Domain:        Eukaryota

Kingdom:     Animalia

Phylum:       Arthropoda

Class:           Insecta

Order:        Coleoptera

Family:      Bostrichidae

Genus:     Rhyzopertha

Species:      R. dominica Binomial

Name:       Rhyzopertha dominica (Fabricius, 1792)

R. dominica is thought to originate from the Indian subcontinent, but now has a cosmopolitan distribution. It is a serious pest of stored products throughout the tropics, Australia and the USA. It is also found in temperate countries, either because of its ability for prolonged flight or as a result of the international trade in food products. It is predominantly found in forested and grain storage environments.[4] As such, human interaction has aided in the widespread of R. dominica through the commercial transportation of grain.[4] A testament to their inhabitation of grain is the acquisition of the name “Australian Wheat Weevil”, symbolizing their predominant infestation of wheat in Australia.[4]

Host Range
It is commonly found within store bought products and pest of stored cereal grains, including rice, wheat, sorghum, oat, pearl millet, malt barley from the family Poaceae, and chickpeas, peanuts and beans from the family Leguminosae.[4] R. dominica seems to be preadapted for feeding on dry grains.[4] It feeds on the whole grain in both larval and adult stages.[4] It is also a major pest of peanuts. Moreover, infestation of wheat in Australia is reported.[4] Adults and larvae of R. dominica feed primarily on stored cereal seed including wheat, maize, rice, oats, barley, sorghum and millet. They are also found on a wide variety of foodstuffs including beans, dried chillies, turmeric, coriander, ginger, cassava chips, biscuits and wheat flour. There are several reports of the lesser grain borer being found in or attacking wood (Potter, 1935), as is typical of other Bostrichidae. R. dominica has been reported to produce progeny on the seeds of some trees and shrubs (acorns, hackberry [Celtis occidentalis] and buckbrush [Symphoricarpos orbiculatus]) (Wright et al., 1990).

Eggs: The egg is typically white when first laid, turning rose to brown before hatching. The egg is ovoid in shape, 0.6 mm in length, 0.2 mm in diameter. The eggs are ovoid in shape, laid loosely in grains.

Larva: There are usually four larval instars. The larvae are scarabaeiform, the first two instars are not recurved, the third and fourth instars have the head and thorax recurved towards the abdomen. The widths of the head from the first to the fourth instar are 0.13, 0.17, 0.26 and 0.41 mm, and the lengths of the larvae are 0.78, 1.08, 2.04 and 3.07 mm, respectively. The larvae are white to cream coloured, with biting mouthparts and three pairs of legs. The young larvae are mobile in grain bulks but become immobile and gradually more C-shaped as they complete their development concealed within grain or flour.

Pupa: The pupae are 3.91 mm in length, with 0.7 mm between the eyes. At the end of the abdomen, the male pupae have a pair of 2-segmented papillae fused to the abdomen for their entire length, whereas female papillae are 3-segmented and project from the abdomen.

Adult: The average R. dominica are 2.1–3.0 millimetres in length.[1] Their body is cylindrical and displays a reddish brown coloration with 11 antennal segments and a 3-segmented antennal club.[1] The pronotum is located near the base of the body with no depressions.[1] In addition, the basal part of the pronotum has a wrinkled appearance and rasp-like teeth at the front.[1] Distinct tubercles on the R. dominica are found on the anterior margin, but appear to be slightly apart at the median.[1] Moreover, it has clear elytral strioles that are angularly rounded at the apex, and short, yellowish, bent setae. The elytra are parallel-sided, the head is not visible from above. Externally there are no major recognizable differences between male and female adults of R. dominica.[1]

Rhyzopertha dominica is morphologically superficially similar to some other species within the family Bostrichidae, particularly those in the subfamily Dinoderinae. Bostrichids can be distinguished from other beetles due to their rasp-like pronotum, 5-segmented tarsi and straight antennae with 3-3 segments.[4] The genus Rhyzopertha is monotypic, consisting of only R. dominica. Further classification of this genus places it within the subfamily Dinoderinae.[4] It is possible to confuse the lesser grain borer with other storage insect pests such as the Large Grain Borer – LGB (Prostephanus truncatus) and the maize weevil (Sitophilus zeamais). However, the saw-toothed front edge of the pronotum in the lesser grain borer family (Bostrichidae) is very distinctive. In contrast, the LGB is larger (3-4.5 mm long), dark brown in colour, its body surface has many small wart-like outgrowths (tubercles) and the end of its body terminates in a straight edge. The end of the body of the maize weevil is more rounded than that of the lesser grain borer, its head is visible from above and mouthparts are ‘beak-like’ and the antennae elbowed.

