Cut to Disarm Plant Defence: A Unique Oviposition Behaviour in Rhynchites foveipennis (Coleoptera: Attelabidae)

SIMPLE SUMMARY: Female Rhynchites foveipennis damages fruit stems when laying eggs in pears; the consequence of this interesting behaviour is poorly studied. The present study tested the hypothesis that the oviposition behaviour disarms the host plants’ defence by a series of comparative experiments. Our findings showed that when fruit stems were intact, the survival rates of eggs and larvae were only 21.3–32.6%, respectively, and the larvae weighed only 3.2–4.1 mg 30 days after oviposition. In contrast, when the fruit stems were damaged, the survival rates of eggs and larvae increased to 86.1–94.0%, respectively, and the larvae weighed 73.0–74.9 mg 30 days after oviposition. The contents of tannin and flavonoids in the pears did not change significantly, but eggs were crushed and killed by the callus in the pears. Once the stunted larvae were transferred to picked-off pears, the growth and development could recover rapidly. The authors propose that the oviposition behaviour can increase the survival and growth of the offspring, and thus is a strategy to disarm the plant defence. ABSTRACT: Female weevils of the family Attelabidae (Coleoptera: Curculionoidea) possess a unique behaviour of partially cutting the branches connecting egg-bearing organs of their host plants during oviposition. However, the consequence of such behaviour remains unclear. Using Rhynchites foveipennis and its host pear (Pyrus pyrifolia), the present study tested the hypothesis that the oviposition behaviour could disarm the host plants’ defence. We compared the survival rates, growth rates, and performance of eggs and larvae under two conditions: (1) the fruit stems were naturally damaged by the females before and after oviposition, and (2) the fruit stems were artificially protected from the females. When fruit stems were protected from female damage, the survival rates of eggs and larvae were only 21.3–32.6%, respectively; and the larval weight was 3.2–4.1 mg 30 days after laying eggs. When the fruit stems were damaged, the survival rates of eggs and larvae reached 86.1–94.0%, respectively; and the larval weight reached 73.0–74.9 mg 30 days after laying eggs. The contents of tannin and flavonoids in the pears did not change significantly along with the oviposition and larval feeding, but weevil eggs were crushed and killed by the callus in the pears. Once the stunted larvae in branch-growing pears were moved into the picked-off ones, the growth and development recovered. The findings indicate that the oviposition behaviour can significantly increase the survival of the offspring. Our study suggested that the oviposition behaviour of attelabid weevils is a strategy to overcome plant defence.