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New Zealand Plant Protection 68 (2015): 445

Detecting and controlling Serratia marcescens in a laboratory colony of Mastrus ridens

W.R.M. Sandanayaka, V.A. Davis, S.D.G. Marshall and J.G. Charles

ABSTRACT

Mastrus ridens (Hymenoptera: Ichneumonidae) is an ecto-parasitoid of cocooning Cydia pomonella (codling moth, CM) larvae, and has been introduced into New Zealand in a classical biocontrol programme. Large numbers of M. ridens are currently being reared in the laboratory on diapausing CM larvae for release into apple-growing regions. Within the rearing colony, a bacterial epizootic was discovered that killed both CM larvae and developing M. ridens. DNA from infected CM larvae was amplified using bacterial 16s rDNA primers, with sequencing identifying the bacterium as Serratia marcescens - a common species associated with insects. The epizootic probably arose from CM larvae in oviposition cages. The rearing method has been modified to minimise the presence of bacteria. Mastrus ridens pupae are now removed from the corrugated cardboard rolls (in which they develop on CM larvae) and held in emergence containers that have been sterilised by washing with sodium hypochlorite. Any diseased adult M. ridens are detected by the red colour of their abdomen and only healthy adults are selected as parents for subsequent generations. Improved hygiene and selection of healthy adult parasitoids successfully controlled the S. marcescens epizootic.

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