Predicting larval stage distribution of Lobesia botrana (Lepidoptera: Totricidae) at three constant temperatures

Authors: PRETO, CINDY - University Of California, Davis; BELLAMY, DAVID - Plant And Food Research; Walse, Spencer; ZALOM, FRANK - University Of California, Davis

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2018
Publication Date: 12/11/2018
Citation: Preto, C., Bellamy, D., Walse, S.S., Zalom, F.G. 2018. Predicting larval stage distribution of Lobesia botrana (Lepidoptera: Totricidae) at three constant temperatures. Journal of Economic Entomology. 112(2):585-590. https://doi.org/10.1093/jee/toy374.
DOI: https://doi.org/10.1093/jee/toy374

Interpretive Summary: European grapevine moth has the potential to impact the export of grapes and grape products from the United States. Phytosanitary treatments, conducted prior to export, are typically required to control this insect pest. The efficacy of such treatments must be demonstrated using the most treatment-tolerant life stage. Therefore, researchers must track development across life stages as a function of age, quantifying the relative distribution of life stages over the time-course of treatment and its assessment. Here, we evaluate the accuracy of using the measurement of larval head capsule width to diagnose a particular instar. Moreover, we use the measurement to describe inconsistencies in the maturation of specimens within an age group spanning only 24-h. We then expand the description to identify the effect of temperature on divergence in rates of maturation within each life stage, and across the entire timespan of development. Results indicate that head capsule width is an accurate proxy, and that the development of European grapevine moth, reared as in this study, is generally predictable. Anomalies in development are briefly discussed, further emphasizing how this work aids the evaluation of how efficiently a treatment controls European grapevine moth.

Technical Abstract: European grapevine moth, Lobesia botrana (Denis and Schiffermüller) (Lepidoptera:Tortricidae), is an invasive pest species subject to regulatory control under the International Plant Protection Convention. An extensive infestation of this insect was detected in California vineyards in October 2009 resulting in the initiation of post-harvest 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 determine the particular stadia of larval development for insects obscured from direct observations is necessary to be able to ensure that the most tolerant life stage is accurately targeted. L. botrana were reared from egg to eclosion at three different temperatures: 16, 20, and 24°C (60% RH; 16:8 L:D). Daily samples (=15) were taken of larvae and pupae to determine the chronologic 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 non-linear 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.