An Assessment of Cold Hardiness and Biochemical Adaptations for Cold Tolerance Among Different Geographic Populations of the Bactrocera dorsalis (Diptera: Tephritidae) in China

The cold hardiness of larvae, pupae, and adults of the oriental fruit fly, Bactrocera Dorsalis (Hendel) (Diptera: Tephritidae) was characterized first, and then body water, total sugar and glycerol contents, and activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and alcohol dehydrogenase (ADH) of different geographical populations subjected to suitable rearing conditions and under sublethal low-temperature stress were compared. The cold hardiness of different populations was well correlated with the latitudes of distributions. The northern marginal population (31.6° N) had higher cold tolerance than southern populations (23.1° N and 24.3° N). Among different life stages, larvae had the least cold tolerance, whereas pupae had the most tolerance. Under suitable rearing conditions, the marginal population had lower activities of all four tested enzymes than that of the southern populations and also had lower body water and higher total sugar and glycerol contents. The low-temperature stress induced higher SOD, CAT, POD, and ADH activities of all tested life stages and of all tested populations with higher increase intensity in adults and pupae than in larvae. The increase intensity was higher in the marginal population than in the southern populations. Pupae in the marginal population and adults in the southern populations showed the largest activity enhancement, which agreed with the insect's overwinter stages in their respective locations. Lower temperature stress lowered body water and total sugar contents and increased glycerol contents. The results revealed a strong correlation between the cold hardiness of a population and the concentration or activity of various biochemicals and enzymes known to be involved in cold tolerance. The marginal population of B. dorsalis might have evolved a new biotype with better adaption to low temperature.