Effect of host insect sterols on the development and sterol composition of Steinernema feltiae.

Steinernema feltiae (= Neoaplectana carpocapsae), 'All' strain, was propagated in larvae of the corn earworm, Heliothis zea, which contained various sterols, in order to determine how the sterol composition of the host affects the growth, development and sterol composition of this insect-parasitic nematode. S. feltiae completed its life cycle normally in insects containing primarily cholesterol, cholestanol or 7-dehydrocholesterol, although the sterol composition of the dauer stage was affected by the sterol composition of the host. When the nematode was reared in insects containing primarily cholesterol, 55% of the sterol in the dauers was cholesterol and the other 46% was lathosterol. In contrast, cholestanol (70%) and lathostetrol (31%) were the sterols present in nematodes reared in H. zea containing primarily cholestanol. Cholestanol (43%), lathosterol (34%), campestanol and/or another 24-methylsterol (23%) and cholesterol (1%) were the sterols present in nematodes reared in H. zea containing campestanol and cholestanol as its major sterols. Lathosterol was the major sterol present in nematodes reared in H. zea containing principally 7-dehydrochlesterol. Therefore, in each case, S. feltiae metabolized some host sterol to lathosterol but the relative percentage of lathosterol in the nematode increased as it was exposed to delta 0-, delta 5- and delta 5,7-sterols, respectively. The ability of S. feltiae to utilize different host sterols may, in part, explain its success in parasitizing a wide variety of insects.