Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Curculionidae
Genus: Sitophilus
Species: S. oryzae


Binomial Name: Sitophilus oryzae (Linnaeus, 1763)
Synonyms:
Calandra funebris Rey, 1895
Calandra minor Sasaki, 1910
Calandra sasakii Takahashi, 1928
Curculio bituberculatus Fabricius, 1781
Curculio frugilegus De Geer, 1775
Curculio oryza Linnaeus, 1763

It is distributed worldwide. It prefers tropical or subtropical environments but can survive temperate regions in protected situations.

পোষক পরিসীমা
Rice, wheat, barley, occasionally peas; Raw processed cereals such as pasta. Although S. oryzae is primarily a pest of stored products, it can also attack cereal plants in the field.

Egg: The eggs are shiny, white, opaque and ovoid to pear-shaped.

Larva: The larva is legless and stays inside the hollowed grain kernel. It is fat with a cream-colored body and dark head capsule. Larvae are white, legless grubs that develop within the kernel and will not be detected in sieve samples or Berlese funnel samples.

Pupa: The pupa is also white but has legs, wings, and the snout of the fully-grown weevil.

Adult: The adults are usually between 3 and 4.6 mm long, with a long snout. The body color appears to be brown/black, but on close examination, four orange/red spots are arranged in a cross on the wing covers [1]. Usually red-brown, dull with coarse microsculpture. Scutellum usually have lateral elevations closer together than their length and evidently more than half as long as scutellum.

-Males with median lobe of aedeagus evenly convex dorsally in cross section.
-Females with lateral lobes of internal, Y-shaped sclerite broader and rounded apically, more narrowly separated.

It is easily confused with the similar looking Maize weevil (S. zeamais). The maize weevil is typically somewhat larger than the rice weevil, but rice weevils as large as the largest maize weevils and maize weevils nearly as small as the smallest rice weevils have been found. Some external features can be used to differentiate the vast majority of adults, but the only reliable features are on the genitalia. Both species can hybridize. The genitalic structure of hybrids is unknown [1].

S. oryzae and S. zeamais are almost indistinguishable from each other externally; identification is by examination of the genitalia. Both have the characteristic rostrum and elbowed antennae of the family Curculionidae. The antennae have eight segments and are often carried in an extended position when the insect is walking. Both species usually have four pale reddish-brown or orange-brown oval markings on the elytra, but these are often indistinct.

Both species can be separated from Grananry weevil (S. granarius) by the presence of wings beneath the eltyra (absent in S. granarius) and by having circular, rather than oval, punctures on the prothorax.

Thus the similar species are:
Granary weevil (Sitophilus granarius)
Maize weevil (Sitophilus zeamais) – morphologically nearly identical

The rice weevil is one of the most serious stored grain pests worldwide. This pest of whole grain originated in India and has been spread worldwide by commerce. It now has a cosmopolitan distribution. It is a serious pest in the southern United States. The rice weevil is replaced by the granary weevil north of North Carolina and Tennessee. Both the adults and larvae feed on whole grains. They attack wheat, corn, oats, rye, barley, sorghum, buckwheat, dried beans, cashew nuts, wild bird seed, and cereal products, especially macaroni. The adult rice weevil can fly and is attracted to lights. When disturbed, adults pull in their legs, fall to the ground, and feign death. The larval rice weevil must complete its development inside a seed kernel or a man-made equivalent, like macaroni products. Larval rice weevils have been known to develop in hard caked flour. The adult female eats a cavity into a seed and then deposits a single egg in the cavity, sealing in the egg with secretions from her ovipositor. The larva develops within the seed, hollowing it out while feeding. The larva then pupates within the hollow husk of the grain kernel.

Rice weevils are usually found in grain storage facilities or processing plants, infesting wheat, oats, rye, barley, rice, and corn. Although not often found in the home, they are sometimes found infesting beans, birdseed, sunflower seeds, dried corn, and too a lesser degree macaroni and spaghetti. Rice weevils do not bite, nor do they damage wood or furniture.

