BIOLOGY OF SULPHURETYLENCHUS ELONGATUS (NEMATODA: SPHAERULARIIDAE), AND ITS EFFECT ON ITS HOST, SCOLYTUS VENTRALIS (COLEOPTERA: SCOLYTIDAE)

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Abstract
The developmental stages of Sulphuretylenchus elongatus, an abundant nematode parasite of Scolytus ventralis, are described. The life cycle was generally synchronized with its host, nematode reproduction usually occurring in the adult beetle after it had attacked a new tree. Reproduction occasionally occurred in the host larva. In these cases encapsulation of some nematode eggs and larvae was observed and the host usually died. Free-living infective stage nematodes emerged from the host, mated in the bark beetle galleries, and the female nematode reinfected bark beetle larvae by penetrating the cuticle.Parasitism by S. elongatus caused delayed emergence, limited flight, and aberrant attack behavior by infected S. ventralis. Female bark beetles were sterilized by heavy infection and partially sterilized by light or moderate infection. The effects of parasitism on males was not as severe. Some egg and larval mortality was attributed to nematode attack, and adult survival was reduced by infection.Parasitism was slightly higher in female bark beetles. The incidence of parasitism decreased somewhat in the upper levels of the tree. Host density appeared to have little effect on per cent parasitism although the degree of super-parasitism increased with host density.