Rhyzopertha dominica is found mainly in cereal stores, and food and animal feedprocessing facilities. It has also been trapped using pheromone-baited flighttraps several kilometres from any food storage or processing facility (Fieldset al., 1993). The lesser grain borer is characterized as both an internal and external feeder and is a serious pest of both whole kernel stored grain and cereal products. The adults and larvae bore into undamaged kernels of grain, reducing them to hollow husks. They are also able to survive and develop in the accumulated “flour” produced as the seeds are chewed up. The lesser grain borer is primarily a pest in stored wheat and corn, but it can infest tobacco, nuts, beans, bird seed, biscuits, cassava, cocoa beans, dried fruit, peanuts, spices, rodenticide baits, and dried meat and fish.

Rhyzopertha dominica follows a 4-stage life cycle: egg, larval, pupal, and adult.[4] The mating behaviour in the R. dominica follows within 24 hour after the individual ecloses from the pupal stage.[4] The females do not display any courtship behavior such as initiation of mating or attempt to attract male beetles.[4] In some instances, the males will attempt to mate with other males, whereas this type of interaction is absent in females.[4] Female attraction to the male occurs upon physical contact, whereby the close proximity allows for the olfactory senses to detect the male produced pheromones.[4] The pheromones are also responsible for the attraction between male beetles.[4] Stimulation from the pheromones is characterized (in both male-to-male and male-to-female interaction) by an excited and rapid walking motion; the head, thorax, and antennae are extended forward and up, in the direction of the pheromone source.[4] When they are around a pheromone source, the beetles walk around with their antennae extended and they actively palpate the abdominal area.[4] The males will initiate a palp mediated mating response and mount the beetle if it were a female.[4] This occurs after he touches his maxillary palp to the tips of her elytra.[4] While mounting the female, the male moves to the posterior dorsal surface.[4] The male walks forward and taps lightly on top of the female’s elytra and thorax with his palpi.[4] Contact with the vagina is made when the last sternite of the male beetle is lowered and the aedeagus protrudes to the vagina.[4] Once the male is firmly mounted, copulation has been achieved.[4] Copulation lasts for 2 hours and can occur multiple times in R. dominica, as females require more than one mating to fertilize effectively all the eggs produced during her lifetime.[4] Externally there are no major recognizable differences between male and female adults of R. dominica.[4] A reported minor difference is the last ventral abdominal sternite of the female, seen as pale yellow as compared to the uniformly brown males.[4]

 R. dominica is a major pest of wheat (Flinn et al., 2004) and rice (Chanbang et al., 2008a,b) around the world. Both larvae and adult produce frass and cause weight losses by feeding on grains. R. dominica infestation can reduce rice to dust (Emery and Nayak, 2007). There are three aspects of the impact of R. dominica infestation: loss in the quantity of stored grain, loss in quality of stored seeds (Sánchez-Mariñez et al., 1997) and the cost to prevent or control infestations (Cuperus et al., 1990; Anonymous, 1998). On wheat and rice, larvae consume both germ and endosperm during their development in grain and thus produce more frass than Cryptolestes ferrugineus and Sitophilus granarius (Campbell and Sinha, 1976). R. dominica is also capable of damaging grain, causing weight losses of up to 40%, compared to 19%, 14% and 10% for S. oryzae, Tribolium castaneum and Ephestia cautella, respectively (Sittusuang and Imura, 1987). Weight loss from individual kernels has also been reported with different varieties of triticale, a wheat-rye hybrid (Baker et al., 1991), and in rice infested with R. dominica (Nigam et al., 1977). R. dominica feeding on seed germ reduces germination rates and vigour of the grains and may be followed by secondary pests and fungi (Bashir, 2002). Food production and nutritional value: R. dominica infestation of wheat, maize and sorghum grains resulted in substantial changes in the contents of calcium, phosphorus, zinc, iron, copper and manganese (Jood et al., 1992). Jood and Kapoor (1992) also observed a reduction in the starch digestibility of maize, rice and sorghum in response to R. dominica infestation. Single or mixed populations of Trogoderma granarium (Khapra beetle) and R. dominica resulted in substantial reductions in the contents of total lipids, phospholipids, galactolipids and polar and nonpolar lipids of wheat, maize and sorghum (Jood et al., 1996). R. dominica has also been reported to decrease vitamin contents of grain; 75% level of infestation of cereal grains caused losses of 23 to 29% (thiamine), 13 to 18% (riboflavin) and 4 to 14% (niacin) we (Jood and Kapoor, 1994). Chapatis prepared from flours with more that 50% R. dominica and T. granarium infestation level tasted bitter (Jood et al., 1993). At 75% infestation level there was a significant reduction in protein nitrogen and true protein contents of three cereal grains (Jood and Kapoor, 1992). Economic impact: It is difficult to estimate the actual costs incurred for the control of R. dominica because it is generally found in mixed population with other stored-product insect pests that also cause damage. The species R. dominica associates with vary depending upon the region and stored commodity. Two or more live ‘grain-damaging’ insects per kg of wheat resulted in an infested designation on the grain inspection certificate (FGIS, 1997). R. dominica produces insect-damaged kernels (IDK) when adults emerge from the kernels. If wheat contains more than 32 IDK per 100 g it is designated as sample grade, which cannot be sold for human consumption, and its market value drops dramatically (FGIS, 1997).

