Laboratory studies on control of the maize weevil Sitophilus zeamais by the parasitoid Anisopteromalus calandrae.

Abstract

Anisopteromalus calandrae (Howard), a cosmopolitan parasitoid, attacks several beetle pests of stored products, including the maize weevil, Sitophilus zeamais (Motschulsky). Two laboratory experiments were conducted at ambient conditions (25-29 °C, 60-70% RH, natural photoperiod). A short-term experiment evaluated the density of A. calandrae (0, 4, 8, 12, 16, or 20 per box) for the optimal production of parasitoids in 3825-cm 3 boxes containing milled rice. The percentage of parasitoid emergence was highest and the percentages of weevil emergence and parasitoid-induced mortality i.e., parasitoid mortality resulting from superparasitism were relatively low with 16 females per box rather than with smaller (0 to 12) or larger (20) numbers of females added per box. The decline in parasitoid emergence at the highest parasitoid density tested (20 females per box) was probably due to superparasitism. A long-term experiment was conducted to determine the parasitoid densities (0, 2, 4, 6, 8, or 10 per bottle) that most effectively suppress weevils in milled rice during 6 months of storage in 1-l bottles. To simulate repetitive release of parasitoid, the same number of parasitoids was introduced after each monthly sampling. The number of maize weevils decreased as parasitoid density increased. The best control was obtained with 10 female parasitoids per bottle. At this density, the number of emerged weevil remained stable from the third to the sixth month. Based on the short-term experiment, a parasitoid-host ratio of 1:47 will produce the largest number of parasitoids. Based on the long-term experiment, a parasitoid-host ratio of 1:30 will provide the best control of maize weevils in a monthly release program. The current results indicate that large-scale experiments on biological control of the maize weevil with A. calandrae are now needed.