Pharaxonotha are 1.59 to 5.09 millimetres (0.063 to 0.200in) long and 0.60 to 1.89 millimetres (0.024 to 0.074in) wide. They have large eyes and the "clubs" (enlarged ends) of their antennas have three segments. Most species are pale yellow-brown to medium brown in color, but some have elytra (the hardened fore-wings of beetles) that are black to dark-brown or with black to dark-brown spots. Differentiation between species of Pharaxonotha depends on part on details of the female genitalia.[4]
With the exception of Pharaxonotha kirschii, all species of Pharaxonotha are obligate symbionts of species of cycads in the Americas in the genera Ceratozamia, Dioon, Microcycas, and Zamia.[a] The beetles live and breed in the pollen strobili (reproductive cones) of male plants (cycads are dioecious, with male and female cones on separate plants), consuming pollen and the tissues of cones. They also transfer pollen from the male plants to ovule strobili on female plants.[6] The beetles have been associated with cycads since the early Jurassic, about 200 million years ago.[7]
Cycads are thermogenic, capable of raising the temperature of at least some tissues. In particular, thermogeneis has been observed in the male (pollen) and female (ovule) cones (strobili) of Zamia plants. Male cones ready to shed pollen heat up early in the evening, and then cool down, while receptive female cones heat up about three hours later and then cool down. Pharaxonotha beetles have receptors for infrared radiation on their antennae, by which they appear to detect the elevated temperature of the cones on Zamia plants. Pharaxonotha beetles have been observed moving to cones on male plants when the cone's temperature is elevated, crawling into openings in the cone and emerging covered with pollen, and then moving to the cones on female plants when their temperature is elevated, again crawling into openings in the cone, presumably transferring the pollen. Each Pharaxonotha species typically pollinates just a few closely related cycad species.[8]
Life cycle
Newly emerged adult beetles go to male cones on Zamia plants that are ready to dehisc (split open). The adults feed on pollen and lay eggs in the cones. Mating has not been observed, but presumably occurs inside the cones. Eggs are large compared to adults, and quickly hatch. The larvae also feed on pollen early on, but switch to eating cone tissues after the first couple of instars. At the end of the larval stage the larvae eat a hole through the outer layer of the cone, fall to the ground, and burrow into the soil to pupate. Adults emerge from the pupal stage in four to seven days, and then either seek out a fresh male cone or burrow into the ground, possibly until their exoskeletons harden.[9] Late season pupae may enter diapause and remain in the soil until the next coning season.[10]
Species accepted in databases
Species in the genus Pharaxonotha listed in databases include:
Pharaxonotha kirschiiReitter, 1875 i c g is found in litter on forest floors from Texas and Louisiana in the United States south to Panama and as a pest in stored foods elsewhere.[13]
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