Natural plant defense systems and plant-pest signaling is an exciting field of research, with new complexities constantly being revealed. Plants can use chemical signals to direct the behavior of pests in a variety of ways, including reproductive cycles. Researchers at the University of Wisconsin –Madison have discovered an interesting defensive response in tomato plants. When the defense response is triggered, these plants can release chemicals that encourage caterpillars to stop eating the plant, and instead eat each other. This induced cannibalism response has largely been undiscovered in plants, but has many exciting implications for pest management, as well as plant evolution and pathogen transmission.
Turning Caterpillars Into Cannibals
Normally herbivorous insects turning to cannibalism as a survival mechanism is not uncommon in the insect world, but this behavior is typically associated with extreme conditions where suitable food sources are limited. This research suggests that plants may be able to turn this survival mechanism against insects though through chemical signaling.
Methyl jasmonate is chemical released by plants as a stress response. It can signal other nearby plants to increase defenses against insect predators. Researchers sprayed methyl jasmonate at different rates on isolated, container grown tomato plants, then released beet armyworm caterpillars, to study the induced chemical responses by the plants. They found that with the high rates of methyl jasmonate, tomato plants used their own defensive chemical signaling responses to induce the caterpillars to eat each other, and not the plant.
Implications for Agricultural Pest Control
While methyl jasmonate was use to induce the plants chemical defense systems, the actual chemical, or chemicals, used to induce cannibalism in the caterpillars is not yet known. This study could be the first step into discovering plant signaling tools that could be used by farmers to prevent pest damage.
Also, in this study large amounts of cannibals were used, enough to consume all the leaves on the untreated plants. This would only naturally occur in an extremely severe infestation. Furthermore, the cost to the plant and/or fruit with increased chemical defenses, was not determined. The chemicals used to deter pests may have a negative impact on fruit quality or flavor, or the increased energy in production of these chemical defenses could result in less energy for fruit production. These aspects will be looked at in future studies
Another interesting implication which researchers are looking into, is how induced cannibalism may effect pathogen transmission, both from insect to insect, and insect to plant. It is unknown if increased cannibalism would increase or decrease the rate of spread of insect pathogens. It is also unknown what role this could play in development of insecticide resistance.
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