Depressed flour beetle Palorus subdepressus Fig 518d

Adults are about 3 mm long and uniformly brown. The sides of the front of the head extend backward to conceal the front portion of the eyes. Eggs are sticky and food particles adhere to them. Fecundity is about303 eggs at30 °Cand 70% RH and 635 eggs at 30 °C and 80% RH. At 70% RH, eggs hatch in 3 days at 32.5 °C and 20 days at 17.5 °C. Larval development is through 7-9 instars; on wholewheat at 70% RH it is 28 days at 35 °C, and 96 days at 20 °C. Humidity threshold for development is 60-70% RH at 20 °C. Pupal chambers are constructed in the food material; the pupal period is 4 days at35 °C and 14 days at 20 °C. This species infests wheat, rice, maize, sorghum, sago (Metroxylon spp.) flour, peanuts, illupe nuts (Madhuca spp.), pollards, and ginger.

Other Palorus These beetles are usually secondary invaders in the grain storage habitat. They are often found in old grain residues, and locations that have sustained infestations of Sitophilus. Larvae feed on yeast, molds, and all life stages, and the frass of primary pests. Adults of P. gmialis are distinguished by the presence of pronotal punctures with setae; it is distributed in the oriental region where it infests rice and a variety of spices. P. Jicicola and P. cerylonoides are found in Africa and the oriental region, and they infest rice, wheat, and peanuts. P. cerylonoides infests flour mills and in natural habitats it lives under the bark of trees. P. laesicollis (Fig. 5.18c) occurs in Africa where it is associated with broken maize kernels, oats, and under the bark of trees.

Yellow mealworm, Tenebrio molitor, and dark mealworm, Tenebrio obscurus (5.19c-e) Adults are about 14 mm long and the body is shiny, dark brown to black. The thorax is finely punctured and the forewings are longitudinally striated or grooved. Full-grown larvae are about 25 mm long, yellowish brown, and well sclerotized. Eggs are covered with a sticky secretion that causes flour and other particles to adhere to them. Egg-laying behavior is irregular, with infrequent periods between oviposition. T. obscurus females lay about 62 eggs per day, while T. molitor females lay about 40 eggs per day. Fecundity for T. obscurus is about 463 eggs, and for T. molitor about 276 eggs. Hatching is in 6 days at 30-35 °C and 17 days

Figure 5.19 Coleoptera: Tenebrionidae. (a) Tribolium castaneum; (b) T. confusum; (c) T. molitor; (d) T. obscurus; (e) Tenebrio molitor larva.

at 15 °C, and is most successful at 71% RH. Larval development is usually complete in 1 year, but some take 2 years. Larval molt for T. obscurus is 14 or 15 and 17-19 for T. molitor. Reared on graham flour and meat scraps, T. obscurus reaches the adult stage in 105-675 days, and T. molitor reaches the adult stage in 30-649 days. The pupal period is about 15 days; for T. molitor it is 7 days at 25-35 °C and 48 days at 15 °C. Full-grown larvae pupate or remain in the larval stage for many months with little change in size or appearance; both species overwinter as larvae. Mealworm larvae can survive for long periods without food or moisture. Adults have well-developed wings, and both species are attracted to lights.

The common names are derived from the general color of the immature stages. The larvae, pupae, and adults of these two beetles are similar in form, size and color. They are cosmopolitan, but T. molitor is common in north temperate regions, and T. obscurus is generally distributed in temperate and other regions. Both are nocturnal and prefer dark, moist habitats. Larvae feed on refuse grain, coarse cereal, and mill products. They also feed on animal material, such as meat scraps, dead insects, and feathers.

Red flour beetle, Tribolium castaneum; confused flour beetle, Tribolium confusum (Fig. 5.19a, b) Adults are about 3.5 mm long and reddish brown. T. castaneum and T. confusum are very similar in appearance and morphological separation is difficult. The confused flour beetle, T. confusum, was named because of the confusion pertaining to its identity. Antennae of T. castaneum have a three-segmented club; antennae of T. confusum have a four-segmented club. Full-grown larvae are 6-7 mm long, yellowish white, head and terminal segment brown, and with distinctly pointed urogomphi.

Eggs are laid directly on flour or other food material, and they are attached to the surface with a sticky substance; about 90% of the eggs laid are viable. The oviposition period of T. castaneum is 148 days at 27 °Cand 174 days at 21 °C; the ovipo-sition period ofT. confusum is 235 days at 27 °C and 277 days at 21 °C. Fecundity for both species is about 950 eggs; it is about 84 eggs at 25 °C and 30% RH, 413 eggs at 23 °C and 30% RH, and 539 eggs at 32.5 °C and 70% RH. Larval development is influenced by food, temperature, and humidity. The number of larval instars ranges from five to 11, but usually there are seven or eight. Optimum temperature for T. castaneum is 35-37 °C at 70% RH, and development is completed in 19-22 days, and 30 days or less at 30 °C and 30% RH. Minimum temperature for development is 20-22.5 °C; the maximum is 37.5-40 °C. Optimum conditions for T. confusum are 32.5 °C and 70% RH, and development is completed in 25 days, and 30 days or less at 30-35 °C, and 30% RH. T. castaneum and T. confusum feed on certain species ofseed-borne fungi. The red flour beetle is capable ofcompleting development on eight species offungi, and the confused flour beetle on seven species. Development is also enhanced by predation and feeding on other insects in grain. Population growth rates increase when food is supplemented with eggs or adults of the Indian meal moth, Plodia interpunctella. Pupae are formed in sheltered locations in the infested material; the pupal period is 4-6 days. Adult Tribolium live for about 3 years, and females lay eggs for more than 1 year. Males ofT. castaneum at 20-27 °C live about 547 days; females live about 226 days. Males ofT. confusum at 20-27 °Clive about 634 days; females live 447 days.

These two species readily infest plant and animal products. Larvae have been recorded from grain, flour and other cereal products, peas, beans, cacao, nuts, dried fruits, medical drugs, spices, milk chocolate, dried milk, and hides. Wholewheat flour and milled products of grain are favored foods. Larvae or adults do not attack sound or undamaged grain. Adults of T. castaneum can flyshort distances, but the adults ofT. confusum have not been observed to fly. Tribolium species have been associated with grain and flour for thousands of years. A Tribolium species was recovered from a jar probably containing grain in an Egyptian pharaoh's tomb. Prior to becoming a household pest, Tribolium species are believed to have lived under tree bark. T. confusum is probably African in origin, and T. castaneum originated in the Indo-Australian region.

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