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Datasheet

Prostephanus truncatus (larger grain borer)

Summary

  • Last modified
  • 11 October 2017
  • Datasheet Type(s)
  • Pest
  • Invasive Species
  • Preferred Scientific Name
  • Prostephanus truncatus
  • Preferred Common Name
  • larger grain borer
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Uniramia
  •         Class: Insecta
  • Summary of Invasiveness
  • P. truncatus spreads rapidly in trade moving in infested consignments of maize and dried cassava. Trade flows have a profound effect on its speed of movement. Nevertheless, it can fly and does use this as a means of dispersal....

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Pictures

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PictureTitleCaptionCopyright
Adult beetle, lateral view.
TitleAdult
CaptionAdult beetle, lateral view.
Copyright©Georg Goergen/IITA Insect Museum, Cotonou, Benin
Adult beetle, lateral view.
AdultAdult beetle, lateral view.©Georg Goergen/IITA Insect Museum, Cotonou, Benin
Typical cylindrical bostrichid shape, declivity flattened and steep, with many small tubercles over its surface; body 3-4.5 mm long.
TitleAdult
CaptionTypical cylindrical bostrichid shape, declivity flattened and steep, with many small tubercles over its surface; body 3-4.5 mm long.
CopyrightNRI/MAFF
Typical cylindrical bostrichid shape, declivity flattened and steep, with many small tubercles over its surface; body 3-4.5 mm long.
AdultTypical cylindrical bostrichid shape, declivity flattened and steep, with many small tubercles over its surface; body 3-4.5 mm long. NRI/MAFF

Identity

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Preferred Scientific Name

  • Prostephanus truncatus (Horn)

Preferred Common Name

  • larger grain borer

Other Scientific Names

  • Dinoderus truncatus Horn

International Common Names

  • English: grain, borer, larger; greater grain borer; scania beetle
  • Spanish: barrebador de los granos; barrenador del grano mayor; barrenador grande de los graneros

Local Common Names

  • Germany: Bohrer, grosser Korn-

EPPO code

  • PROETR (Prostephanus truncatus)

Summary of Invasiveness

Top of page P. truncatus spreads rapidly in trade moving in infested consignments of maize and dried cassava. Trade flows have a profound effect on its speed of movement. Nevertheless, it can fly and does use this as a means of dispersal.

On a local scale, the pest flies from environments where population density is high or food exhausted to seek new hosts, usually in subsistence farmers' granaries. It locates stored product hosts, such as maize and dried cassava either by chance or because they are already infested and harbour males releasing aggregation pheromone. This type of host selection leads to very dense populations of the pest in a few farm stores surrounded by other stores showing no signs of infestation.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Uniramia
  •                 Class: Insecta
  •                     Order: Coleoptera
  •                         Family: Bostrichidae
  •                             Genus: Prostephanus
  •                                 Species: Prostephanus truncatus

Notes on Taxonomy and Nomenclature

Top of page Prostephanus truncatus was first described by Horn, 1878 as Dinoderus truncatus, and has been referred to as Stephanopachys truncatus by Back and Cotton (1938). The genus Prostephanus was erected by Lesne (1898) to accommodate this and three other species; P. truncatus is the only one of these species known to be associated with stored products.

The most commonly used English name for the species is larger grain borer (LGB) although some countries favour greater grain borer (GGB) which gives the correct semantic distinction from the lesser grain borer (Rhyzopertha dominica).

The adults may be identified using the keys of Fisher (1950), Kingsolver (1971) or Haines (1991). A key to both larvae and adults is given in Gorham (1991). The taxonomy, systematics and identification of P. truncatus have been reviewed recently by Farrell and Haines (2002).

Description

Top of page Larva

The larvae are white, fleshy and sparsely covered with hairs. They are parallel-sided, i.e. they do not taper. The legs are short and the head capsule is small relative to the size of the body.

Adult

The adult has the typical cylindrical bostrichid shape. The declivity is flattened and steep and has many small tubercles over its surface. The limits of the declivity, apically and laterally, are marked by a carina. The antennae are 10-segmented and have a loose three-segmented club; the 'stem' of the antenna is slender and clothed with long hairs and the apical club segment is as wide as, or wider than, the preceding segments. The body is 3-4.5 mm long.