1. A variety of methods have been used to detect insect pests of stored products, including R. dominica.
2. The simplest method is to sieve a 200-1000 g sample of the grain and look for adults. However, only a small sample of the grain is inspected using this method and larvae, pupae and adults inside the grain kernels are not detected.
3. Temperature, carbon dioxide, sound and feeding damage can be used as indirect indicators of insect infestation. Insects release heat as they respire, and at high insect densities, ‘hot spots’ can be created. Thermometers, either attached to the end of a probe or wired permanently into a storage structure with a remote electronic readout, give a quick and accurate picture of grain temperature. However, hot spots can be very localized and difficult to detect, and insects can cause significant damage before they are detected.
4. Feeding holes in grain and other commodities also indicate the presence of some insects, but sampling using sieves or traps is needed to identify which insects have caused the damage. All of these detection methods are not specific for R. dominica, and grain samples are required for verification of the insect species.
5. Large amounts of flour tunnels and irregularly shaped holes in commodity
6. Sweet odor in the grain.

1. Plants/Seeds/external feeding Damage is distinctive and heavy Adults and larvae feed on germ and endosperm reducing kernels to shells of bran Adults and larvae also burrow through kernels

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Commercial and agricultural methods are being implemented to manage infestation and pest control of R. dominica.[4] Approaches includes minimizing pest migration and build-up within grain storage areas, through thorough cleaning of the equipment before harvest, sealing storage, spraying bins and units, and cleaning up any grain spills.[4] Close monitoring of the temperature in storage areas is a crucial step of managing, as it can influence the insect population.[4] Harvested wheat temperatures ranging from 27 to 34 °C (81 to 93 °F) is optimal for insect reproduction and growth.[4] R. dominica are more vulnerable to the cold than other grain pests.[4] Temperatures below 15 °C (59 °F) are unfavorable for R. dominica to maintain their bodily activities.[4] To compensate, they become dormant, but this greatly increases their susceptibility to death at temperatures of 2 °C (36 °F) or lower.[4] Thus, aeration or grain drying, where grain is mechanically ventilated, can also be used to manage infestation through the maintenance of low temperatures in storage areas.[4] Unfortunately, R. dominica cannot be completely controlled solely with aeration. Although it is recommended for quality of grains, feasible and effective in reducing insect growth rate, damage from fungi and moisture.[4] Research shows that soft x-ray methods are also being used to identify potential infested wheat kernels.[14] Despite all efforts to manage R. dominica, they remain a detrimental pest in the production of wheat, rice and pasta.[14]