The adult female rice weevil lays an average of 4 eggs per day and may live for four to five months. The full life cycle may take only 26 to 32 days during hot summer months, but requires a much longer period during cooler weather. The eggs hatch in about 3 days. The larvae feed inside the grain kernel for an average of 18 days. The pupa is naked and the pupal stage lasts an average of 6 days. The new adult will remain in the seed for 3 to 4 days while it hardens and matures.
Adult rice weevils are able to fly, and can live for up to two years. Females lay 2–6 eggs per day and up to 300 over their lifetime. The female uses strong mandibles to chew a hole into a grain kernel after which she deposits a single egg within the hole, sealing it with secretions from her ovipositor. The larva develops within the grain, hollowing it out while feeding. It then pupates within the grain kernel and emerges 2–4 days after eclosion.
Male S. oryzae produce an aggregation pheromone called sitophilure ((4S,5R)-5-Hydroxy-4-methylheptan-3-one) to which males and females are drawn. A synthetic version is available which attracts rice weevils, maize weevils and grain weevils. Females produce a pheromone which attracts only males.
Its gammaproteobacterial symbiont Candidatus Sodalis pierantonius str. SOPE is able to supply rice weevil with essential vitamins like pantothenic acid, riboflavin, and biotin. During larvae development, bacteria rely on up-regulation of type three secretion system genes and genes for flagellum so they can infect insect stem cells.
The adult female rice weevil lays an average of 4 eggs per day and may live for four to five months (producing 250-400 eggs). A single generation can be completed in around 28 days. The eggs hatch in about 3 days. The larvae feed inside the grain kernel for an average of 18 days. The pupal stage lasts an average of 6 days (5-16 range). The new adult will remain in the seed for 3 to 4 days while its cuticle hardens and matures.
In a nutshell:
Adults are able to fly.
Adults live 4 to 5 months.
Females generally lay eggs within a kernel but they may lay multiple eggs per kernel and more than 1 larvae can develop within a single kernel.
Adults make a small, circular emergence hole , compared to a large, oblong emergence hole made by the granary weevil.

S. oryzae is universally regarded as one of the most destructive primary pests of stored cereals such as barley, maize, rice and wheat. It does not often breed in non-cereal foods, although it does attack split peas and pasta. It can attack cereal plants in the fields. Voracious feeding on whole grains by this insect results in weight loss, fungal growth, quality loss through an increase in free fatty acids and it can even completely destroy stored grain in all types of storage. Invasion by this primary pest may cause grain heating and may facilitate the establishment of fungal colonies, secondary insect pests, and mite pests.

S. oryzae and S. zeamais are very important pests of cereals. In maize or sorghum, attack may start in the mature crop when the moisture content of the grain has fallen to 18-20%. Subsequent infestations in storage result from the transfer of infested grain into stores or from the pest flying into storage facilities, probably attracted by the odour of the stored grain.

In stored maize, heavy infestations of these pests may cause weight losses of up to 30-40%, although losses are commonly 4-5%.

Generally, both adults and larvae feed on whole cereal grains, including wheat, rice, barley, maize, groundnuts, cassava, beans, millet, and sorghum; but the females can lay eggs and develop on solid products made of cereals, such as pasta. S. oryzae can infest maturing grain, especially maize in the field, in the southern USA and in other warm and tropical regions.


According to Rubbi and Begum (1986), in Bangladesh the population of Sitotroga cerealella was highest, followed by S. oryzae and then Rhyzopertha dominica, and the percentage loss in weight of the rice followed the same order.

Sittisuang and Imura (1987) reported that brown rice lost 19% of initial kernel weight over 14 weeks of infestation with S. oryzae. In India, stored rice (unhusked) samples, drawn from six districts of Himachal Pradesh, were infested with S. oryzae (69%); the average weight loss in storage was 2.11%, and ranged from 1.09% to 3.10% (Thakur and Sharma, 1996). The effect of feeding by larvae and adults of S. oryzae on the weight of rice and wheat grain was determined in laboratory tests. The maximum weight loss caused to single kernels by individual larvae was 57% for rice and 19% for wheat (Banerjee and Nazimuddin, 1985).

In Egypt, weight losses attributable to S. oryzae and S. granarius in grain stored, under natural conditions, at 25°C and 70% RH, ranged from 56-74% in rice (Koura and El-Halfawy, 1972).

Adults feed on whole seeds or flour.
Larvae develop in seeds or pieces of seeds or cereal products large enough to house larvae but will not develop in flour unless it has been compacted.
Feeding contributes to heating and infested grain is often damp due to moisture added by the insects’ respiration.

Plants/Seeds/ internal feeding

Increased moisture levels and heating on the surface
Seeds with round holes formed by exiting adults

Diseases and Disorders:
Gregarina sitophili
Pathogens Carried:
Gregarina sitophili

Control of weevils involves locating and removing all potentially infested food sources. Rice weevils in all stages of development can be killed by freezing infested food below −18 °C (0 °F) for a period of three days, or heating to 60 °C (140 °F) for a period of 15 minutes.
The most important aspect of control is location of the source of the infestation. Place sticky traps around the room to locate the infestation, if not initially or easily located. Sticky traps with a higher density of rice weevils attached are probably closest to the infestation site. Common sources of infestations include decorative “Indian corn” saved from Thanksgiving, wild bird seed, dry plant arrangements that contain wheat or other seed heads, popcorn, beanbags or toys stuffed with grain, macaroni products, and seeds for sprouting. Infested materials should be destroyed or disposed of. All life stages can be killed by extreme heat (120°F for one hour) or cold (0°F for a week). The best control measure is to store products likely to be infested in pest-proof containers of plastic, glass, or metal. Seeds and nuts can be stored long term by adding a 1 inch cube (16 ml) of dry ice (solid carbon dioxide) to a quart mason jar of seeds and sealing the lid. The carbon dioxide atmosphere discourages all stored product pests.
Infestations in non-food areas can be treated with space sprays or crack and crevice treatments with residual insecticides having rice weevils listed on the label. Infestations in large quantities of grain are controlled by fumigation.

