Technical Factsheet

Basic

4 October 2022

Rhyzopertha dominica (lesser grain borer)

Publication: PlantwisePlus Knowledge Bank

https://doi.org/10.1079/pwkb.species.47191

Identity

Preferred Scientific Name: Rhyzopertha dominica (Fabricius)
Preferred Common Name: lesser grain borer
Other Scientific Names: Apate pusilla Fairmaire 1850; Apate rufa Hope 1845-47; Bostrychus moderatus Walk.; Dinoderus frumentarius Motschulsky 1857; Dinoderus pusillus Horn 1878; Ptinus fissicornis Marsham 1802; Ptinus picus Marsham 1802; Rhizoperta dominica (F.); Rhizopertha dominica Lesne 1896; Rhizopertha pusilla Stephens 1830; Rhizopertha rufa Waterhouse 1888; Rhyzopertha pusilla Fabricius; Synodendron dominica Fabricius; Synodendron dominicum Fabricius 1792; Synodendron pusillum Fabricius 1798
International Common Names: English
American wheat weevil
grain, borer, lesser
grain, borer, stored
grain, eater, small
weevil, Australian wheat; Spanish
barrenador grande de los granos
barrenador menor de los granos
capuchino de los granos
escarabajo de los granos
gorgojo da los creales
gorgojo de los cereales
pequeño barrenador del trigo
taladrillo de los granos; French
bostryche des grains
capucin des grains
perceur (petit) des céréales
perceur des cereales, petit
petit perceur des céréales; Portuguese
besourinho do trigo armazenado
Local Common Names: Czechoslovakia (former)
korovník obilní; Germany
Getreidekapuziner; Hungary
Gabonaalszu; Indonesia
Gabah-bubuk; Israel
norer hatiras; Italy
punteruolo dei cereali; Netherlands
Graanboorder, kleine; Norway
kornborer; Poland
kapturnik zbozowiec; Turkey
ekin kambur biti; Yugoslavia (Serbia and Montenegro)
kapuciner
rizoperta
zitni kukuljicar
EPPO code: RHITDO (Rhyzopertha dominica)

Pictures

Adult
Dorso-lateral view of adult R. dominica (museum set specimen).
©Georg Goergen/IITA Insect Museum, Cotonou, Benin

Adult - line drawing
Adults 2-3 mm long, reddish-brown and cylindrical. Elytra parallel-sided, head not visible from above, pronotum has rasp-like teeth at the front.
NRI/MAFF

Rhyzopertha dominica
Clemson University - USDA Cooperative Extension Slide Series, Clemson University, bugwood.org
Refer to Bugwood: http://www.bugwood.org/ImageUsage.html

Rhyzopertha dominica
Gary Alpert, Harvard University, bugwood.org
Refer to Bugwood: http://www.bugwood.org/ImageUsage.html

Rhyzopertha dominica
Whitney Cranshaw, Colorado State University, bugwood.org
Refer to Bugwood: http://www.bugwood.org/ImageUsage.html

Distribution

Host Plants and Other Plants Affected

Host	Host status	References
Arachis hypogaea (groundnut)	Unknown
Avena sativa (oats)	Main
Capsicum frutescens (chilli)	Other
Cicer arietinum (chickpea)	Unknown
Coriandrum sativum (coriander)	Other
Curcuma longa (turmeric)	Other
Glycine max (soyabean)	Unknown
Hordeum vulgare (barley)	Main
Lens culinaris subsp. culinaris (lentil)	Unknown
Manihot esculenta (cassava)	Other
Oryza sativa (rice)	Main
Panicum (millets)	Main
Pennisetum (feather grass)	Main
Pennisetum glaucum (pearl millet)	Unknown
Phaseolus (beans)	Other
Sorghum bicolor (sorghum)	Main
stored products (dried stored products)	Main
Triticale	Unknown
Triticum (wheat)	Main
Triticum aestivum (wheat)	Main
Triticum spelta (spelt)	Unknown
Triticum turgidum (durum wheat)	Main
Triticum turgidum subsp. durum	Unknown	Suma et al. (2010)
Vigna angularis (adzuki bean)	Unknown
Vigna mungo (black gram)	Unknown
Vigna radiata (mung bean)	Unknown
wheat flour	Other
Zea mays (maize)	Main
Zingiber officinale (ginger)	Other
Zizania palustris (northern wild rice (USA))	Unknown

List of Symptoms/Signs

Symptom or sign	Life stages	Sign or diagnosis
Plants/Seeds/external feeding

Prevention and Control

Physical control

Physical control of R. dominica involves the manipulation of the temperature, relative humidity, atmospheric composition (air gases composition), sanitation, ionizing radiation and the removal of adult insects from the grain either by sieving or air. All these practices may be helpful in eliminating or reducing insect pest infestations to a tolerable level (Jayas et al., 1995).