Sanitation and hermetic sealing: Cleaning during grading operations, drying, cool storage and hermetically sealed packaging can all play an effective role in conserving the seed viability with residue free pest control. Grain packaging in airtight structures is one of the most important physical methods controlling R. dominica. Aeration and drying: One of the more effective non-chemical control methods is to cool the grain with aeration fans, which gradually suppresses insect population growth in the storage period. Reducing grain moisture content reduces the number of eggs produced and the survival of offspring and adults. There are 3 types of drying: ambient air drying, sun drying and mechanical drying. In ambient air-drying system, air is heated and passed through grain to produce a relatively high vapor pressure gradient between the moisture in the grain and the moisture in the drying air (Jones et al., 2012). Radiation: Radio-frequency heat treatment is increasingly used as a new thermal method for the disinfection of post-harvest insect populations in agricultural commodities (Tang et al., 2000). The application of this method leaves no chemical residue and provides acceptable product quality with minimal environmental impacts (Wang et al., 2003). Controlled atmosphere: Reducing temperatures to below 34°C reduces the rate at which the population of R. dominica increases. R. dominica cannot complete its life cycle below 20°C. Commercial units are available for both types of cooling. Increasing grain temperature to above 34°C also reduces the rate at which the population of R. dominica increases. Although R. dominica is one of the most heat tolerant of all stored grain insect pests, it can be controlled by heating the grain to 65°C in 4 minutes, and rapidly cooling it to below 30°C. Manipulation of storage temperature is a relatively new technology that may be used to a greater extent in the future. The manipulation of gases (nitrogen (N2), oxygen (O2) and carbon dioxide (CO2) within storage structures has been widely studied for the control of insect infestations. Inert dusts: Inert dusts have been used as a traditional method of insect control for thousands of years (Glenn and Puterka, 2005). Stored grain insects are more vulnerable to these dusts as they feed upon dry grains and possess relatively larger surface to volume ratio (Stathers et al., 2004). There are several types of inert dusts being used in insect control programs, such as ash, lime, clay, diatomaceous earth (DE) and silica aerogel. The most effective inert dusts are DE and silica aerogel.

The use of natural enemies to control R. dominica and other stored grain insects has been limited in developed countries because of the low tolerance (0-2 insects/kg grain) of insects in stored grain. However, because of the interest in controlling insect pests without the use of insecticides, there has been renewed interest in predators and parasites (Brower et al., 1991). Despite this, research on the potential use of bio-control agents of stored grain insects has been limited to a small number of species. Predators: There have been several laboratory studies on the use of predators of R. dominica (Brower et al., 1991). Teretriosoma nigrescens is a histerid beetle that is found in Central America, where it primarily feeds on Prostephanus truncates, a species closely related to R. dominica. It is able to feed on R. dominica. However, the ability of T. nigrescens to significantly reduce R. dominica populations has yet to be determined (Markham et al., 1994). Xylocoris flavipes (Hemiptera: Anthocoridae) is a predator of many stored product insect pest (Rahman et al., 2009). The cadelle Tenebroides mauritanicus also feeds on grain, mites and stored-product insect eggs, including Rhyzopertha (Bousquet, 1990). The predatory mites Cheyletus eruditus and Pyemotes ventricosus feed on a wide variety of stored product insect eggs (Asanov, 1980; Brower et al., 1991), but their effect on populations in the field has not been determined. Among the four Cheyletus species found in storage structures of Central Europe, only C. eruditus is employed for the biocontrol of stored grain insect pests (Lukáš et al., 2007). Parasites and parasitoids: Most of the parasitoids that attack the primary beetle pests are in the families Pteromalidae and Bethylidae. These hymenopteran parasitoids are very small, do not feed on the grain and can easily be removed from the grains by using normal cleaning processes. Choetospila elegans is a small pteromalid wasp that attacks R. dominica and certain other coleopteran and lepidopeteran insect pests. The wasp normally parasitizes larvae that are feeding inside the grain. At 32°C, a wasp takes approximately 15 days to complete its development on R. dominica; the generation time of C. elegans is almost half that of R. dominica. In the presence of hosts, female wasps live for 10-20 days at 32°C. A single female C. elegans is capable of parasitizing up to six R. dominica per day. Another hymenopteran parasitoid, Anisopteromalus calandrae, is effective at reducing R. dominica populations. The hymenopteran parasitoid Anisopteromalus calandrae suppressed R. dominica populations in all types of storage bag except those made of polythene.The egg parasitic mite Acarophenax lacunatus significantly reduces the population of R. dominica (Faroni et al., 2000; Gonçalves et al., 2004). Entomopathogens: The use of entomopathogenic fungi has been evaluated extensively in laboratory and field studies against R. dominica. The pathogenicity of entomophaghous fungi depends upon various physical (temperature, relative humidity, application time of fungal insecticide, dark and light period etc.) and biological factors (the specific host species, host pathogen interaction etc.). Unlike other microbial control agents, fungi possess the ability to infect the insects through cuticle (Boucias and Pendland, 1991; Thomas and Read, 2007). More recently, various native entomopathogenic fungi, isolated from different components of the maize agroecosystem, how shown virulence against R. dominica and two other stored maize insect species. Paecilomyces and Metarhizium were the most abundant genera isolated from the soil, wheras the isolates of Purpureocillium lilacinum were the best in controlling target insect species (Barra et al., 2013).

