# Bt insecticide and row covers: match the method to the pest URL: https://leafwrit.com/mt/biological-control-malta/ Reviewed: 2026-10-29 ## Bt insecticide and biological control: identify the method before using it Match a Bt insecticide to the identified pest and larval stage. Bacillus thuringiensis is a soil bacterium. Its strains affect different insect groups, including caterpillars and other larvae. Check the strain and target on the product label. Susceptible larvae must eat Bt, and young larvae are most affected. Apply an authorised formulation where those larvae feed, following its label instructions. Commercial Bt preparations contain other ingredients as well as the bacterium. Read the complete formulation, handling instructions and safety information. Match the actual product through the [Maltese authorisation route](/mt/authorised-pesticides-malta/). In the professional or non-professional product categories, find the exact registered name. Open its linked label documents and check current administrative status for the intended use. Compare the formulation and concentration against the supplied pack before deciding. For a Bt offer, distinguish the species, subspecies or strain, formulated concentration and intended target. Spores allow reproduction; insecticidal proteins act after susceptible larvae eat them. Plant-incorporated Bt protectants are produced within transgenic crops, while microbial sprays are separate formulations. On foliage, UV light, weather and plant enzymes break down Bt; spores also wash off. Use the formulated product’s label for storage and repeat-treatment instructions. ### Compare Bt strain, feeding mechanism and preparation Bt aizawai and Bt kurstaki target caterpillars of moths and butterflies. Bt israelensis targets immature mosquitoes, flies and gnats. Bt tenebrionis and Bt japonensis target beetle larvae. Read the strain designation beside the pest name when comparing a proposed microbial product. After ingestion, Bt toxins activate in the susceptible insect’s alkaline gut and break down its lining. The larva dies through infection and starvation. This feeding mechanism makes access to treated food important: distinguish an exposed young caterpillar from a larva already sheltered in a fruit cavity. Commercial preparations include sprays, dusts, granules, concentrates and pellets. Check the form supplied with the quotation and the handling instructions for that preparation. During mixing, assess the complete formulation and the exposure created by pouring a dust or measuring a concentrate. ### Bt spores after application Soil microbes can break down spores, and acidic soil reduces their growth into new bacteria. Spores can remain dormant in most natural soil conditions. On plants, material can arrive naturally in rain splash from soil or through infected insects and animal droppings. ## Before choosing the best insecticide for corn earworm: identify the caterpillar Before choosing a natural pesticide for caterpillars on plants, identify the species, feeding site and finished formulation. The natural option described above is Bt: the aizawai and kurstaki strains target caterpillars of moths and butterflies. If you need an organic caterpillar pesticide, ask your control body to assess its use within the certified system. In Maltese potatoes, corn earworm refers to Helicoverpa armigera, also called cotton bollworm. After the first captures, intensify monitoring on the crop. Helicoverpa zea is the species called corn earworm or tomato fruitworm. Newly hatched larvae have dark heads, conspicuous tubercles and hairs. Larger larvae vary greatly in colour. Examine fine lines, bristle bases and short spines when identifying a specimen. Helicoverpa zea eggs are ribbed and slightly flattened at the top. Their ribs are coarser than the striations on looper eggs. Photograph an egg under magnification to show that surface structure. Larvae enter fruit and sometimes move between fruits. Internal cavities contain waste and cast skins. Check the feeding site before assessing how a proposed intervention would reach the larva. ## Before choosing the best insecticide for rice bug: identify the feeding site Ask what the name rice bug describes before choosing a product: developing grain in the field and insects in a grain store require different investigations. Leptocorisa acuta adults and nymphs feed on grains at the milky stage. Feeding leaves brownish discoloured patches on the husk and chaffy grains. Examine grain development alongside the insect. In a standing rice crop, examine flowering and grain filling alongside insect feeding. In stored grain, inspect beetles, moths, concealed immature stages and residues in handling systems. Keep the crop or store identity with the specimen. ## Row covers for crops: keep pests out while maintaining crop access When comparing a floating row cover with supported crop covers, check material, aperture, plant clearance and pollination access. Covers change temperature and moisture according to fabric weight. Check conditions beneath the material alongside crop height and flowering. Fabric touching plants can cause sunburn and allow insects to nibble through the mesh. Maintain clearance as foliage grows and follow the material’s installation instructions. Secure cover edges against the soil. Reseal them after weeding or harvest and repair holes. Inspect the perimeter as well as the fabric over the crop. Cucumber varieties requiring insect pollination need pollinator access during flowering. Parthenocarpic varieties set fruit without pollination. Establish which variety you are growing before closing a cover. Use parthenocarpic cucumber varieties when the enclosed crop will not receive insect pollination. Inspect cucumbers inside the cover for spider-mite injury as well as beetle feeding. Check the barrier outside: mites can cause substantial damage beneath netting. Non-woven polyester or polypropylene covers differ from insect mesh. Floating fabric offers frost protection as well as pest exclusion, with protection varying by fabric weight. Insect netting admits air, water and light while acting as a barrier. Compare weight, permeability, durability, aperture, support and price. Pests can persist in soil, weeds or debris before a cover is installed. Inspect the bed and remove infested host material before enclosure. Pests already beneath the cover may increase while natural enemies remain outside; Phytoseiulus persimilis, which preys on twospotted spider mite, is one such enemy. ### Install the barrier before pest arrival Choose mesh fine enough to exclude the target insect. Install the cover at planting or during the crop’s vulnerable stage, before insects reach the host. Plan mulching and weed access before closing the tunnel. Secure edges with sandbags, rocks, bricks or buried fabric, and allow enough slack or support for continued growth. Compare installation labour with time spent opening the enclosure for harvest and resealing it. For pollinated crops, include access for bees in that work plan. Inspect the covered plants for retained pests, overheating and moisture changes as growth fills the available space. ## Next step Identify the pest and feeding stage, then check the proposed formulation through the [Malta authorisation guide](/mt/authorised-pesticides-malta/). Keep the observations in the [IPM monitoring sheet](/mt/ipm-monitoring-sheet/) and compare leaf damage with the [tomato pest guide](/mt/tomato-pest-management/).