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CUES: Center for Urban Ecology and Sustainability

MNLA Pest Newsletter, April 2006, no: 2

Red maple flowers in April

Photo: Tree Canada Foundation

Photo: Spruce budworm larva


Vera Krischik and Mary Rogers, Department of Entomology, University of Minnesota, contact us at



Landscape and Nursery

Asian ambrosia beetle
Xylosandrus crassiusculus

(Coleoptera: Scolytida


IPM of Midwest Landscapes (UMN)

North Carolina IPM

Purdue University

Time: Females emerge from trees from April to July to bore into trees and lay eggs

Hosts: Honeylocust, redbud, peach, plum cherry, persimmon

The Asian ambrosia beetle was first discovered in the U. S. in South Carolina in 1974. It is found from Florida to Texas; east to Virginia, Maryland, and Delaware; and north to Michigan and Indiana. It is a pest of nursery stock. In Indiana it has been reported on honeylocust and redbud, but it is also known to feed on peach, plum, cherry, and persimmon. It is currently believed to move around on rootstock.

Smaller branches or caliper trees are most commonly attacked. All life stages can be found inside the galleries. Eggs are laid in this tunnel, and the young larvae hatch and chew out small egg cradles that radiate from the adult tunnel like teeth on a comb. The larvae apparently do not eat wood; they feed on ambrosia fungi that grow on the surface of the wood in the tunnels and egg cradles. Female ambrosia beetles possess specialized structures called mycetangia in which the ambrosia fungus is carried in from one host plant to the next.

Infestations normally can be identified by toothpick-like spines of boring dust protruding from holes made in the host plant by females excavating their galleries. Unlike other scolytids, which normally attack only stressed or damaged plants, Asian ambrosia beetles attack apparently healthy plants. Individual plants may host up to 50 beetles. It is almost impossible to save heavily infested plants. When mature, females leave infested plants and fly to new host plants. Males do not fly. There are several generations per year.

Trapping: In a Japanese beetle trap place 70% ethanol in a pop bottle with a rope wick. AAB are attracted to traps baited with ethyl alcohol in the spring and early summer and the trap numbers correlate very well with attacks on trees most of the time. In the mid summer to fall and winter, trap catch with ethanol does not adequately represent the AAB present.

Research at the University of Florida demonstrated that 5 to 10 attacks can kill trees 3 inches or less in diameter. Onyx (bifenthrin) at the rate of 32oz/100gal will prevent most AAB attacks. Lower rates provided some degree of prevention but were inconsistent. Talstar F at 40oz/100 was also effective. However, Thiodan efficacy was variable, as was Dursban. Tame, orthene, and tempo did not work. Other research indicates that permethrin appears to have repellant properties.

The black twig borer, Xylosandrus compactus, is one of the few ambrosia beetles that attack many kinds of trees and shrubs that appear to be in good health. Over 224 plant species in 62 families are susceptible to the black twig borer.

Mossy rose gall

Spiny rose gall
Diplolepis bicolor

(Hymenoptera: Cynipidae)


Pests of Roses (UMN Extension)

Mossy rose gall

Time: May, June

Hosts: Roses

Mossy rose galls are caused by a cynipid gall wasp. These galls are common on wild roses of North America, from Ontario to Alberta in Canada and throughout most of the northern United States. They are becoming common on Rugosa cultivars. The presence of these insects is indicated by the formation of spherical, golf ball-size, spiny galls on the canes of host plants.

Hybrid rugosas are particularly susceptible to this disfiguring gall. The development of these galls is stimulated in the spring by newly hatched larvae. The galls encase the larvae until adult wasps emerge the following spring. The galls are unsightly and alter the plant's shape. They also stress the host plant, behaving like nutrient sinks, drawing nutrients away from the rest of the plant. Large numbers of galls can result in death of the plant. 

