Control of the grass grub, Costelytra zealandica (white) (Coleoptera: Scarabaeidae), by application of the bacteria Serratia spp. causing honey disease

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Abstract
Isolates of Serratia marinorubra and S. liquefaciens pathogenic for Costelytra zealandica (White) were artificially cultured and applied to field populations of larvae of C. zealandica in New Zealand in the late summer and autumn of 1984. In four trials, when bacteria were applied from February to late March, high levels of disease transmission were recorded. Three months after application, significant (P<0·05) reductions of 30–59% in the larval populations were obtained, and 47% of the remaining larvae in the treated plots were diseased, suggesting the long-term effect would be greater. Treatment resulted in a 30% increase in dry matter production in the pastures. There was no consistent difference between the bacterial isolates tested. Application of the bacteria in May had no effect on the larvae, suggesting that they were no longer susceptible. It is concluded that these pathogenic isolates should be developed further as microbial insecticides for control of C. zealandica.