Distribution

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P. truncatus is indigenous in Central America, tropical South America, and the extreme south of the USA as a major, but localized, pest of farm-stored maize. It was introduced into Tanzania, probably in the late 1970s, and has become a serious pest of stored maize and dried cassava in that part of East Africa; it has since spread into Kenya, Burundi, Rwanda, Malawi, Zambia, Mozambique, Namibia and South Africa, and is almost certainly present but unreported from several other countries in the region. It was first found in West Africa in Togo in 1984 and it has since spread to Benin, Nigeria, Ghana, Niger and Burkina Faso. A separate outbreak occurred in Guinea Conakry.

P. truncatus could potentially invade all maize and cassava growing areas of tropical and sub-tropical Africa, and it is the only recent example of a serious storage pest invading on a regional or continental scale. It remains a quarantine threat to other maize growing regions in the Old World.

There are several records of interceptions of P. truncatus, including Canada (Manitoba), the USA (Arizona, Montana, New York and New Jersey), Germany (interception from Guatemala), Israel and Iraq (IIE, 1995).

A record of P. truncatus in Thailand is now known to be based on a misidentification (R. Hodges, Natural Resources Institute, UK, personal communication, 2006).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ChinaAbsent, intercepted onlyIIE, 1995; EPPO, 2014
-Hong KongAbsent, intercepted onlyIIE, 1995
IndiaAbsent, intercepted onlyIIE, 1995; EPPO, 2014
-Uttar PradeshAbsent, intercepted onlyIIE, 1995; EPPO, 2014
IraqAbsent, intercepted onlyIIE, 1995; EPPO, 2014
IsraelAbsent, intercepted onlyIIE, 1995; EPPO, 2014
PhilippinesAbsent, intercepted onlyIIE, 1995
ThailandAbsent, invalid recordEPPO, 2014

Africa

BeninRestricted distributionIntroduced1984 Invasive Hodges, 1994; IIE, 1995; EPPO, 2014
Burkina FasoRestricted distributionIntroduced1991Hodges, 1994; IIE, 1995; EPPO, 2014
BurundiRestricted distributionIntroduced1984Hodges, 1994; IIE, 1995; EPPO, 2014
GhanaRestricted distributionIntroduced1989 Invasive Hodges, 1994; IIE, 1995; EPPO, 2014
GuineaRestricted distributionIntroduced1987Hodges, 1994; IIE, 1995; EPPO, 2014
KenyaPresentIntroduced1983 Invasive Hodges, 1994; IIE, 1995; IPPC-Secretariat, 2005; EPPO, 2014
MalawiPresentIntroduced1992Hodges, 1994; IIE, 1995; EPPO, 2014
MozambiqueWidespreadIntroduced1999 Invasive Anon, 2004
NamibiaRestricted distributionIntroducedRhodes, 1998
NigerRestricted distributionIntroduced1994IIE, 1995; Adda et al., 1996; EPPO, 2014
NigeriaRestricted distributionIntroduced1992Hodges, 1994; IIE, 1995; EPPO, 2014
RwandaPresentIntroduced1993Hodges, 1994; IIE, 1995; EPPO, 2014
SenegalPresentGueye et al., 2008; Gueye et al., 2008
SenegalPresentGueye et al., 2008; Gueye et al., 2008
South AfricaRestricted distributionEPPO, 2014
TanzaniaWidespreadIntroduced<1981 Invasive Hodges, 1986; IIE, 1995; EPPO, 2014
TogoPresentIntroduced1984 Invasive Hodges, 1986; IIE, 1995; EPPO, 2014
ZambiaWidespreadIntroduced1993Hodges and Pike, 1995; EPPO, 2014

North America

CanadaAbsent, intercepted onlyEPPO, 2014
-ManitobaAbsent, intercepted onlyIIE, 1995; EPPO, 2014
MexicoPresentNative Invasive Hodges, 1986; IIE, 1995; EPPO, 2014
USARestricted distributionEPPO, 2014
-ArizonaPresentNativeIIE, 1995; EPPO, 2014
-CaliforniaPresent Not invasive IIE, 1995; EPPO, 2014
-District of ColumbiaPresentIntroduced1878 Not invasive IIE, 1995
-MontanaAbsent, intercepted onlyIIE, 1995; EPPO, 2014
-New JerseyAbsent, intercepted onlyIIE, 1995; EPPO, 2014
-New YorkAbsent, intercepted onlyIIE, 1995; EPPO, 2014
-OklahomaPresentEdde and Phillips, 2006
-TexasPresentNativeIIE, 1995; EPPO, 2014