The most effective control is physical removal and disposal of galls in autumn after leaves have dropped and galls are visible. It is important to dispose of all galls since even a single missed gall can produce and reintroduce 30 to 40 mature wasps to the garden the following spring. Imidacloprid soil applications might be effective.

Roseslug sawfly

Bristly roseslug sawfly
Cladius difformis

Curled rose sawfly
Allantus cinctus

(Hymenoptera: Tenthredinidae)


Pests of Roses (UMN Extension)

Time: May, June

Hosts: Roses

Three species of sawflies feed on rose foliage. All three species are light green with orange heads and late larvae can reach 3/4 inch (19 mm) in length. Rose sawflies "skeletonize" leaves by chewing away a layer of the leaf except for the veins. The thin layer remaining turns clear or brown between the uneaten veins. The older larvae of the bristly roseslug and curled rose sawfly chew holes rather than skeletonizing the leaves.

Begin to scout for sawfly larvae in early May. Roseslugs feed through June and are not seen again until the next spring. The curled rose sawfly also has one generation per year. The bristly roseslug has several generations throughout the summer. Sawflies often feed on the undersides of leaves, so inspect all leaf surfaces. Sawflies are small, dark, non-stinging wasps. Sawfly larvae skeletonize rose leaves.

These larvae resemble butterfly or moth caterpillars, but can be identified by the number of fleshy legs (prolegs) that follow the front three pairs of legs. Sawflies have five or more pair of prolegs, while caterpillars have less than five.

Avoid spraying the rose flowers, as many conventional insecticides are highly toxic to bees. Use acephate (Orthene), carbaryl (Sevin), bifenthrin (Talstar) or a soil drench of imidacloprid.

Eastern tent caterpillar
Malacosoma americanum

(Lepidoptera: Lasiocampidae)


IPM of Midwest Landscapes (UMN)

Time: April

Hosts: Apple, crabapple, pear, plum, and wild cherry are preferred, but a wide variety of other forest, fruit and shade trees are hosts.

Overwintered eggs hatch as host tree buds begin to unfold in the spring. Larvae are gregarious and construct a communal web or tent, which grows as they develop and from which they emerge to feed. There is one generation a year. Black egg masses overwinter on twigs. Silken webs in tree forks may be unsightly. When infestations are sufficiently severe, trees can be completely defoliated.

Eggs hatch when red maple blooms in the first week of April (Herms). Look for larval silken tents on preferred hosts in early April. Also look on preferred hosts in the dormant season for approximately 18 mm long, black egg masses. Adult moths are light brown, 25 mm long, with two diagonal white stripes across the forewings. Wingspan is 37 to 50 mm. Larvae can grow to 50 mm or more in length. They have black heads, a white stripe down the length of the back and yellow lateral stripes with blue spots.

In the dormant season, prune and destroy egg masses. Destroy webs and their contents as soon as they appear.

Chemical control: Use Bacillus thuringiensis var. kurstaki when trees are flowering to protect pollinating bees. Spray foliage when tents first appear.

Biological control: A diverse assemblage of parasitoids and predators attack this highly conspicuous species. These include parasitic wasps Hyposoter spp. (Ichneumonidae) and Bracon spp. (Braconidae), tachinid flies, hornets, yellow jackets, ants, predatory stink bugs, and birds. Epizootics of an NPV virus decimate populations in peak years.

Biorational pesticides: Bacillus thuringiensis var. kurstaki, diflubenzuron, insecticidal soap, pyrethrin, spinosad, tenbufenozide.

Conventional pesticides: acephate, bifenthrin, carbaryl, chlorpyrifos (nursery only), cyfluthrin, malathion, permethrin.

Forest tent caterpillar
Malacosoma disstria

(Lepidoptera: Lasiocampidae)


IPM of Midwest Landscapes (UMN)

USDA Factsheet

Time: Mid to late May

Hosts: Alder, aspen, ash, basswood, birch, cherry, elm, hawthorn, maple, oak, peach, poplar, willow and flowering fruit trees

Young larvae hatch when leaves are beginning to unfold in mid- to late May. Colonies of larvae stay together and move about in single file. They do not make silken tents. Cocoons are constructed within folded leaves or bark cracks. In mid summer, eggs are deposited in black masses, which encircle twigs. There is one generation a year. Black egg masses overwinter on twigs.

