Biological control of Plodia interpunctella (Lepidoptera: Pyralidae) by single and double releases of two larval parasitoids in bulk stored wheat

The Indian meal moth, Plodia interpunctella is a world-wide economically important pest of stored-products and processed food commodities including bulk grain. Two larval parasitoids, Habrobracon hebetor and Venturia canescens were studied under laboratory conditions to suppress small populations of P. interpunctella in 30-L polyethylene jar filled with 20 kg wheat. Twenty 3 to 4-week-old moth larvae were released into the jar and were allowed to produce webbings in the grain for 3–4 d. Then 10, 20 or 40 female parasitoids were added. A further batch of parasitoids was added to half of the jars 4 d after the first batch, 7–8 d after the introduction of P. interpunctella.Treatments comprised untreated control, only V. canescens or only H. hebetor released, and the combination of both parasitoids per release. After two weeks, the grains were sieved, the numbers of surviving parental parasitoids recorded and the cocoons of moths and parasitoids were collected from each jar and kept under controlled conditions of 25 °C. The emerged moth adults and parasitoid progeny were recorded until day 42.The highest mortality (93%) was observed with a single release of 20 H. hebetor plus 20 V. canescens (host-parasitoid ratio 1:1 for each parasitoid species). The various numbers of H. hebetor and V. canescens alone or in combination, once or twice released, led to mortalities between 50% and 80% that did not differ significantly. The single release of 10 H. hebetor or 10 V. canescens resulted in the lowest mortalities of P. interpunctella ranging from 34% to 39%. The different treatments affected the number of parasitoid offspring produced. Venturia canescens progeny occurred in all trials with combinations of the two parasitoid species. The single release of 20 H. hebetor resulted in more progeny emerged compared to all other treatments. For application in biological control, our data suggest the combination could be as least as effective as the release of H. hebetor alone.

► Parasitoid induced mortality ranged between 50 and 80%.
► Highest mortality was observed with single release of 20 Habrobraconhebetor + 20 Venturiacanescens.
► Lowest mortality was observed with single release of 10 H. hebetor or 10 V. canescens.
► Most parasitoid progeny was recorded with single release of 20 H. hebetor.
► Venturia canescens progeny occurred in all trials with both parasitoid species.