SANITARY METHODS

Good store hygiene plays an important role in limiting infestation by S. oryzae and S. zeamais. The removal of infested residues from last season’s harvest is essential.

TEMPERATURE

The effect of low temperatures on S. oryzae and S. zeamais was investigated by Nakakita et al. (1997). Both hatching and metamorphosis of each species were inhibited at 10°C. Population increase of S. oryzae was completely suppressed at 15°C, while a small number of F1 beetles of S. zeamais emerged.

When the pupae of S. oryzae, Corcyra cephalonica and Sitotroga cerealella were exposed to temperatures of 35-45°C for 24-72 h, S. oryzae was the most vulnerable species. A very high incidence of sterility was induced in the adults emerged from pupal exposures at 40°C (Sharma et al., 1997).

Beckett et al. (1998) used conductive heating to quickly obtain and maintain moderate temperatures in grain while minimizing grain moisture loss (Beckett et al., 1998).

RADIATION

S. oryzae was more susceptible to gamma radiation than S. granarius. Doses of Ú1.0 kGy resulted in 100% mortality within 3-6 days for S. granarius, and within 4 days for S. oryzae (Ignatowicz, 1997). A sterilizing dose of gamma radiation from Cobalt-60 was determined for adults of S. oryzae, S. zeamais, S. granarius on rice, maize and wheat grains as 70, 60 and 80 Gy, respectively (Franco et al., 1997).

Radio frequency and microwave dielectric properties of stored-grain insects were investigated and their implications for potential insect control are reported by Nelson et al. (1997, 1998).

NATURAL ENEMIES
Both S. zeamais and S. oryzae are commonly parasitized by pteromalids (and occasionally other Hymenoptera). Common pteromalid parasites found in the Tropics include Anisopteromalus calandrae, Lariophagus distinguendus and Choetospila elegans [Theocolax elegans].
Acaropsellina docta, Anisopteromalus calandrae, Bacillus thuringiensis thuringiensis, Beauveria bassiana (white muscardine fungus), Carcinops troglodytes, Cerocephala dinoderi, Cerocephala oryzae, Lariophagus distinguendus, Microsporidium sitophili, Pteromalus cerealellae, Tenebroides mauritanicus (cadelle), Theocolax elegans are some known natural enemies [6].
An experiment found that A. calandrae significantly reduced the number of S. oryzae emerging from scattered infested wheat, thus protecting uninfested wheat inside cotton, burlap, and polypropylene bags placed adjacent to the infested wheat [9].

HOST-PLANT RESISTENCE

Laboratory studies were conducted on different sorghum varieties (Leuschner and Manthe, 1996) to study the relationship between resistance to S. oryzae and grain nutrient content (Torres et al., 1996). The relative resistances of 36 improved and local sorghum varieties were assessed in Nigeria (Bamaiyi et al., 1998). Eight land races of sorghum collected in Ethiopia showed significant variation by genotype in soluble phenolic content suggesting that the soluble phenolic content could be used as an indicator of resistance (Ramputh et al., 1999).

Chunni and Singh (1996) evaluated 64 wheat varieties for resistance to S. oryzae. Singh et al. (1998) screened 15 varieties of maize and Thakur (1999) and Thakur and Sharma (1996) screened 20 rice varieties.


BOTANICAL EXTRACTS

A number of plant extracts have been tested for activity against S. oryzae including Ocimum basilicum, Capsicum frutescens, Piper guineense, Tetrapleura tetraptera and Eichhornia crassipes (Gakuru and Foua-Bi, 1996); Dicoma sessiliflora and Neorautanenia mitis (Chimbe and Galley, 1996); Ricinus communis (Mahgoub and Ahmed, 1996); Labrador tea (Ignatowicz and Wesolowska, 1996); Melilotus officinalis and M. albus (Ignatowicz, 1997); Withania somnifera (El-Lakwah et al., 1997); Gardenia fosbergii (Kestenholz and Stevenson, 1998); many Asteraceae (Ignatowicz, 1998); Thujopsis dolabrata var. hondai (Ahn et al., 1998); Eucalyptus tereticornis (Khan and Shahjahan, 1998); Allium sp. (Trematerra and Lanzotti, 1999); Decalepis hamiltonii (George et al., 1999); Chenopodium multifidum, Flaveria bidentis, Aristolochia argentina and Tagetes erecta (Broussalis et al., 1999).

