The squash bug, Anasa tristis , is a serious pest of squash and pumpkins and a lesser pest of melons and cucumbers.
Squash bug eggs are oval shaped and yellowish-brown. After oviposition they are fairly light and will darken with age. Eggs are oviposited in clusters of 4 to 40 in fairly uniform rows, often on the underside of leaves between the forks of the veins. Nymphs are approximately 1/8 inch long. The young nymphs are boldly colored with a red head, antennae, thorax and legs, and a green abdomen. Nymphal color fades with age to a gray/white with black legs and antennae. The 5th instar nymph appears very similar to the adult with wing buds instead of complete wings. The adult squash bug has a gray/white body with black legs and antennae. The overlapping structure of the wings on the adult makes an X in the center of the insects back. When these insects are crushed they give off an unpleasant odor.
The squash bug overwinters as an adult in protected areas. In Pennsylvania the adults emerge in mid June, although they will often not enter a host field until the vines begin to "run". The adults may continue ovipositing eggs for more than a month and for this reason nymphs and adults will often be present in the field throughout the summer. Emerging adults will feed, mate and begin oviposition in approximately 10 days. The eggs will hatch in 1 to 2 weeks and it requires 4 to 6 weeks for the nymphs to pass through the 5 larval instars before becoming an adult. The squash bug does not have a pupal stage, instead each nymphal instar appears more like the adult. After completing the 5th instar the nymph goes into a resting stage where it completes its growth into an adult. The squash bug has only one generation per year.
Like all true bugs the squash bug has piercing-sucking mouthparts. Both adults and nymphs feed on the host plant by piercing the plants epidermis and sucking out the sap. While it is unclear if the squash bug injects a plant toxin, feeding can cause extensive amounts of damage. The physical process of squash bug feeding removes sap, which interferes with normal nutrient transfer in the plant. Certain varieties of squash are nearly impossible to grow in some areas of the country.
Squash bug feeding first appears as yellow spots which later turn black. Vines which have been fed upon will often turn black and dry out. For this reason squash bug feeding may be mistaken for bacterial wilt. Feeding can completely destroy small plants and vines.
As with many insects, proper cultural controls can significantly reduce squash bug populations minimizing the probability that populations will increase to damaging levels. Removing debris after harvest from around the field can kill overwintering squash bug, reducing the following year's population. Often it is possible to trap squash bugs for manual extermination. Placing old boards in the field before cool nights will often attract squash bugs to spend the night under these structures. Early the next morning the bugs can be captured and eliminated. Use of resistant varieties of vines can significantly reduce damage.
Any plants observed to be wilting should be examined for squash bugs. The bugs are very stealthy and will often attempt to hide behind stems and leaves. The most critical time for squash bug control is when plants are at seedling, as young plants do not have the strength to tolerate significant feeding. If you suspect squash bug damage but are having difficulty finding the bugs, you can attempt to sample for the bugs by placing a board in the field as described in the previous paragraph. Be sure to check the board in the early morning before squash bugs spending the night there disperse.
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