Aggregation of entomopathogenic nematodes, heterorhabditis spp. and steinernema spp., among host insects at 9 and 20 degrees C and effects on efficacy

The negative binomial distribution (NBD) with density-dependent k was used to test and describe the distribution of nematodes in Otiorhynchus sulcatus, Galleria mellonella, and Spodoptera exigua at 9 and 20 degrees C. Aggregation was greater in O. sulcatus than in the other two hosts. In case of G. mellonella exposed to the heterorhabditid HF85, the distribution of nematodes in the insects was random. There was only a small effect of low temperature on aggregation; this effect was stronger for O. sulcatus than for the other two hosts. Aggregation of nematodes among insects in a population increases the infection chance of already infected insects and decreases the infection chance of uninfected insects. Consequently, more nematodes will have to penetrate O. sulcatus than G. mellonella or S. exigua to cause the same proportion of infection in a population. The relevance of aggregation of nematodes for control O. sulcatus is discussed. Copyright 1999 Academic Press.