Infectivity and Specificity of Canadian and Czech Isolates of Steinernema Kraussei (Steiner, 1923) To Some Insect Pests At Low Temperatures in the Laboratory

Abstract

The infectivity of steinernematid nematodes varies with temperature. Five insect species, namely codling moth, Cydia pomonella; mealworm, Tenebrio molitor; blow fly, Sarcophaga bullata; March fly, Bibio marci; and web spinning sawfly, Cephaleia abietis were exposed to a Canadian (# 76) isolate of Steinernema kraussei at 7°C. C. abietis was exposed to the Canadian isolate # D and Czech isolate Vimperk at 4°C. These experiments were done in Petri dishes filled with moist sand, exposure time was 250 h and inoculum ranged from 50 to 800 infective juveniles (IJs). The highest larval mortality occurred in lepidopteran and coleopteran species, C. pomonella (73-100%) and T. molitor (28-70%), respectively. Few dipteran larvae, S. bullata and B. marci, were killed. The mortality of C. abietis larvae ranged from 2% (isolate # 76, at 50 IJs/dish) to 30% (isolate Vimperk, at 400 IJs/dish) at 7°C, but was negligible at 4°C. The intensity of infection expressed as the number of adult nematodes recovered from the insect cadavers, was greatest in C. pomonella where it ranged from 16 to 25% of the initial IJ inoculum, but was almost zero for both fly larval species. When analysed and fitted to the modified Anderson host-parasite model, the data confirmed a significant level of Steinernema parasitism for C. abietis, T. molitor, and C. pomonella larvae at low temperatures, and showed that the two species of fly larvae tested were almost fully resistant to parasitism by S. kraussei. Natural adaptation of the Czech Vimperk isolate to C. abietis may have enhanced this isolate's infectivity when compared with that of the Canadian nematode isolates.