Screening dead eggs of the West Indian sweet potato weevil, Euscepes postfasciatus (fairmaire) (coleoptera: Curculionidae), by the brine-flotation technique

Abstract

In the artificial rearing of the West Indian sweet potato weevil, Euscepes postfasciatus, dead eggs should be screened before egg-seeding on an artificial diet because they could become sources of bacterial or fungal contamination of the diet. We tested whether the dead eggs of the weevil could be removed using the brine-flotation technique. When the eggs were mixed with 14% saltwater in a glass a few days before hatching and freshwater was gently added to the glass, we were able to recognize three categories of eggs: (1) Eggs floating on the surface of the freshwater, (2) eggs suspended at the boundary between the saltwater and freshwater, and (3) eggs that had sunk to the bottom of the saltwater. The hatchability of (1) and (2) did not differ significantly, while the hatchability of (3) was extremely low (< 11%) and significantly lower than that of (1) and (2). Therefore, the number of dead eggs to be planted on a diet can be reduced by discarding the (3) eggs. Saltwater submersion of the eggs, per se, did not produce any undesirable effect on hatching. However, the mean hatchability of (1) and (2) was 72%, indicating that dead eggs could not be thoroughly excluded by the brine-flotation technique.