Night attack by thread caterpillars

“Doughnut” caterpillar is the popular name given to some types of caterpillars that, when touched, quickly curl up, similar to a doughnut, remaining like that for some time, as if they were dead. Caterpillars belonging to the genera Agrotis, Anicla e Perhydrome are popularly known and are part of a complex of thread caterpillars that attack various crops, such as tobacco, tomato, cotton, vegetables, garden plants and other food crops. They are insects belonging to the Noctuidae family, subfamily Noctuinae, have underground habits and are characterized by living, during the day, buried or under cultural debris, close to the plants they attack. At night, to feed, they go to recently germinated or transplanted plants. Damage is characterized by cutting the stem at ground level (collar region) or slightly above (hence the name “cutworm”), causing the plants to fall. Several plants per caterpillar are destroyed in a single night. In tubers, they can cause superficial damage, boring them. Other caterpillars that are not “threaded” in certain situations present themselves as such, and section the base of the plant stem, as is the case of Spodoptera frugiperda, Paracles fusca, Pseudaletia sequax. One of the reasons that seem to contribute to this fact is in relation to human actions, which alter the environment and displace fauna from their natural habitat, such as, for example, the practice of monoculture. In search of other survival niches, in search of food and a place to reproduce, insect species begin to feed on other plants to survive, becoming problems for certain cultures in different situations.

Of the genres mentioned here, Agrotis ipsilon is the most cited regarding the occurrence of soil pests in the establishment of a crop. However, there is a gap in studies that elucidate the species of cutworm that damage crops in different producing regions. This is due to the fact that many screwworms present wide morphological variation in the adult and larval stages, leading to erroneous conclusions regarding the determination of the species(s). Therefore, studies with the aim of understanding the species of caterpillars, as well as elucidating their biology, are extremely important so that control measures can be taken more safely.

Agrotis ipsilon It is a cosmopolitan and polyphagous species, being able to feed on crops in the sowing phase, tuberous plants, vegetables and fruits. A caterpillar it is brown with a dorsal line and black tubercles on each segment; At its maximum size it measures 40mm to 50mm in length. In the first instars it feeds on leaves close to the ground and in the last instars it cuts plants below or at ground level. It is active at night, hiding under leaves or clods of soil during the day. At the end of the larval period, it passes into the pupal stage. It is bright brown in color and measures approximately 20mm to 30mm in length in a loose soil cell. After ten to 20 days the adult with a wingspan of 35mm to 50mm, the forewings being dark grey, sometimes with black spots in the form of a broad transverse band; hindwings pearly with a narrow margin. The thorax and abdomen are gray. Adults lay eggs singly or in groups mainly in weeds. They rarely lay eggs on corn and soybean plants, for example. Thus, areas infested with weeds prior to corn planting are favorable for the presence of weeds. A. ipsilon as they serve as a place for egg deposition. Lower areas in the fields, close to areas with permanent vegetation and excess crop residue (such as in direct planting areas), are favorable to the appearance of A. ipsilon.

Agrotis malefida (Guenée, 1852)

Its host is a wide variety of garden crops and plants. A mariposa Its characteristic wingspan ranges from 28mm to 45mm, forewings with a well-developed clavicular spot, a large, dark kidney and a very small orbicularis. Deposit the eggs in humid places, low stems and foliage. To the larvae They reach around 35mm in length when fully developed. They have a dark gray color on the dorsal and ventral part with two whitish or pale stripes along the sides, separated by a dark line. A pupa is located in the soil.

Underground agrotis (Fabricius, 1794)

O adult It has forewings with a lighter anterior edge and an orbicular and reniform spot with a darker stripe. Wingspan from 34mm to 42mm. You eggs are deposited in small groups on the surface of leaves seedlings close to the ground, on cultivated land or on damp soil. A larva it is gray-brown with faint diagonal dorsal markings. When well developed, it reaches a length of approximately 40 mm. First-instar larvae feed on young leaves near the ground; later they disperse acting as screwworms, they feed at night and hide during the day. The phase of pupa occurs in the soil.

willow peridrome (Hubner, 1808)

It is a polyphagous insect with a preference for vegetables and seedlings, but it also feeds on fruits and sprouts. You eggs They are placed in groups on leaves, branches, on the ground, etc. The larva it has a smooth texture and variable color: from pale gray to soft brown speckled with red and yellow; mid-dorsal line ending abruptly in succession with light spots; W-shaped design and yellow spot on the 8th abdominal segment of the developed larva. Line below the spiracles yellow. O adult has a wingspan of 30mm to 50mm; color varying from reddish-brown to light brownish-gray, with black or brown spots, with a kidney-shaped spot in the center of the forewings; hind wings pearly gray.

Anicla ignicans (Guenée, 1852)

Caterpillar green measuring about 35mm in length when at maximum development, brown to yellowish-brown or bright green in color, sometimes with black spots; with a dorsal line and a prominent subspiracular line; light brown to green reticulated head. A caterpillar it feeds on various native and cultivated plants such as potatoes, tobacco, watermelon, melon and, especially, grasses, such as rice, wheat, oats, corn, ryegrass, etc. Pupates in the ground. Adults They have a wingspan of 30mm to 35mm, light yellowish-brown or grayish-brown forewings speckled with black, with a central spot and pale gray distal margins.

Driving

In Brazil, there is a huge lack of information regarding the management of screwworms. The most recommended control method for controlling screwworms has been the use of baits containing an attractant mixed with an insecticide recommended for the insect and the crop. In Brazil, insecticides are officially registered only for A. ipsilon. The curative application of insecticides to control screwworms has been preferred over preventive application, as it cannot be predicted whether an infestation will occur or whether it will be large or small. Other tools to assist in management, such as the use of degrees/day to predict larval development to know when cutting plants will begin and the use of pheromone traps are already being studied in other countries.

Click here to read the full article in issue 77 of Cultivar Hortaliças e Frutas.