European apple sawfly

1. Introduction
2. Description
3. Biology
4. Damage
5. Monitoring and threshold
6. 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 1930s. It has been present in southwestern Quebec since 1979 and was first detected in eastern Ontario in 1987. Damage from this insect in Ontario is concentrated mainly in the apple-growing area east of Brockville and the Ottawa Valley. In 1998, European apple sawfly was documented in the Kingston area and by 2008 European apple sawfly spread westward and became established as far west as Port Hope.

Description

Eggs are 0.8 mm long, shiny, oval and transparent. Newly hatched larvae measure about 1.7 mm in length and are light cream coloured with a black head and caudal (rear) shield (Figure 4-56). By the time larvae reach the mature fifth instar, they are 9-11 mm long, and their head and shield have become pale brown in colour (Figure 4-57). There are five larval instars. The adult is 7-8 mm long with light orange to yellow head, antennae, lower body and legs - the upper body is dark brown and shiny (Figure 4-58). The female is slightly larger than the male.

Figure 4-56. Larva of European apple sawfly

Figure 4-57. Mature European apple sawfly larva

Figure 4-58. Adult European apple sawfly (Dr. Charles Vincent, Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC)

Biology

European apple sawfly overwinters as a mature larva in a cocoon a few centimetres below the soil surface. The larva pupates in the spring and adults emerge during the pink stage of apples. The female European apple sawfly lays 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 8-10 days, newly hatched larva burrow into the apple and feed on tissue just below the skin. As the larva matures, it tunnels deeper into the seed cavity and feeds on one or two seeds. Larva often move between developing fruitlets. Larva matures in four to six weeks, then leave the fruit (which has usually dropped), burrow into the soil and form a cocoon in preparation for pupation. There is one generation per year. Diapause may last for up to three years.

Damage

First instar larvae feed beneath the fruit skin and create a heavily russeted, winding, ribbon-like scar that spirals out from the calyx end (Figure 4-59). If larva ceases feeding at this early stage, for whatever reason, this damage will likely be seen on mature fruit at harvest. If this tunneling stops early, tunneling scars are short and indistinguishable from damage caused by the tarnished plant bug.

Figure 4-59. Typical sawfly injury at harvest

Second instar larvae tunnel into fruit towards the seed cavity. Reddish-brown frass is often seen protruding from an exit hole in fruit (Figure 4-60). Larval feeding into the core of the apple often causes fruit to abort, while sub-surface feeding creates scars visible on the fruit at harvest.

As the larva molts and matures, it moves towards the seed cavity or adjacent fruit. As the larva feeds internally, it enlarges its exit hole with wet, reddish-brown frass on the side of the fruit. The larva moves to other fruit in the cluster to continue feeding. A single larva can damage several apples. Damaged fruit drops during the "June drop" period. In insecticide-free apple orchards in Quebec, approximately 4% of the apple crop in affected orchards can be damaged by European apple sawfly.

Figure 4-60. Young fruitlets injured by sawfly larval feeding

Injury from secondary feeding causes 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 from European apple sawfly usually appears before codling moth damage occurs. European apple sawfly damage appears in orchards two to three weeks after petal fall - coding moth larvae and damage appear five or more weeks after petal fall.
   
2. The smell of the frass of European apple sawfly is strong - codling moth frass is odourless.
   
3. European apple sawfly larva is yellowish white and has seven abdominal legs. Codling moth larva is larger than European apple sawfly larvae, pinkish-white in colour and has five abdominal legs.

Monitoring and threshold

Monitor European apple sawfly using 3D visual traps consisting of non-UV white sticky boards that mimic blossoms. (Figure 4-61). 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 woodlots or fence rows. The traps are checked for adult sawflies twice a week.

Figure 4-61. White sticky 3D trap used to monitor adult sawflies

There are two times when European apple sawfly can be controlled with an insecticide:

• pre-bloom - adult European apple sawfly are usually controlled by broad-spectrum 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 are controlled by application of an insecticide. This is the most effective timing for controlling this pest and it is important not to delay this application.

The action thresholds for post-bloom timing are:

• six European apple sawfly per trap if a pre-bloom insecticide has been applied
  
• three European apple sawfly per trap if no pre-bloom insecticide has been applied

Management

European apple sawfly has no known natural enemies in North America. Researchers from Agriculture and Agri-Food Canada have initiated a classical biological program. The species-specific larval parasite Lathrolestes ensator (Brauns) (Figure 4-62), has been introduced to Quebec and eastern Ontario orchards. Once this parasite is established, these sites will be used as seed orchards to disseminate the larval parasite to sawfly infested orchards. This is not a stand alone method of control but is used in conjunction with reduced-risk pesticides and cultural methods to reduce the population of European apple sawfly. For a list of the products available to manage European apple sawfly, refer to OMAFRA Publication 360, Fruit Production Recommendations.

Figure 4-62. Lathrolestes ensator female (Dr. Charles Vincent, AAFC, Saint-Jean-sur Richelieu, QC)