Infectivity by nematode-bacteria association on the potato weevil <i>Phyrdenus muriceus</i>

Abstract

Bacteria of the genus Photorhabdus (Enterobacteriaceae) are motile, gram-negative, symbiotically associated with juveniles of entomopathogenic nematodes from the genus Heterorhabditis (Heterorhabditidae). Nematodes retain the Photorhabdus bacterial cells intheir intestine and transport them into an insect host. Upon locating an insect host,Heterorhabditis penetrates through natural openings (mouth, anus, spiracles), or directlyinto the hemocoel via the integument, subsequently releasing bacteria into the hemolymph. Once in the hemolymph, Photorhabdus begins multiplying simultaneously releasing toxinsvirulent enough to kill the insect within 24 hrs. Phyrdenus muriceus (Coleoptera: Curculionidae) is a pest of cultivated solanaceae affecting egg-plant, potato and tomato. Considerable damages on these crops are produced by this pest affecting both the aerial andunderground parts of the plants. Infectivity of the entomopathogenic complex Heterorhabditis bacteriophora and the symbiotic bacterium Photorhabdus luminescens isolated from soil samples collected from an orchard of La Plata was tested against pupae of P. muriceus. This stage was considered to be a suitable target to control at field due to its permanence into the soil. Plastic containers (8.5 cm diameter x 5.5 cm height) were used with sterile soil forming a 2 cm high layer. Pupae were added to the soil surface and exposed to a concentration of 5.000 infective juveniles (IJs) / insect. Mortality of 70% (n=10) occurred at 48 hrs after infection. In figure 1, we can appreciate nematodes inside the body of the pupae (B and C). The cadavers showed the typical red wine coloration due to the release of the endosymbiotic bacteria in the hemocoel (Fig. 1 B-D) unlike non-parasitized pupae (Fig. 1A). The complex nematode-bacteria was effective to parasite and kill Phyrdenus muriceus pupae. Future studies should be carried out to determine its use as biological control for this horticultural pest.