liaoning clade, allowing this clade to better control WAA in early spring. Meanwhile, the developmental duration from oviposition to adult emergence of the Shandong clade was longer than that of the Liaoning clade, and the cold tolerance of one of these, the more northerly Liaoning clade, is greater than that of the other, the more southerly Shandong clade. All of these factors imply differences in the pest control ability of the two clades of A. mali in their respective regions.