Pakistani isolates of S. bifurcatum and S. affine were evaluated for pathogenicity of T. castaneum and L. serricorne (larvae and adults each) at different concentrations (Fig. 1) and temperatures (Fig. 2) by filter assay in laboratory conditions.
Pathogenicity of Steinernema bifurcatum
Significant differences in mortality rates were detected among the insect tested (ANOVA: F = 6.56; df = 3, 12; P < 0.05), and the nematode concentration showed significant differences (ANOVA: F= 4.5; df = 3, 12; P < 0.05). S. bifurcatum caused a high mortality at 200 IJs of L. serricorne larva (ANOVA: F =0.051; df = 3, 8; P < 0.05), L. serricorne adult (ANOVA: F=0.069; df = 3, 5; P < 0.05), T. castaneum larva (ANOVA: F= 0.188; df = 3, 8; P < 0.05), and T. castaneum adult (ANOVA: F= 0.034; df = 3, 8; P < 0.05) as compared to 50 and 150 IJs. All insects showed significant mortality rates with 200 IJs of S. bifurcatum. Both insects’ larvae showed above 90% mortality with the concentration @ 200IJs (Fig. 1). The nematode concentration showed a significant variance (ANOVA: F= 0.311; df = 3, 5; P < 0.05) as compared to control treatment. Insect pests, L. serricorne and T. castaneum (larvae and adult each), were also exposed to 3 different temperatures 15, 30, and 45°C. Significant differences in mortality were detected among the insects tested at different temperatures. S. bifurcatum showed the highest mortality that was 92 and 88% of L. serricorne larvae and adult, respectively, at 45°C (ANOVA: F= 9.2; df = 3, 20; P < 0.05) and T. castaneum larvae and adult showed 95 and 93%, respectively (ANOVA: F= 9.2; df = 3, 20; P < 0.05). S. bifurcatum showed less significant at 15°C where 55% and 50% larval mortality of L. serricorne and T. castaneum, respectively, and 62% and 58% mortality of L. serricorne and T. castaneum adults, respectively, were recorded at 200 IJs (Fig. 1).
Pathogenicity of Steinernema affine
Significant differences in mortality were detected among the insects tested (ANOVA: F= 0.015; df = 3, 8; P < 0.05) and among concentrations (ANOVA: F = 0.011; df = 3, 5; P < 0.05). S. affine significant difference showed a high mortality rate 90% of L. serricorne larvae at the concentration of 200IJs (ANOVA: F= 4.2, df = 3, 12; P < 0.05) and L. serricorne adults showed 88% mortality (ANOVA: F=0.03, df= 3, 8; P < 0.05) (Fig. 2). There was a non-significant difference at concentrations of 50 and 100 IJs of S. affine which caused 30% and 45% larval mortality of L. serricorne and 27% and 40% adult mortality of L. serricorne, respectively. S. affine showed a significant difference against T. castaneum larvae at the concentration of 200 IJs (ANOVA: F= 0.39; df = 3, 8; P < 0.05); T. castaneum adult less significant at 50 and 100 IJs (ANOVA: F= 0.098; df = 3, 8; P < 0.05). S. affine was also tested at the 3 different temperature degrees 15, 30 and 45°C. Significant differences in mortality rates were also found among the tested temperature degrees (ANOVA: F = 0.011; df = 4, 10; P < 0.05) at 15, 30, and 45°C. S. affine showed 90% mortality rate of L. serricorne larvae at 15°C (ANOVA: F= 10.8; df = 3, 20; P < 0.05). There was a non-significant difference in case of adults of L. serricorne at 30 and 45°C (ANOVA: F= 10.8; df = 3, 20; P < 0.05), i.e., 59 and 55% mortality, respectively. Significant differences in mortality rates were detected among the T. castaneum larvae and adults (ANOVA: F= 15.8; df = 3, 8; P < 0.05). S. affine showed 95% mortality of T. castaneum larvae at 15°C (ANOVA: F= 10.8; df = 3, 20; P < 0.05) whereas 57 and 52% at 30 and 45°C, respectively. There was a non-significant difference (ANOVA: F= 15; df = 3, 8; P < 0.05) in case of adults of T. castaneum 50 and 52% at 30 and 45 °C, respectively.