Caterpillar, fungus in cahoots to threaten fruit, nut crops: study
CHICAGO, Nov. 7 (Xinhua) -- Researchers at the University of Illinois (UI) have found that Aspergillus flavus, a fungus that produces carcinogenic aflatoxins that can contaminate seeds and nuts, and navel orangeworm caterpillar work in concert to overcome plant defenses and resist pesticides.
The study has been newly published in the Journal of Chemical Ecology.
They did tests to measure caterpillar mortality and time to pupation in a variety of conditions. The tests included a caterpillar strain that was susceptible to pyrethroid pesticides and another that was resistant.
And the tests revealed that the caterpillars developed much more rapidly in the presence of the fungus, regardless of the natural or man-made toxins that were also present. Larvae exposed to the plant defensive compound xanthotoxin developed nearly twice as fast when the fungus was also present. Larvae fed a diet containing xanthotoxin or bergapten, another phytochemical in the same class as xanthotoxin, also lived much longer in the presence of the fungus than when exposed to the chemicals alone.
The caterpillars differed in their response to pesticides, with and without their fungal partner. The pesticide-susceptible caterpillars had higher mortality in the presence of the pesticide and fungus than when exposed to the pesticide alone. Pesticide-resistant caterpillars were unaffected by the pesticide, whether or not the fungus was present.
When the researchers incubated the fungus with the pesticide bifenthrin before the caterpillars came on the scene, however, caterpillar mortality went down.
"It's very likely that this caterpillar has managed to colonize so many new crops because its partner fungus can break down the chemical defenses of the tree crops that it encounters," said UI entomology professor and department head May Berenbaum. "It's also giving this caterpillar an extra edge because the fungus is breaking down some of the pesticides that growers are using to combat the caterpillar."[ Editor: WPY ]