The cassava hornworm is a major cassava pest in southern Brazil, responsible for crop losses as high as 50% in many areas. The chief means of control has been insecticides which are costly for the country's small farmers. Scientists now believe that the pest can be controlled by efficiently using natural enemies of the hornworm in integrated pest control programs. A new method of biological control, using a virus found in the hornworm's larvae, may totally replace chemical methods. The practice is producing excellent results in hornworm-infested areas of Brazil. Upon application to the crop, the virus kills 90% to 100% of the hornworm larvae.
The hornworm virus, Baculovirus erinnyis, naturally infests cassava hornworm larvae in Brazil, especially in the Santa Catarina area. During initial treatment efforts, infected hornworm larvae were collected from the field, liquefied in blenders, and combined with water in a homogeneous mixture. This mixture was then sprayed on the cassava crop. Recently, researchers have found that infected larvae can also be frozen and stored for a period of time. Furthermore, the virus can be isolated and turned into powder through a laboratory process involving liquefaction, separation, filtration, centrifugation, and vacuum-drying.
Preliminary work on this means of control was done by Brazilian entomologist Aurea Tereza Schmitt from EMPASC (Empresa de Pesquisa Agropecuária de Santa Catarina), who was trained in handling baculovirus at the Centro Internacional de Agricultura Tropical (CIAT) in Colombia. Returning to Brazil, she refined the process so successfully that it is now in widespread use in hornworm problem areas. She also developed methods of freezing and storing liquid extracts from the infected larvae.
In 1986, field experiments were conducted in Columbia to evaluate three sources of virus preparations: 2-year-old powdered virus, infected hornworm larvae frozen for four years, and recently collected infected hornworms. Researchers found that mixtures made from recently collected infected larvae worked most effectively for hornworm control, resulting in 100% mortality within 7 days after application. The virus from 4-year-old frozen larvae produced 67% mortality, indicating that the virus can be stored in infected hornworms for a considerable period. The powdered form of the virus resulted in only 20% mortality, possibly due to the low concentration used.
Today the hornworm virus is being used effectively in many areas of Brazil as a safe and cost-efficient means of pest control. Farmers are shown how to collect, prepare, store, and apply the infected hornworm larvae. The method of use has been described in pamphlets, newspapers, and audiotutorial units and has been broadcast on TV and radio programs in some areas of Brazil. Frozen virus is now available on a semi-commercial basis.
Jack Reeves, Centro Internacional de
Agricultura Tropical (CIAT)
Apdo. aereo 6713, Cali, COLOMBIA