Sawfly

Sawflies are a group of insects belonging to the order Hymenoptera, including bees, ants, and wasps. Despite their name, sawflies are not flies; their name derives from the saw-like ovipositor females use to cut into plant tissues to lay their eggs. Sawflies are plant-eating insects, and many species are considered pests due to their destructive habits as larvae.

Host Plants

Sawflies have a wide range of host plants, which varies depending on the species. For instance, the Pine Sawfly infests various species of pine trees, while the Rose Sawfly, as the name suggests, primarily infests rose plants. Other species of sawflies can infest fruit trees, hardwood trees, shrubs, and a wide array of garden plants.

Regions impacted

Sawflies are a global problem impacting regions wherever suitable host plants are found, including North America, Europe, Asia, and Australia. The specific regions impacted can vary by the particular species of sawfly, as some have more restricted ranges.

Description

Adult sawflies are wasp-like in appearance, but they do not have the pinched waist typical of wasps and bees. They are usually small to medium in size, varying from 2.5 to 20 mm long, and their color can range from black to metallic green or blue.

The larvae resemble caterpillars and are often mistaken for them. They have a rounded head and a fleshy, elongated body which can be green, brown, yellowish, or multicolored depending on the species. They also have more prolegs (fleshy, stubby, leg-like appendages) on their abdomen compared to caterpillars.

Life Cycle

The life cycle of sawflies starts when females use their saw-like ovipositor to insert eggs into plant tissues. After a week or two, the larvae hatch and start feeding on the plant, often in groups. This feeding stage can last a month or more, during which the larvae may go through several molts, becoming larger each time.

Once fully grown, the larvae drop to the ground and pupate, either in the soil or in a cocoon on the plant, depending on the species. They overwinter as pupae and emerge as adults in the spring to start the cycle over again. Some species may have more than one generation per year.

Damage and Detection

Sawflies can cause significant damage to host plants, particularly when their populations are high. However, because their feeding patterns and the types of damage they cause can vary by species, it’s crucial to know the signs to look for.

Damage

Sawfly larvae primarily feed on the leaves of host plants. The type and severity of damage they cause depend on the sawfly species and the host plant. Here’s how sawfly damage typically manifests:

• Skeletonizing: Some species of sawflies consume all of the leaf tissue except for the veins, resulting in a “skeletonized” appearance. This is a common symptom of sawfly damage.
• Defoliation: In severe infestations, sawflies can completely defoliate a plant. This not only harms the plant but can also lead to its death if it occurs repeatedly or in combination with other stresses.
• Windowing: Some sawfly species only eat the surface layer of leaves, leaving a transparent layer. This damage is known as “windowing” and is another common symptom.
• Leaf Rolling and Mining: Certain species of sawflies roll leaves or create “mines” by tunneling between the upper and lower surfaces of a leaf. This results in discolored, curled, or distorted leaves.

Detection

Detecting a sawfly infestation early can help mitigate damage. Look for the following signs:

• Visible Larvae: Sawfly larvae are often the most noticeable sign of an infestation. They resemble small, colorful caterpillars and are usually found on the undersides of leaves.
• Chewed Leaves: Look for leaves with a “skeletonized” or “windowed” appearance, or leaves that have been curled or mined.
• Premature Leaf Drop: Sawfly larvae often cause premature leaf drop as they consume leaf tissue.
• Sawfly Adults: Adult sawflies look similar to wasps or bees but do not sting. While they are not usually seen in large numbers, the presence of adult sawflies can indicate a potential infestation.

Remember, the best way to manage sawflies is through regular monitoring and early detection. If you spot these signs of damage and can identify the culprit as sawflies, it’s time to consider control measures to protect your plants.

Prevention and Control

The prevention and control of sawflies involve several integrated pest management (IPM) strategies. The goal of these strategies is to manage the sawfly population in a way that minimizes damage to host plants while avoiding unnecessary harm to beneficial insects and the environment. Here are some strategies for preventing and controlling sawflies:

Regular Monitoring: Regularly inspect plants for signs of sawfly larvae and damage. Sawfly larvae are often found on the undersides of leaves, and their damage typically appears as skeletonized or defoliated leaves. Early detection can help you respond quickly and minimize plant damage.

Encourage Natural Predators: Promote the presence of natural predators such as birds, predatory insects (assassin bugs, rough stink bugs, spined soldier bugs, twospotted stink bugs), lizards, frogs, ants, and predatory wasps. These predators can help control sawfly populations naturally.

Healthy Plants: Healthy plants are more resistant to pests, including sawflies. Keep your plants healthy with proper watering, fertilizing, and pruning practices.

Manual Removal: For smaller infestations, sawfly larvae can be manually removed from plants. They can then be destroyed or relocated far from susceptible plants.

Insecticidal Soaps or Horticultural Oils: Insecticidal soaps or horticultural oils can be applied to infested plants. These treatments work by smothering the insects. Make sure to thoroughly coat both the tops and bottoms of leaves, as well as the stems, for maximum effectivenes

Pesticides: If other measures fail, pesticides may be required. It’s important to use these sparingly and as a last resort, as they can also harm beneficial insects. Use a product labeled for use against sawflies, and always follow the manufacturer’s instructions.

Soil Cultivation: For sawfly species that pupate in the soil, cultivating the soil in the late fall or early spring can help disrupt their life cycle. This can expose the pupae to predators and harsh weather conditions.

Plant Resistant Varieties: Some plants or plant varieties are resistant to sawflies. If sawflies are a recurring problem, consider choosing resistant varieties when planting or replanting.

Professional Help: For persistent or severe infestations, consider seeking help from a professional pest control service. They can provide expert advice and services tailored to your specific situation.

Remember that the best control strategy often involves a combination of these methods. The goal is not to completely eradicate sawflies, which would be nearly impossible, but to keep their population at a manageable level where damage to plants is minimized.