Predicting Larval Stage Distribution of Lobesia botrana (Lepidoptera: Tortricidae) at Three Constant Temperatures

European grapevine moth, Lobesia botrana (Denis and Schiffermüller), is an invasive pest species subject to regulatory control under the International Plant Protection Convention. An extensive infestation of this insect detected in California vineyards in October 2009 resulted in the initiation of postharvest research intended to ensure continuing trade of California table grapes by preventing the unintentional introduction of L. botrana to uninfested export destinations. Having the ability to accurately predict and confirm the particular stadia of larval development of insects obscured from direct observations, such as those being mass-reared in diet for use in phytosanitary control experiments, is necessary to be able to ensure that the most tolerant life stage is accurately targeted. Lobesia botrana were reared from egg to eclosion at three different temperatures: 16, 20, and 24°C (60% RH; 16:8 [L:D] h). Daily samples (≥15) were taken of larvae and pupae to determine the chronological distribution of life stages until daily samples comprised 100% pupae, after which only adults were counted. Head capsule measurements of all sampled larvae were taken (n = 2,820) and analyzed using nonlinear least squares (NLLS) fitting to Gaussian curves to describe stadia-specific head capsule demarcations and the probability of misclassifying instars due to overlapping life stage distributions.