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Sawfly Damage & How to Get Rid of Them

A sawfly in the family Argidae, resting on grass.

True sawflies have a saw-like appendage right at the tip of their bodies, and from this, they get their name “sawflies.”  The basal hymenopteran lineages have developed these saw-like ovipositor cutting and have been separately categorized into paraphyletic grouping. The female sawflies use this appendage to inject their eggs into upper leaf surface. Sawflies have phylogenetic relationships with wasps because they are Hymenopterans as well; however, they don’t have a tendency to sting people. Sawflies are rare to find because they don’t fly around on an average day. Mostly they can be sighted around flowers and buds where sawfly offspring cause damage to the foliage. These larval sawflies cause most of the harm in various ways as they feed on plants. You can observe the holes within leaves, and even worse these common pests can consume all the tissue between the veins of the leaves leaving them skeletonized. A low-level sawfly infestation can have the ability to do little cosmetic damage which can be stopped with pruning. Nevertheless, a large-scale infestation can completely destroy a full grown tree.

Sawfly Identification

A macro shot of a sawfly peeking over the top of a green leaf.There are different ways to identify the presences and traces of sawflies and their larvae in the surrounding areas of your home. For this, you need to know their size and appearance, their diet and feeding preferences, the habitat they choose and different stages of their life.

1. Appearance and size

Mostly the size of these sawflies larvae ranges from half of an inch to one inch. Different sawfly species have different colors and patterns on their bodies and commonly have a black head. Some of them also have black eye spots on their back. Most of them look like hairless caterpillars, but they are not. You can easily distinguish them from their prolegs which are false legs, which are a fleshy projection that looks like legs on their abdomen. The sawflies have 6 or more prolegs while caterpillars only have 2 to 5 prolegs. The largest sawflies belong to Tenthredinidae family with over 7500 species of the insect around the globe.

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2. Diet and feeding

The sawfly larvae behave similar to lepidopteran larvae and are eaters of plant foliage. They feed on different kinds of evergreen plant hosts. They feed on various species of pine trees, larch, tamarack, spruce, ash, birch, mountain ash, poplar, willow, cherry, plum, pear, cotoneaster, hawthorn different types of rose plants. Adult pear sawfly doesn’t restrict itself to pear plants, but its larvae also feed on cherry, plum and quince leaves.

3. Range and habitat

Sawflies live in a diverse natural world. Different types of sawflies have various kinds of range and habitats as well as they are found on native shrubs and infested trees including paperbacks, eucalypts as well as bottlebrushes. Pine sawfly is a distinctive sawfly that consumes previous season’s pine needles and moves from branch to branch after devouring all of them. The larch sawflies are found on various species of larch as well as Tamarack. Iris sawfly larvae feed on leaves of iris plants. The spruce sawflies prefer blue spruce, black spruce and white spruce that are most commonly found. Some of them also prefer eating mountain ash as well.

4. Reproduction and life cycle

Sawfly populations begin to grow in May and continue with their growth till June. Larch sawflies start their feeding in early June and are commonly found on short shoots of previous season twigs. The spruce sawflies also begin in late May or early June. Their larvae complete their full growth cycle by July. It is the case with most of the sawfly species. The larvae spend their winter under the soil, and then the adult sawflies emerge and start laying eggs in the leaves, and then the larvae appear and start feeding on the leaves.

Types of Sawflies

Five main types of sawflies are living on the species. These are as follows:

1. Currant sawfly

The larvae of currant sawflies have tan or green colored spots, and they have a tendency to strip the foliage off the plants.Conifer Sawfly Larvae - Diprion pini on grass stem.

2. Conifer sawfly

The conifer sawflies have the ability to devastate their host plants which are conifer trees, as they feed on their needles and build tunnels in their shoots and buds.

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3. Pear and cherry sawfly

These small larvae resemble green orange caterpillars and tend to skeletonize the leaves of their host plants as the adults lay eggs on those leaves.

4. Pecan sawfly

The larvae of pecan sawflies leave holes in the leaves after they are finished feeding on the leaves of a pecan tree.

5. Willow leaf sawfly

The damage to the willow tree can easily be recognized by different sized fleshy galls that develop after the sawflies are done the feeding. These galls also form on the spots where the female sawflies search for the best place to inject their eggs into the leaves and keep their larvae protected from the parasites.

