Lectures 20 and 21 Root-feeding insects

Weevils Rostrum

Three important examples of the root weevil complex.  Black vine weevil Otiorhyncus sulcatus  Strawberry root weevil O. ovatus  Woods weevil Sciopithes obscurus

(1) grow strong varieties of strawberries, (2) allow poultry to run in the strawberry patches (3) trap adults under boards or straw (4) spray, if you feel you must, with arsenate of lead, two pounds of powder to 100 gallons of water (5) clean up and burn old leaves and refuse in the fields or gardens A 1926 version of what we would call, IPM! The black vine weevil

Typical leaf damage caused by root weevils. Females have to feed on leaves to mature their ovaries.

More Adult Weevil Damage

Weevils before feeding on foliage Weevils after feeding on foliage

The root weevils are common to the northern half of U.S. and southern half of Canada. The most destructive form is the larval form as grubs feed on roots and lower stems. There are hundreds of hosts, a few would be: yews, rhododendrons, strawberries, many green house plants and Douglas-firs in nurseries.

The flightless, parthenogenic females hide under boards, litter, and trash during the day. At night they climb plants and feed on leaves. Egg laying occurs during early summer through July. Eggs are found at the base of host plants. After hatching the grubs move into the soil and feed on roots. Later instars move to the root crown, feed on the stem and pupate just under the soil. Adults then emerge and continue to feed during warm fall and winter days. Adults are long lived, often more than 3-yrs.

Grubs feeding on roots of rhododendrons Leaf notching

Sharon Collman picking weevils out of nursery containers Larvae found in containers Intense root and stem damage caused by grubs

Black vine weevil Severe damage caused by root-feeding weevil grubs

Damage by root weevils on rhododendron in PNW

Pest mgt. -- Adult control should begin when adults emerge in May-June. Larval control is done in autumn. Azadirachtin bifenthrin cyfluthrin acephate beneficial nematodes Beauvaria bassiana Plant weevil-resistant Rhododendrons: R. edgeworthii R. leuteum R. mergeratum R. trichostomum And others

The Scarabaeidae: Scavengers and Herbivores Dung beetle -- scavenger saprophage Leaf chafers -- herbivore

A good illustration on the importance of saprophagous insects is what happened in Australia. Cattle were introduced into vast areas of northern Australia, an area with few saprophagous insects that fed on dung.

A suite of saprophages were introduced into Northern Australia to recycle the large amounts of accumulating cattle dung. Introduction of these beetles was a resounding success.

Processing by the beetles was beneficial to pasture growth.

Dung rollers are fascinating to watch Some scarabs are metallic colored and used in jewelry

The root and leaf-feeding scarabs (the leaf chafers) severely damage grasses, crops and nurseries.

The ten-lined June beetle is a scarab. Larvae feed on roots Adults feed on leaves of hardwoods

Leaf chafer adults feed on foliage, while the grubs feed on roots

Leaf chafers include the May beetle, June beetle, Japanese beetle, rain beetle and others. The ones destroying lawns belong to the Phyllophaga spp. In the PNW these are the June beetles that include several species. Adults are nocturnal and attracted to lights. June beetles emerge from pupal cells in the soil during April- June (depends on the weather). Adults feed on foliage of birch, elm, ash, maples, and other hardwoods. Later each female lays eggs in the soil and larvae feed on roots of turf or pasture grass. The population overwinters as larvae and the last instar constructs a pupal cell.

White grubs -- Larvae are variable in size with robust, cream-colored bodies and black heads. Grubs feed on roots. Turf damage generally appears as patches of dead turf that are not anchored to the soil. Symptoms may occur from spring through fall. Control -- beneficial nematodes, imidacloprid Bacillus popillae MACH 2 Other insecticides How -- Treat when grubs are active near the soil surface. irrigate treated area immediately after application

Another Root Pest The European cranefly whose larvae feed on stems, root crowns and roots of grasses

The Crane Flies: Tipulidae Tipulid larva (“leather jacket”)

More on the tipulids Leather jackets

C.P. Alexander Alexander, born 1889 and died During his career he described almost 11,000 species of Tipulidae and he wrote 1017 articles, 20,000 pages of books, and produced 15,000 of his own illustrations. His contribution to entomology is immense. The Tipulidae – crane flies J. R. Vockeroth Recipient of the 2003 C.P. Alexander Award by the International Society of Dipterology

The European crane fly: Tipula paludosa Alex., a turf pest Leatherjackets feeing on roots of turf

European cranefly Larvae hatch in the late summer and feed on roots, root crowns and shoots through winter and into spring, causing turf damage anytime between Jan-May. Affected lawns often thin out severely in early spring when normal turf starts vigorous growth. Starlings and other birds are attracted to infested lawns and may cause accelerated turf damage as they search for larvae. Cranefly larvae can be controlled easily with recommended insecticides. Monitor turf starting in Jan, and consider treating when larval populations reach 25+ per sq. ft or when damage is apparent.

European crane fly in Laurelhurst Leather jackets

Another Root-feeding Insect: Sod Webworm Belong to the moth family Pyralidae which include the snout moths.

Sod webworm damage Damage most common on wet parts of the lawn

Sod Webworms (Chrysoteucia topiara) Larvae feed at bases of grass blades and on new tender roots. You can look at the base of the dying sod and observe the chopped-off blades

Damage begins as relatively small, irregular spots of dead and dying grass. During sod webworm outbreaks the spots coalesce and major damage ensues.

May-June (Late Spring) See erratic flying moths hovering over your lawn at dusk; Erratic flying moths attracted to lights; Lay eggs in slight lawn irregularities – aeration holes; Summer Larvae feed on grass blades and succulent roots: Fall & Winter Pupate in early fall and overwinter as pupae Late Spring Next adult generation emerges

Remember we said that the sod webworm prefers a wet site? What site is wetter than cranberry bogs? When this insect, Chrysoteucia topiara, is found killing cranberries, it’s called the cranberry girdler. When this insect girdles Douglas-fir seedlings in nurseries it’s still called the cranberry girdler. And it’s a serious pest!

Management of cranberry girdler: Douglas-fir seedlings Damage – Larvae feed on the roots and lower stem of seedlings. Damage occurs when seedlings are grown or planted near to grass fields, which are the primary habitats for this insect. Diagnosis – On the lower stem and seedling taproot look for patches where bark and cortex have been removed. Biology:

Management of the cranberry girdler attacks on Douglas-fir seedlings In nurseries, avoid using cover crops that would provide host material for the insect. Cultivate or apply herbicides to non- nursery areas to control grasses and weeds. Monitor the population with pheromone traps:

The pheromone traps also will be used to time application of pesticides. Mach-2 or other product used to control root-feeding insects should be applied: * 3-5 weeks after the start of moth flight to reduce seedling damage (the target would be early instars). * Additional pesticide treatment may be made in late summer to get the last instar before pupation.

Cranberry girdlers They girdle and kill Douglas-fir seedlings.