Viability Studies on Eggs and Infective Larvae of Nematodirus spathiger (Railliet, 1896), a Trichostrongylid Nematode of Ruminants

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Abstract
After exposing 3rd stage infective larvae of Nematodirus spathiger on pasture plots at various times of the yr. they possess unusual ability to survive the annual complex of weather conditions of Maryland. Although more living larvae were recovered from the test plots during the summer and fall than during the winter and spring, many of those recovered during the former period were in poor condition and exsheathed, whereas all those recovered during the latter period were sheathed and in excellent condition. In the winter-spring period 70% of the larvae recovered were from grass, whereas in the summer-fall period 90% were from humus and sub-surface soil. Various laboratory expts. revealed that desiccation imposed the greatest hardship on the larvae. After drying 2 mos. at room temp., 82% lived, but none after 5 mos. Those dried and kept at 40[degree] - 42[degree]F had a survival rate of 6% at 6 mos. and 1% after 12 mos. Survival of partially embryonated eggs dried at room temp. was 70% after 3 mos. with negative results at 4 mos., whereas the survival rate of eggs dried at 40[degree]F was 85% at 3 mos.,20% at 4 mos., 10% at 5 mos., and negative about 6 mos. Some survival of eggs was noted after a 2-yr. exposure in fecal material kept at 40[degree]F. Freezing temp. of 28[degree] - 30[degree]F had relatively little effect on the larvae. After 3 mos. 98.7% survived, and 25% lived after 10 mos. exposure. Larvae subjected to alternate freezing and thawing had a survival rate of 72% after 7 mos., and 37% after 10 mos. exposure. Larvae kept at 35[degree]F for 11 mos. in water had a survival rate of 48%.