Effect of soil temperature and moisture on the pathogenicity of two species of entomopathogenic nematodes (Rhabditida: Steinernematidae)This study investigated the impact of soil temperature and soil moisture on the virulence of the entomopathogenic nematodes Steinernema carpocapsae and S. feltiae. The effects of temperatures of 10, 15 and 25 °C and humidity of 6% and 12.5% were tested against the larvae of Tenebrio molitor. The nematodes were tested in two concentrations of 50 nematodes and 500 nematodes per box. S. carpocapsae was generally significantly more efficient at the highest temperature (25 °C) than S. feltiae, especially at the lower concentration of 50 nematodes per box. S. feltiae recorded higher insect mortality at lower temperatures (15 °C and 10 °C). The virulence of both tested nematode species was low (0-26%) at 10 °C after 7 days, but in the case of S. feltiae increased to 66% after 14 days. The efficacy when tested with 6% moisture at 15 °C was low (4% for both nematode species) compared with 12.5% moisture, where after seven days it reached 54% for S. carpocapsae and 70% for S. feltiae, although generally, S. feltiae was more efficient under dry conditions than S. carpocapsae. Insect mortality inreased significantly after remoistening of the soil, especially with S. feltiae (500 nematodes per box) where mortality reached 46% two weeks after remoistening.

The survival and infectivity of infective juveniles of the entomopathogenic nematode Steinernema feltiae (Rhabditida: Steinernematidae) were determined after being exposed to 8 insecticides (a.i. kinoprene, lufenuron, methomyl, metoxyfenozide, oxamyl, piperonyl-butoxide, pyriproxyfen, tebufenozide), 7 acaricides (a.i. azocyclotin, clofentezin, diafenthiuron, etoxazole, fenbutatinoxide, fenpyroximate, tebufenpyrad) and 4 fungicides (a.i. captan, fenhexamid, kresoxim-methyl, nuarimol) under laboratory conditions. S. feltiae was tolerant to all tested insecticides and fungicides, mortality during 72 hours varied from 2.26% to 18.68 % and from 7.04% to 8.86%, respectively. Acaricides with a.i. fenpyroximate and tebufenpyrad considerably influenced the S. feltiae ability to infect larvae of Tenebrio molitor. Tebufenpyrad caused 95% and fenpyroximate 85% reduction in S. feltiae virulence. These results suggest that S. feltiae can be applied in combination with all tested pesticides except the acaricides with a.i. tebufenpyrad and fenpyroximate.

Can pre-colonisation of the soil substrate increase the efficacy of entomopathogenic nematodes (Rhabditida: Steinernematidae)?The effects of soil pre-colonisation with entomopathogenic nematodes Steinernema feltiae, S. carpocapsae and S. arenarium on the mortality of Tenebrio molitor larvae were tested under laboratory conditions. The soil was inhabited with the nematodes for 7 days prior to the addition of the larvae. Nematode concentrations of 50 and 500 infective juveniles per box were used. S. carpocapsae reacted to pre-colonisation negatively and the efficacy decreased at the concentrations tested. S. arenarium showed generally low efficacy against Tenebrio molitor larvae and pre-colonisation showed only a slight positive effect on the efficacy of this species. S. feltiae increased its efficacy at the concentration of 500 infective juveniles per box compared with other tested nematodes.