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Worm Control Trichogramma are often recommended for lepidopteran pests. Trichogramma are wasps that are parastitoids of the eggs of other insects. They are some of the tiniest insects on earth. There are many species of Trichogramma wasps, each specialized for different types of insect eggs. Those used to control worms in greenhouses attack many different species of moths, including fruitworms, armyworms, and pinworms. These parasitoids reproduce within the host egg but repreated releases are recommended to ensure the large populations needed for control. The adults are relatively short-lived and will not attack larval stages. Even small numbers of worms can do a lot of damage. Prevention is the best strategy. Make sure to screen all opennings (even window screen will do) and watch for moths resting near entryways and lights from night activity. They can be easily sucked into a negative pressure greenhouse once the outside door is openned. Double entry doors help. Fans used to inflate double layered plastic ceilings can introduce moths if they vent to the inside. Microbial pesticides, Bacillus thuringiensis (Bt) products will help to control the larval stage of moths, the worms. Several types of Bt insecticides are available for the different types of insect pests. Bacillus thuringiensis var. kurstaki is formulated for use against moth larvae, but is most effective on small (young) worms. Larger (older) larvae , especially tomato fruit worms, may not be effectively controlled. To be effective, the microbial toxins must be consumed by the larvae, and in high enough concentrations to disrupt it's gut membranes and allow bacteria to pass into the insect body. The toxin is only effective in the alkaline guts of lepidopterans. Predators can be effective in attacking eggs and small larvae. Lacewings are usually recommended for aphids, but moth eggs are also on their diet. Minute Pirate Bugs attack a variety of small pests, including eggs and small larvae, but are believed to not prefer hunting on tomato leaves, perhaps because of the irritating glandular hairs, and thus tend to leave the crop. The large Chinese Praying Mantis starts small, emerging from overwintering egg cases, and is a voracious predator against most greenhouse pests. However, it also attacks other beneficials. It could be useful if introduced in mid-spring, to combat late season thrips, aphids, and worms. It does not affect predators in the soil media. |