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. These structures may range from well-sealed barrels holding several kilograms to 100-t capacity metal bins. The structures should be pressure-tested to confirm airtightness. Portable hermetic storage bags are also available (Garcia-Lara et al., 2013).

Removing insects by sieving is not equally effective for all species as several insect species, including R. dominica, spend most time of their life cycle remaining inside the grain or kernel. Impacting the grain, either by moving the grain using a pneumatic conveyer or dropping the grain onto a spinning, studded disc, can reduce R. dominica populations by over 90%. Good sanitation, particularly the removal of spilt grain around storage facilities, is a preliminary step in reducing insect populations that can infest grain in storage.

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. The Kansas State extension program has advocated early aeration as the best non-chemical insect suppression method; a study conducted in Kansas, USA, exhibited that aeration starting from harvesting, using automatic fan controllers, allowed safe storage of grain for several months (Reed and Harner, 1997).

A moisture content (mc) of 25% is not uncommon in newly harvested grain in humid regions, but grains with 14% mc can be safely stored for 2-3 months. For longer storage periods, from 4-12 months, the moisture content must be reduced further. 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 vapour pressure gradient between the moisture in the grain and the moisture in the drying air. This gradient causes moisture to move from the grain into the air, where it is then exhausted from the grain bulk to the outside atmosphere. (Jones et al., 2012). In many countries in Asia, Africa, and Latin America grain drying is achieved by spreading a thin layer of grain in the sun, on the threshing floor or on rooftops. A mechanical way to remove the water from wet grains is by blowing (heated) air through the grain. Mechanical drying of wheat grain is not practiced in many the developing countries, which largely rely on sun drying. At 34°C and 14% moisture content there were 109 R. dominica adults produced per female per generation; 10 adults at 10% moisture content, 0.3 adults at 9% and none at 8% moisture content (Birch, 1953).

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). Janhang et al. (2005) evaluated the efficiency of radio-frequency heat treatment against R. dominica both on the seed surface and inside the seed. The rice kernels with 10.4% moisture content and 93% germination rate were treated with radio frequency heat treatment at 27.12 MHz at 70, 75, 80 and 85 °C for 180 seconds. 100% mortality of R. dominica was achieved in all treatments; however, the rice seed quality was also decreased at higher temperatures. Phosphine-resistant adults were found to be more tolerant than phosphine-susceptible adults toward soft-electron and gamma radiation (Hasan et al., 2006).

More recently, a flameless catalytic infrared emitter was used to disinfest hard red winter wheat containing different life stages (eggs, larvae, pupae and 2-week-old adults) of R. dominica (Khamis et al., 2010). Approximately 94% mortality of all R. dominica life stages occurred when 113.5 g of wheat was exposed for 60 s at a distance of 8.0 cm from the emitter, resulting in wheat temperatures that ranged between 107.6 ± 1.4 and 113.5 ± 0.5°C. These findings suggested this technology as a promising tool for disinfestation of stored wheat (Khamis et al., 2010).

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. In temperate countries, grain temperatures can be reduced by forcing air from outside through the grain, especially in winter. Grain can also be cooled by aeration using refrigerated air. 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. Commercial units that can handle 150 t of grain/h have been developed in Australia. The running costs of these units are comparable to those of chemical control. Care must be taken to ensure that the commodities in storage are only heated briefly so that the quality of the grain is not reduced. Heat disinfestation of grain has the potential for higher market acceptance than chemically treated grains.

Two interrelated ways have been used to make the method more affordable: one is to decrease typical grain treatment temperatures and hold these temperatures for a time sufficient for disinfestation; the other is to increase the rate of heating to induce physiological heat shocks, thereby bringing about faster insect mortality.

Using a spouted bed, the rates of heat-tolerant species R. dominica mortality were recorded over a range of grain temperatures (50°C to 60°C) at 12% moisture content. It was observed that when the initial rate of heating was increased by increasing the air inlet temperature from 80-100°C, the time required for a given level of mortality was significantly decreased. Moreover, decreasing the target grain temperature and increasing the treatment period accounted for additional cost savings. For instance, at the most rapid rate of heating, grain that reached 60°C required 0.73 min of heat soak for 99.9% mortality and cost a theoretical US$ 2.72/t, while grain that reached 55°C required 23.62 min for the same level of mortality and cost US$ 1.87/t. By 50°C, 22 h were required, but the theoretical running cost was reduced to US$ 1.25/t (Beckett and Morton, 2003). 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. The two main approaches involve increasing CO₂ concentration and reducing oxygen in the storage vicinity. To control the insect infestations, oxygen levels must be maintained below 1% for 20 days, or carbon dioxide levels maintained at 80% for 9 days, 60% for 11 days or 40% for 17 days. The storage structures should be sealed properly before the addition of gases (Annis and Graver, 1990).

