Spodoptera litura (Fabricius)

Spodoptera litura is a sporadic pest of cotton but in years of its outbreak it can create real problems by extensive defoliation of plants. The female lays egg in masses which are covered by scales from female body. The young larvae skeletonise the leaf on which the eggs hatch. As the larvae grow in size, they consume more food and could feed on any part of the leaf. In case of severe infestations, even fruiting bodies are attacked.

Spodoptera litura a polyphagous pest is also known as tobacco caterpillar. It is a serious pest of tobacco nurseries. Spodoptera litura is also a sporadic pest of cauliflower, cabbage, castor, cotton, groundnut, potato and lucerne. It has been recorded from over 100 cultivated and wild host plants. In years of its outbreak it causes serious losses to several crops. The eggs are laid in masses on the under surface of the leaves and are covered by the hairs from female body. On hatching, larvae initially feed in groups and later-on, the larvae spread out and make holes and eat away the entire leaf. If suitable measures are not adopted, the pest is capable of defoliating entire nurseries. If due care is not taken the pest could be carried away along with infested seedlings to the planted crop where the larvae could continue to carry out their damaging spell.

Spodoptera litura is an important insectary host for

parasitoids - Telenomus remus Nixon, Campoletis chlorideae Uchida, Tetrastichus israeli (Mani and Kurian)

predators - Canthecona furcellata Wolff

others, entomopathogens- its own nuclear polyhedrosis virus (SINPV), Steinernema spp., Heterorhabditis spp., Nomueraea rileyi (Farlow) and others.

The culture of Spodoptera litura is started by collecting eggs from the fields of castor, cauliflower, lucerne, tobacco etc. The eggs collected are first kept in a different place than the actual production unit so that the parasitoids emerging and the diseases etc. are eliminated.

The culture can also be established by collecting the gravid females from the light traps. Once the pure culture is established the mass production is commenced from the first laboratory generation established.

Ten pairs of newly emerged moths of S. litura are placed in well ventilated plastic container (20 x 15 cm). The inner walls of the container are lined with paper to obtain eggs. The bottom of the container is lined with sponge covered over by blotting paper. The moths are provided with 50% honey solution, and water on two cotton swabs placed in small plastic cups. The eggs which are generally laid in batches on the paper provided are cut out with the help of scissors. Freshly laid egg masses are sterilized by dipping in 10% formalin for 30 minutes, washed in running water for 30 minutes, dried on blotting paper and kept for hatching in sterilized 20 gms capacity vials.

The eggs can also be surface sterilized in 0.05 per cent solution of sodium hypochlorite (NaOCl) by placing the freshly laid egg masses for 5 minutes. These eggs are washed several times in the running tap water to remove the traces of NaOCl. The traces of NaOCl could be neutralized by dipping the eggs in 10% sodium thiosulphate solution and again the eggs are washed thoroughly under running tap water. The surface sterilized eggs are kept in plastic tubes (7.5 x 25 cm) on moist tissue paper for continuing the stock culture. After 3 days the newly hatched larvae are transferred to bouquets of castor leaves (the leaves are surface sterilized with NaOCl as described for eggs and dried under fan making a bouquet) and kept in plastic container (22 x 15 cm). The bouquets are changed twice a week. The larvae are full fed within 20-28 days and they pupate in the sterilized sand layer provided at the bottom of the container. The pupae are collected 3 days after all the larvae enter the sand. The pupae collected again are surface sterilized with Na OCl as described for eggs. The extra moisture is soaked by the blotting sheet on which the pupae are gently rolled. The pupae are sexed and kept on a lid over a wet sponge in adult-emergence cage (22 x 15 cm). After 10 days freshly emerged males and females are collected daily from their respective emergence cages, with plastic sticks provided touching the top lid for easy movement of the moths emerged in breeding cage used for obtaining the eggs as described above.

S. litura can also be multiplied on semisynthetic chickpea based diet used for Helicoverpa armigera. There are the following five ingredients of the diet which is mainly used at NBAII.

390 ml of water is mixed with A and blended for 2 minutes. Agar - agar is boiled in the remaining 390 ml of water and added to A. Blender is again run for 1 minute. C is added to the mixture of A and B and blender run for 1 minute. Finally D is added. Approximately 20% of the diet prepared (when it is still hot) is poured @ 200 ml diet per petridish while remaining 80% of diet is poured @ about 500 ml per petridish for 1st and 2nd step rearing of the larvae.

In the 1st step of rearing of early instar larvae, the rearing unit is prepared by placing a sponge piece of 25 x 25 x 0.5 cm on a glass sheet of 25 x 25 x 0.2 cm. The sponge is covered with a single layer of soft tissue paper. A small plastic container (3 x 0.5 cm) containing 200 surface sterilized eggs of S. litura is placed in the center over the tissue paper. A petridish (21 x 2.5 cm) containing about 200 ml of diet is placed inverted over the tissue paper. The eggs hatch within 24 h and neonate larvae crawl and spread on the diet.

In the second step rearing of late instar larvae till pupation, translucent rectangular plastic boxes (28 x 18 x 6 cm) with lid are modified to rear the late instar larvae. One window (10 x 2.5 cm) each on four sides of the box is cut and covered with a fine plastic mesh to provide sufficient ventilation and prevent moisture accumulation inside the box. A 2 cm thick layer of the sterilized sand is spread at the bottom of the box. A small piece of tissue paper (15 x 15 cm) is kept at the center over the sand.

The diet in the petridish containing 200 larvae is divided in to five equal pieces. One piece of diet bearing 40 larvae is kept in plastic box over the tissue paper so that the sand does not soil the diet. In this way 5 boxes are charged with larvae from 1 petridish. A plastic grill (26 x 22 cm) with holes (2 x 1.5 cm) is fitted into the box in such a manner so that it form a crest higher than the brim of the box. Thick cake of diet (about 500 gm) in a petridish is divided into two equal pieces. One such piece is kept on the top of the crest and the lid of the box is then tightly fitted so that the diet and grill crest become flat just beneath the lid. After consuming the small quantity of diet on tissue paper the larvae crawl and perch on the grill and feed from the ceiling of the box. The boxes are stacked and left intact for 3 days. During this time the diet is almost completely consumed. Now another piece of fresh diet (about 250 gm) is kept on the crest in each box and the boxes are closed and stacked again. During the last 3/4 days of larval stage the food consumption is maximum and so is the fecal matter accumulation on the sand layer. After 20 days from hatching the larvae bury themselves in sand and start pupating. In a period of 25 days all the larvae pupate and the chitinization is complete. The boxes are now ready for the pupal harvest. The pupae are collected, cleaned, sterilised and placed in adult emergence cages. The freshly emerged moths are then placed in oviposition cages.