Parasitic Wasps to kill caterpillars
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Butterflies and Moths are beautiful creatures, and are useful pollinators of our plants. However their young can be a terrible pest. Caterpillars eat voraciously as they need to pack in a lot of food in a very short time if they are going to emerge as adults. They are designed to eat leaves and their powerful little biting jaws can munch through swathes of foliage overnight leaving only the ribs behind.
Trichogramma are the most widely used parasatoid in the world and are routinely used to control moths in forests all over China, Russia, and North America. These tiny wasps are less than 1mm in length, and survive only by laying their eggs within the eggs of moths and butterflies, killing the caterpillars and using up their food.
Trichogramma brassicae are supplied as eggs on cards (very like encarsia) and if you hang out the cards in a warm light spot the Trichgramma will hatch out and go seeking suitable food. Trichogramma is best used early season, because it affects the eggs, and has no effect on existing caterpillars or adults.
The females of Trichogramma spp search out suitable host eggs of Lepidoptera and lay eggs within them. When the eggs hatch, the larvae consume the egg contents and then pupate within the empty egg shell or chorion of the host. Small host eggs will contain a single parasitoid larva, but larger eggs may contain more than one.
These host eggs will then produce parasitoid adults, rather than larvae of the host. Crop damage is therefore reduced, but is rarely eliminated completely. The parasitism rates reported in the literature vary widely, with typical reported rates between 40% and 80%.
Trichogramma spp are the most widely used biological control agents in the world.
Cabbage White Caterpillars
The Small Cabbage White Butterfly larva is probably the most destructive of all of the caterpillars, devouring cabbages and other cruciferous crops all over the world.The adult male has one spot on the wing and the female has two - both have a pale yellow underside to the wings. The caterpillars are green and difficult to spot among green leaves, especially when they lie along the ribs. The Large White is a larger version of the small white with much more pronounced black markings. The caterpillars are patterned and larger and much easier to spot.
Codling Moth Caterpillars
There is another caterpillar that does a lot of damage - the caterpillar of the codling moth The caterpillars feed inside the fruits of apple (Malus), quince (Cydonia oblonga), pear (Pyrus) and other wild and cultivated fruit. The adults of the codling moth emerge emerge in late May-June and lay eggs on or near developing fruits from June to mid-July. After hatching, the small white, brown-headed caterpillar bores into a fruit and feeds in the core region for about four weeks until fully grown. Then they hibernate (usually on the ground or under loose bark) and they pupate in the following spring. This life cycle makes it possible to treat the caterpillars in the Autumn, and set traps for monitoring the adults in Spring. Traps for Codling Moth
There are many other caterpillars which damage trees, vegetables, fruit and flowers. Some of the most notorious inside glasshouses are the tortix moth caterpillars and their relatives. Other new problems outside are the oak processionary moth and the horse-chestnut leaf-mining moth. Green caterpillar moths curl the leaves around them like a blanket so they can't be seen. Then there is the Citrus Leaf Miner Moth whose caterpillars leave waxy trails in the young leaves. Traps for Citrus Leaf Miner
Instructions for use
Separate the cards from each other, and hang each one on a branch in a shady place about half way down affected plants. (For smaller plants that won’t support a card just fix the card somewhere near the crop – these are flying insects and will seek their prey). The predators will hatch out of the scales (leaving the black dots still on the cards), and the only time you are likely to see the insects is soon after they hatch, when they may sit on the card before flying off.
Temperatures above 15-20°C give best results, but use early before you get too much damage. Do not use chemical sprays for a month before introducing them. Reduce heavy infestations of caterpillar, as far as possible, by non-chemical means, such as removing affected leaves, before putting the cards out.
Try to keep the cards as cool as possible to avoid them hatching until they are on the plants– 6 to 10 degrees is ideal. The cards should be used within a day or two of receipt.