Raspberry worm: fruit-eating larvae

Berries are one of the tastiest goodies to grow in the garden. Growing raspberries isn't too difficult as long as you can control the trifecta of the pests that commonly attack them: raspberry borer, raspberry beetle, and raspberry fruit worm.

The raspberry fruit worm (Byturus unicolor) is the larval stage of a small brown beetle that attacks raspberry plants. Despite its name, this pest is not limited to just raspberries. You can also eat loganberries, boysenberries, wild blackberries, salmonberries and thimbleberries.

The raspberry fruit worm is a major pest for farmers who grow the raspberry fruit commercially. Not only do they reduce the overall yield of the plants through damage to the flower buds, but they also contaminate the fruit and make it unsuitable for sale in markets.

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Overview raspberry fruit worm

The adult beetle form of the raspberry fruit worm. Source: tree growth

The history of the raspberry fruit worm in North America is well documented with the earliest records dating from the late 19th century. These records show that the raspberry fruit worms have plagued berry producers in the northern United States and Canada in the past. The raspberry fruit worm is also known as the western raspberry fruit worm due to its distribution in western parts of the continent such as Washington State and British Columbia Province.

The raspberry worm develops into small beetles (1/4 ″) and a reddish-brown color with tiny hairs that cover the entire body. These hairs are a distinguishing feature of the species. Female beetles lay small eggs on flowers or green fruits. Small whitish-yellow maggots or fruit worms hatch from the eggs. Although the raspberry fruit worm Byturus unicolor develops into a beetle, this species is related to, but different from, the raspberry beetle Byturus tomentosus.

Raspberry fruit worm life cycle

Adult beetles overwinter in the ground and hatch in early spring, between mid-April and mid-May, to feed on leaves close to the ground. They wander up the sticks and are attracted to flower buds. Adult beetles mate and adult females lay their eggs on these flower buds and unripe fruits. When the eggs hatch, the small larvae have direct access to the raspberry fruits and continue to eat until the fruits are ripe in late summer. The larval stage usually lasts 30-40 days. Fruit worms pupate and become full-grown beetles in autumn after ripe fruits fall to the ground.

Common living spaces

Adult raspberry worm beetles overwinter in the ground and under leaf litter from autumn to early spring. They emerge in early spring to feed on sugarcane plants and mate, working their way up from the lower leaves to the new Primocanes, Floricanes, and flower buds. Their larvae are typically found in the developing raspberry fruit.

What do raspberry fruit worms eat?

The raspberry fruit worm attacks the living tissue of raspberry plants and is most active in spring and summer. Adults feed on the young leaves and flower buds, leaving an intervenal pattern of damage on the raspberry leaves. This means that you can see chewing streaks between the leaf veins. This skeletonized leaf damage pattern can help you diagnose this pest problem. The fruit worm is typically located inside the berry and drills the developing fruit from the inside out.

How to fight raspberry fruit worms

Raspberry fruit worm larvaeA raspberry fruit worm larva. Source: OSU Ken Gray Insect Image Collection

The best time to control raspberry fruit worms is during the adult stage, before they can lay eggs. The fruit worms are so small and live in the fruit that it becomes time-consuming and tedious to hand-pick at this stage. Also, many commercial growers are unable to hand-pick worms when using machines to harvest fruit.

Organic or chemical control

Stay vigilant and monitor the raspberry plants for these beetles in early spring. Examine the lower leaves for damage and use sticky traps near the raspberry plants to monitor their population. You can try hand picking the beetles and soaking them in a little soapy water to kill them without the use of chemicals.

If you need to use chemical controls, you can try treating your plants with spinosad, a biologically approved microbial pesticide, or with pyrethrin, another organic spray made from chrysanthemum flowers. Follow best practices to make sure your use of chemicals does not harm the bees. Spray the sticks when the beetle activity is felt and again when the flowers begin to form and clusters of flowers separate. Raspberry fruit worm beetles are most active on warm evenings, so spraying can produce the best results in these conditions. Do not spray when the flowers open as these flowers will begin to attract pollinators.

Environmental control

Some studies have shown that the raspberry fruit worm problem is more common where there are more weeds. Remove weeds and debris from around raspberry plants to remove a possible shelter for hibernating adult beetles. There are several wild rubus, or blackberries, that can host raspberry fruit worms. Remove these wild hosts like thimbleberries and blackberries around your raspberries to isolate the fruit worm population.

Prevent raspberry fruit worms

After the raspberry harvest, lightly rake the area around each plant to break up or kill hibernating adult beetles. Raising chickens allows them to be released to feed around the raspberry canes and they can eat the hibernating adult beetles before they hatch the following spring.

frequently asked Questions

Damage in adult raspberry fruit wormsDamage from the raspberry fruit worm beetle. Source: joke

Q: Are raspberry worms harmful to humans?

A: Raspberry worms are not known to cause harm to humans if swallowed. However, they cause great economic damage to farmers by contaminating fruit and making it unsaleable.

Q: Are there worms in raspberries?

A: Several types of worms can be found in raspberries, including the raspberry fruit worm and also the larvae of the spotted winged drosophila, Drosophila suzukii, a type of vinegar fly.

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