Potential of entomopathogenic nematodes for the control of the banded fruit weevil, Phlyctinus callosus (Schonherr) (Coleoptera: Curculionidae)

Entomopathogenic nematodes (EPN) were evaluated for their potential use as biological control agents against Phlyctinus callosus, the banded fruit weevil (BFW). The susceptibility of larvae and adults to EPN was evaluated using 400 infective juveniles (IJ) per insect after 4 days in 24-well bioassay trays. The nematode isolates used were all able to infect BFW, although the larvae were found to be more susceptible than were the adults. The percentage mortality for BFW larvae ranged from 41 to 73% and for BFW adults from 13 to 45%. The most effective isolate, SF41 of Heterorhabditis zealandica, was used to investigate the effect of vertical movement of nematodes in sand and sandy loam soil, at specified concentration and temperature. A higher (82.2 +/- 0.084%) percentage mortality rate was obtained with the sandy loam soil, than with the use of sand (67.5 +/- 0.12%). The LD50 and LD90 values after 4 days of incubation were 96 and 278 IJ/50 mu l, respectively. Nematodes were inactive below 15 degrees C, with the highest mortality of 74 +/- 0.081% for BFW larvae recorded at 25 degrees C. Heterorhabditis zealandica was able to complete its life cycle successfully in sixth-instar BFW larvae after a period of 22 days. The study showed BFW larvae not to be as susceptible to nematode infection as they need a high concentration (400 IJ/larva) and 4 days to give effective control.