Chrysodeixis includens

Soybean looper

General

In Brazil, the species has become a serious phytosanitary problem in the soya bean crop, with various outbreaks occurring, either in isolation or associated with the velvetbean caterpillar. C. includens is a polyphagous insect that can develop on at least 73 host plants, belonging to 29 families. Initially, the caterpillars of the pest were observed attacking beans (Phaseolus vulgaris), cabbage, okra, sweet potato, tobacco, and tomato, these being the most frequent host plants of the pest. Later on, attacks on cotton and soya bean were also seen. In addition to these crops, attacks have been seen on sunflower, lettuce, and cauliflower). Despite its wide range of host plants, C. includens is an insect with preference and better adaptation to soya bean.

Appearance and life cycle of the Soybean looper.

The eggs are round and measure about 0.5 mm. They are initially light cream in colour, turning light brown as they come close to hatching. The females lay around 600 eggs. Eggs are deposited singly, mainly on the undersides of the leaves. The embryo takes around 2.5 days to develop. The newly-hatched caterpillars are light green, with longitudinal white stripes and black dots. They reach 40 to 45 mm in length in their final larval stage. With each instar, the caterpillar undergoes a noticeable change in colour, from light brownish-green, to translucid lime green. The Soybean looper has six instars, and characteristic internal processes in the mandible that distinguish it from the cabbage looper Trichoplusia ni. The total consumption of soya bean leaves by the caterpillars is between 64 cm2 and 200 cm2. After the final larval instar, the caterpillar is transformed into a pupa, which takes place inside a cocoon (silk threads), usually on the underside of the leaves. The pupa is pale yellow to pale green in colour at the start of its development, with irregular dorsal pigmentation up to 48 hours before it emerges. The pupal period is completed in seven to nine days, until the emergence of the adults. As the days pass, the pupa become darker. The standard colouration, however, depends on the type of diet to which the caterpillar is exposed. In general, caterpillars of C. includens that feed on leaves will create dark green pupae. Mating occurs at night. The dry period is favourable for its development. The adults are greyish-brown, with two silver markings on the first pair of wings. When at rest, the wings of the moth form an angle of approximately 90 degrees. It has a wingspan of approximately 28 mm. The base of the wing is lighter. The lifespan of the adult moth is around 15 days. Mating usually occurs between at night. The sex pheromone is very important for the females in this process. The biological cycle is around 25 days.

Damage and symptoms

The feeding habit of this caterpillar is ascending: in other words, it feeds from the bottom of the plant to the top. The smaller caterpillars attack the leaves, tearing them and leaving small, light-coloured marks; as they grow, they become more voracious and completely destroy the leaves, damaging even the thinner stems. The stripped leavesgive the plant a lacy appearance. When infestation is high plants have a reduced productivity

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