Look for shot holes in foliage from mid to late May when larvae begin to be active. Feeding is complete by the end of June. It is important to detect serious infestations early to prevent defoliation.

Where possible, egg masses can be cut from trees and destroyed. Small populations of larvae can also be physically removed.

Adult moths are buff-colored with two darker oblique bands on the forewings. Wingspan is 25 to 38 mm; adults are approximately 18 mm long with wings folded. Mature larvae are approximately 50 mm long, blue and gray with oval white spots along the back.

Chemical control: Bacillus thuringiensis var. kurstaki can be sprayed to control young larvae. Larger populations of older larvae can be controlled with a residual insecticide.

Biological control: The large gray parasitic fly, Sarcophaga aldrichi, often becomes very abundant during forest tent caterpillar outbreaks. Known as the friendly fly, this native parasite lands on any object, including people. This insect is very important for naturally reducing forest tent caterpillar outbreaks. Hyposoter spp. (Ichneumonidae) and Bracon spp. (Braconidae) are also parasitoids of forest tent larvae. An NPV virus and a fungal pathogen, Entomophthora, also can occur in outbreak populations.

Biorational pesticides: Bacillus thuringiensis var. kurstaki, diflubenzuron, insecticidal soap, pyrethrin, spinosad, tenbufenozide, pyrethrin.

Conventional pesticides: acephate, bifenthrin, carbaryl, chlorpyrifos (nursery only), cyfluthrin, malathion, permethrin.

Forestry, Christmas Tree, Landscape

Balsam twig aphid
Mindarus abietinus

(Hemiptera: Aphididae)


IPM of Midwest Landscapes (UMN)

Time: May to Aug

Hosts: All species of fir, balsam and Fraser, some spruce and pine species.

There are three stages of aphids which appear during the year: brown-gray, wingless females, followed by blue-gray forms with a white waxy covering, and then by winged forms capable of migrating. There are several generations per year. Eggs overwinter on bark.

Needles may become deformed or glued together by sticky honeydew, so that they subsequently yellow and fall prematurely. New spring growth may be stunted or deformed and the bark roughened.

As buds swell, look for wingless females on buds. Also look for white forms on new needles in June. Look for curled needles as a result of aphid feeding, and for copious amounts of honeydew.

Cultural control: Avoid planting trees too close.

Chemical control: Horticultural oil can be applied as a dormant spray if eggs are detected in large numbers. Applications of well-timed sprays may be used in spring if numerous overwintering aphids are present on new growth.

Biological control: Ants, yellow jackets, bigeyed bugs, damsel bugs, assassin bugs, minute pirate bugs, lace-wings, earwigs, predatory thrips, lady beetles, ground beetles, soldier beetles, hover fly larvae, and predaceous midges are all important predators. Aphidius wasps (Braconidae) are important parasitoids.

Biorational pesticides: insecticidal soap, horticultural oil.

Conventional pesticides: acephate, azadirachtin, bifenthrin, carbaryl, chlorpyrifos (nursery only), deltamethrin, imidacloprid.

Spruce budworm
Choristoneura fumiferana

(Lepidoptera: Tortricidae)


IPM of Midwest Landscapes (UMN)

US Forest Service

Spruce budworm adult

Spruce budworm larva
Photos: Virginia Tech Entomology

Time: May, June

Hosts: Spruce

The spruce budworm is one of the most destructive native insects in the northern spruce and fir forests of the Eastern United States and Canada.

