Stem borer (Lepidoptera: Sesiidae) in Cucurbita

The harm to squash plants wrought by E. cucurbitae is well known to gardeners and farmers throughout the study area, and I have crossed paths with this borer on several occasions. Larvae may occur in main stems or leaf petioles, which they tunnel extensively, ejecting large amounts of pale frass. Unlike many borers, the damage and accumulated piles of frass are usually externally visible. I observed larvae or their damage in summer squash and field pumpkin (C. pepo), but they may also occur in "cucumbers, gourds, and other cucurbits" (Benson and United States Department of Agriculture 1911).

Smaller, younger larvae found in cucurbit plants may have a very dark, almost black head capsule and prothoracic shield, along with black pigmentation on the terminal segment of the abdomen, while on older larvae the head is reddish or brownish and the prothoracic shield may be more or less unpigmented except for two distinctive diagonal brown lines. Based on the images and information in Chittenden (1908), Coin et al. (2026), and University of Georgia - Center for Invasive Species and Ecosystem Health (2026), these represent different instars of the same species. Below, for the sake of comparison, I have included images of both a younger and an older larva encountered in the survey.