Sap beetles are small, oval-shaped insects that can become a nuisance in gardens and fruit crops. They are attracted to fermenting fruits, vegetables, and other overripe plant matter, making them a common problem for many growers. As these pesky insects can cause damage to your plants and ruin your harvest, it’s essential to find effective ways to eliminate them from your garden.
There are several methods to control sap beetles, ranging from basic prevention strategies to targeted insecticide applications. Home gardeners can take advantage of traps using fermenting plant juices or other baits like stale beer and molasses mixtures to capture these beetles away from their crops. Field sanitation and practicing crop rotation are also essential, helping minimize the attractants for sap beetles. If needed, chemical insecticides can also be used by following proper action thresholds and rotating modes of action, as advised by extension experts.
Identifying Sap Beetles
Sap beetles (Nitidulidae) are generally small, ranging from 1/8 to 1/4 inch long, with an oval and flattened shape. They usually possess dark colors, with occasional orange or yellow spots. A key identifier of sap beetles is their antennae, which have a club (knob) at the end1. Some physical features include:
- Small size (1/8 to 1/4 inch)
- Oval and flattened shape
- Dark-colored, sometimes with orange or yellow spots
- Clubbed antennae
Sap beetles, like other beetles, undergo complete metamorphosis, which includes four stages: egg, larva, pupa, and adult. They usually feed on sap and decaying plant tissues.
Common Species of Sap Beetles
There are various species of sap beetles. Some common species include the strawberry sap beetle, the dusky sap beetle, and the picnic beetle2. Below is a comparison table of the common species.
|Strawberry Sap Beetle
|Orange or yellow spots
|Fruit and vegetable juices
|Dusky Sap Beetle
|Dark brown to black
|Black spots on wings
|Corn, fruit trees, and vegetables
|Four yellowish dots on wing covers
|Fruit, tree sap, and fungi
Damage Caused by Sap Beetles
Affected Plants and Crops
Sap beetles cause damage to a variety of plants and crops, including:
- Fruits: strawberries, raspberries, tomatoes, melons
- Vegetables: sweet corn
- Other: corn silk, rotting vegetation, fermenting plant juices
These pests often target damaged or overripe produce and are attracted to plant sap and fermenting plant juices.
Signs of Sap Beetle Infestation
Fruits and Vegetables
Sap beetle damage to fruits and vegetables is characterized by:
- Deep cavities in berries
- Injured sound fruits (e.g., tomatoes)
- Holes in corn silk
For example, sap beetles may damage strawberries when the fruit is infected with a disease, leaving deep cavities in the berries similar to slug damage1.
In sweet corn, sap beetles can act as primary pests when populations are high. They are attracted to damage caused by other pests like corn earworm, which then become entryways into cobs for sap beetles2. Keep an eye out for:
- Holes in corn silk
- Beetles hiding in husks
Soil and Rotting Vegetation
Sap beetle larvae live in soil and feed on rotting vegetation, so finding them in your garden soil may also be an indication of an infestation3. Signs include:
- Larvae in soil near affected plants
- Presence of rotting plant material
Preventing Sap Beetle Infestations
Sanitation and Garden Maintenance
Proper sanitation is crucial for preventing sap beetle infestations. Keep your garden clean by doing the following:
- Remove overripe fruits and rotting vegetation
- Clear weeds and debris from the soil
A well-maintained garden reduces the chances of sap beetles finding food sources. Additionally, avoid piling up wood or creating wooded areas close to your garden, as sap beetles often inhabit these spaces.
Physical Barriers and Exclusion
Physical barriers can help protect plants from sap beetles:
- Cover plants with lightweight mesh or cloth
- Install row covers on vegetable beds
- Use insect netting or exclusion bags on individual fruits
Implementing these physical barriers keeps sap beetles at bay and maintains a healthy garden environment.
Timing Harvests and Planting Varieties
The timing of your harvests and planting specific varieties can deter sap beetles:
- Harvest fruits and vegetables as soon as they ripen
- Choose sweet corn varieties with tighter or more extended husks
|Sweet Corn Variety
A well-timed harvest diminishes the availability of overripe fruit that attracts sap beetles. Furthermore, tight or extended husks on sweet corn varieties help protect the kernels from sap beetle infestations.
Controlling Sap Beetles
Natural Predators and Beneficial Insects
There are several natural predators that feed on sap beetles, helping control their population:
- Spiders: Excellent predators of beetles, including their larvae and eggs
- Apes: Feed on sap beetles and other pests
- Slugs: Consume sap beetle eggs and larvae
Additionally, beneficial insects such as ladybugs and predatory mites can help control secondary pests like aphids and spider mites that sap beetles might attract.
Traps and Baits
Trapping and baiting are effective approaches to controlling sap beetles:
- Yeast mixture: Create a simple homemade bait by mixing water, yeast, and sugar. Place it in small containers near affected areas.
- Vinegar traps: Fill a jar or container with vinegar and a drop of dish soap. The soap reduces surface tension, causing beetles to sink and drown.
Pros and Cons of Traps and Baits
|Not always effective
|Requires continuous monitoring
In some cases, chemical control is necessary to manage sap beetles:
- Insecticides: Use products such as Sevin (carbaryl), bifenthrin, permethrin, or malathion following label directions.
