Colour of heterorhabditis zealandica-infected-Galleria mellonella dependent on the Photorhabdus symbiont, with two new nematode-symbiotic associations reported.

Bacterial symbionts associated with entomopathogenic nematodes (EPNs) play an important role in terms of the insecticidal properties of nematodes in pest control. Galleria mellonella larvae, shortly after being infected with three different strains of Heterorhabditis zealandica, which were isolated from South African soil, changed from pale white to steel grey-blue (blue), bright red, and yellow with a green tint (green), respectively. The genetic relatedness of the bacterial symbionts that were isolated from the three strains of H. zealandica was determined by means of comparing the 16S rRNA, recA, gyrB, dnaN, gltX and infB gene sequences. Subsequently, comparing the concatenated sequences revealed the presence of three distinct Photorhabdus species. The H. zealandica strain SF41, associated with Photorhabdus heterorhabditis, produced 'blue' G. mellonella larvae. The H. zealandica strain MJ2C, associated with Photorhabdus thracensis, yielded 'green' G. mellonella larvae, while the H. zealandica strain LLM associated with Photorhabdus laumondii subsp. laumondii yielded red larvae. The colour changes in G. mellonella larvae were found to have been instigated by a particular Photorhabdus species associated with H. zealandica. The red and 'green' phenotypes of G. mellonella larvae were found to represent new combinations of Heterorhabditis and Photorhabdus. In future studies, the colour of infected G. mellonella larvae needs to be reported as a phenotypic character, as it indicates the different bacterial species associated with the same nematode host, as shown in the case of H. zealandica.

Entomopathogenic nematodes for control of insect pests above and below ground with comments on commercial production.

Entomopathogenic nematodes (EPNs) have been utilized in classical, conservation, and augmentative biological control programs. The vast majority of applied research has focused on their potential as inundatively applied augmentative biological control agents. Extensive research over the past three decades has demonstrated both their successes and failures for control of insect pests of crops, ornamental plants, trees and lawn and turf. In this paper we present highlights of their development for control of insect pests above and below ground. The target insects include those from foliar, soil surface, cryptic and subterranean habitats. Advances in mass-production and formulation technology of EPNs, the discovery of numerous efficacious isolates/strains, and the desirability of reducing pesticide usage have resulted in a surge of commercial use and development of EPNs. Commercially produced EPNs are currently in use for control of scarab larvae in lawns and turf, fungus gnats in mushroom production, invasive mole crickets in lawn and turf, black vine weevil in nursery plants, and Diaprepes root weevil in citrus in addition to other pest insects. However, demonstrated successful control of several other insects, often has not lead to capture of a significant share of the pesticide market for these pests.

Heterorhabditid Behavior in the Presence of the Cabbage Maggot, Delia radicum, and its Host Plants.

The behavior of Heterorhabditis zealandica Poinar strain T327 was investigated in the presence of the cabbage maggot, Delia radicum L., and plants that are susceptible to D. radicum infestation. Newly formed puparia and freeze-killed third instar larvae were attractive to infective nematodes. Newly harvested infective nematodes did not respond to the puparia, whereas 1-month-old and 2-month-old nematodes reached the insect targets within 15 minutes. There were no significant differences in the ability of similar-sized, third instar larval D. radicum and Galleria mellonella L., the greater wax moth, to attract nematodes. There was a tendency for a greater number of insects to attract more nematodes. The roots of ball cabbage and radish were equally attractive to nematodes, but rutabaga roots neither attracted nor repelled the nematodes. Germinated seeds of radish attracted nematodes, and there was a tendency for more numerous germinated seeds to attract more nematodes.