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BIO-CONTROL OF CANE BORERS Sugarcane crop is damaged by a number of insects. Among them the cane borers cause considerable loss in cane yield and sugar recovery. While leaf sucking insect pests can be controlled with insecticides, the control of sugarcane borers is difficult due to their peculiar feeding habit inside the cane. Biological control has proved to be an effective method of controlling the sugarcane borers, especially stalk borer Chilo auricilius for which no chemical control is yet available. Trichogramma chilonis and Cotesia flavipes are the two main parasites of this borer. Trichogramma chilonis is also parasite of other borers viz. Shoot borer, top borer and internode borer. The two parasites of stalk borer are reared in the biocontrol laboratory. Trichogramma chilonis is a minute wasp-like parasite which attacks the egg stage of its host insect. In the laboratory, it is multiplied on its laboratory host Corcyra cephalonica, also known as rice moth. The rice moths are raised on crushed Sorghum seeds inside rectangular wooden boxes. 2.5 Kg of crushed white Sorghum seeds are placed per box and 0.5 cc of corcyra eggs are spread over it. Before this the Sorghum seeds are sterilized in an oven at 50°C for about an hour to kill the undesirable organisms. Within about a week’s time, the larvae emerge out and start feeding on the Sorghum seeds. From 45th day onwards, the adults of corcyra start emerging. These adult moths are daily trapped and inserted in an oviposition cage where they lay their eggs. A single moth can lay as many as 200 eggs. The eggs fall down through a coarse sieve of the cage and are collected and cleared by passing through a fine sieve. The cleared eggs are sterilized by keeping them under UV ray tube for about 45 minutes so as to kill the embryo. The eggs needed for further raising the corcyra culture are not sterilized under the UV ray tube. The sterilized eggs of corcyra are evenly glued on a piece of card at the rate of about 20,000 eggs per card. These cards are then exposed to the adults of Trichogramma chilonis in the ratio of 6:1 for 24 hours. During this period, the Trichogramma adults will parasitize the corcyra eggs by laying their eggs inside the host eggs, i.e. corcyra, After 5 days of parasitization, the corcyra eggs turn black indicating th development of Trichogramma adults within. On the 6th day these parasitized tricho cards are ready to be stapled on the underside of sugarcane leaf at the rate of 20,000 parasitized eggs per acre.
ROOT BORER STALK BORER The rearing technique of Cotesia flavipes is different from that of Trichogramma. Unlike Trichogramma, which attack the egg stage, Cotesia attacks the larval stage of the host insect. Therefore, here there is need to rear the larvae of stalk borer which act as the host of Cotesia. The larvae are multiplied on an artificially prepared diet depending upon their nutritional requirement. The adults of Cotesia are allowed to parasitize the larvae by exposing them to stalk borer larvae. After observing closely and confirming about the parasitization, the host and the parasite are separated. Stalk borer larvae are again inserted in the tubes having their artificial diet. The Cotesia adults will emerge out once their developmental period is completed and they are then released in the field as adults. The control of pyrilla, a leaf sucking insect is also successful with parasites, Epiricania melanoleuca, Tetrastichus pyrillae and Cleiloneurus pyrillae which can be reared in the laboratory. The names of parasites, predators and pathogens which control different insect pests are as under: Root borer is also becoming a serious insect pest of sugarcane particularly in early high sugar varieties. This insect should be controlled using cultural methods and insecticides. Deep harvesting of cane, irrigating the fields once a month and soil application of Chloropyriphos or Confidor in the last week of August are effective in controlling this insect. White grub has also been observed to damage sugarcane in patches in some areas in India. In Australia white grub is the most serious insect pest of sugarcane. This insect is controlled in Australia with soil application of two insecticides, Biocane and Suscon at the time of planting. Naturally occuring Adelina disease of white grub present in soil has recently been reported to keep this insect in check.While top borer incidence can be kept under control with parasite Trichogramma japonicum and cutting of second brood affected shoots in May, soil application of Phorate and Carbofuran systemic insecticides in June against the third brood is the most effective method of controlling this borer in susceptible varieties.
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