Strawberry blossom weevil, Anthonomus rubi

The strawberry blossom weevil attack plants in the Rosaceae family and is a major pest of strawberries and raspberries. It is native to Europe, also occurring in Canada. The strawberry blossom weevil can be a sporadic pet, with severe damage possible in certain fields or areas. If left unmanaged in these areas, up to 80% yield losses can result in soft fruit crops, predominantly strawberries. Adult weevils feed on strawberry plant foliage and females oviposit eggs within developing flower buds (one egg per bud) before severing the stalk. Larvae mature within the unopened buds and feed on wilting plant tissue.

Russell IPM manufactures and supplies a pheromone lure and traps for the strawberry blossom weevil. Begin monitoring with pheromone traps at the start of flower stem extension in spring to give early warning of the infestation and to help with decision-making.

Biology

Adult: Adult males and females are black, 2– 4 mm in length, with a scattered greyish pubescence and a long snout about 40% of the length of the body. If the individuals are disturbed, the snout and legs may be folded under the body. The antennae are inserted about two thirds of the distance down the snout from the base and are elbowed at the first segment. This first segment is longer than the total length of the remaining segments.

Eggs: Eggs are 0.5 x 0.4 mm in size, oval, white and translucent. They are found inside flower buds.

Larvae: Larvae are 3.5 mm long, dirty creamish-white, legless, with a brown head. The body has a noticeable C shape and is wrinkled. It is found inside severed, withered flower buds

Strawberry blossom weevils emerge as adults from debris at the bottom of hedgerows in April onwards on warm sunny days. They invade strawberry crops, with populations peaking around mid-May. After only a short time feeding, mating occurs. Females oviposit eggs within developing flower buds (one egg per bud). The females will then partially sever the stalk of the host plant just below the bud in which they deposited their egg, causing the bud to wither. Eggs hatch in 5–6 days and each larva feeds on the shrivelled receptacle and other floral parts beneath the canopy of withered petals and sepals. Larvae develop rapidly and are fully fed in about 2 weeks. Pupation occurs in situ and the new adults emerge about 2 weeks later. The overwintered adult weevils continue to reproduce and cause damage into late summer, moving to new crops or wild hosts such as wild rose or bramble that provide flower buds for oviposition. However, the new adults that emerge from the withered buds are not reproductively active and do not cause severing damage. They feed for a few weeks on young strawberry leaves but do not reproduce. They migrate to overwintering sites in August.

Nature of Damage

The female strawberry blossom weevil inflicts damage to their host plants flower buds by partially severing the stalk just under the bud. After mating, the female deposits eggs singly in unopened flower buds. Damage starts shortly after flower stem extension and continues until all flower buds have opened. The open flowers are not attacked in this way. Fortunately, the weevil often preferentially severs smaller secondary flower buds which have thinner flower stalks, rather than the primary blossoms. However, the first primary flower buds are prone to attack. Severing damage is usually patchy and most intense at the margins of fields close to the weevil’s overwintering sites or close to earlier flowering crops from which the invading adults have migrated.

Begin monitoring with pheromone traps at the start of flower stem extension in spring to give early warning of the infestation and to help with decision-making. The pheromone lure contains a male sex aggregation pheromone, which attracts both males and females. The Anthonomus rubipheromone lure can be used with the Green Vane Trap.

Application Guidelines

Russell IPM manufactures and supplies a pheromone lure and traps for the strawberry blossom weevil, Anthonomus rubi. The green vane pheromone trap data will give early warning of the infestation and alert the user to invasion of the weevils before population levels build up.

Pheromones

The following notes are general guidelines on implementing pheromone monitoring programmes. Local conditions and practices can vary, so please consult your local advisers for precise advise in your area.

Lures

Lures can be changed every 6-8 weeks to get the most accurate results.

Lures handling

Pheromone lures are a very sensitive tool. They can be affected by exposure to elevated heat and direct sunshine. Wear gloves to handle the lures as direct touching by hand may cause cross contamination leading to mixed catches in the trap. Some contaminants, such as nicotine, may have a repellent effect reducing trap catch.

Lure Storage

The lures can be stored for long periods (several years) in a freezer (at about -20˚C) if the pack is sealed. Lures can also be stored in a fridge at higher temperatures (4˚C) for periods of up to 1 year. Although the pheromone is not harmful to humans, lures should not be kept in a freezer or fridge where food is stored.

Trap Selection

The Green vane trap is recommended for monitoring this insect. The green vane trap can also be used to monitor the tarnished plant bug, Lygus rugulipenis.

Trap Density

For monitoring, use two or more traps in each host crop field. Traps should be sited in places where adults are likely to migrate into the crop in spring. The crop margin next to the hedgerows or woodland where the adults may have overwintered in hedge bottoms is a good position, or else where adults may migrate from neighbouring crops which have flowered earlier.

For protected crops, traps should be set at the ends of tunnels near the entrance where weevils are likely to enter from hedgerows, head- lands or adjacent infested crops.

Trap Position

The traps base should be partially buried in the soil to stop it from falling over. Do not bury it too deeply as this can result in larger numbers of ground beetles entering the trap unintentionally. Make sure that the top of the trap is below the boom height of a sprayer.

Data and Interpretation

Collect data weekly or more frequently if possible. Weevils captured may be removed on each sampling occasion which makes counting new arrivals easier, but this is not strictly necessary. Decisions on pesticide application should not be taken solely on the trap catch data. Climatic and biological considerations should be taken in account.