Blastobasis moth – additional information

Life cycle

There is one generation per annum in the UK with a very small partial second flight of adults in the autumn and early winter.

Adults of the first main generation fly in June and July, about the same time as codling moth.
Eggs are laid (on average 70 per female at a rate of 20 per day) on foliage or amongst debris on the tree. Eggs kept at constant temperatures of 8, 18 or 25oC hatch after 44, 7 and 4 days respectively.
Larvae occur from July to October. Initially, they feed on debris such as in the rolled edge of a dead leaf, in a dead flower or burrowed into shrivelled fruitlets.
Older larvae construct a shelter of dead leaves and flowers webbed together.
Damage to fruits occurs from late July onwards consisting initially of small single holes. As the larvae grow the damage becomes more extensive.
When fully fed in the autumn or early winter, larvae leave their feeding sites and move to the soil or amongst debris on the ground where they form a silken cocoon in which they pupate.
A small proportion of very early maturing larvae pupate and emerge the same year, giving rise to a small second flight in the autumn or early winter. If eggs are laid, they are unlikely to develop successfully.

Pest status

A serious, but local, pest of apple, especially Bramley. Attacks foliage and fruit.

Other hosts

Apple and beech appear to be the main hosts in the field. The pest can be abundant in beech hedges, which can act as a source of infestation for apple orchards.

In the laboratory, the larvae will feed on the leaves of a wide range of plants including alder, beech, blackcurrant, bramble, cherry, Cotoneaster, dock, hawthorn, field maple, pear, plum, rose, sallow (Salix sp.), and strawberry.
They can also be reared to adult on rose hips, hawthorn berries and dead leaves and flowers of apple trees.

Varietal susceptibility

It is probable that all apple varieties may be attacked but there are considerable differences in the susceptibility of different varieties:

Varieties with fruits that are short stalked and/or which hang in clusters and where dead leaf and flower debris accumulates round the stalks tend to suffer the most damage.
Bramley and Egremont Russet are amongst the most susceptible.
Cox and Worcester are moderately susceptible, Golden Delicious is less susceptible.

Distribution

A native of Madeira, it was first found in Britain in 1946 initially restricted to the London area. Now widely distributed and locally common especially in beech hedges and apple orchards in some localities.

Damage

Larvae feed on the flesh of apple fruits around the stalks or where fruits are touching or where fruits are in contact with leaves or branches.

They tie leaves and plant material together with silken webbing to make a shelter often attached to the surface of a fruit or branch.
Large areas of skin and flesh are removed, wounds tend to weep and becoming covered by a sticky mass of black frass.
They are usually surface feeders but sometimes penetrate more deeply into the flesh.
Crop losses can be very high, approaching 100%.
Larvae also feed on the bark of branches and the wounds may become infected with canker.

Other pests with which Blastobasis may be confused

Larvae of several leaf-rolling tortrix moths cause similar, though less severe damage, including larvae of the summer fruit tortrix moth, Adoxophyes orana.

The damage caused by Blastobasis tends to be more severe and wounds tend to weep and become contaminated with black frass and there are deeper excavations into the flesh.

Recognition

Adult (resting)
9-11 mm long, forewings pale ochreous yellow each with four darker spots and scattered darker scales. Hindwings paler. Lie still when disturbed (e.g. by beating) characteristically scuttling round on its back sporadically.

Egg
Very pale green becoming orange-brown prior to hatching. Oval, 0.7 mm long and 0.4 mm wide. Eggs can be laid on the undersides of leaves and on dead leaves in the tree.

Larvae
Up to 10-13 mm long; purplish-brown and shiny, lighter underneath. With a darker head and prothoracic plate, rather plump.

Other pests with which Blastobasis may be confused
Larvae of several leaf-rolling tortrix moths cause similar, though less severe damage, including larvae of the summer fruit tortrix moth, Adoxophyes orana.

The purplish-brown colour of Blastobasis larvae is distinctive.

Monitoring

Beating for adults
Unlike most moths, adult Blastobasis can be sampled using the beating method, as when dislodged from the vegetation they do not fly but fall onto the beating tray, where they either lie still or scuttle around on their backs.

Beating should be used to determine the flight period.
For each beat sample, a sharp tap should be made to a branch with a beater over a beating tray.
No economic thresholds have been developed but presence of the moth is probably sufficient to justify the application of insecticide treatment.

Fruit damage
Inspecting fruits for damage, either whilst developing on the tree, windfalls, at harvest, or during grading (remembering that badly damaged fruit may have been discarded at harvest), indicates if the pest has been present and whether treatment is likely to be required the next season.

Pheromone traps
The sex pheromone of Blastobasis has been partially identified by East Malling Research and Natural Resources Institute. Attractive lures have not yet been developed.

Forecasting

Forecasting methods for Blastobasis have not been developed. However, limited information indicates that the first adult flight starts at approximately 130 day degrees above 10oC and the peak flight occurs at approximately 240 day degrees.

Chemical control

Blastobasis often goes unnoticed until harvest when the damage is done and it is too late to take remedial action for the current season. Insecticidal controls need to be timed to control caterpillars as they hatch from eggs.

The flight and egg hatch of blastobasis coincides approximately with that of the first generation of codling moth, so sprays times for codling moth that are effective against Blastobasis should control both pests.
Chlorantraniliprole (Coragen) offers incidental control of blastobasis when applied for Codling moth control. For best fruit protection, it should be applied during egg-laying at the ‘ovicide’ timing, before egg-hatch and fruit penetration occurs.
Pyriproxyfen (Harpun) is approved for use on apples to control codling moth and may offer incidental control of blastobasis. It inhibits egg hatch, metamorphosis of nymphs to adults and reduces the fecundity of adult females. However, as a new product to the UK in 2020, further experience of its use is required to inform growers and agronomists of its efficacy at controlling blastobasis.
It is probable that indoxacarb (Steward or Explicit) is also effective.
The insecticidal protection should be maintained continuously by spraying a suitable insecticide at 2-3 week intervals from 1 week after the start of the flight period until 2-3 weeks after the end of the flight period, remembering that the maximum number of applications of any insecticide used.
Bacillus thuringiensis has little activity against blastobasis.
Synthetic pyrethroids are highly effective but their use should be avoided because they are harmful to the orchard predatory mite Typhlodromus pyri.
It should be noted that the use of the sex pheromone mating disruption system RAK 3+4 for codling moth and summer fruit tortrix moth control, fails to control blastobasis, so careful monitoring should continue for blastobasis with this system and be prepared to use specific control measures.

Insecticide resistance

Resistance of blastobasis to insecticides is not known to occur but has not been investigated.

Cultural control

Cultural control options for this pest are limited. Beech hedges often harbour the pest, so removal of these if the pest is present is likely to be helpful.

Thinning fruits so that they only occur singly will also reduce damage substantially.
Where larvae are found on fruits during picking at harvest, they should be killed.

Natural enemies

Little is known about the natural enemies of blastobasis. No parasitic wasps have been reared from samples of larvae collected in the field.

It is probable that a wide range of generalist insect predators such as anthocorids, mirids, lacewing larvae, earwigs etc. feeds on eggs and young larvae.
Numerous earwigs are often present in the vicinity of semi-mature caterpillars feeding in shelters amongst fruits and leaves.
The shelters appear to provide good protection against them but, sometimes, vacant shelters occupied by earwigs are found giving the impression that earwigs might be important predators of blastobasis.

Biological control

Biological control methods have not been developed. Unfortunately, sprays of Bacillus thuringiensis have only limited efficacy against the pest.

Apple Best Practice Guide