The effectiveness of CO₂ at different temperatures (20, 25, 30, 35 and 40°C) and exposure intervals (6, 12, 18, 24, 30, 36, 48, 54 hr) was tested against the life stages of different stored grain insects including R. dominica. The eggs of R. dominica were particularly tolerant at 20°C, which required extended exposure to treatment (54 and 48 hr, respectively) to prevent the egg survival. The adults were highly susceptible and a 24-hr exposure at 20°C or 6-hr at temperatures of >30°C were enough to achieve 100% mortality (Locatelli and Daolio, 1993). The combination application of carbon dioxide (5-20%) with the fumigant ethyl formate significantly enhanced the effectiveness of the fumigant against R. dominica and living stages of some other stored grain insect species (Haritos et al., 2006).

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. Silica aerogels are man-made powders with smaller and more uniform particle sizes than DE. A major portion of silica aerogel and DE is made up of silicon dioxide, which dehydrates the insect body by both cuticle lipid absorption and abrasion (Quarles and Winn, 1996). Although DEs have low mammalian toxicity (Athanassiou et al., 2004), most DE formulations are used at considerably high application rates for the effective insect pest control (Vayias et al., 2006). At high concentrations, DE reduces grain bulk density by 9% and flow rate by 39% (Jackson and Webley, 1994), which is considered unacceptable for many large-scale commercial farms. These levels of loss may be more acceptable for households or subsistence farms.

DEs from different geological sources have different efficacies (Nwaubani et al., 2014), and the concentrations required to control infestations must be assessed before use. Other factors determining the efficacy of any DE formulation include: test insect population (Wakil et al., 2013), test insect species (Vassilakos et al., 2006), exposure interval (Baldassari et al., 2008), dose rate (Wakil et al., 2010) and temperature and relative humidity (Chanbang et al., 2007).

R. dominica is relatively tolerant to DE, and concentrations between 500 and 1000 ppm are required to control populations (Subramanyam et al., 1994). However, by the introduction of enhanced DE formulations, an effective control of this insect species is possible, even at a dose rate of 50 ppm (Wakil et al., 2011; Riasat et al., 2013). Furthermore, the combined use of DE with other insect control methods could provide effective control of R. dominica (Lord, 2005; Athanassiou et al., 2008; Riasat et al., 2011; Wakil et al., 2012; 2013).

Host plant resistance

Although there are substantial differences in the resistance of host varieties to R. dominica (Kishore, 1993; Cortez-Rocha et al., 1993), the use of resistant varieties has not been exploited as a method of control. Resistant varieties often do not prevent insect infestations, but reduce the rate at which infestations develop, and increase mortalities. Host resistance would enable the crop to be stored for a longer period before extensive damage is caused by insect populations. 28 different varieties of short, long and medium size rice kernel exhibited variable level of resistance to R. dominica, as measured on the Dobie Index of susceptibility (Chanbang et al., 2008b).

Adult R. dominica mortality due to DE treatment was generally greater on more resistant varieties of rough rice compared to less resistant varieties (Chanbang et al., 2008a).

The susceptibility of six milled rice varieties (IR-64, Ciherang, Membramo, Cibogo, Sembada, and Intani-2) to R. dominica was studied under laboratory conditions (Astuti et al., 2013). The susceptibility was measured on the basis of number of eggs laid by female insects, the number of F1 progeny emerged, the weight loss of infested samples and also using the Dobie index of susceptibility. Milled rice varieties with high phenolic content and hardness may show resistance to R.dominica infestation.

However, caution is needed with regard to the introduction of resistant varieties as a method of control of R. dominica; the insect may overcome host plant resistance, as it has developed resistance to insecticides, and the development of further resistance management strategies would be required.

Botanical insecticides

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). The essential oils obtained from different plant species repel several insect pests and possess ovicidal and larvicidal properties. Although they are considered by some as environmentally compatible pesticides (Cetin et al., 2004), some botanicals, especially essential oils, are toxic to a broad range of animals, including mammals (Bakkali et al., 2008). Suthisut et al. (2011a,b) found that some natural products were actually more dangerous to use than the commercial insecticides, because much more of the product is needed to control the insects than the fumigant or the synthetic contact insecticide.

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).

Biological control

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.

