Milky disease (Bacillusspp.) occurrence and experimental infection in larvae ofCostelytra zealandicaand other Scarabaeidae

Abstract

Milky disease was transmitted experimentally to larvae of Costelytra zealandica (White), Costleya (= Chlorochiton) suturalis Fabr., and Odontria striata White (Melolon‐thinae) by feeding and by intra‐haemocoelic injection of spores of Bacillus popilliae and two unnamed New Zealand Bacillus strains, and also to Pericoptus truncatus Fabr. (Dynastinae) by intrahaemocoelic injection and to C. zealandica by housing the larvae in soil containing the spores. The infection rate resulting from any of these methods rarely exceeded 5 %, and was usually much less. Monthly records from a 2‐acre (approx. 0.8 ha) field plot showed an initial infection rate of up to 62% in lst‐and 2nd‐instar C. zealandica larvae. Most of these were transient, non‐lethal infections which did not develop to a visibly milky condition. Evidence from field records and from the survival of diseased larvae held in the laboratory suggested a total mortality from milky disease in this population, throughout the season, of more than 20%. Records from 21 other sites are summarised.