The first recorded outbreak of the spruce budworm in the United States occurred in Maine about 1807 and 1878. Since 1909 there have been waves of budworm out breaks throughout the Eastern United States and Canada. The States most often affected are Maine, New Hampshire, New York, Michigan, Minnesota, and Wisconsin. These outbreaks have resulted in the loss of millions of cords of spruce and fir.

Balsam fir, white, red, and black spruce are suitable host trees and some feeding may occur on tamarack, pine, and hemlock. Spruce mixed with balsam fir is more likely to suffer budworm damage than spruce in pure stands.

Use insecticides in May when larvae are feeding on needles before entering buds. Use BT, spinosad, acephate, bifenthrin, chlorpyrifos, carbaryl

In the spring, after several days of warm weather, larva emerges from hibernation and begin feeding. Early feeding is first confined to the new buds of staminate flowers if present, or the larva mines the previous year's needles if staminate flowers are scarce. The new flower buds provide a ready source of food before the vegetative buds expand. The larva migrates to the end of a twig and bores into a needle or an expanding vegetative bud. When the larva is in the fifth instar, it begins tying the tips of twigs together with silk, forming a small nest. The new foliage is eaten first. In epidemic situations, old needles and bark (near branch tips) may also be consumed to such a degree that branch tips and terminal shoots are destroyed. During late June through mid-July, depending on the weather, the larva completes development and stops feeding. Adults emerge in July to lay eggs.

Biorational pesticides: insecticidal soap, horticultural oil.

Conventional pesticides: acephate, azadirachtin, bifenthrin, carbaryl, chlorpyrifos (nursery only), deltamethrin, imidacloprid.

Pine tortoise scale
Toumeyella parvicornis

(Hemiptera: Coccidae)


IPM of Midwest Landscapes (UMN)

Pine tortoise scale females

Time: May to June; late July to Sept

Hosts: Jack, Scotch, and Virginia pine are preferred, but Austrian, mugo, red, slash, Swiss mountain, and white pine are also susceptible.

Adult female scales are reddish brown. They are convex and 4 to 7 mm in diameter. Males are small, flat, and translucent. Flying adult males resemble gnats. Crawlers are mostly transparent and common on needles.

Overwintering adults are found on twigs; young nymphs on foliage. Crawlers hatch in late June to early July. There is one generation a year. Mated females overwinter on twigs

The conspicuous sooty mold that grows on their honeydew secretions is perhaps the first symptom of heavy infestation by these insects. Branch tip needles may yellow from feeding damage, and dieback may occur. Injury most frequently occurs on seedlings and saplings, which can be killed in heavy infestations. Mature trees may also be damaged.

In spring, look for female scales at the base of needles. In late June to early July, look for transparent crawlers that settle on needles. Look for ants, wasps, and flies which are attracted to honeydew produced by the scales. Also look for sooty mold growing on honeydew and for needle yellowing.

To conserve beneficial insects, use short duration, low residual insecticides such as horticultural oil, insecticidal soap, and insect growth regulators (IGR).

Foliar applied broad spectrum insecticides, such as acephate, carbaryl, imidacloprid, and pyrethroids should only be used when scale populations are high--beneficial insects will be also killed.

Dormant season oil treatments may be used for soft scales that overwinter as immatures, and for armored scales that overwinter as eggs under female covers (delayed dormant).

Summer oil treatments will smother exposed eggs, crawlers, and immature females.

Insect growth regulators (IGR), such as pyriproxifen, disrupt molting and is used for crawlers.

Soil applied systemic insecticides or trunk injections, such as imidacloprid: Apply imidacloprid in fall for crawlers in spring; not effective against armored scales which feed at different sites than soft scales. Less harmful to beneficial insects than foliar-applied, broad spectrum insecticides.