Insecticide grain protectants worldwide are also ineffective for R. dominica management. Many of these protectants are either not effective or the pest has developed resistance to them.[4] The protectant include organophosphorus insecticides such as chlorpyrifos methyl, fenitrothion, pirimiphos methyl and malathion.[4] When infestations become severe, fumigation is a suggested form of control.[4] The fumigant phosphine is key to controlling R. dominica since it targets all insect life stages, is easy to utilize, effective, feasible, and is a residue-free tactic.[4] Unfortunately, due to active dispersal, R. dominica also actively spreads its resistance genes.[11] Over the last 15 years, due to environmental concerns and insect pest resistance to conventional chemicals, interest in botanical insecticides has increased. Botanical insecticides are naturally occurring insecticides which are derived from plants (Golob et al., 1999; Isman, 2000). Compared to synthetic compounds they are less harmful to the environment, generally less expensive, and easily processed and used by farmers and small industries. Botanical insecticides are used in several forms, such as powders, solvent extracts, essential oils and whole plants, these preparations have been investigated for their insecticidal activity including their action as repellents, anti-feedants and insect growth regulators (Weaver and Subramanyam, 2000). The introduction of powdered leaves of Salvia officinalis L. and Artemisia absinthium L. to wheat grains was very effective in reducing population size and delaying development time of R. dominica (Klys, 2004). Natural feeding inhibitors found in either wild or cultivated plants are usually alkaloids and glycosides. The mode of action of these compounds is complex and poorly understood, although it is found that insects exposed to such substances usually stop feeding, resulting in a decreased body weight or even death if the insects fail to feed for a long period of time. Plant essential oils and solvent extracts are the most studied botanical methods of controlling stored grain insect infestations (Stoll, 2000; Shaaya et al., 2003; Moreira et al., 2007; Rozman et al., 2007; Rajendran and Sriranjini, 2008). Moreira et al. (2007) reported that R. dominica was more susceptible than Sitophilus zeamais and Oryzaephilus surinamensis to hexane crude extract of Ageratum conyzoides, experiencing more than 88% mortality after 24 h of exposure. Plant oils are also used for their fumigant activity against R. dominica (Lee et al., 2004) on the basis of their efficacy, economic value and use in large-scale storages. In spite of the wide-spread recognition of insecticidal properties of plants, few commercial products obtained from plants are in use and botanicals used as insecticides presently constitute only 1% of the world insecticide market (Rozman et al., 2007). Other alternatives such as the use of ozone as a fumigant is also being tested on immature stages, larvae or pupae, which are more prone to being effected as compared to adults.[12] Aside from the evolution of resistance, the internal feeding technique of R. dominica confers protection from potential insecticides by creating safe spaces and shelter within the grain mass.[13] Further studies suggest that fumigants are not the only method of detecting and pest management implemented in the grain industry.[4]

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https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/chaetocnema#:~:text=Chaetocnema%20basalis%20Baly%201877%3A%20310.&text=It%20is%20found%20in%20Asia,this%20genus%20reported%20as%20pests. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/chaetocnema#:~:text=Chaetocnema%20basalis%20Baly%201877%3A%20310.&text=It%20is%20found%20in%20Asia,this%20genus%20reported%20as%20pests.

1. Park, Sangwook; Lee, Seunghwan; Hong, Ki-Jeong (2015). “Review of the family Bostrichidae (Coleoptera) of Korea”. Journal of Asia-Pacific Biodiversity. National Science Museum of Korea + Korea National Arboretum (Elsevier). 8 (4): 298–304. doi:10.1016/j.japb.2015.10.015. ISSN 2287-884X. S2CID 85722776.

2. https://edis.ifas.ufl.edu/publication/IG117

3. “Rhyzopertha dominica (Fabricius)”. CABI Crop Protection Compendium. Archived from the original on 2012-02-18.

4. ^ Jump up to: a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl Edde, Peter A. (2012). “A review of the biology and control of Rhyzopertha dominica (F.) the lesser grain borer”. Journal of Stored Products Research. Elsevier. 48 (1): 1–18. doi:10.1016/j.jspr.2011.08.007. ISSN 0022-474X. S2CID 84377289.

5. https://www.grainscanada.gc.ca/en/grain-quality/manage/identify-an-insect/primary-insect-pests/lesser-grain-borer.html

6. https://pubmed.ncbi.nlm.nih.gov/?term=lesser+AND+grain+AND+borer+OR+rhyzopertha+dominica&filter=years.2000-2024

7. Wakil, W. (2022). Rhyzopertha dominica (lesser grain borer) [dataset]. In CABI Compendium. CABI Publishing. https://doi.org/10.1079/cabicompendium.47191

8. https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.47191