Field release of egg parasitoid

In Sri Lanka, farmers have begun cultivating in the Yala season. But for maize farmers the severe damage caused to their crops due to the Fall Armyworm (FAW) infestation during the Maha season, particularly from November – December last year is still fresh in their minds. Alarmed by the heavy foliar damage caused due to FAW infestation, farmers set fire to their maize cultivations during this period in a state of panic, little realizing that the pest was here to stay. The average yield loss due to Fall Armyworm in the Maha season was later estimated as 12 percent according to the Department of Agriculture.

The Department is using the ongoing Yala season to conduct on-field research and studies of fall armyworm behavior and experiment sustainable control mechanisms. 

An important action was to explore and utilize biological control measures, particularly the use of natural enemies such as predators, parasitoids and pathogenic microbes for fall armyworm management in the field. The aim of this activity is to minimize the indiscriminate use of pesticides by farmers as it destroys the natural enemies of the fall armyworm. The use of pesticides also has a heavy economic burden on smallholder farmers who have to continuously apply pesticides after the first spray. Some of the pesticides do not work in fall armyworm control as the pest becomes resistant to it while exposure to pesticide can be toxic for farmers and the environment.  

Implementation of an Integrated Pest Management (IPM) mechanism with more emphasis on biological control methods and conservation of natural enemies is another key action undertaken.

The Department of Agriculture with technical assistance from the Food and Agriculture Organization of the United Nations (FAO) has begun island-wide surveys to identify some prominent natural enemies. Two prominent parasitoids; an egg parasitoid and a larval parasitoid, have so far been identified by the Horticultural Crop Research and Development Institute (HORDI) in Gannoruwa.

The larval parasitoid belonging to the Tachinidae familyare tiny fly species commonly found in maize growing areas of Sri Lanka. This species lays its eggs directly in the body of the fall armyworm caterpillar and the parasitism rate in chemically untreated maize fields in Gannoruwa, Ambagaswewa, Redeemaliyadda and Meegahakula exceed 80 percent.  

The egg parasitoid (Telenomous remus) is a wasp, 0.6 mm in size, that lays its eggs inside young fall armyworm eggs thereby attacking the fall armyworm. According to Senior Entomologist at HORDI, Dr. Nimal Premaratne Bandara, these parasitoids were collected from chemically untreated or neem extract treated maize fields in January and February this year at the Seed Certification Service Field at Gannoruwa, Peradeniya. “We estimated this egg parasitoid parasitized around 80 to 90 percent of fall armyworm eggs,” he says. The offspring of the parasitoid develop within eggs of the fall armyworm of which they then emerge as adults. Field release of laboratory multiplied adult parasitoids were initiated in fall armyworm affected maize fields in the Uva Province of Sri Lanka, commencing from April this year. Approximately 600 adult parasitoids (3-5 days old) were released in three maize fields (40 days aged crop) in the Mahayaya area in Pinnagolla, Mahiyanganaya and another 700 adult parasitoids released in a 5-acre maize field in Mahakumbura, Amunuyaya. It was observed, that the parasitoids had naturally spread to surrounding fields as well.

“When the insects were released, I was worried about the repercussions. I was worried that my crop will be destroyed,” said a farmer. “But agriculture officers informed us that some of these pests exist in our fields and they helped us to identify the natural enemies. Now neighboring farmers too are eager to adopt these natural control methods.”

The initial observations have shown that the use of these natural enemies are positive. The Fall Armyworm Task Force has decided to conduct Integrated Pest Management (IPM) demonstrations combining with the release of parasitoids in four districts for further observations. The results from these field experiments will be necessary to build the confidence of farmers who resort to spraying pesticide as soon as fall armyworm infestation is evident. Therefore, the outcome of the studies conducted will be transformed to action through farmer field schools, field days and demonstrations.

Under the FAO funded project, Emergency Response to Enhance Technical Capacity for Early Warning, Monitoring and Management of Fall Armyworm in Sri Lanka, the Department of Agriculture will be conducting investigations and research to identify potential natural control mechanisms. This includes laboratory rearing, identification, multiplication of prominent predators, parasitoids and pathogenic microbial, inoculate and introductory release in affected maize fields and enhancement of the habitat of these natural enemies.