Nursery and Greenhouse

Western flower thrips
Frankliniella occidentalis
(Thysanoptera: Thripidae)


Western Flower Thrips in Commercial Greenhouses (UMN Extension)

Western Flower Thrips Feeding Scars and Tospovirus Lesions on Petunia Indicator Plants

Agdia DAS ELISA and ImmunoStrip test

Interiorscape Website (CUES)

Thrips damage
University of Florida

Time: All year in GH

Hosts: Many flowering plants

The western flower thrips feeds on the flowers and foliage by inserting its modified left mandible into the tissue, and sucking the fluids from cells. Oviposition and feeding scars reduce the aesthetic quality and marketability of ornamental plants. When thrips feed on developing tissues, affected cells are unable to expand, and mature leaves and petals are distorted. When thrips feed on expanded tissue, effected cells become filled with air, which imparts a silvery appearance. These thrips spread tomato spotted wilt (TSWV) and impatiens necrotic spot viruses (INSV).

Females lay eggs in tender plant tissue. The eggs hatch in 2 to 14 days, depending on temperature. First instar larvae begin feeding on egg eclosion. Second-instar larvae also feed on plant tissue, usually in flowers. These larvae are found in the protection of perianth of the flower or within developing terminal foliage. Late in the second instar they stop feeding and move down the plant to pupate. Thrips develop through two quiescent, non-feeding pupal stages in the soil, plant litter or in a protected area on the plant. Adults emerge and resume feeding on flowers, buds, and terminal foliage. The entire life cycle from oviposition to adult emergence can take 12 days in hot weather to 44 days in cool weather.

Larvae: The larvae develop through two instars and are distinctly yellow. Second instars become whitish prior to molting.

Prepupae and Pupae: Both prepupa and pupa are yellowish, quiescent non-feeding stages. The antennae and wing pads are typical for most thrips species. Pupae are found on soil and debris.

Adults: Western flower thrips is about 1 mm long, with the female larger than the male. The female varies from yellow to dark brown, and has a more rounded abdomen. The male is always pale yellow and has a narrower abdomen.

Management: Rotate classes of insecticides to prevent resistance.

Insecticides (trade name, common name, class):

Adept 25W*


insect growth regulator



insect growth regulator

Avid 0.15EC


macroycylic lactone

Azatin XL*



BotaniGard ES*

Beauvaria bassiana

fungus (biological)

Conserve SC



Talstar Flowable



Biological control agents (order from insectary like Rincon-Vitova)

Predatory mites

Hypoaspis miles (WFT only), Neoseiulus (Amblyseius) cucumeris, Iphiseius (Amblyseius) degenerans,

Parasitoids (GH thrips only)

Thripobius smilutens

Nematodes (WFT only) Heterohabditis bacteriophora, Steinernema spp., Thripinema nickelwoodii

Predatory insects

Orius spp., Chrysoperla spp.


Greenhouse thrips
Heliothrips haemorrhoidalis



Interiorscape Website (CUES)

Time: All year in GH

Hosts: Many flowering plants

Greenhouse thrips move relatively slowly and rarely fly. They prefer a cool, shady, and fairly moist atmosphere. These thrips feed in colonies on the foliage and fruit. They select neither the youngest nor the oldest leaves on which to feed. Often the flowers/fruit is preferred to the leaves. Since males are not common, reproduction is usually by parthenogenesis (laying unfertilized eggs). Males were first found in 1940.

Each female deposits 25 to 50 eggs in slits in the leaves. Under optimum conditions the time for development is 17 to 20 days for the eggs, about 13 days for the two larval instars, and about 5 days for the prepupal and pupal stages. The adults can live 7 weeks on plants growing in the greenhouse. All stages can be found throughout the year in greenhouses. Dark spots of excrement are often noticeable on the leaves and fruit.

Larvae: The first larval instar is white; the second instar is yellow. Both instars have red eyes.

Pupae and Prepupae: The pupa and prepupa do not move about freely. These stages are yellowish with red eyes. Pupae are slightly larger, with longer wing pads, and antennae bent back over body. They become darker with age. Pupae are found on leaves.

Adults: The head and central area of the body have a distinct network of lines. The body is dark brown with the posterior end much lighter; the legs are uniformly yellow.

