Beet webworm Loxostege stricticalis L. is the most dangerous sunflower pest
Ubiquitous in Bulgaria. The caterpillars damage plants from 35 families, especially sunflowers, beets, legumes, cereals, hemp, maize and millet.
In Bulgaria it develops 3–4 generations per year. The imago’s flight is from April to October. The most massive flight is in June–July. Imagoes are active at dusk and at night. One female lays 150–160 eggs on the underside of the leaves. Eggs are laid in a scattered pattern —singly or in groups of 5–10 eggs, over a period of 5–25 days. The eggs are parasitized by a trichogramma. The threshold of economic harm is 5–10 caterpillars/m2. On weak and thinned crops —3–5 caterpillars/m2. The caterpillars feed on the above —ground parts of plants, leaves, flowers and shoots, entangling them with spider threads. Caterpillars carry out mass migration. They pupate in soil, plant debris in vertically arranged cocoons. They overwinter as caterpillars in cocoons in the soil. The meadow butterfly is characterised by periodic mass
Displacement of trichogramma
Scattered egg laying makes it difficult for female trichogramma to displace, as they have poor displacement ability and cannot search for eggs at greater distances. Therefore, a minimum of 3 displacements are required for beet webworm densities.
Monitoring with pheromone traps. In 2–5 males/trap — after 3 days the trichogramma is displaced.
Capsule displacement. At high numbers of the pest 1–2 displacements for each generation at a rate of 200 capsules/ha. In one capsule there are 300–500 trichogrammas, which is 1.2–1.25 g/ha. Mass breeding of the beet webworm occurs at 10–12 years of age. The rest of the time the numbers are not very high.