General
The velvetbean caterpillar Anticarsia gemmatalis is considered the main foliage feeding pests in the Americas and is one of the most common species affecting the soya bean crop. Its season of occurrence is correlated with the latitude where the crops are located; it has been observed that at lower latitudes, the attacks occur earlier while in the south of the country, the attacks occur later. It attacks Alfafa (Medicago sativa), Cotton (Gossypium hirsutum), Peanut (Arachis hypogaea), Rice (Oryza sativa), Potato (Solanum tuberosum), Broccoli (Brassica oleracea L. var. italica), Sugarcane (Sacharum officinarum), Collard greens (Brassica oleracea), Cauliflower (Brassica oleracea var. Botrytis), Peas (Pisum sativum), Beans (Phaseolus vulgaris), Tobacco (Nicotiana tabacum), Manioc (Manihot esculenta), Passion Fruit (Passiflora edulis), Maize (Zea mays), Rubber tree (Hevea brasiliensis), and soya bean (Glycine max).
Appearance and life cycle.
The eggs are round, initially green but turning reddish-brown over time. They are usually deposited singly, on the undersides of the leaves or occasionally, on the stems and petioles. The eggs are laid in early night, As the temperature drops and the humidity increases, the egg-laying increases. The caterpillars vary in colour from light to dark green, and hatch two to three days after the eggs are laid. The larval stage generally includes 5 or 6 instars but may include up to 8 instars. Caterpillars larger than 15 mm may be green or black and have three longitudinal white lines along the back and four pairs of abdominal legs, as well as a terminal pair. It loops as it crawls and is often confused with the small Soybean looper caterpillar (Chrysodeixis includens). The pupa is light green, turning a shiny, dark brown over time. The length of the pupal stage varies, depending on the temperature. The warmer the temperature, the shorter the pupal stage. The adult moth is greyish-brown. It has a characteristic line that runs diagonally across both wings. In conditions of high infestation or food shortages, its colour darkens. During the day, these months can be found in shaded spots, at the base of the plants. The life cycle is completed in 33 to 34 days, and there may be four or six generations per year.
Damage and symptoms
The younger caterpillars tear the leaves, causing small, light-coloured marks, initially perforating the leaves but leaving the central and lateral leaf veins intact. The leaves consumed in the first three stages (caterpillars up to 10 mm) make up 5% of the total amount consumed throughout its lifetime. From the fourth to the sixth stages, the caterpillars consume around 95% of the total, which is 100 to 120 cm2 per caterpillar. If not controlled in time, this insect can strip large quantities of leaves (> 30%), causing loss of productivity in the crop.
It occurs mainly between November and March, with a population peak in from January or February, depending on the region. The velvetbean caterpillar can strip an entire crop of its leaves if not controlled in time.