Symptoms shown by late-stage larvae of the West Indian sweet potato weevil Euscepes postfasciatus (Coleoptera: Curculionidae) infected with Farinocystis sp (Neogregarinida: Lipotrophidae)

Pathogen outbreaks often represent a major issue when mass rearing target insects for biological control, even when applying sterile insect techniques (SIT). Here, we aimed to improve existing screening techniques used to detect a neogregarine Farinocystis sp. that infects the West Indian sweet potato weevil Euscepes postfasciatus Fairmaire (Coleoptera: Curculionidae) mass reared under the SIT program. Our results revealed that infected lateinstar larvae exhibited swelling symptoms, and that their body weight and head width significantly increased compared to uninfected larvae. The head width to body weight ratio differed between infected and uninfected larvae; yet, head width was highly correlated with body weight in both cases. Visual diagnosis based on the appearance of the late-instar larvae showed concordance of almost 90 % with the current diagnostic methods of optical microscopy and PCR. Thus, the swelling symptoms observed in late-instar larvae were directly noticeable. Therefore, visual diagnosis, based on larval appearance, represents a feasible, low-cost technique for the early detection of Farinocystis sp. infection of the West Indian sweet potato weevil.