Stored-Product Insects: Biology

1. Stored-Product Insects: Biology

2. Beetles: Coleoptera • 600 species representing 34 families are associated with stored products. • Only a few species are economically important. • Identification and biology of economically important species.

3. Weevils • Family: Curculionidae or snout beetles • Rice weevil, Sitophilus oryzae (Calandra sasakii or S. sasakii) • Granary weevil, Sitophilus granarius • Maize weevil, Sitophilus zeamais

5. Rice Weevil • Reddish brown to nearly black. • Four reddish or yellowish spots on elytra. • Has fully developed wings (2nd pair). • Pronotum densely pitted with irregular-shaped punctures; a smooth narrow strip extends down the middle of pronotum.

7. Rice weevil Maize weevil

8. Maize weevil • At one time was referred to as the larger strain of the rice weevil. • Darker than rice weevil. • Has the reddish or orange spots as in rice weevil. • Pronotum densely pitted with round punctures. • Strong flier.

9. Granary weevil • Chestnut brown in color. • No wings under elytra. • No colored markings on elytra. • Pronotal pits oval (2x longer than wider).

11. Weevils • Worldwide in distribution. • S. granarius – temperate climates. • Pests of whole grain. • S. granarius: Chick peas, corn, oats, barley, sorghum, rye, kafir, buckwheat, and millet. • Cannot breed in finely ground materials- but can breed in macaroni and noodles and caked milled products. • Lay eggs within endosperm of kernels. • Cavity chewed out and egg laid by female into the cavity. • Gelatinous material is deposited as ovipositor is withdrawn.

12. Material hardens-egg plug. • 2 or more eggs/kernel; cannibalism-1 survives. • After hatching larva burrows into seed. • Tunnel size increases. • 4 instars. • Pupal cell formed after last instar. • Newly emerged adults stay within kernel until cuticle is tanned.

14. S. granarius • At 21oC, takes 57-71 days from egg to adult emergence at 50-80% RH. • At 25C and 70% RH – 45 days. • Females live for 174 days. • Lay 200 eggs. • Oviposition is influenced by population density, age, temp., and RH. • Eggs laid at 17, 21, 25oC = 43, 100, 268, respectively. • Oviposition = 0.2 – 2 eggs/female/day. • Egg hatchability = 80%.

15. S. oryzae • Oviposition to adult emergence = 35 days at 27C and 69% RH. • 29.1oC – 25 days. • Egg hatchability = 75%. • Each instar duration = 5 days. • Temperature ranges = 15.2 – 34oC. • Developmental period increases if there are >2 larvae/kernel. At 29.1oC – 36 days. • At 1 weevil/50 kernels of wheat = 344-384 eggs/female at 25-29.1oC. • No eggs laid at 13oC or above 35C and on grain at or below 10% mc. • Least cold-hardy of the weevils.

16. S. zeamais • Egg to adult emergence = 35 days on HRWW at 27oC and 69% RH. • Hatchability = 75%. • Oviposition = 3.4 eggs/female/day. • Egg production decreases below 60% RH. • At 29.1oC and 70% RH, males live for 20 weeks on wheat at 14% moisture; females live for 18 weeks. • Cold tolerance: intermediate to that of S. granarius and S. oryzae.

17. Lesser grain borer: Rhyzopertha dominica • Australian wheat weevil. WWI wheat imports from Australia. • Widespread in Gulf states. • Dark brown to black. Ridges on pronotum. Head deflexed. • 1/8th of an inch long. • Larvae: Has 3 pairs of true legs.

19. Cosmopolitan. • Infests whole cereals and cereal products, chickpeas, pumpkin seeds, dried potato, edible bulbs, wood. • Oil seeds and spices (except for cardamom) are unsuitable for larval development. • Unable to develop on whole pulses; needs broken pulses. • Sorghum and barley – less satisfactory for development than wheat, rough rice, brown rice and pearl millet. • Can develop on kibbled wheat. • Population growth is rapid on wheat. • Eggs laid singly within kernels. • Larval development rapid on grain than on flour from the same grain. • First instar burrows into any rift in the seed coat. Third instar incapable of locomotion. 4th and 5th instars similar to 3rd. • Pupation takes places inside kernel at the end of the larval tunnel. • Males and females develop at the same rate.

20. Temperatures: 18.2 – 38.6oC on 14% moisture wheat. • Egg-to-adult shortest (25 days) at 34oC. • Immature mortality is also low (22%) at 34oC. • 1st instar mortality 53% at 22C and 86% at 38.2oC. • Development slower on grain < 12% moisture. • Oviposition increases if there are damaged kernels. • Fecundity greatest between 26 and 34oC on 9-14% moisture wheat. • Total number of eggs/female = 415. • Oviposition period = 112 days. • Excellent fliers.

21. Foreign Grain Beetle, Ahasverus advena • Occurs in grain and cereal products, copra, cocoa beans, peanuts, dried fruits, herb, spices, and roots. • Occurs in large numbers when produce is moldy. • Breeds on pure cultures of molds.

23. Can breed on wheat germ or rolled oats or whole wheat flour without visible mold if yeast is added. • Egg-to-adult on rolled oats + yeast = 22 days at 27oC and 75% RH. • Eggs laid singly or in clusters of 2-3. • Instars, 4-5. Fully-grown larvae construct a chamber. Brownish substance from anal aperture helps in attaching pupae to substrate. • Females start egg laying 3-4 days after emergence for 20-30 days. • Eggs, 1-4/day to 8-12/day. • Oviposition peaks at 15 days and again at 90-105 days.

24. Mated males lives for 159 days; females for 208 days. • Unmated one’s live an additional 100 days longer. • Cannot develop on some molds as they are toxic. • Larval survival greater at 66-92% RH. • Low humidity increases instar number from 4 to 5. • Egg laying > at 75% RH (1.5 eggs/day at 27oC) and is 0.1 egg/day at 58% RH.

25. Grain Beetles, Cryptolestes spp. • 6 Species • C. ferrugineus (Rusty grain beetle) • C. pusillus (Flat grain beetle) - restricted by low temp and low RH. • These 2 are cosmopolitan • C. turcicus - throughout temperate regions except for New Zealand. • C. pusilloides - East Africa, Australia, and South America. • C. capensis - Europe and South Africa. • C. ugandae - Limited to Central Africa.

26. C. ferrugineus

27. Food Preferences • C. ferrugineus • C. pusillus • Wheat, flour, oilseeds, cassava root, dried fruit, chillies, bean cakes. • Wheat, corn, rice, barley, cottonseed, copra, coffee berries, bulbs, nutmegs.

28. Development and Population Growth

29. Best larval food for these 2 species is wheat germ, followed by wheatfeed. • Larvae feed on germ and also on endosperm. • Rye most susceptible to attack followed by wheat, corn, rice, and barley. • Molds in diet favor development. • Unable to feed on sound grain, but attack grains with the slightest imperfections. 1st instars seek small openings in the pericarp.

30. Eggs are laid singly in furrows of kernels. • Oviposition continues for 34 weeks. • Mean fecundity = 242 eggs/female. • Instars, 4. • Adults and larvae cannibalistic. • Optimum RH for development: > 90%. • Crowding reduces oviposition, prolongs developmental time, and increases mortality.