- Warning: Chemical treatments can affect non-target organisms, so use them as a last resort.
Pros and Cons of Chemical Control
|Possible harm to beneficial insects
Note: Sanitation is crucial in controlling sap beetles. Regularly remove ripe and diseased produce to prevent their attraction. Proper sanitation can help minimize pest problems and the need for chemical treatments.
Overwintering and Future Generations
Sap Beetle Overwintering Behavior
Sap beetles, also known as picnic beetles, overwinter as adults in various sites outside gardens, often in wooded areas1. During the winter months, they survive the cold temperatures by seeking shelter in leaf litter, under bark, or in other protective spaces.
Implications for Future Pest Management
A key aspect of managing sap beetles as a garden pest is understanding their life cycle. Sap beetles lay eggs near fermenting and decaying plant materials, such as fruits and vegetables like muskmelon2. Within about 30-35 days, the larvae will have fed for approximately three weeks, transforming into pupae and eventually emerging as adults3.
Effective pest management strategies should focus on:
- Timing: Targeting beetles during their overwintering phase, when they are inactive and vulnerable.
- Sanitation: Removing decaying and fermenting plant material, which attracts beetles and provides a breeding ground.
- Physical barriers: Using protective covers, such as netting or fine mesh, to prevent beetles from reaching susceptible plants in your garden.
Understanding the overwintering behavior of sap beetles can help inform future pest management efforts and minimize their impacts on your gardening efforts4. By creating an unfavorable environment for sap beetles and implementing timely, targeted interventions, a more successful and enjoyable gardening experience can be achieved.
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Picnic Beetle
Subject: Bugs eating strawberries
Location: Zone 5 – New York
July 11, 2012 8:04 am
Can you tell me what kind of bug this is and how to keep it away from the strawberries?
This is a Fours Spotted Sap Beetle, Glischrochilus quadrisignatus, and it goes by the other common names Picnic Beetle or Beer Beetle. According to BugGuide it is: “attracted by the odour of fermenting fruits and vegetables; the adult beetles fly into beer or soft drinks at summer picnics.” The strawberry in the photo appears to be dirty as well as rotting. We suspect something else might have done the initial damage. Do you place straw on the ground around the strawberry plants? That will help to discourage snails and slugs which love to eat strawberries. If the strawberry in question was damaged by a slug and it then began to rot, that might have attracted the opportunistic Picnic Beetle. If the Picnic Beetles are actually doing the initial damage, which we doubt, you can always leave a glass of beer in the area of the strawberry plants in the hope the beer will be more attractive to the Picnic Beetles than the strawberries.
Letter 2 – Picnic Beetle
Subject: Can I stop losing my mind?
Location: Brooklyn, NY
June 10, 2014 9:24 pm
I live in Brooklyn, with ever-present fear of bedbugs. Found this thing crawling on a shirt on top of a dresser today and about came unglued but later concluded it wasn’t a bedbug. It’s about 2.5-3mm long, and revealed wings only after it had flailed, stuck, upside down for a little bit in a small glass container I put it in to try to figure out what it was. I’ve put too much time into internet searches in my effort to identify this bug and thus figure out if I need to keep freaking out/do something. Any help you can provide with the ID would be much appreciated.
We don’t know anything about the loss of your mind, but if it is any consolation, it is our observation that a mind isn’t that important in the Third Millenium. As you have already determined, this is not a Bed Bug, and it sure looks to us like a beetle because of the clubbed antennae and what appears to be mandibles. We will do some research and attempt to identify your distinctive looking beetle soon. We plan to step away from the computer and read through Arthur V. Evans new book: Beetles of Eastern North America. We just had a curious thought, which we hope doesn’t put you over the edge, but we think this looks like a Carrion Beetle.
Carrion like dead meat? Am I dead meat?
Thanks–if it helps I can try to get a better photo of it now that it’s daytime and my daughter is not sleeping in the room with the real camera.
Freaky but interesting?
Thanks so much. Look forward (sort of?) to hearing back from you–
I did, btw, think it looked like some silphidae pictures last night but wasn’t sure, and I’m not cleaning any bones or anything around here, I promise!
It was crawling on a shirt my husband got free from a run in Central Park but that was last week and I thought he’d washed the shirt…?
Good Morning Evangeline,
We believe we have identified your beetle as a Bark Gnawing Beetle, Peltis septentrionalis, thanks to Arthur V. Evans new book: Beetles of Eastern North America, where it states: “Adults found under bark of conifers in association with red banded (Fomitopsis pinicola) and brown staining cheese (Oligoporus fragilis) polypores. Across Canada and northern United States; in eastern North America south to New York and Minnesota; Eurasia.” Here is an image from BugGuide. Your individual appears shinier, but other than that difference, which might be an illusion because of flash photography, we believe it is a good match. So, we hope we didn’t alarm you with the Carrion Beetle speculation.
You all are awesome!!! The bug is a bit shiny but looks very much like the one linked.
Correction, courtesy of Karl: June 12, 2014
Hi Daniel and Evangeline:
Close, but the carapace does not look right. I believe it is actually a Sap-feeding Beetle, probably a Six-spotted Sap-feeding Beetle, Prometopia sexmaculata (Nitidulidae: Nitidulinae). They are also known as Picnic Beetles. Regards. Karl