According to a new study, beet armyworms or asparagus fern caterpillars, this well-known tomato pest, can turn to cannibalism if exposed to high concentrations of methyl jasmonate. This chemical can make leave behind heavily sprayed leaves and turn to their fellow pests.
Previous observations showed that off-putting or limited food supplies could sometimes cause a shift in insects, which makes them turn against one another. This new study looked to determine if beet armyworms would present the same behavior.
Pest Caterpillars, Induced to Start Eating One Another
To do so, Orrock decided to make tomato leaves, their primary food source, unappealing. He did so by spraying them, in various quantities, with methyl jasmonate. Plants naturally produce this chemical when they feel that they are under attack.
Orrock and his team placed tomato plants in isolated containers. Then, they sprayed the plants with either low, medium, or high methyl jasmonate concentrations or a control solution. The team then placed eight caterpillar larvae in each container. These were then counted daily, to see how many remained. The researchers also weighed the plants each day, to determine the remaining plant material.
Monitoring showed that the caterpillars carried on as expected in the control and low chemical concentration containers. They simply ate the tomato leaves, as usual, until the plants ran out. In the medium and high-level groups, however, things took a more savage turn, more quickly.
All of the beet armyworms eventually started eating one another. Still, things went south faster in the more chemically active groups, where the plants remained mostly intact. The pests started attacking one another since the beginning as their main source of food was already off-putting.
All of the caterpillars grew at similar rates, ones thanks to eating plants, the others by consuming their fellow beet armyworms. Those that had no colleagues, but also no unsprayed plants, presented low growth rates.
“The next step in this work is to figure out whether accelerated cannibalism would slow, or increase, the rate of spread of insect pathogens,” states Orrock in a news release.
Another element that needs studying is whether the beet armyworms would turn to cannibalism if they had other plant variants to eat, besides the tomato plants.
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