Leaf miner control

Dac-line s.

Dacnusa sibirica

How does it work?

Dacnusa sibirica is a widespread parasitoid of leafminer larvae. It is commercially of interest as a parasite of Liriomyza bryoniae, and L. huidobrensis, as well as of the Chrysanthemum Leafminer Chromatomyia syngenesiae. It does not perform well against the leafminer Liriomyza trifolii.

It is an endoparasitoid, which lays eggs within the host without immediately killing it. The parasite larva develops slowly within the host, feeding on non-vital tissues until the host pupates. D. sibirica does not, therefore, prevent further leaf damage from occuringoccurring, as leafminer larvae continue to grow and feed, extending the mine, while parasitised. The mine containing the parasitised host larva therefore continues to extend as the larva feeds and grows, so that leaf damage is not stopped by parasitism. With species of Liriomyza, the host larva will emerge from the leaf and may drop to the ground and pupate quite normally, but an adult Dacnusa sibirica will emerge from the pupa instead of an adult leafminer. The size of the next generation of leafminer is therefore reduced.

This is in contrast to parasitism by Diglyphus isaea, where the parasite larva is paralysed and ceases to feed: the mine does not extend, and no leafminer pupa forms. Parasitism by Dacnusa sibirica is therefore less obvious than that by Diglyphus isaea, so that assessment of efficacy is more difficult in the short term.

Dacnusa sibirica is often reported to be more tolerant of low light levels, short days and low temperatures than is Diglyphus isaea. For this reason it is normally recommended that Dacnusa sibirica is used during the winter months in protected crops in Northern Europe, and that it be augmented or replaced by Diglyphus isaea when temperatures and light levels improve in April. Recent results have suggested that failure of Diglyphus in the winter is related more to the timing and method of release than to the weather conditions.

At a constant temperature of 18°C, Dacnusa sibirica develops from egg to adult in approximately 27 days. At 21°C development occurs within 19 days, while at 24°C this reduces to less than 16 days. This is shorter than the development of Liriomyza spp., which taketakes 32, 24 and 19 days respectively at the same temperatures.

A fecundity of 225 eggs per female has been reported at 15°C, laid over a period of 18 days. In the same series of experiments, fecundity was reportedly to reduced to 94 eggs per female at 20°C, and to decreasinge still further at higher temperatures. Oviposition periods decreased to approximately 6 days at higher temperatures. These are laboratory figures, and it is unlikely that the same levels of fecundity will be achieved in a crop, whichere the parasite must search for the host, and where there are many causes of mortality.

When and where should you use it?

Dacnusa sibirica can be used in any crop where Liriomyza spp. or Chromatomyia spp. causecauses problems, and where some damage to the leaves can be tolerated. Use Dacnusa sibirica during the coolest part of the growing season, and avoid using it when temperatures routinely reach 25°C during the day. Make initial introductions when numbers of mines are low, and continue releases until control is obtained.

How should you use it?

Release Dacnusa sibirica into the crop as soon as possible after delivery, ideally in the late evening or early morning. Release in bright sunshine should be avoided, as the parasites may fly to the top of the greenhouse and be lost through the vents.

Keep the bottles cool and horizontal until the parasites are to be released. ready to release the parasites.

With the bottle still horizontal, remove the cap in the area to be treated.

Release the wasps by gently tilting the cap end upwards, and tapping the bottle while walking amongst the plants. Place the bottle at the end of a row when finished to allow any remaining wasps to escape.

When should you not use it?

Do not use Dacnusa sibirica as the sole means of control when leafminer populations are well established, or when large numbers of adults leafminer flies are present. In this situation, reduce the population by making one or more treatments with a compatible chemical (where available) before releasing any leafminer parasitoid.

What will it do?

Dacnusa sibirica will help to maintain populations of Liriomyza spp. and other Dipteran leafminers below economic damage thresholds on tomato crops when used as recommended. It can be used on other crops where some leaf damage can be tolerated. It is recommended that the use of Dacnusa sibirica be combined with that of Diglyphus isaea for optimum control throughout the growing season.

What will it not do, and what are the control options?

Dacnusa sibirica will not normally eradicate leafminers at economic release rates, nor will it give rapid reductions of large existing leaf miner populations, or remove existing damage caused by leaf miner larvae.. It is not suitable for use on crops where there is no tolerance of leaf damage. Dacnusa sibirica is normally used as part of a programme with Diglyphus isaea for optimum control of leafminer. Diglyphus can also be used alone.

The insecticides abamectin and cyromazine may also be used for leafminer control where they are registered on the crop concerned, and are useful where populations are high initially. Abamectin can damage existing biological controls, but surface residues are rapidly degraded by UV light.. It is ideally used to reduce existing leafminer populations early in the growing season. Cyromazine will affect Dacnusa sibirica populations by killing parasitised host larvae.

Chemical compatibility

There are a number of pesticides for whitefly and spider mite control thatwhich are compatible with the use of DDacnusa sibirica..