The parasitoid Copidosoma koehleri provides limited control of the potato tuber moth, Phthorimaea operculella, in stored potatoes

The potato tuber moth Phthorimaea operculella (Zeller) is a major pest of potatoes in the field, and of tubers stored under ambient temperatures post-harvest. The encyrtid parasitoid Copidosoma koehleri (Blanchard) effectively controls the pest in the field in some countries. We tested whether C. koehleri can also reduce tuber moth populations in storage. Tubers stored indoors and outdoors in Israel, under controlled initial tuber moth infestation levels, received 1–2 releases of adult parasitoids during an eight-week storage period. Tubers were repeatedly sampled for infestation, and reared out until adult insect emergence. In the indoor storage experiment, parasitoid populations increased and tuber moth populations were significantly reduced. Nevertheless, tuber infestation reached 100% in C. koehleri-treated tubers and in untreated controls. In potatoes stored in heaps outdoors, parasitized hosts were rarely recovered, and infestation levels of parasitoid-treated heaps did not differ from untreated controls. We discuss possible reasons for C. koehleri’s limited efficiency as a biological control agent.