The biology of the oak bark beetle, Scolytus intricatus (Ratzeburg) (Coleoptera: Scolytidae), in southern England

Abstract

AbstractScolytus intricatus (Ratz.) is a potential vector of oak wilt and is distributed throughout Europe wherever oak (Quercus) occurs. Its biology was studied in England in Monks Wood National Nature Reserve, Cambridgeshire, Alice Holt Forest, Surrey, and the New Forest, Hampshire, in 1977–83. S. intricatus was univoltine. Oviposition occurred from June to September in the bark of cut or weakened oak (Q. robur) over 5 cm in diameter. Eggs were laid in a single batch in maternal galleries cut across the grain of the cambium and phloem. The mean egg batch size was 17–36. Eggs hatched after 10–14 days, and the larvae ate the phloem and underwent five, or occasionally six, instars. The beetle overwintered as third-fifth-instar larvae, which were cold hardy and were located in cells in the phloem or outer xylem. Pupation occurred in spring, in cells in the bark or outer xylem. Emergence occurred between mid-May and mid-July and spanned a period of 3–4 weeks. The sex ratio was 1:1. Males and females differed externally by the presence of a tuft of setae on the frontal-clypeal suture of the head of the male. Newly emerged adults fed on twigs of live oak, but twig feeding was not obligatory for sexual maturation. Mating was observed during attacks on new hosts, which occurred in June-September. The eulophid Entedon ergias Wlk. was an endoparasite of larvae while larvae of the dolichopodids Medetera and Dolichopus and woodpeckers were predators.