Cannibalism being tested for pest control

Herbivorous pests such as the fall armyworm eat each other when their food is of poor quality or if it runs out, new research published in the journal Nature Ecology and Evolution has shown.

Biologists from the University of Winconsin in the US used tomato plants to study how cannibalism can be used as a pest management strategy. They set caterpillars of the small mottled willow moth to attack tomato crop and observed the crops for days. Normally, attacks trigger a defensive reaction in the tomato plants, which then produced methyl jasmonate, or just MeJA, an airborne chemical that is produced in response to environmental stresses, to activate the plant’s defense mechanisms. Through the airborne chemical, plants sense when surrounding plants are under attack, then produce their own MeJA.

TURNING ON THEMSELVES

After exposing the tomato crop to various amounts of MeJA to trigger a defensive reaction, the scientists observed the plants for days. A week later, they observed that the plants that got a stronger dose of MeJA had lost less biomass than plants that received a weaker dose of MeJA.

The researchers then fed leaves from cued plants and non-cued control plants to single catterpillars in containers. The jars also contained a set number of dead caterpillars. Two days later, the team observed that caterpillars fed with leaves from the treated plants had turned onto the dead larvae earlier, and had eaten more of them, than those fed with leaves from control plants.

On discovering that what they are feeding on is no longer tasty, the caterpillars can either eat the unpleasant plant or turn on themselves.

These results come at a time when Kenya, and the East African region generally, are battling the fall armyworm which is threatening its food reserves. The Food and Agriculture Organisation of the United Nations (FAO) reported that as May 23, 2017 the worm had affected more than 143,000 hectares of land in major maize and wheat-producing counties in Kenya.

RECOVERING MAJOR LOSSES

The annual loss could be 40 million bags of maize valued at Sh120 billion, assuming that the cost of one bag remains at Sh3,000. The Ministry of Agriculture and organisations such as Kenya Agricultural and Livestock Research Organisation (KALRO) have been exploring other non-chemical means that do not involve pesticides to eliminate the pests. An entomologist from KALRO, Muo Kasina, says non-chemicals would not harm the environment or encourage resistance of the pests to the pesticides available.

The use of natural means to get rid of pests is hardly anything new. They could be as basic and rudimentary such as pouring ash on the pest to advanced technology, and there has been documented evidence that some plants can persuade the pests that feed on them to be more predatory towards other species.

Other plant researchers welcomed this innovative study. Anurag Agrawal, who studies plant–animal interactions at Cornell University in Ithaca, New York, told the journal Nature that the study suggests that farmers could foster cannibalism as a pest-management strategy. MeJA can do more than just make a plant taste bad. The chemicals can attract natural enemies like predators and parasitoids that will eat herbivores.

In 2013, KALRO used pheromones to reduce sandflies which barred Kenya’s avocado from being exported to South Africa. Pheromones are chemical substances produced by insects to modify how members of their species relate to them.

Some countries such as the United States of America have managed to keep massive fall armyworm losses at bay by planting genetically modified maize. Cassava has also been cited in studies to be immune to some pest’s appetite because of the cyanide the tuber plant produces.