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How to identify it
- The adult is a stout moth about 1/2 inch long (slightly longer, says Iowa State) with a wingspan of 1 to 1 1/2 inches. It flies by day, looks like a wasp and buzzes loudly in flight.[1][3][4][5]
- The abdomen is orange to rusty orange with black dots or bands.[1][3][4][5]
- The front wings are opaque and the hind wings clear with dark veins; at rest the hind wings are folded and hard to see. The hind legs are fringed with reddish hairs.[1][2]
- Caterpillars are white or cream with a brown head and somewhat maggot-like, growing to about 1 inch long; UMass gives 1 to 1 1/2 inches.[1][2][4][5]
- Eggs are small, flat and brown, about 1/25 inch long, laid one at a time on stems and leaf stalks near the base of the plant.[1][2][3][5]
- Extension guides call this moth Melittia cucurbitae; iNaturalist now lists it as Eichlinia cucurbitae.[4][5][6]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Squash bug | Squash bugs also wilt squash vines, but they are flat, grayish-brown bugs found on leaves and stems, with bronze egg clusters under the leaves. Borer wilt comes with sawdust-like frass pushed out of holes at the vine base.[7][2] |
| Bacterial wilt and Fusarium wilt | These diseases also make vines wilt, but they leave no entrance holes or sawdust-like frass near the base of the vine.[4] |
Where it lives
A key or serious pest of squash and pumpkins in extension reports from Minnesota, Wisconsin and Iowa to Kentucky and Massachusetts. Minnesota and Wisconsin see one generation a year, while Kentucky and Massachusetts report one to two.[1][4][3][2][5]
Biology and life cycle
The borer spends the winter 1 to 2 inches deep in the soil near old host plants, as a full-grown larva or a pupa in a cocoon.[2][1][5][4]
Moths emerge about when vines begin to run: late June or early July in Minnesota, Wisconsin and Massachusetts, from about mid-June in Kentucky, where flight continues through mid-August. Wisconsin ties emergence to about 900 growing degree days (base 50 °F), when roadside chicory is in full bloom.[1][4][5][2]
Females lay eggs singly at the base of the plant; UMass puts each female's total at 150 to 200. Each larva bores straight into the stem soon after hatching.[1][2][5]
Larvae feed inside the stem for 14 to 30 days by Kentucky and Wisconsin's count, or four to six weeks by Minnesota and UMass's, then exit and burrow into the soil to pupate.[2][4][1][5]
In hot seasons Massachusetts traps pick up a second flight in late August. Those late moths can lay eggs while fruit is present, and the larvae sometimes bore into hard squash and pumpkin fruit.[5]
Damage and signs
- Tunneling larvae destroy the tissue that carries water, so a runner or the whole plant wilts suddenly, at first only in strong midday sun and later even in the morning.[1][2][4]
- Look near the plant base for holes packed with moist, sawdust-like frass, greenish to orange or yellow-brown. One to several borers may be inside.[1][2][3]
- A borer in the main stem can kill the whole plant, while one in a runner kills only that runner; the stem base may turn mushy and rot. Iowa State notes infested plants often live and produce anyway.[4][1][2][3]
- Thick-stemmed squashes suffer most, including Hubbard, buttercup, acorn, zucchini, crookneck and pumpkins. Thin-stemmed butternut squash, cucumbers, melons and watermelons are seldom attacked.[2][1][4][5]
- UMass reports summer squash yields can drop by a third with more than 5 larvae per plant, while pumpkins can carry heavy infestations without yield loss. Vining types tolerate more than bush types because they root at the nodes.[5]
Health risk
The squash vine borer is a moth that only mimics a wasp. Its damage is to squash, pumpkins and other cucurbits, where the caterpillars feed inside the stems.[1][2]
Control
Prevention
Grow crops that are seldom attacked, such as butternut squash, cucumbers and melons, or put in a second planting of summer squash in early July so it matures after egg-laying ends. Wisconsin adds that earlier plantings tend to have fewer problems.[1][4][5]
Keep them out
Cover vines with row cover, anchored at the edges, once they start to run or when moths appear. Minnesota keeps it on for about two weeks after the first moth is seen; UMass keeps plants covered from transplanting to flowering. Remove it at bloom so bees can pollinate.[1][4][5]
Skip row covers where cucurbits grew last year, because borers overwintering in that soil can emerge under the cover. Rotate planting spots instead.[1][5]
Sanitation
Pull and destroy plants killed by borers, remove vines soon after harvest so remaining larvae can't finish developing, and till or plow in fall or spring to disturb pupae in the soil.[1][2][3][5]
Traps and physical control
Watch for moths from the last week of June. They are drawn to yellow, so a yellow pan of soapy water can catch them and show when to act; pheromone traps also show when males are flying.[1][5]
At the first frass or wilting, slit the stem lengthwise with a sharp knife, kill the borers, and mound moist soil over the cut. Burying a few vine nodes encourages extra roots.[1][2][4][3]
Biological control
Hubbard squash is highly attractive to the moths and can be planted as a trap crop, then destroyed while larvae are still inside the stems.[4]
Pesticides
Sprays only work before larvae enter the stem. Treat the vine base when vines start to run or moths appear, then repeat: two applications 7 days apart (Kentucky), 7 to 10 days apart (Minnesota) or two to three at 5 to 7 days (Wisconsin).[2][1][4]
Minnesota names carbaryl, permethrin, bifenthrin and esfenvalerate, and Wisconsin pyrethroids or carbaryl. Broad-spectrum sprays can kill bees, so if a spray is needed during flowering, apply it in the evening.[1][4]
Borer or wilt disease?
