Aphytis

Description

Aphytis lingnanensis

Aphytis are important biological control agents of red scale and other armoured scale insects. They are used effectively in citrus and passion vine where red scale can be a serious pest.

Adult aphytis are tiny yellow wasps capable of short flights within a tree, or from one tree to the next. They are very slow to spread over longer distances. Adult wasps live for about two weeks under field conditions and each female is capable of laying over 100 eggs.

The adult female wasp lays her eggs under the scale cover. After hatching, the developing aphytis larva feeds on the scale insect, ultimately killing it. The next generation of aphytis emerges about three weeks later to mate and continue the cycle. Adult wasps also feed on scales directly.

Target pests

Armoured scale insects, including:

• Red scale Aonidiella aurantii
• Oriental scale Aonidiella orientalis
• Oleander scale Aspidiotus nerii

Armoured scale insects live on plants underneath the protection of hard scale covers. Adult females produce eggs that hatch into crawlers with six legs. Crawlers move to find a suitable place to settle, but can also be spread by wind, birds and fruit pickers. When the crawlers settle, they start feeding and produce circular covers by secreting waxy filaments.

Scale insects feed by sucking sap. They attack all plant parts but are most prominent on the fruit. Heavy infestations may cause discolouration, leaf drop and shoot distortion, leading to bark splitting, twig dieback and even tree death. Chemical control of scale insects is difficult because the hard waxy cover protects them. The development of resistance to pesticides by scale insects is also an increasing problem.

Suitable crops/environments

Citrus is the main crop attacked by red scale, but other hosts include passionfruit, ivy, olives, walnuts and roses. Papaws and a wide range of ornamentals, such as palms and ferns, are hosts for oriental and oleander scales.

Aphytis wasps prefer healthy, well- foliaged trees that provide shelter from extremes of heat and low humidity. Dust is harmful to most beneficial insects and mites, so effective pest management is unlikely in dusty areas such as along roadways. Irrigation can help to minimise dust.

Citrus trees up to three years old are usually poor candidates for biological control because they offer little natural shelter for beneficial organisms.

Before release

Aphytis should be released annually. The wasps may build up naturally without being released, but it will take much longer for numbers to reach those of an orchard where releases have been made. This can lead to higher scale populations at harvest, together with reduced quality and yield.

In winter, cooler temperatures and a change in the availability of suitable stages of scale for parasitism lead to a decline in aphytis numbers. It is best to release aphytis in spring and early summer before the scale insects have built up to damaging levels. Best results will be achieved if multiple releases are made during the season. Avoid using toxic chemicals four weeks before and four weeks after any parasite release.

At release

Aphytis are supplied in paper cups each holding 10,000 wasps. Each cup contains seven green paper strips and a piece of paper towel impregnated with sugar and water as a food source. Release by opening the cup and placing the paper strips, the paper towel, and the lid into individual trees in a regular pattern to achieve the appropriate release rate. The cup itself is placed at the tenth release point. A separate brochure showing recommended release patterns is available on request.

Recommended release rates

• Citrus: minimum 25,000 wasps per hectare (2.5 cups per hectare)
• Passionfruit: minimum 50,000 wasps per hectare (5 cups per hectare)

Aphytis will give best results when used as part of an IPM program including a multiple release strategy. Contact us for details on our attractive multiple release pricing policy.

A note on release rates: Unlike chemicals which generally exhibit a clearly defined dose response curve, with beneficial insects, more is always better. However, they are costly to produce and the goal should be to achieve the best results at minimal cost. We are constantly trying to strike a balance between cost and efficacy. There are many factors that should be considered including the value of the crop, the magnitude of the pest population and the activity (or otherwise) of naturally occurring beneficial species. Also unlike chemicals, where it is common to respond to pest populations that have already exceeded some ‘economic threshold’, we recommend establishing beneficials early in the life of the crop before pest populations reach threatening levels. In most cases our releases are inoculative and we anticipate that our beneficials will establish and breed up within the crop to give long term control. As a general principle, 2-3 releases of modest numbers is better than a single large release – this reduces risk, improves establishment and accelerates the development of multiple overlapping generations of the beneficial species.

After release

It is difficult to detect the adult wasps after release because they spend most of their life cycle developing within and feeding on the scale insects. Microscope examination of scale insects on fruit samples will indicate parasitism levels. Regular monitoring by an experienced scout is recommended to check that the aphytis have established.

Cultural practices to aid establishment

Farm practices that reduce wind, increase humidity and minimise dust in the orchard will aid the establishment of aphytis. Windbreaks and overhead irrigation are effective means of achieving these conditions. Weeds and cover crops between rows also increase humidity within the orchard. Some weeds can be useful as a supply of nectar for adult aphytis to feed on.

High populations of ants interfere with parasites and reduce their performance. In these situations ants should be controlled by selective spraying or should be excluded from the crop.

Chemical use

Aphytis are very effective parasites of scale insects but they are delicate organisms and are easily harmed by pesticides. Nutritional sprays, copper fungicides and some miticides are safe for use with aphytis.

No synthetic pyrethroids should ever be used. Organophosphate and carbamate insecticides are toxic and must also be avoided. If the latter are applied, at least four weeks should elapse before the release of parasites. If a clean-up spray is warranted for scale control, an application of narrow-range petroleum spray oil is recommended. Drift of pesticides from neighbouring blocks should also be prevented.

Aphytis are usually despatched by overnight courier where available and should be received within one or two days. Honey is placed under the lids of the cups to provide food for the wasps.

On arrival, aphytis should be released as soon as possible. In the event of adverse weather such as extreme heat or high rainfall, they may be stored for one or two days before release in a dark room at about 17°C. Aphytis should not be refrigerated. Extra honey should be placed under the lids as food for the wasps if the original supply has already been consumed.

Other natural enemies of red scale

• The small parasitic wasp Comperiella bifasciata
• The scale-eating ladybird Rhyzobius lophanthae
• The predatory ladybird Chilocorus circumdatus