Central America and Caribbean

Costa RicaPresentNativeHodges, 1986; IIE, 1995; EPPO, 2014
El SalvadorPresentNativeHodges, 1986; IIE, 1995; EPPO, 2014
GuatemalaPresentNativeHodges, 1986; IIE, 1995; EPPO, 2014
HondurasPresentNativeHodges, 1986; IIE, 1995; EPPO, 2014
NicaraguaPresentNative Invasive Hodges, 1986; IIE, 1995; EPPO, 2014
PanamaPresentNativeHodges, 1986; IIE, 1995; EPPO, 2014

South America

BrazilAbsent, formerly present1993IIE, 1995; EPPO, 2014
-Minas GeraisAbsent, formerly presentEPPO, 2014
ColombiaPresentNativeHodges, 1986; IIE, 1995; EPPO, 2014
PeruPresentHodges, 1986

Europe

FranceAbsent, intercepted onlyIIE, 1995
GermanyAbsent, intercepted onlyIIE, 1995; EPPO, 2014
ItalyPresentSuma and Russo, 2005
-SicilyPresentSuma and Russo, 2005

History of Introduction and Spread

Top of page P. truncatus was probably introduced accidentally into Africa in the late 1970s, but was first recorded in 1981. It was introduced separately into East and West Africa and a summary of its spread into 11 African countries is provided by Hodges (1994). In Zambia, for example, it was first recorded near the Tanzanian border in 1993, but was subsequently spread throught the country in 1995 following the importation of infested maize (Sumani, 2000).

Risk of Introduction

Top of page P. truncatus remains a quarantine threat to maize-growing regions in the Old World. The phytosanitary measures that should be taken against P. truncatus in international trade have been reviewed by Tyler and Hodges (2002).

Hosts/Species Affected

Top of page P. truncatus is a serious pest of stored maize and dried cassava roots, and will attack maize in the field just before harvest. Attempts to rear the species on cowpea, haricot beans [Phaseolus vulgaris], cocoa, coffee beans and rough rice in the laboratory have been unsuccessful, although development is possible on soft wheat varieties, and adult feeding may damage these other commodities (Shires, 1977).

P. truncatus behaves as a typical primary pest of farm-stored maize; whole grains are attacked, on the cob, both before and after harvest. P. truncatus is also a pest of farm-stored cassava, particularly cassava chips. The adults bore into a wide range of foodstuffs and other materials including wood, bamboo, plastic and soap. Extensive populations of P. truncatus occur in the natural environment, and it has been recorded from a number of tree species in Central America (Rees et al., 1990; Ramirez-Martinez et al., 1994) and Africa (Nang'ayo et al., 1993, 2002; Nansen et al., 2004) in some cases associated with twig girdling by cerambycid beetles (Borgemeister et al., 1998).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Arachis hypogaea (groundnut)FabaceaeOther
Dioscorea (yam)DioscoreaceaeOther
Manihot esculenta (cassava)EuphorbiaceaeMain
Phaseolus vulgaris (common bean)FabaceaeOther
Sorghum bicolor (sorghum)PoaceaeOther
stored products (dried stored products)Main
TriticaleOther
Triticum aestivum (wheat)PoaceaeOther
Zea mays (maize)PoaceaeMain

Growth Stages

Top of page Post-harvest

Symptoms

Top of page Adults tunnel through stored maize grain or other starchy products, such as dried cassava chips, creating large quantities of dust. Larvae and pupae may be found in the tunnels made by the adults.

List of Symptoms/Signs

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Seeds

  • internal feeding

Biology and Ecology

Top of page P. truncatus may be attracted to maize grain and dried cassava over short distances. However, field studies in both Mexico and Togo suggest that there is no long-range attraction of adult P. truncatus to maize grain or cobs, or dried cassava; this is not surprising because wood is the major host of this beetle. It has been shown in laboratory tests that upwind flight is mediated by a male-released aggregation pheromone and not by host volatiles (Fadamiro et al., 1998) and field studies provide strong evidence that host selection, in the case of maize and cassava, occurs by chance (Birkinshaw et al., 2002). Details of host selection can be found in Hodges (1994), Scholz et al. (1997) and Hodges et al. (1998).

