Squash Vine Borer

Squash Vine Borer

Squash vine borer
Type:	Insect
Binomial:	Melittia cucurbitae
Family:	Sesiidae
Order:	Lepidoptera
Metamorphosis:	Complete
Damaging stages:	Larvae
Season:	Midsummer

The squash vine borer (Melittia cucurbitae, often referred to as SVB) is a devastating and hard to control pest of cucurbit crops.

Description

This insect is a diurnal species of sesiid moth that attacks both wild and cultivated varieties of squash and other members of the cucurbit family. The moth is often mistaken for a bee or wasp because of its movements, and the bright orange hindleg scales. The caterpillar is a grub-like borer.

Symptoms and Signs

Wilting of lower leaves and frass are the initial indications, quickly followed by the wilting and death of the entire plant.

Ecology

The females typically lay their eggs at the base of leaf stalks, and the caterpillars develop and feed inside the stalk, eventually killing the leaf. They soon migrate to the main stem, and with enough feeding damage to the stem, the entire plant may die. The petioles of the lower leaves and stem should be monitored for entry holes and frass, which appear before damage becomes evident.

Host plants

Hosts include members of the family Cucurbitae, primarily the squashes (Cucurbita).

Control

• Cultural controls: Farmers often plant summer squashes successively either in flats or in situ, to ensure further production even after SVBs are present. Plantings are done every 2 to 4 weeks during the growing season.

For vining varieties such as winter squashes, compost or soil can be hilled over the nodes to encourage further rooting.

• Resistant varieties: Some varieties of squash are less vulnerable to infestation from SVBs. If they have been a problem in the past, there likely will be a problem with future plantings.
• Physical removal: The stems may be slit open with a knife to allow access to the borers. The cut section is then covered with soil or compost to encourage further rooting and prevent dehydration through the cut. Less destructively, but with less precision, the borer(s) can be pricked through the stem with a needle, wire, or toothpick.

If plants are severely wilted, the best approach is simply to remove the plant. The borers should be destroyed before the plant is composted to prevent them from maturing.

• Barriers: Row covers can be used as a barrier to the adult moth before the plants start producing female flowers, but these must be removed to allow pollination. If planting successively, new plantings can be kept covered until they are large enough to produce heavy crops.
• Pesticides: Few pesticides are effective, because the borers are protected by the plant stem.

• Nicotine Sulfate: Only effective against the adult moth

• Organic pesticides: Few pesticides are effective, because the borers are protected by the plant stem. However, Bt can work if injected.

• Bt injection: The biocontrol Bt can be used against SVBs, but must be injected into the stem, as sprays will not penetrate to where the caterpillars are feeding inside the stem. This can be done using a syringe needle, or alternatively use a plastic syringe (such as is used for giving medicine to an infant). The Bt should be mixed to the highest concentration permitted on the label, as it will be diluted once injected by the plant's fluids. Using a large-gauge needle, inject the fluid through the holes left by the borers where frass is expelled. Sterilize the needle with alcohol when moving from plant to plant to avoid transmitting bacterial and/or viral infections.
• Rotenone: Only effective against the adult moth
• Pyrethrum:Only effective against the adult moth

Oftentimes frass on the stem of a squash plant is the first symptom of infestation. The second symptom follows soon - the death of the plant

Zucchini squash plant stem cut open to show borers