May Colorado Insect checklist of some common insect-related events – Denver metro and Boulder, Denver South and East
This is a generalized checklist of when some of the more important insect-related events tend to occur in our area. Year to year variations are considerable – this should be used as a guideline to anticipate and help recognize common insect occurrences.
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DENVER METRO & BOULDER
Early May
Household/Miscellaneous Insects
Miller moths: Flights into areas often begin in early May.
Tick season: The next two months are the peak season for tick activity and the spread of Colorado tick fever.
Lawns
Spider mites: Injury by bank grass mites increases. Clover mite populations should be decreasing.
Trees/Shrub Insects
Brown-headed ash sawfly: Continue to monitor ash for evidence of infestations.
Hackberry psyllid: Adults return to trees and lay eggs on the emerging leaves.
Honeylocust pod gall midge: Adults begin laying eggs on new growth. First-generation begins.
Pine needle scale: Crawler emergence typically begins around mid-May, about the time of lilac peak bloom. Check infested plants.
Elm leaf beetle: Adults return to trees and chew holes in leaves.
Southwestern pine tip moth: Egg-laying occurs when new needles emerge on pines.
Honeylocust plant bug: Nymphs have hatched and begun to damage new growth.
Peachtree borer: Larvae causing peak injury to bases of trees at this time
Tent caterpillars: Larvae may be seen making tents on various fruit and shade trees. Forest tent caterpillars are also active.
Slugs: Slugs may cause peak damage to seedlings during cooler weather.
Cooley spruce gall: Eggs hatch and young nymphs move to feed on new growth. Galls are initiated.
Pine needle scale: Egg hatch may begin during warm seasons.
Late May
Household/Miscellaneous
Miller moths: Peak flights typically occur at this time.
Tree/Shrub Insects
Brown-headed ash sawfly: Peak period of injury in most seasons.
Pine needle scale: Crawler emergence typically begins around mid-May, about the time of lilac peak bloom. Check infested plants.
Oystershell scale: Crawler emergence typically occurs in late May. Check infested plants.
Bronzed cane borer/rose stem girdler: Adults emerge from cranberries, currant, rose.
Oak borers: Treatments should be made to high-risk sites.
Fruit tree leafrollers: Leafrolling may begin to be observed on many trees/shrubs.
Elm leafminer: Egg-laying by adults may be expected.
Hackberry psyllid: Current season galls begin to be visible as small eruptions on leaves.
Cooley spruce gall: Current season galls are readily visible upon close inspection. Small nymphs are present in chambers of the gall.
Rabbitbrush beetle: Peak feeding injury by larvae.
Pinyon tip moths: Larvae start to tunnel into terminals.
Douglas-fir tussock moth: Egg hatch may begin. Monitor infested trees.
Leaf curling aphids: Aphids curl the new growth of many plants at this time.
Currantworm: Larvae chew leaves of currant and gooseberry. Damage starts in the interior of the shrub.
European elm scale: Overwintered females feed intensively and begin to produce large amounts of honeydew.
European elm bark beetle: Adults emerge and feed on twigs. Most new transmission of Dutch elm disease occurs at this time.
Codling moth: Sprays after petal fall can help control the first generation. Monitor flights with pheromone traps.
Garden Insects
Seedcorn maggot: Early planted beans, corn, and melons are susceptible to seedcorn maggot damage.
Currantworm: Larvae chew leaves of currant and gooseberry. Damage starts in the interior of the shrub.
Strawberry injuries: Millipedes and slugs tunnel the ripening berries.
Narcissus bulb fly: Adult stages emerge and lay eggs on narcissus, daffodils, and hyacinth.
Flea beetles: Adults are present on cabbage family (crucifer flea beetles) and nightshade family (potato flea beetle) plants.
DENVER SOUTH AND EAST
Early May
Household/Miscellaneous Insects
Miller moths: Flights into areas often begin in early May.
Tick season: The next two months are the peak season for tick activity and the spread of Colorado tick fever.
Lawns
Spider mites: Clover mite populations should be peaking and may begin a natural decline.
Sod webworms, cutworms: Damage to lawns by webworms and cutworms begin at this time.
Trees/Shrub Insects
Hackberry psyllid: Adults return to trees and lay eggs on the emerging leaves.
Brown-headed ash sawfly: Pinhole feeding wounds indicate early-stage infestations.
Honeylocust plant bug: Check trees for newly emerged nymphs.
Elm leaf beetle: Adults return to trees and chew holes in leaves.
Southwestern pine tip moth: Egg-laying occurs when new needles emerge on pines.
Walnut twig beetle: Overwintered adults in trunk bark move to branches and begin tunneling.
Honeylocust plant bug: Nymphs have hatched and begun to damage new growth.
Peachtree borer: Larvae causing peak injury to bases of trees at this time
Tent caterpillars: Larvae may be seen making tents on various fruit and shade trees. Forest tent caterpillars are also active.
Slugs: Slugs may cause peak damage to seedlings during cooler weather.
Cooley spruce gall: Eggs hatch and young nymphs move to feed on new growth. Galls are initiated.
Pine needle scale: Egg hatch may begin during warm seasons.
Zimmerman pine moth: Period ending during which larval control is possible.
Late May
Household/Miscellaneous
Miller moths: Peak flights typically occur at this time.
Honeybee swarms: Many honeybee colonies produce swarms during sunny days
Tree/Shrub Insects
Brown-headed ash sawfly: Peak period of injury in most seasons.
Pine needle scale: Crawler emergence typically begins around mid-May, about the time of lilac peak bloom. Check infested plants.
Oystershell scale: Crawler emergence typically occurs in late May. Check infested plants.
Bronzed cane borer/rose stem girdler: Adults emerge from cranberries, currant, rose.
Oak borers: Preventive treatments should be made at this time at high-risk sites
Fruit tree leafrollers: Leafrolling may begin to be observed on many trees/shrubs.
Hackberry psyllid: Current season galls begin to be visible as small eruptions on leaves.
Cooley spruce gall: Current season galls are readily visible upon close inspection. Small nymphs are present in chambers of the gall.
Rabbitbrush beetle: Peak feeding injury by larvae.
Pinyon tip moths: Larvae start to tunnel into terminals.
Leaf curling aphids: Aphids curl the new growth of many plants at this time.
Currantworm: Larvae chew leaves of currant and gooseberry. Damage starts in the interior of the shrub.
Codling moth: Sprays after petal fall can help control the first generation. Monitor flights with pheromone traps.
Honeylocust plant bug: Injury usually peaks towards the end of the month.
Garden Insects
Seedcorn maggot: Early planted beans, corn, and melons are susceptible to seedcorn maggot damage.
Currantworm: Larvae chew leaves of currant and gooseberry. Damage starts in the interior of the shrub.
Strawberry injuries: Millipedes and slugs tunnel the ripening berries.
Narcissus bulb fly: Adult stages emerge and lay eggs on narcissus, daffodils, and hyacinth.
Flea beetles: Adults are present on cabbage, radish, and related plants.
Slugs: Slug injury should continue at high levels.