Seasonal population dynamics of inoculated and indigenous steinernematid nematodes in an organic cropping system

Abstract

This study was based on naturally occurring and inoculated populations of steinernematid nematodes. The nematode populations were monitored in spring and autumn in 2 consecutive years in an organic cropping system and changes in population size were related to the presence of potential insect hosts. Nematode populations were estimated in terms of nematode incidence (percentage of positive soil samples) by using Tenebrio molitor larvae as bait. The population of naturally occurring nematodes (Steinernema affine and S. feltiae) was generally low (0-17% incidence for S. affine and 0-18% incidence for S. feltiae). Inoculated S. feltiae established well in half of the plots where inoculation had been performed and reached incidences of 87%. Establishment of inoculated nematodes, and population dynamics in general, was clearly influenced by the presence of insect hosts. In crops with high densities of potential hosts (Sitona lineatus in pea and partly Delia radicum in cabbage), nematode incidence increased from spring to autumn, whereas nematode incidence remained unchanged or decreased when few hosts were present (in barley, carrots, alfalfa and leek).

Behaviour and Population Dynamics of Entomopathogenic Nematodes Following Application

“…This was presumed to be due to reproduction in larvae of the bean weevil Sitona lineatus L. (Coloptera: Curculionidae) which were abundant in the bean crop and may have persisted in the clover (Susurluk & Ehlers). Similarly, nematode incidence (percentage of soil cores with EPN) increased from spring to autumn in crops with high densities of potential hosts -S. lineatus in pea and Delia radicum L. (Diptera: Anthomyiidae) in cabbage (Nielsen & Philipsen, 2004b). Availability of suitable insects and low disturbance by ploughing, harrowing or other soil movements were factors that favoured longer term EPN persistence (Susurluk & Ehlers).…”

Diseases in insects produced for food and feed

“…For example, Heterorhabditis georgiana (and other species from that genus) could infect both M. domestica, A. domesticus and T. molitor (Shapiro-Ilan et al, 2009). Each insect species can also be susceptible to a range of nematodes, an example is T. molitor, which is susceptible to both Heterorhabditis bacteriophagae (Brown et al, 2006), S. feltiae and Steinernema affine (Nielsen and Philipsen 2004). Nematodes from the genera Steinernema and Heterorhabditis are dependent on a certain level of humidity in order to survive and infect.…”