Fresh fruit is a delicious treat straight from the garden. Fruit plants like raspberries are great investments in your garden because they are perennials and produce fruits that are expensive to purchase and transport. Growing berries brings its own unique challenges, one of which is the raspberry beetle, Byturus tomentosus. Another pest is the raspberry fruit worm Byturus unicolor, which is discussed in detail in another article.
Raspberry beetles are a significant pest in areas of the world where raspberries are grown. They not only affect raspberries, but also other cane fruits such as blackberries, tayberries, boysenberries or loganberries. The adult beetles damage the early leaves and flowers of these plants and the larvae eat their way through the fruit and can be a nasty surprise at your harvest!
Since these beetles only have one generation per year, they tend to do the most damage to the fruits that ripen in July. Fruits that ripen after August are less affected as the larval population decreases significantly.
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Overview raspberry beetles
A raspberry beetle on a leaf. Source: S. Rae
Adult raspberry beetles are pale brown in color and about 4 mm (1/8 of an inch) long, and their bodies are covered with tiny hair. They originate from Europe, where they are a major agricultural pest, and were later introduced to other parts of the world, including China, Japan, and California. These bugs are a nuisance to farmers as adults damage leaves and flowers, and larvae damage fruit, causing discoloration and contamination.
Life cycle of a raspberry beetle
Adult raspberry beetles hatch in spring and their population peaks in July. These beetles feed on young Primocan leaves and unopened flowers first, and then congregate to feed on opened flowers and stamens. Adult beetles begin to mate after the first raspberry flowers have fully opened.
Female beetles lay eggs in the one to three weeks after the first flowers have opened. They lay one elongated egg per flower that is about 1.2 mm long and 0.4 mm wide. Eggs hatch during the green fruit stage and almost all hatch during the berry development stage in the pink fruit stage. Due to their strategic position, newly hatched larvae immediately start feeding on young fruits. Each female beetle can lay up to 120 eggs! At this point, they can do significant damage to the fruits by eating multiple fruits and tunneling between them. In late summer, these larvae migrate into the ground to hibernate as pupae before hatching as adult beetles the following spring.
Common living spaces
Raspberry beetles hibernate in the soil at the base of their host plants. If you observe a raspberry beetle infestation in one year, it is likely that you will have this pest the following year and will need to be more vigilant in monitoring from April onwards. As adults, these beetles can be seen on the growth tips of plants and flowers. Likewise, eggs are laid on flowers and the larvae are also found on fruits that are formed from these flowers.
What do raspberry beetles eat?
Both adult raspberry beetles and larvae cause damage to sugar cane plants. As adults feed on the growing tips of the plants, they can interveninally damage the expanding leaves. They can also fly to move from different plants or along different heights of the same plant. Larval damage occurs within the berries, causing browning, discoloration, and an overall decrease in the quality of fruit production.
How to control raspberry beetles
Byturus tomentosus. Source: urjsa
As with many other pests, we recommend an integrated pest control approach when fighting the raspberry beetle so as not to harm other wild animals and beneficial insects. Gardeners should be extra vigilant about chemical controls, as these beetles and larvae can be found on flowers that attract pollinators. If possible, start with non-chemical methods first.
Organic or chemical control
Sprays containing pyrethrins and spinosad are effective against this pest. Carefully follow the directions on your package and perform a test spray before using any penetrative product. Use the pesticide on raspberries at the pink fruit stage and reapply two weeks later.
Environmental control
These defects are visible to the naked eye. If you spot bugs, hand-pluck them from your plant and keep an eye on susceptible plants if you've had an infestation in the past. Encourage the presence of natural predators in your yard such as birds, ground beetles, and hedgehogs.
For the home gardener, there are several trap options on the market such as: B. sticky white traps and water traps. The problem with sticky traps is that they are not specific to this species and cannot specifically target insects. If you are using glue traps, set them up early in the season when the plants first sprout and place them so that they aren't obscured by too many leaves. Water traps use the scent of host plants to bait certain species and can be used to control both male and female raspberry beetles.
Home gardeners can also try a method called "beating" the cane, which involves placing cloth, tarpaulin, or an old baking sheet under the cane and shaking it vigorously without damaging the cane. Beetles fall off the plant and can be killed with soapy water. You can repeat this process throughout spring and early summer and ideally before the eggs are laid.
Prevent raspberry beetles
There are several types of wild berries that appear to be resistant to raspberry beetles. Agricultural researchers have worked to create commercially available hybrid plants with this resistance in order to mitigate the beetle infestation in the future.
frequently asked Questions
Raspberry beetle standing on a blackberry flower bud. Source: Allan Hopkins
Q: When should I spray my raspberry beetle?
A: We recommend using a combination of control methods and spraying when absolutely necessary. Since these beetles and their larvae eat the flowers of sugar cane plants, spraying can cause additional damage to pollinators. If you need to spray, spray at night when there is less pollinator activity.
Q: Do raspberries have worms?
A: There are several "worm" pests, including the raspberry beetle found in fruits. These include the larval stage or larvae of the raspberry beetle, the raspberry fruit worm (which is the larvae of another related beetle), or the spotted-winged drosophila larvae.
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