Feb 25, 2016
Squash bugs put dent in cucurbit crop production

A noted problem insect in the United States for more than a century, the squash bug continues to do considerable damage to crops, particularly in light of the trend away from conventional insecticides to newer strategies, including organic approaches.

Helene Doughty, a research specialist senior at Virginia Tech’s Hampton Roads Agricultural Research and Extension Center, was a lead author of an article on squash bugs prepared for the Journal of Integrated Pest Management.

“Squash bug remains an important economic pest of cucurbit crops in the United States, particularly in areas where CYVD (cucurbit yellow vine disease) occurs,” Doughty said. “For conventional growers today, a number of insecticides, particularly pyrethroids and neonicotinoids, are registered that provide effective control of the pest. However, these insecticides pose risks to non-target organisms such as natural enemies and pollinators and are not the most IPM-compatible control options.”

Doughty said a “combination of preventative and curative control measures provide a number of options to effectively manage this pest using an IPM approach. A greater focus on scouting for the pest before applying pesticides, awareness and conservation of natural enemies in the agro-ecosystem and use of more selective narrow-spectrum insecticides, if and when they are needed, would provide a more sustainable approach to managing this pest.”

The squash bug Anasa tristis is an endemic species of the Americas that feeds on plants in the family cucurbitaceae. This piercing-sucking insect is particularly damaging on cucurbita vegetables like squash and pumpkin, but may attack other cucurbits as well.

“The pest is particularly abundant and damaging on plants in the genus Cucurbita (zucchini, summer squash and pumpkins),” Doughty said. “Squash bug has become problematic in recent years due to changes in insecticide use strategies by conventional growers, dramatic increases in organic vegetable production, and increasing incidences of cucurbit yellow vine disease, a phloem-clogging bacterial disease transmitted by the bug.”

CYVD, which is most common in Oklahoma and Texas, has begun showing up in other states in the Midwest and East. Squash bugs gravitate toward zucchini and other summer squash, along with pumpkins, and occasionally will strike cucumbers, watermelons and winter squash. Bacteria-infected plants experience rapid yellowing and wilting of the leaves, and subsequent decline.

Ovipositing squash bug female and eggs.
Ovipositing squash bug female and eggs.

Doughty described the adult squash bug as typically showing a brindled grayish brown color, 1.4 to 1.6 cm in length and 0.75 cm wide at the widest part of the abdomen. She said eggs are deposited in groups, often on the undersides of leaves. Clutch size can vary from only a few to more than 40 eggs, averaging 18 eggs per mass. As the female lays the eggs, she incorporates an adhesive to adhere each egg in the mass to the surface of the leaf.

The nymph stage has five instars. Immediately following egg hatch, first instars (neonates) are 2-3 mm in length and light green in color with red legs, head and thorax, which later darkens to black. Second instars are less than 3 mm long, a darker green color with black appendages. With each successive molt, the nymph’s size increases, it becomes lighter gray in color and the end of the abdomen widens into a teardrop shape. The fourth and fifth instars have a more distinct thorax and wing pads and are less than 6.5 mm and 9.5 mm long, respectively.

Doughty said squash bugs overwinter in the adult stage and emerge from the soil or ground litter in the spring. Cooler spring temperatures may delay emergence of adults. After emergence, overwintered adults immediately seek out cucurbit plants on which to feed and mate.

Adults prefer to remain hidden during the day. They also can emit a distinct, unpleasant odor, similar to stink bugs, when disturbed. Gravid females can lay eggs 7-10 days after their emergence. They often prefer to deposit eggs on the undersides of leaves next to leaf veins.

The squash bug typically completes its entire life cycle in six to eight weeks, and development can be predicted based on heat-unit accumulation.

In the southern United States, egg development time is typically six to 15 days, according to Doughty.

“Nymphs have a strong disposition toward aggregating, particularly after egg hatch on leaves and on fruit following leaf desiccation,” Doughty said. “Both adults and nymphs prefer sheltered areas, with a partiality for the base of plants. Squash bug adults can be observed hiding in the center of plants, under large leaves, wilted leaves and in the transplant holes of plastic mulch.”

“In field surveys conducted in community gardens throughout Virginia in 2014 and 2015, we observed significantly more squash bug egg masses on zucchini squash compared with other squash varieties, gourds or other cucurbit species,” Doughty said.
“Squash bug is a piercing-sucking feeder. During the feeding process, adults and nymphs pierce through the leaf with their stylets.

“Plants colonized by squash bug nymphs in the second through fourth leaf stage may quickly succumb to feeding,” Doughty said. “In addition, feeding injury occurring at flowering and fruit set can significantly impact fruit production.”

Doughty referenced trials that observed yield reductions of over 50 percent in untreated summer squash plots invaded at flowering and fruit set by the squash bug. A laboratory and greenhouse study cited by Doughty reported a decrease in vegetative growth rate and ovulate flower productivity in summer squash with increasing numbers of the squash bug. In watermelon, seedlings also experienced more frequent mortality with increasing squash bug density.

“The piercing of the fruit tissue by the squash bug certainly adds to the potential for diseases by creating an opportunistic gateway for the common squash fruit pathogens described as anthracnose, choanephora fruit rot, gray mold rot and rhizopus soft rot,” Doughty said. “Subsequently, a greater incidence of fruit rot in storage can be observed as a result.”

CYVD is a recent challenge for cucurbit growers, Doughty said. Adult squash bugs harbor the bacterium during winter diapause and can infect plants the following spring upon emergence. CYVD can inflict heavy losses to watermelon, pumpkin, cantaloupe and squash.

For more on squash bug control, see “Control measures can negate squash bug woes.”

— Gary Pullano, associate editor




Current Issue

VGN April Cover

Insect Eavesdropper allows growers to “hear” what’s happening in fields

Managing wildlife on the farm

Southwest Florida’s Worden Farm manages challenges

Pennsylvania Vegetable Growers Association says farewell to leader

Southeast Regional Show recognizes leaders

Veg Connections: Biopesticides and beneficial insects

Business: Why do most succession plans fail?

60 years of advocating for agricultural employers

Keeping CSA members engaged and loyal

see all current issue »

Be sure to check out our other specialty agriculture brands

produceprocessingsm Organic Grower