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In an evolutionary battle with the stem borer moth Chilo partellus, certain maize landrace varieties have forged strong relations with both the parasitic wasp Trichogramma bournieri and the larval parasitoid Cotesia sesamiae, neither of which is a friend to the stem borer. Observations regarding the maize/wasp alliance’s brutal ovicide of the stem borer moth are reported in a recent article by Tamiru et al. and evaluated by Maurice Sibelius.

Triggered by the deposit of eggs on maize leaves by the moth, the plant releases its arsenal of irresistible (if you’re a wasp) herbivore-induced plant volatiles (HIPVs). This rallies not only the parasite wasp cavalry to enjoy the defenceless egg banquet, but also calls forth an army of larval-parasitic wasps that sweeps the area and dispatches any invaders that dodged the first bullet, a great strategic deployment of indirect arsenals that effectively bring together natural enemies while the supreme commander sits it out on the sidelines. What’s disturbing, however, is that this intricately evolved defence mechanism is absent in commercially bred hybrid varieties of maize, exemplifying how some such varieties can be genetically weaker than their wild counterparts for important survival traits. As Faculty Member Sebilus states,

The work presented in this article represents a landmark example supporting the idea that traits involved in indirect plant defence are better conserved in landraces. This paves the way for developing strategies of resistance breeding by introgression of these traits into commercial hybrid varieties of maize.

Indeed, further concern that genetically modified and other commercially bred varieties have been shown to escape to grow unchecked in the wild, potentially outcompeting wild varieties and thus eradicating some valuable phenotypes. In this case, plant-produced HIPVs as biological weapons surely trump the use of synthetic, petroleum-based insecticides, arguing for the preservation of wild phenotypes.

The pea aphid, picture by Shipher Wu (photograph) and Gee-way Lin (aphid provision), National Taiwan University

Finally, while dark days may be ahead if you’re a stem borer moth egg, the future is bright if you’re a pea aphid. It had earlier been noted that pea aphids are able to feast with uninterrupted enthusiasm on their host. As now revealed in a study conducted at the Center for Chemical Ecology at Penn State by Danielle Whittaker and Ellen Ketterson, evaluated here, pea aphids have the ability to suppress the release of HIPVs, thus silencing the plant’s call to arms and avoiding massacre by wasp and other insect enemies. The importance of this study was to show that the strategic success of aphids is due to chemical suppression rather than the ‘stealth’ feeding mechanism of piercing plant tissue instead of chewing. Other insect herbivores have been shown to benefit from this adaption of the pea aphid while feeding on the same plant. As such, it seems that in this bug-eat-bug world, the pea aphid is top dog.