Danger to Humans

Adult sawflies are wasps, but they don’t sting, and their larvae are also not dangerous to humans. However, upon disturbance, the larvae have the tendency to release an irritating secretion into the eyes or onto the skin. Even then the secretions are not harmful to the humans or pet animals as well. These insects are considered to be economic pests as they have a tendency to destroy their host plants. For instance, the different species of pine sawflies can damage various species of pines, and one of these outbreaks did occur back in 1998 in Finland. These insects are also considered to be a major pest in horticulture as different species prefer different host plants for feeding. For example, giant wood wasp also known as giant horntail looks similar to a hornet but cannot sting. They belong to parasitic family Orussidae. Their larvae make tunnels in the wood and cause massive financial damage.

Sawfly Damage

The most of the damage is caused by sawfly larvae that feed on their preferred host plants. The nature of this sawfly damage is associated with a particular species of the plants. Some sawfly larvae leave notches or holes in the leaves, and other species leave the leaves completely skeletonized by consuming all the plant tissue between the veins. They might also spin the web or roll up the leaves while some of the species also leave foliage galls. Different types of sawfly species also build tunnels within the shoots. The damage will be very little if the size of the tree is massive and the number of larvae is small. On an occasional basis, major sawfly outbreaks occur, and they do a considerable amount of damage to entire trees especially if the trees are young. The larvae of the sawflies only feed on leaves and might leave the midrib of a tree if in the case of a major outbreak.

How to Treat Sawfly Infestation?

Gooseberry sawfly (Nematus ribesii) caterpillar feeding on currant leaf.The use of control products for sawfly infestation must be focused on the larvae stage. The new generation of larvae feeds on plant foliage. Most of the Sawfly larvae resemble caterpillars and slugs. Therefore, it is essential to understand their distinct habitat and appearance and have enough sawfly information, as the insecticides that work on caterpillars don’t have any effect on sawfly larvae. To control small scale infestation handpicking these slug-like sawfly larvae would be the ideal measure. Parasitic wasps and beetles as well as many other species in Eulophidae attack sawflies and eat them and beetle larvae prey on their older larvae and serve as useful sawfly parasites. Make sure that you don’t use broad spectrum insecticides or they will kill beneficial insects as well. You can use narrow-range oils and insecticidal soap for this purpose.  You can also cultivate the soil to expose the overwinter pupae to freezing temperatures.

1. Biological control

Biological control programs are beneficial in the case of controlling the sawfly infestations. The aerial application of a biological agent containing a virus will ensure that only the sawfly and its larvae are affected, and it’s not limited to their single family. Abietiv is used as a biological agent as it has the tendency to kill the sawfly and its larvae. This agent has been employed in Newfoundland for many years, and it does not have any side effects for humans, cattle, pets, birds, or other beneficial insects.

2. Chemical defense

As mentioned above, the best period to control sawflies is during their larvae stage which hatches out during the later part of spring or early part of summer and starts feeding on plants. Spinosad is a natural insecticide that will control these larvae, and you can also use some conventional pesticides such as Malathion as well. Some insecticides such as Bacillus Thuringiensis only affect caterpillars but won’t hurt sawflies. Therefore, it is essential to identify the sawflies and differentiate from other species of insects.

3. Call a pest management professional

If you are not sure what species of sawfly you are dealing with or you don’t have much information regarding how to differentiate them from other insect species, then the best solution for you is called a professional sawfly insect control for this purpose. They are equipped with plenty of information about different types of insects and also have access to various kinds of new insect killers to control the sawfly infestation. Their expert professional advice will enable you to take good care of the sawfly infestation at your home. You can also reach out to your local extension office for this purpose as well.

Conclusion

Most of the sawflies attack only one kind of plant or the closely related species. For this reason, the sawfly species are named including their host plants.  For instance, dusky birch sawfly, oak sawfly, pear slug or pear sawflies, pine sawfly, rose slug sawfly, raspberry sawfly, elm sawfly, dogwood sawfly, ash sawfly and many others. They are not harmful to humans either in adult stage or larva stage. However, they have the tendency to do a considerable amount of plant damage especially if the larvae are in huge numbers. Their larvae may look like slugs or caterpillars, and the insecticides made for caterpillars and slugs won’t affect them. Hence, it is essential for you to identify and differentiate them from other similar looking insects. They feed on leaves, and after feeding, a large outbreak can leave the trees completely skeletonized as these larvae consume the plant tissue of the leaves. Active biological or chemical control is essential, and if you don’t have much information about these larvae, then you can also call the pest management professionals as well.