,  , The size of infective Steinernema arenarium juveniles is variable and ranges from 724 to 1408 ㎛. Effects of harvest time and infective juvenile size on pathogenicity, development, and reproduction were examined in the last instar of the great wax moth, Galleria mellonella. Harvest time of infective juveniles (IJs) of S. arenarium affected pathogenicity. IJs harvested at the 10th day from trapping were more pathogenic than those harvested the 3rd day from trapping. Mortality of G. mellonella also depending on harvest time, i.e, 100% died within 48h when IJs were harvested at the 10th day, without relation to size. However, mortality was 40% in the small size group (SSG) compared with 18% in the large size group (LSG) within 48h when IJs were harvested at the 3rd day. Establishment of S. arenarium within the host was different depending on IJ size. The number of established IJs was 1.8 in the SSG, 3.3 in the LSG, and 3.2 in the mixed size group (MSG) when IJs were harvested at the 3rd day, and 5.3 in the SSG, 7.4 in the LSG, and 7.6 in the MSG when IJs were harvested at the 10th day. The length of the female adult was 7,070.5 ㎛ in the SSG and 7,893.9 ㎛ in the LSG and that of the male was 1,460.5 ㎛ in the SSG and 1,688.2 ㎛ in the LSG when IJs were harvested at the 3rd day. The length of the female adult was 7,573.6 ㎛ in the SSG and 8,305.4 ㎛ in the LSG and that of the male adult was 1,733.4 ㎛ in the SSG and 1,794.4 ㎛ in the LSG when IJs were harvested at the 10th day. Harvest time and size of IJs did not influence numbers of progeny or size of IJS.

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