During a field study, Flinn et al. (1998) observed that C. elegans suppressed R. dominica by 91% in 27 ton bins of stored wheat compared with control bins. In another study it was found that suppression of R. dominica population growth by parasitoid wasps was significantly higher at 25°C than at 32°C and that 25°C resulted in a very high level of population suppression (99%) compared to the control (Flinn, 1998). 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 highest percentage (81%) suppression occurred in calico bags and the lowest suppression (57%) occurred in polypropylene bags (Mahal et al., 2005).

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). Beauveria bassiana (Ascomycota: Hyphomycetes) and Metarhizium anisopliae (Ascomycota: Sordario) are the most extensively studies fungal species in this regard (Lord, 2005; Vassilakos et al., 2006; Athanassiou et al., 2008; Wakil and Ghazanfar, 2010).

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).

Entomopathogenic fungi have also been tested in combination with other control tactics: for example, Isaria fumosorosea with enhanced diatomaceous earth and the plant extract bitterbarkomycin (Riasat et al., 2013); B. bassiana and enhanced diatomaceous earth (Wakil et al., 2011); B. bassiana admixed with a diatomaceous earth formulation (Riasat et al., 2011); and B. bassiana with thiamethoxam and a diatomaceous earth formulation (Wakil et al., 2012). The results demonstrated that such combined controls could be an effective strategy to control R. dominica in stored wheat.

Bacillus thuringiensis var. tenebrionis has been investigated for the control of R. dominica (Keever, 1994; Mummigatti et al., 1994). Most B. thuringiensis varieties are ineffective against beetles; however, R. dominica was one of the more susceptible beetles to B. thuringiensis var. tenebrionis, with more than 75% mortality in 17 days at 250 ppm (Mummigatti et al., 1994). Toxins of 36 available subspecies of B. thuriengensis were evaluated against larvae and adults of R. dominica. The spore crystal complex of B. thuringiensisdarmstadiensis obtained from Germany was the most effective against larvae, but the same subspecies from USA and Japan could not effectively control R. dominica (Beegle, 1996).

In a recent study, the combination of Cry3Aa protoxin and protease inhibitor (potato carboxypeptidase) resulted in delayed development, increased mortality and progeny suppression of R. dominica (Oppert et al., 2011).

Entomopathogenic nematodes (EPNs) are endoparasites of insects (Gaugler, 2002), that enter into host through natural body openings and release mutualistic bacteria inside the host’s body that kills it within 24-48 hours. Their low toxicity to vertebrates (Boemare et al., 1996), exemption from registration in the USA by the Environmental Protection Agency (Kaya and Gaugler, 1993), commercial availability (Grewal, 2002) and ability to seek their host actively (Campbell and Lewis, 2002) make EPNs potentially good biological control agents for stored-product pests. However, they have not proved very effective against R. dominica; R. dominica suffered only 35% adult mortality to two EPN species (in Heterorhabditidae and Steinernematidae) (Ramos-Rodríguez et al., 2006). Similarly, at 20⁰C, the mortality of adult R. dominica in wheat treated with Steinernema feltiae and Steinernema carpocapsae (at 20,000 infected juveniles per ml) did not exceed 23 and 42%, respectively (Athanassiou et al., 2010a).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

•

EU pesticides database (http://ec.europa.eu/food/plant/pesticides/eu-pesticides-database/)

•

PAN pesticide database (www.pesticideinfo.org)

•

Your national pesticide guide

Impact

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).

Laboratory experiments have estimated that one R. dominica consumes 0.15 g of wheat in its life time (Campbell and Sinha, 1976; Storey et al., 1982). If all R. dominica completed their life cycle from 1976 to 1979 in the USA, they would have consumed 300,000 metric tonnes of wheat annually, or 0.5% of the total of stored wheat. Similar calculations, assuming R. dominica eats 0.15 g during its lifetime, give 8000 tonnes of maize (0.004% loss of total harvest) and 2000 tonnes of oats (0.02% loss) consumed annually by R. dominica.

Data collected from 1998 to 2002 from wheat stored in commercial grain elevators in south-central Kansas, USA, revealed that C. ferrugineus, R. dominica and T. castaneum were the primary insect species found in collected wheat samples. In the top 3.7 m of grain, R. dominica made up 44% of the insects found in the samples, and from 3.8 to 12.2 m it was present at 84% (Flinn et al., 2010). In 2008, R. dominica caused serious damage to grain in an Indonesia government storage unit (Astuti et al., 2013).

The cost of controlling storage pests can be substantial. The Environmental Protection Agency in the USA estimated that 270,000 kg of aluminum phosphide pesticide was used annually between 1987 and 1996 for wheat in storage, roughly one third of the total aluminium phosphide used in those years (Anonymous, 1998).

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Published online: 4 October 2022

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