Bacterial wilt and Fusarium wilt can look the same from a distance. Check the base of wilting vines for entrance holes; if sawdust-like frass is there, split the stem carefully to confirm larvae.[4]
Fields damaged before are likely to be damaged again, so check old trouble spots first.[4]
Where sources disagree
Bt: Minnesota says Bacillus thuringiensis does not work because larvae inside stems are protected from foliar sprays, while UMass lists Bt formulations, especially those from B. aizawai, among materials for hatching larvae.[1][5]
Egg hatch: 7 to 10 days (Kentucky, Wisconsin), about one week (Minnesota) or 10 to 15 days (UMass).[2][4][1][5]
Front wing color: metallic green (Minnesota, Iowa State), greenish-brown (Wisconsin) or black (UMass); Kentucky describes the whole moth as dark gray.[1][3][4][5][2]
Generations: one a year in Minnesota and Wisconsin, one to two in Kentucky and Massachusetts.[1][4][2][5]
Common questions
- What is the orange sawdust at the base of my zucchini or squash?
- That material is frass from squash vine borer larvae feeding inside the stem. Slit the stem lengthwise near the hole to find and remove them, then cover the cut with moist soil.[1][2]
- Is the orange and black flying insect around my squash a wasp?
- It may be the squash vine borer moth, which flies by day, buzzes loudly and mimics a wasp; the orange abdomen with black dots is the giveaway.[1][2][3]
- Can I save a squash plant with borers?
- Often. Cutting out borers and burying the stem in moist soil can let the plant reroot, but sprays won't reach larvae already inside.[1][2][4]
- When should I start watching for squash vine borer?
- Start checking plants for moths, eggs and frass in late June. In degree-day terms, monitoring begins near 900 to 950 (base 50 °F), with moths emerging around 1,000.[1][4][2]
Sources
- University of Minnesota Extension, “Squash Vine Borers.” extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-insects/squash-vine-borers (accessed 2026-11-11)
- University of Kentucky Entomology, “ENTFACT-314: Squash Vine Borer and Squash Bug (revised January 2026).” entomology.ca.uky.edu/ef314 (accessed 2026-11-11)
- Iowa State University Extension and Outreach, “Squash Vine Borer (Yard and Garden).” yardandgarden.extension.iastate.edu/encyclopedia/squash-vine-borer (accessed 2026-11-11)
- University of Wisconsin-Madison Extension (Wisconsin Horticulture), “Squash Vine Borer.” hort.extension.wisc.edu/articles/squash-vine-borer/ (accessed 2026-11-11)
- UMass Amherst Extension Vegetable Program, “Squash Vine Borer (Vegetable fact sheet).” www.umass.edu/agriculture-food-environment/vegetable/fact-sheets/squash-vine-borer (accessed 2026-11-11)
- iNaturalist, “Eichlinia cucurbitae taxon page (order and family).” www.inaturalist.org/taxa/1410301 (accessed 2026-10-06)
- University of California Statewide IPM Program, “Squash Bugs (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/squash-bugs/ (accessed 2026-11-11)