Ion Staunton*

You have hidden enemies: the pests that work away inside plant tissue.

These pests are not shy; they just choose to get inside because they can, the tucker is good… and because they have less trouble with predators (and growers).

 Codling (and other) moths

Just to be different, let’s start the life cycle with the pupae, the longest stage in the third generation of the season.

When finished its destruction of the inside of an apple, the fully-fed pinkish larva, now about 15mm long with a dark brown head leaves the fruits and heads to the trunk of the tree attaching itself to the bark while spinning its cocoon. By the time you’ve picked the last of your fruit in autumn, next year’s pest problem is waiting in residence in (almost) plain sight if you go looking.

Codling Moth does not have an alternate host plant as do Light Brown Apple Moth and others that can be hosted on other vegetation… even the weeds between the crop trees.

The Codling Moth cocoon survives the winter and when the spring days lengthen and warm, the first of three generations p.a. of moths emerge, mate and the female (about 10mm long and with brown-grey banded forewings with a fringe, held along the body) chooses to lay single flat eggs on new fruit just after petal fall or on a nearby leaf. Once hatched, the tiny white caterpillar with a black head moves to the developing fruit and bores down inside, usually adjacent to the stalk.

They moult about five times as they outgrow their cuticle before leaving the fruit between two and four weeks later and head off to pupate in the cocoon stage on the bark… they can’t help repeating their routine.

The second generation of the codling moth is a little faster, getting through in about five-to-six weeks and the third generation (which includes the overwintering cocoon) is often more than six months. 

By the way, you may well find cocoons in crevices in and around your packing shed,

The ‘good thing’ is that the moths do not fly far.

Your population of codling moths are essentially yours alone, mostly confined to your orchard (unless you have a next-door apple grower with only a wire fence as a boundary.

Control. In the ‘olden days’ pupal traps meant wrapping the trunks using hessian or corrugated cardboard to encourage pupation… but that is time consuming and if you forget to destroy the pupae before spring, you just increased your problem. Parasitic wasps do a better job because they ‘know’ where the pupae are. A virus has been successful, but you need to time its application carefully.

There are also pheromone tactics being used.

Pheromone traps can catch male moths and when you notice the increase in catch, you can possibly predict when the next egg-hatching is likely to occur so you can time a residual (or systemic) insecticidal application to kill the little caterpillars before they enter the plant (or have the systemic insecticide circulating in readiness).

The other pheromone tactic is to use slow-release dispensers to ‘saturate’ the orchard air, which confuses the hell out of the moths looking for a mate… and yes, this sexual disruption still results in less egg laying and fruit infestation.

There are about 90-odd products registered for codling moth control with the AVPMA. Talk to an agronomist or your insecticide reseller for more detailed advice.

Note. There are other ‘insider’ caterpillar pests such as yellow peach moth (which also gets into custard apples), oriental fruit moth which bores into the growing tips of peaches, nectarines, etc., so that the tip dies before branching into multiple shoots and then the caterpillar goes looking for fruit.

Macadamia nut borer moths lay a scale-like egg on or near the nut and about five weeks later the moth emerges from a badly damaged nut.

And then there are leaf miners (a minor pest).

A tiny moth lays its eggs on the underside of young leaves and the hatching caterpillar burrows in under the surface to eat between the upper and lower surface.

You will see pale trails as the result of this mining process.

The pupal cocoon is usually on the edge of the leaf and the whole process takes about three weeks.

Citrus Gall Wasp

About 2mm long, the shiny black female wasp (four wings) lays eggs just through the new bark of citrus in spring.

The larvae feed in the sap stream until mid-winter and then pupate still inside the distorted gall, which the plant has built around them.

The new adults emerge in spring, mate and lay eggs within a couple of weeks and so the life cycle is one year almost to the day.

The disruption of the flow of plant nutrients in an attempt (futile) to rid itself of the invading larvae makes the twisted gall and doubtless restricts the flow of nutrients to fruit.

Control is by systemic insecticides (be aware of withholding periods) or by another native, parasitic wasp. The gall is usually pruned out by growers as soon as it is noticed… why not?

Fruit fly

The Queensland Fruit Fly has become so famous it is now referred to as QFF.

And it is a true fly.

The adult is about 8mm long, has a pair of membranous wings and a couple of halteres, or balancing clubs, which are the modified wings just astern of the real wings (wasps of similar size and appearance have four wings).

The head is mostly reddish eyes, sucking mouthparts and, the thorax and abdomen are brownish with a yellow triangle at the junction.

Eggs are laid in small batches into fruit as soon as the female’s ‘pressure test’ tells her that she can pierce the skin.

The hatching, legless maggot will be able to start eating its mostly liquid diet as it grows to about 7mm long. Pupation is in the soil.

Fruit that has been picked and discarded is even more preferred for egg-laying.

Maggots hatching in such a dump are immediately in gourmet ‘heaven’ because they hatch inside juicy fruit.

The timing of the cycle speeds up as the weather warms up (and the fruit gets softer and juicier). The egg and larval stage is about eight or so days and the pupal stage is about six days as the maggot transforms into an adult, which can live for many months feeding on juices.

Control is improving. Once it was just traps to entice adults inside, then came various systemic insecticides which are sprayed on the leaves and absorbed into the sap stream, which becomes toxic to the maggot feeding inside the fruit.

Now there are serious gains being made releasing sterilised males to disrupt egg production. The Government is nearby to help you. But you already knew that.