Adaptations of larvae and pupae of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), to living in flooded soils

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Experiments and observations were conducted to investigate some of the physical and behavioral adaptations of larvae and pupae of the rice water weevil, Lissorhoptrus oryzophilus Kuschel, for living in flooded conditions, with the ultimate goal of improving methods for rearing this insect in the laboratory. Larvae have hydrophobic exocuticles and well-developed tracheal systems which are adapted for breathing in air. When larvae were placed in water, the hydrophobic properties of the exocuticle resulted in a very thin layer of air between the surface of larval body and water. Survival rates of larvae placed individually in water in test tubes open to air suggest that larvae can obtain oxygen from this air bubble by means of the tracheal system. Survival rates of larvae were lower in test tubes in which oxygen exchange was prevented by plugging tubes at the water line. Larvae could also secure an adequate supply of oxygen directly from air, as indicated by survival rates of larvae placed individually in test tubes without water but under conditions of high relative humidity. A detailed description of the larval tracheal system is presented. Larvae possess modified, hook-like spiracles that allow them to penetrate rice roots. Larvae were observed to make for themselves small chambers near or attached to roots and to use these modified spiracles to pierce rice roots in order to gain access to air found in the dense aerenchyma of rice roots. Similarly, before the pupal molt, larvae make a hole in a root and build their cocoons at the base of the hole, thus connecting the cocoons with aerenchyma. © 2006 Kansas Entomological Society.

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Journal of the Kansas Entomological Society

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