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For several years a consistent incidence of nonparasitic mortality of pupae of the eye-spotted bud moth, Spilonota ocellana (Denis & Schiffermuller), was observed in Door County, Wisconsin, apple and cherry orchards. The pupae revealed no obvious external injury and when dissected most of them contained dried organic matter with little or no visible adult structures. A similar phenomonon has been observed with other insects (Regan 1923) ; and recently Samuelson (1961) reported a 20%-unaccountedfor pupal mortality in the cotton square borer, Strymon melinus (Hubner), and Dobson (1961) found that 19% of wheat bulb fly, Leptohylemyia coarctata (Fallen), pupae died from unknown causes. The importance of a “pupal viability”figure in experiments was recognized by Bay and Legner (1963), and Legner and Bay (1964) in culturing Hippelates eye gnats, where certain percentages of reared pupae died without development of adult structures. Pupal viability in their experiments and in current experiments by the senior author with house flies, Musca doinestica L., was influenced to a large degree by the amount and kind of food available to the larvae (Legner and Bay 1961). In nature examples of deleterious effects of severe winters and storms on insects have been noted (Carter 1961, Richards 1961, Shands et al. 1956) ; however, the existence of more discreet mortality factors in natural insect populations dining apparent optimum developmental conditions is often overlooked or ignored.

Thuricide® (a microbial insecticide having 30 × 109 spores of Bacillus thuringiesis Berliner per gram) applied on apple for control of the eye-spotted bud moth, Spilonota ocellana (Denis and Schiffermuller), apparently retarded spring larval development and produced noticeably smaller larvae. Mortality of the spring larvae in the Thuricide-treated section was 16.5% on Red Delicious and 18.7% on Cortland. In the check only 1.5% and 9.5% mortality occurred on Red Delicious and Cortland respectively. Significantly greater numbers of summer larvae were collected in the check than in the treated sections Reared adult moths from the Thuricide block were significantly smaller than those from the check. This size difference was greater with later adult formation periods. The length and width of both males and females in the Thuricide-treated section decreased significantly with later formation periods but increased significantly in size in the check with later formation periods. The immediate effects of Thuricide on the eye-spotted bud moth population were not considered economic control; however, the long-range effects might be promising.