Effect of Soil Texture and Moisture on the Activity of Entomopathogenic Nematodes Against Female Boophilus annulatus Ticks

Abstract

Soil texture, chemistry and moisture have a profound effect upon the activity and persistence of entomopathogenic nematodes (EPNs). Whereas nematodes’ natural habitat is within the soil, ticks and other arthropod pests prefer to stay on the soil surface and under stones or leaf litter; they spend much of their life cycle in the humid environment of the soil upper layer, therefore consideration of the effect of the soil environment on nematode activity is a pre-requisite for the sucessful use of EPNs against arthropod pests. In the present study we investigated the effects of soil type, and humidity on various nematode strains and on their effectiveness against ticks. Many infective juveniles (IJs) of Steinernema carpocapsae and S. riobrave were found in the uppermost soil layer whereas the heterorhabditid strains were almost absent from the upper 6 cm of the soil profile. The IJs of S. feltiae, and the S. carpocapsae strain S-20, exhibited an intermediate behavior. It was found that the activity of IJs of S. carpocapsae in the soil upper layer (1 cm depth) was strongly affected by soil type: the greatest number of IJs were recorded from sandy loam soil; less were found in the lighter soils – ‘Marine sand’ and ‘Calcareous sandstone’ – and only very few were recovered from heavy soils. Strikingly, even when the soil moisture was low and the number of nematodes found in the upper layer correspondingly low, tick mortality remained high. The results demonstrate: (a) the possible use of the nematodes as an anti-tick agent; (b) the importance of knowing the exact interaction of nematodes with the immediate environment of the pest, in order to optimize the pest-control activity of the nematode.