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Ministry of Agriculture, Food and Rural Affairs

Squash Bugs

Squash bug eggs Squash bug nymphs Squash bug adult
Click to enlarge.

Beginner

Scientific Name
Anasa tristis

Identification

  • Eggs are laid in small clusters, usually on the underside of the leaf 
  • The bullet-shaped eggs are yellow when first laid, turning reddish-brown as they mature 
  • Nymphs have pear-shaped, pearly grey bodies with darker legs and antennae 
  • As the nymphs grow they become darker and wing pads begin to develop
  • Squash Bug adults have flattened, tear-shaped bodies, brownish-grey with yellow-to-orange markings
  • Squash bugs are commonly found in fairly large colonies with several different stages of development present at the same time

Often Confused With
Tarnished plant bug (adults)
Stink bugs

Period of Activity
Squash Bugs may be present in cucurbit fields throughout the growing season. Squash bug populations tend to build quickly during hot, dry growing conditions.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field.  Count the number of egg masses or squash bug colonies on the plants and divide by 100 to determine the number per plant.  Eggs and young nymphs are often found on the undersides of the leaves. Be sure to monitor field borders and other potential over-wintering sites. 

Thresholds
Spray when the populations reach one egg mass per plant. Insecticides are most effective when targeted at small young nymphs.

Advanced

Scientific Name
Anasa tristis

Squash bugs are more commonly found in pumpkin, squash and zucchini fields, although they may become a pest in other cucurbits. 

Identification
Squash Bug eggs are usually laid in small clusters on the underside of the leaf.  The bullet-shaped eggs are yellow when first laid, turning reddish-brown as they mature. 

Squash Bug nymphs have pear-shaped, pearly grey bodies with darker legs and antennae. As the nymphs grow they become darker and wing pads begin to develop. Squash Bug adults have flattened, tear-shaped bodies. They are brownish-grey with yellow-to-orange markings.

Both the adults and the nymphs suck sap from the leaves, stems and fruit.  The feeding injury may cause the plants to wilt and eventually become necrotic. After the leaves are killed by frost, squash bugs may begin feeding on the fruit.  This causes white discolorations and may impact marketability. Squash bugs may also act as disease vectors, transmitting cucurbit yellow vine disease.

Squash bugs are commonly found in fairly large colonies with several different stages of development present at the same time.

Often Confused With
Tarnished plant bug (adults)
Stink bugs

Biology
Squash bug adults overwinter in sheltered areas, under crop residue and in fence rows.  They begin laying eggs in cucurbit fields in early June.  Nymphs hatch in 1- 3 weeks. It usually takes 5- 6 weeks for the nymphs to reach the adult stage. In Ontario there is usually only 1 generation of squash bugs per year.  Once the nymphs reach maturity, they continue feeding until they enter winter diapause. It is not unusual to find several different stages of nymphs and adults present on the same plant.

Period of Activity
Squash bugs may be present in cucurbit fields throughout the growing season. Squash bug populations tend to build quickly during hot, dry growing conditions.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field. Count the number of egg masses or squash bug colonies on the plants and divide by 100 to determine the number per plant. Eggs and young nymphs are often found on the undersides of the leaves or underneath developing fruit. Be sure to monitor field borders and other potential over-wintering sites.  

Thresholds
Spray when the populations reach one egg mass per plant.

Management Notes

  • Insecticides are most effective when targeted at small, young nymphs
  • Squash bugs like to hide in well sheltered locations. 
  • Good weed control will help reduce the potential squash bug habitat in the field.
  • Squash Bugs will often enter the crop from sheltered areas or adjacent fields used to grow cucurbits in the previous year.