Calcium/calmodulin-dependent protein kinase II of the oriental fruit fly,Bactrocera dorsalis,and its association with rapid cold hardiness

The oriental fruit fly, Bactrocera dorsalis, is a serious insect pest with diverse host range. Furthermore, its invasive and polyphagous behaviors allow this species to expand its habitats. Recent climate change and increase of international trade/transportation facilitate the species expansion from subtropical to temperate regions. Low temperature during winter appears to be the major factor limiting its expansion to temperate zones in the northern hemisphere. This study reports its remarkable ability in rapid cold-hardening (RCH) along with deep supercooling capacity. A brief exposure to 9?°C significantly enhanced cold tolerance of its larvae, pupae, and adults. RCH took 1–2?h for pupae and adults, although it took 24?h for larvae. Supercooling capacity of pupae was also enhanced by RCH treatment from ?13.4?°C to ?16.6?°C. To trace genetic factors associated with RCH, calcium/calmodulin-dependent protein kinase II (Bd-CaMKII) was identified from B. dorsalis and their expression in response to RCH treatment was analyzed. Bd-CaMKII possesses three conserved domains of kinase, calmodulin, and oligomerization. Bd-CaMKII is highly homologous to CaMKII of D. melanogaster and other tephritid flies. Expression levels of Bd-CaMKII in the larvae treated with RCH were significantly increased by approximately 5.5 folds compared to those in control larvae. In addition, expression levels of HSP70 and HSP90 were also increased in response to RCH treatment. These results along with previous studies suggest that cold-hardening of B. dorsalis is functionally associated with its supercooling capacity with increased production of cryoprotectants and HSP through regulatory activity of Bd-CaMKII.