Laboratory evaluation of control of the European corn borer, Ostrinia nubilalis (Hb.) (Lep., Pyralidae) by nematodes of the genus Steinernema (Nematoda, Steinernematidae) at low temperature

Abstract Cold active isolates #76, #102, and #D of Steinernema kraussei and the Czech isolate #B1 of S. feltiae pre‐adapted for the parasitation of European corn borer, Ostrinia nubilalis, were used for the laboratory control of the European corn borer larvae and pupae at low temperature. The experiments performed in Petri dishes were divided into two alternatives, both at a constant temperature of 7°C, exposition time 250 h with 200 infective juveniles and 10 insects per dish. In the first experiment the only non‐ligatured Ostrinia larvae and Canadian isolates were tested, while in the second experiment the Canadian isolate #D and Czech isolate #B1 were compared when using against ligatured larvae of the pest. The average mortality of the pest larvae in the first experiment reached maximally 26% and the average number of adult nematodes recovered by dissection was 7.2 per insect in the best #D isolate. Low efficacy of steiner‐nematids to pest larvae was probably significantly influenced by forming a cocoon by insect. In the second experiment the pest larvae were ligatured before nematode application and forming of the cocoon was blocked. Surprisingly, the #B1 isolate killed on average 88.3% of Ostrinia larvae while the cold active #D isolate killed only 48.3% of the pest larvae. Number of recovered adults per insect by dissection was 30.3 in the #B1 isolate and 10 in the #D isolate. The results were analysed by means of one‐way analysis of variance and of t‐test. The percentage of parasitation (P < 0.01) and number of recovered adults (P < 0.05) were statistically significant between S. kraussei #D and S. feltiae #B1. It is speculated that the adaptability of the #B1 isolate had more significant role for the parasitation than the cold activity of the #D isolate.