Abstract
Normally, when different species of herbivorous arthropods feed on the same plant this leads to fitness-reducing competition. We found this to be different for two of Asia’s most destructive rice pests, the brown planthopper and the rice striped stem borer. Both insects directly and indirectly benefit from jointly attacking the same host plant. Double infestation improved host plant quality, particularly for the stemborer because the planthopper fully suppresses caterpillar-induced production of proteinase inhibitors. It also reduced the risk of egg parasitism, due to diminished parasitoid attraction. Females of both pests have adapted their oviposition behaviour accordingly. Their strong preference for plants infested by the other species even overrides their avoidance of plants already attacked by conspecifics. This cooperation between herbivores is telling of adaptations resulting from the evolution of plant-insect interactions, and points out mechanistic vulnerabilities that can be targeted to control these major pests.
Highlights
When different species of herbivorous arthropods feed on the same plant this leads to fitness-reducing competition
When C. suppressalis larvae were allowed to feed for 7 days on rice plants that were either uninfested, infested by striped stem borer (SSB) larvae alone (SSB), brown planthopper (BPH) nymphs alone (BPH), or both SSB larvae and BPH nymphs (SSB/BPH), the body weight of SSB caterpillars was significantly different among the treatments (F3,165 = 8.46, P < 0.001) (Fig. 1a)
The body weight of SSB larvae was significantly lower when fed on plants that had been infested by SSB larvae than on all other plant treatments
Summary
When different species of herbivorous arthropods feed on the same plant this leads to fitness-reducing competition. It is one thing to demonstrate that two herbivores benefit from jointly feeding on the same plant, it is another to conclude that they actively pursue the plant-mediated benefits We propose such a partnership between the brown planthopper (BPH), Nilaparvata lugens and the rice striped stem borer (SSB), Chilo suppressalis, two of the most devastating pests of rice[37]. Our hypothesis that both insects benefit from attacking the same plant was prompted by our recent finding[27] that BPH performs better on SSB-infested rice plants due to an increased amino acid content, which is beneficial to BPH, and a decrease in levels of toxic beta-sitosterol and campesterol that have been reported to inhibit BPH development[38,39]. This raises the question whether sharing host plants with BPH can help SSB to counter the direct defenses of rice plants and possibly mitigate the defense responses to SSB infestation, and, if so, whether it has adapted its oviposition behavior
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