cAMP assay
Haemocytes were lysed in 65% ethanol for 1 h at 4°C. Lysates were centrifuged (2000×g for 15 min at 4°C), and the collected supernatants were dried under a stream of nitrogen. Contents of cAMP were assessed using the DetectX™ direct cyclic AMP enzyme immunoassay kit according to the manufacture's protocol. Total protein content was assessed using the Lowry method [55]. cAMP levels were expressed as pmol/mg protein.