Management: See western flower thrips.


European crane fly
Tipula paludosa

Marsh crane fly
Tipula oleraceae

(Diptera: Tipulidae)


MN Dept. of Agriculture

Oregon State University

Wash. State University

Larval damage to roots
Photo: MDA

Adults resemble giant mosquitoes
Photo: Janco Tanis,,

Time: Oct to Sept (larvae); Sept to Oct. (adults)

Hosts: Lawns, nursery stock

Crane flies are two-winged flies that are often mistaken for giant mosquitoes. The adults are harmless. The larvae of many crane flies are aquatic and their presence is an indicator of good water quality. Other crane flies are terrestrial decomposers and help break down decaying organic matter.

The crane fly known as the European crane fly in the Pacific Northwest, Tipula paludosa Meigan, is an introduced exotic pest first found in the region in 1965 in British Columbia, Canada. Since then, it has gradually spread into Washington State and parts of Western Oregon and has become the most serious economic pest of lawns, pastures and hayfields in the northwest.

In 1998, a second, closely related crane fly species from Europe was found in the Pacific Northwest. The new species, Tipula oleracea L., is almost identical in appearance to T. paludosa and similar biologically. It is also considered a serious pest of turf and other plants in its native Europe. However, T. oleracea can complete two generations per year (European crane fly has one) and adult T. oleracea emerge in the spring as well as the fall, when most European crane flies emerge.

In Washington and Oregon, crane fly larvae over-winter in lawns. Larger larvae can be found in the top three inches (3") of turf in spring. Infested grass may appear yellow or have dead spots. Adults emerge in late summer and early fall. As adults emerge, the leathery, shiny pupal cases (leatherjackets) are an indicator of where crane fly larvae were living and where the next eggs are most likely to hatch. The adults mate almost immediately after they emerge. The females lay most of their eggs before they make their first flights.

At nurseries where leatherjackets are a chronic problem, susceptible stock should be drenched with an insecticide in October when young larvae are at their most susceptible stage. Sprays should be irrigated in to the top 5 cm of the soil or growing medium in the evening when leatherjackets come to the surface to browse.

Japanese beetle
Popillia japonica
(Coleoptera: Scarabeidae)


IPM of Midwest Landscapes (UMN)

japanese beetle

Japanese beetle traps can attract
unwanted beetles, so place them
away from valuable plants.

Time: May, June, July

Hosts: Grubs on grass roots; adults on foliage

Introduced in 1916 near Riverton, New Jersey. The Japanese beetle is a serious. Grubs feed on the roots of turf grass and adults feed on the foliage of more than 300 plant species. Grubs chew off grass roots and reduce the ability of grass to take up enough water to withstand stresses of hot, dry weather. As a result, large dead patches of grass develop in grub infested areas. The sod on these dead patches can be rolled back like a carpet to expose the grubs and the lack of turf roots. Early recognition of the problem can prevent this destruction.

There are five small, white patches of short hairs along each side of the dorsal abdomen on the beetle. These patches are a key characteristic for identification

Grub populations between 7 and 15 per square foot can cause significant damage to non-irrigated turf. Irrigated turf can withstand a higher grub count because the increase in water compensates for the roots chewed off by the grub.

Timing of pesticide treatment is important. Treating grubs in the spring is also more difficult as they are bigger and do not feed for long before they pupate Larger grubs are more difficult to control with insecticides, and the grubs are difficult to kill in the fall because they are larger. In early July females emerge to lay eggs

Life cycle of Japanese beetle: egg, grub, and adult stages.

life cycle

Imidacloprid (Merit) is not fast acting, so use as a preventative control, not as a rescue treatment. Apply imidacloprid between May 15 and August 30. Halofenzide an IGR (insect growth regulator) (Mach2, GrubEX) is not fast acting, but only use in June to August to control grubs. For adults, use pyrethroid insecticides such as bifenthrin.



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Last modified on March 06, 2013