Seed Beetles

Bruchidae.

These are small (BL 1-10 mm) beetles with a distinctive boxlike or egg shape, slightly broader posteriorly, the head concealed, and with a short, broad, almost weevillike snout. The very short antennae are clubbed or sawtoothed and the elytra abbreviated, exposing the tip of the abdomen.

The larvae feed on seeds, and family members are the principal inhibitors of sexual reproduction in many plants, thus acting as strong selective agents in seed evolution. Although rather host specific, they may not necessarily contribute to plant species richness through their selective efforts (Janzen 1980). Females oviposit on the developing flowers or pods or directly onto newly exposed seeds in dehiscing fruit, and the larvae bore through into the seed. A single larva develops in a single seed; some species may glue several seeds together as a pupal chamber or leave the seed and pupate in a cocoon. Pupation occurs in the seed or seed cavity in the fruit. Legumes are common hosts (Johnson 1985), but many other plants are used as well, such as Cordia, Sesbania, palms, Pithecellobium (Janzen 1983), Acacia, and Enterolobium. The adult leaves the seed through a typically round exit hole. This stage is not known to feed on seeds but probably subsists on nectar and pollen. Bruchids sometimes are called seed "weevils" (gorgojos, gorgulhos), but it seems best to reserve this term for true weevil (Curculionidae) predators of seeds.

Many of the five hundred Neotropical species, especially Acanthoscelides (Johnson 1983, 1990) (fig. 9.16a) and Callosobruchus, are of economic importance as they severely reduce seed productivity in peas, beans, alfalfa, and so on.

According to Bondar (1928), larvae of a bruchid (Pachymerius nucleorum) are frequently found infesting the nuts of various palms and are coveted as food by residents of Bahia, Brazil. The insects, called bichos de coco, are eaten and relished along with the palm fruits. In figurative speech in many parts of the country, a sly or cunning man is known as a "bicho de coco."

Figure 9.16 BEETLES, (a) Seed beetle (Acanthoscelides sp., Bruchidae). (b) Palm weevil (Rhyn-chophorus palmarum, Curculionidae). (c) Palm weevil, larva, (d) Bearded weevil (Rhinostomus barbirostris, Curculionidae). (e) Brentid weevil (Brentus anchorago, Brentidae). (f) Jeweled weevil (Entimus imperialis, Curculionidae).

Figure 9.16 BEETLES, (a) Seed beetle (Acanthoscelides sp., Bruchidae). (b) Palm weevil (Rhyn-chophorus palmarum, Curculionidae). (c) Palm weevil, larva, (d) Bearded weevil (Rhinostomus barbirostris, Curculionidae). (e) Brentid weevil (Brentus anchorago, Brentidae). (f) Jeweled weevil (Entimus imperialis, Curculionidae).

References

Bondar, G. 1928. O bicho do côco. Extr. Cor. Agric. 6(1): 1-18. [Not seen.]

Janzen, D. H. 1980. Specificity of seed-attacking beetles in a Costa Rican deciduous forest. J. Ecol. 68: 929-952.

Janzen, D. H. 1983. Merobruchus columbinus (gorgojo de cenizero, rain-tree bruchid). In D. H. Janzen, ed., Costa Rican natural history. Univ. Chicago Press, Chicago. Pp. 738-739.

Johnson, C. D. 1983. Ecosystematics of Acanthoscelides (Coleoptera: Bruchidae) of southern Mexico and Central America. Entomol. Soc. Amer. Misc. Publ. 56: 1-24, figs. 1-596.

Johnson, C. D. 1985. Potential useful tropical legumes and their relationships with bruchid beetles. 1: 206-210. In K. C. Misra, ed., Ecology and resource management in tropics. Int. Soc. Trop. Ecol., Varanasi, India.

Johnson, C. D. 1990. Systematics of the seed beetle genus Acanthoscelides (Bruchidae) of northern South America. Amer. Entomol. Soc. Trans. 116: 297-618.

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