European Apple Sawfly

Table of Contents

1. Introduction
2. Description
3. Biology
4. Damage
   1. Primary
   2. Secondary
5. Monitoring and Management

Introduction

The European apple sawfly, Hoplocampa testudinea (Klug), is a small clear-winged wasp-like insect accidentally introduced into New York from Europe in the late 1930's . It has been present in southwestern Quebec since 1979 and was first detected in eastern Ontario in 1987. Damage from this insect in Ontario has been concentrated mainly in the apply-growing area east of Brockville and the Ottawa Valley. In 1998, the first European apple sawfly was documented in the Kingston area.

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Description

The adult sawfly is 6-8 mm long (Figure 1); the female is slightly larger than the male. The head, antenna and lower body surface are light orange to yellow; the upper body is dark brown and shiny. The larva measures about 1.7 mm in length at hatch and is light cream coloured with a black head and caudal (rear) shield (Figure 2). By the time the larva reaches the mature fifth instar, it is 9-11 mm long and head and shield have become pale brown in colour.

Figure 1. Adult European apple sawfly.

Figure 2. Larva of European apple sawfly.

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Biology

European apple sawfly overwinters as a mature larva in an earthen cell a few centimetres below the surface of the soil. The larva pupates in the spring and adults emerge during the pink stage of apples. The female European apple sawfly lays its eggs just after the king flower opens. Eggs are deposited singly at the calyx end of the flower, often at the base of or between the stamens.

After eight to ten days, new hatched larva burrows into the apple an feeds on tissue just below the skin. As the larva feeds in the apple, it moves towards the seed cavity and feeds on one or two seeds, then it migrates to another nearby fruit. Larva matures in four to six weeks, then leaves the fruit (which has usually dropped), burrows into the soil and forms a cocoon in preparation for pupation. There is one generation per year. Diapause may last for up to two years.

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Damage

European apple sawfly causes two types of injury to the apple:

Primary

Caused by first instar larva through feeding just under the skin of the fruitlet resulting in a heavily russeted, winding, ribbon-like scar that spirals out from the calyx end (Figure 3).

If the larva ceases feeding at this early stage for whatever reason, this damage is likely to be seen on mature fruit at harvest. If this tunneling stops early, the tunneling scars will be short and indistinguishable from damage caused by the tarnished plant bug.

Figure 3. Typical sawfly injury at harvest.

Secondary

As the larva molts and matures, it moves towards the seed cavity or adjacent fruit. The larvae's feeding to the core usually causes the fruit to abort (Figure 4). As the larva feeds internally, it enlarges its exit hole with wet, reddish-brown frass on the side of the fruit.

The larva will move to other fruit in the cluster to continue feeding. Damaged fruit will drop during the "June drop" period.

Figure 4. Young fruitlets injured by sawfly larval feeding.

Injury from secondary feeding will cause the fruit to drop. Secondary injury by European apple sawfly can be confused with codling moth damage. There are three ways to distinguish these two pests:

1. Damage of European apple sawfly usually appears before codling moth damage occurs.
2. The smell of the frass of European apple sawfly is strong, whereas codling moth frass is odourless.
3. European apple sawfly larva are yellowish white in colour and have seven abdominal legs. Codling moth larva are pinkish-white in colour and have five abdominal legs.

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Monitoring and Management

European apple sawfly are monitored using three-dimensional visual traps consisting of non-UV white sticky boards that mimic blossom colour (Figure 5). Three traps are placed in trees between tight cluster and pink and remain in the orchard until two weeks after petal fall.

They are positioned ideally on the south side of the tree at eye level and along edges of the orchard bordering wood lots or fence rows. The traps are checked for adult sawflies twice a week.

Figure 5. White sticky board used to monitor adult sawflies.

There are two times when European apple sawfly can be controlled with pesticide.

• Pre-bloom - adult European apple sawflies are usually controlled by insecticide applied at pink to control tentiform leafminer or spring feeding caterpillars.
• Post-bloom - shortly after bloom, young, newly hatched larvae of European apple sawfly can be controlled by application of organophosphate insecticide. This is the most effective timing for controlling this pest and it is important not to delay this application from this timing.

The action thresholds for this timing are:

• 6 European apple sawflies per trap if a pre-bloom insecticide has been applied.
• 3 European apple sawflies per trap if no pre-bloom insecticide has been applied.

Chemical thinning of a heavily set apple crop can reduce damage. Further hand thinning to break up apple clusters may help in preventing larvae from moving from one apple to the next.

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