Physiological effects of methyl farnesoate and pyriproxyfen on wintering female crayfish Cherax quadricarinatus

Methyl farnesoate (NM), the predominant juvenile hormone-like compound of c rustaceans, was found in the hemolymph of female Cherax quadricarinatus cra yfish. Administration of NIF to C. quadricarinatus females during their win ter reproductive arrest period had no effect on reproduction; however, it d id have a tendency to accelerate molting. However, since MF caused increase d mortality (similar to 47% survival in the high MF treatment), we were not able to draw definitive conclusions regarding its physiological affect, In contrast, administration of pyriproxyfen, a juvenile hormone analog, did n ot cause significant mortality (95% survival in the high pyriproxyfen treat ment), although it accumulated in high quantities in the hepatopancreas and , to a lesser extent, muscle tissue, ovaries and gills. The highest dose of pyriproxyfen used in this study, 20 mug/gram animal body weight/week, caus ed a delay in spawning, which became statistically significant from the sev enteenth week. This dose of pyriproxyfen caused a tendency of acceleration of molting without any effect on molt increment. The results of this study show that pyriproxyfen does riot seem to be toxic to the crayfish, even in relatively high doses, and might affect the energetic balance between molt and reproduction. (C) 2001 Elsevier Science B.V. An rights reserved.