Application of toxins from the entomopathogenic bacterium, Xenorhabdus nematophila, for the control of insects on foliage.

Larvae of the beet armyworm, Spodoptera exigua, and the diamondback moth, Plutella xylostella, and nymphs of the desert locust, Schistocerca gregaria were controlled by the application of either cell suspensions from the bacterium, Xenorhabdus nematophila or filtrates containing cell-free toxins. Since there was no significant differences between the two treatments it was concluded that toxins produced by the bacterium were responsible for the lethal effects obtained. Cells of Xenorhabdus nematophila were recovered from the haemocoele of the treated insects indicating that the bacterium, which is normally carried into the host by the J3 of Steinernema carpocapsae, was able to enter the host in the absence of the nematode vector. The entry was rapid, cells of Xenorhabdus nematophila being detected in the larvae of P. xylostella within 15 min of application of cell suspensions to chinese cabbage leaves. The possibility of using direct application of cell suspensions of X. nematophila to foliage for insect control is discussed.

The susceptibility of onion thrips, Thrips tabaci to Heterorhabditis indicus.

The potential of the entomopathogenic nematode, Heterorhabditis indicus against Thrips tabaci was tested on foliage and in soil at three concentrations. Soil treatment was more effective than the foliar treatment. At 1.5 million nematodes/m2, nearly 70% mortality was achieved with soil application whereas a similar dose applied to the foliage gave only 55% mortality. Soil application gave better mortality of onion thrips (62 %) at 1 million/m2 compared to foliar application at 1.5 million/m2. Probably this is because the nematodes are more effective against the soil dwelling prepupae and pupae stages of the thrips. The possible explanations for the differences are discussed.