NEEM

Mohapatra et al. (1996) reported that alcohol extracts of Azadirachta indica were superior to aqueous extracts providing 100% protection to rice grains for 6 weeks at a concentration of 1%. The repellent effect of a neem formulation extracted from seeds was evaluated by Suss et al. (1997). Imti and Zudir (1997) reported the efficacy of neem leaf and kernel powders. Sharma (1999) suggested that neem products can be mixed with stored maize to protect the grains up to 9 months from the attack of the major pests. The average mortality of S. oryzae adults treated with Neemazal-W was high and reached 100% at all tested concentrations 14 days post-treatment (El-Lakwah and El-Kashlan, 1999).

Grain may be protected by the admixture of insecticide. Sitophilus spp. have a low susceptibility to synthetic pyrethroids but are readily killed by organophosphorous compounds such as fenitrothion and pirimiphos-methyl. Grain stocks may be fumigated with phosphine to eliminate existing infestation, but these treatments provide no protection against re-infestation. Sitophilus spp., particularly in the pupal stage, have a lower natural susceptibility to the fumigant phosphine and to carbon dioxide used in controlled atmosphere storage than do other species tested and thus inadequate treatments are particularly likely to result in some survival.

In laboratory tests to determine the toxicity of deltamethrin, fluvalinate, chlorpyrifos-methyl, etrimfos and malathion against Sitophilus zeamais and S. oryzae, etrimfos was found to be the most toxic insecticide to S. oryzae (Srinivasacharayulu and Yadav, 1997).

A mixture of fenitrothion, esfenvalerate and piperonyl butoxide was found to be effective against S. oryzae in stored rice until 180 days after treatment (Pinto et al., 1997).

The effects of phosphine on the pupae of S. oryzae, S. zeamais and S. granarius were studied at 15°C. No significant differences were found in pupal mortality between phosphine and the mixture with carbon dioxide (Goto et al., 1996). Mixtures of phosphine plus carbon dioxide reduced levels of resistance to phosphine in populations of S. oryzae and Rhyzopertha dominica (Athie et al., 1998).

Carbonyl sulfide (as gas), carbon disulfide (as liquid) and ethyl formate (aqueous solution) were tested as fumigants in silos of wheat in Australia. Control of S. oryzae, Tribolium castaneum and Rhyzopertha dominica was 99-100% (Desmarchelier et al., 1998).


The results obtained from a study indicate that some essential oils, and in particular those of T. capitata and S. pomifera subsp. calycina might be promising fumigants for the control of important pests of stored grain such as the rice weevil S. oryzae [11].
Another study indicates that the essential oils of A. Judaica, O. vulgare, C. limon, C. viminals, and C. sempervirens could be applicable to the management of populations of S. oryzae [12].
The results from a study indicate that chlorfenapyr is effective for the control of S. oryzae, but its residual efficacy is moderated by the time after application, the surface type and partially by the presence of illumination [13].
The findings from a study demonstrate that the binary mixtures of spinosad with CSIs might be applied to protect wheat grains against S. oryzae as alternatives to conventional neurotoxic insecticides [14].


MODIFIED ATMOSPHERES

Raised levels of carbon dioxide are known to be toxic to many insect species, but S. oryzae has previously been shown to be one of the more tolerant species to this treatment. Annis and Morton (1997) reported acute mortality for all life stages of S. oryzae exposed to 15-100% carbon dioxide at 25°C and 60% RH.

The rates of carbon dioxide production and oxygen consumption by adult S.oryzae on wheat indicated that caution was needed when interpreting fumigant dosage/response data obtained in sealed systems where carbon dioxide concentrations exceed about 1% and changes in respiratory physiology start to occur (Damcevski et al., 1998).

The effectiveness of a controlled atmosphere was verified using generators of inert gases, such as carbonic anhydride and nitrogen, for the disinfestation of wheat stored in vertical silos and horizontal stores (Contessi, 1999). No pest survived at environmental temperature 27°C and temperature of the cereal mass approx. 24°C, but Sitophilus survived when the treatment was less than 12 days. It is suggested that this technique could be used as an alternative to fumigation with toxic gases.

DIATOMACEOUS EARTH

Experiments were conducted using 36 different diatomaceous earths or formulations collected from the USA, Mexico, Canada, Australia, Japan, China and Macedonia. The results indicated that the efficacy of diatomaceous earth against insects depended on different properties of the diatom particles (Korunic, 1997). The source of diatomaceous earth, insect species, grain moisture content, temperature, method of application and duration of exposure all factors influenced the mortality of stored-product insects. For S. oryzae some diatomaceous earths had increased efficacy at lower temperatures and others had decreased efficacy at lower temperatures (Fields and Korunic, 2000).

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