Various caterpillar pests may infest a wide range of greenhouse crops and are usually easily distinguished from other insect damage by large holes in foliage and black frass, or insect excrement, over plant surfaces. The larvae of a number of species of moth are significant pests of greenhouse crops although most are seasonal. Most commonly found species are the green looper (A. gamma and C. chalcites), larvae of the silver Y moth (A. gamma), diamondback moth (Plutella xylostella) and cabbage white butterfly (Pieris rapae), which are pests of brassica crops, and armyworm, leaf roller and leaf miner species. Most species of caterpillar vary in length from 3 to 5 cm with colour dependent on species and including green, grey, brown, banded or striped. Leaf roller larvae species cause damage by both feeding on foliage and also webbing leaves together to provide protection. Leaf roller larvae may damage fruit and are the larvae of a number of different species of moth.
Prevention and control of caterpillar larvae is relatively straightforward but relies on early detection before foliage damage becomes severe. The adult moths which lay eggs on the crop can be excluded through the use of insect screens over vents and control of entrance ways. Where young larvae are seen, these can be controlled with a number of spray options. These include the use of the bacterial control agent Bt (Bacillus thuringiensis), which is available in a number of commercial preparations. Bt is applied as a foliar spray, ensuring complete coverage, and when ingested by caterpillars produces a bacterial toxin in the alkaline digestive system which immediately stops the insect feeding, and results in dehydration and death within a few days.
There are also a number of pesticides with control activity for caterpillars in a wide range of crops, these need to be
applied early before significant damage occurs. For biological control, the parasitic wasp Trichogramma brassicae can be used to control the larvae of the green looper, while the predatory bug Macrolophus caliginosus consumes moth eggs.
Leaf miners are members of the order Diptera and may be particularly damaging in warm tropical areas. Liriomyza leaf miners are a problem on a wide range of ornamental and vegetable crops grown in greenhouses (Perdikis et al., 2008; Parrella and Lewis, 2017). Leaf miners damage foliage by feeding inside the leaf which creates visible pale markings on the leaf surface.
Heavy infestations can make produce such as leafy greens unmarketable. Control of leaf miner for limited infestations is often by removal of the infested leaves with the larvae inside. For larger outbreaks, a systemic pesticide is required to penetrate the leaf surface and control the pest which is protected from contact insecticides.
Source: A Practical Guide Hydroponics and Protected Cultivation by Lynette Morgan