General
The southern armyworm (Spodoptera eridania) is a pest of various agricultural crops in Southern and Central America and the Caribbean. It is a polyphagous species that attacks corn, cotton, rice and soy crops, amongst others. It is considered a pest in areas of cultivation in the savannah.
Appearance and life cycle of the southern armyworm.
A female can lay up to 1000 eggs. The eggs are subspherical, laid in groups on leaves and are generally covered with scales derived from the abdomen of the females. The egg stage lasts for 4 to 6 days. At first the eggs are greenish, and become brown before hatching. The caterpillars go through six instars and are generally found on the lower surface of the leaves, and are more active at night. The development of the larvae takes approximately 14-20 days. Larvae are green or blackish green with a uniform light brown or reddish-brown head throughout the period of development, although their colour pattern is quite variable. When they are fully developed, they have two longitudinal yellowish stripes along their sides, and one on their back. They also display sclerotized regions located on the pronotum and at the end of the abdomen, which is an important characteristic for identifying the species. The pupae are dark brown and 10 to 18 mm long and 5 to 6 mm wide. Pupation only occurs in the soil at a depth of 5-10 cm and lasts 11-13 days. The moths are sturdy and have a wingspan of 28-40 mm, generally greyish-brown in colour, with a black dot at the centre of the forewings and whitish hindwings. They measure approximately 40 mm in wingspan.
Symptoms and damage
The caterpillars cause serious leaf loss and feed greedily when they are young, often leaving only the stems. When they mature, they become solitary and feed on fruits. They feed in an upward direction. S. eridania occurs frequently in soybean and cotton, causing loss of leaves, reducing production of pods and flower buds, impeding normal development of the plant, and opening the way to fungi that cause rotting of pods (soybean) and flower buds (cotton). They are also a notable pest in other crops such as corn, beans, tomato, sorghum, orchards, and vegetables, damaging different plants with feeding, which can cause significant harm.