Adults frequently initiate their attack on stored maize cobs with intact sheaths by boring into the base of the maize cob cores, although they eventually gain access to the grain via the apex of the cob by crawling between the sheathing leaves (Hodges and Meik, 1984). Adults bore into the maize grains, making neat round holes, and as they tunnel from grain to grain they generate large quantities of maize dust. Adult females lay eggs in chambers bored at right angles to the main tunnels. Egg-laying on stabilized grain, like that on the maize cob, is more productive than on loose-shelled grain as the oviposition period is longer, equal in length to the life of the female, and the eggs are laid at a greater rate.

Larvae hatch from the eggs after about three days at 27°C and seem to thrive on the dust produced by boring adults. For example, large numbers of larvae develop and pupate in dust at the base of dense laboratory cultures.

The life cycle of P. truncatus has been investigated at a range of temperatures and humidities (Shires, 1979, 1980; Bell and Watters, 1982; Hodges and Meik, 1984). Development of the larva through to the adult stage at the optimum conditions of 32°C and 80% RH takes 27 days on a diet of maize grain. Humidity within the range 50-80% RH does not greatly affect the development period or mortality; at 32°C, a drop in RH from 80 to 50% (giving maize with an equilibrium moisture content of about 10.5%) extended the mean development period by just 6 days and increased the mean mortality by only 13.3%. This tolerance of dry conditions was confirmed during field studies in Nicaragua and Tanzania in which maize at 10.6 and 9% moisture content, respectively, was heavily infested.

The success of this pest may be partly due to its ability to develop in grain at low moisture. Many other storage pests are unable to increase in number under low moisture conditions. For example, Sitophilus oryzae, a species occurring in the same ecological niche, needs a grain moisture content of at least 10.5% for development. Thus, in dry conditions, P. truncatus probably benefits from the absence of any significant competition from other storage pests.

P. truncatus develops more rapidly on maize grain than on cassava; at 27°C and 70% RH, the respective development periods on maize grain and cassava were 32.5 and 40 days, respectively. Under ideal conditions of temperature and humidity on maize cobs or stabilized maize grain, estimates for the intrinsic rate of increase (r) of P. truncatus are in the order of 0.7-0.8 per week; this is similar to the rate of increase reported for Tribolium castaneum under comparable climatic conditions.

Details of flight performance and factors affecting flight and distribution behaviour have been investigated in the laboratory (Fadamiro and Wyatt, 1955, 1996; Fadamiro, 1997). A field study in Honduras showed flight activity of P. truncatus following a daily bimodal pattern with a major peak at 06.00-08.00 h and a minor peak at 18.00-20.00 h (Novillo, 1991). A similar pattern was observed by Tigar et al. (1993) in Central Mexico and Birkinshaw et al. (2004) in Ghana, but in both these cases the major peak was associated with dusk.

Adults may be sexed using a method described by Shires and McCarthy (1976).

For further detailed information on biology and ecology, consult reviews by Hodges (1986), Markham et al. (1991), Hodges (1994), Nansen and Meikle (2002) and Hill et al. (2002).

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Anisopteromalus calandrae Parasite
Beauveria bassiana Pathogen
Metarhizium anisopliae Pathogen
Pteromalus cerealellae Parasite
Teretrius nigrescens Predator Eggs/Larvae/Pupae Africa; Togo stored maize
Theocolax elegans Parasite
Xylocoris flavipes Predator

Notes on Natural Enemies

Top of page Only one predator, Teretrius (formerly Teretriosoma) nigrescens, has been associated with P. truncatus; this was in Central America. Laboratory studies by Rees (1985), using shelled maize grain (weighed down with glass beads) maintained at 8.5 or 14% moisture content, showed that 10 adult T. nigrescens were able to prevent populations of up to 100 adult P. truncatus from increasing. In the laboratory, T. nigrescens successfully suppressed the growth of populations of P. truncatus on maize cobs in the presence of Sitophilus zeamais and Tribolium castaneum (Rees, 1987). It is known that T. nigrescens in flight find P. truncatus by attraction to male-released aggregation pheromone. However, once the predator has landed it is no longer attracted by the pheromone but by material in the frass of P. truncatus (Stewart-Jones et al., 2004, 2006).

Infestations of P. truncatus in Nicaragua were associated with high levels of parasitic Hymenoptera, accounting for 10% of the total number of insects present, while the P. truncatus population represented 56.5%; these Hymenoptera were not identified. In Tanzania, large numbers of Anisopteromalus calandrae were associated with P. truncatus when few other potential hosts were present (Hodges et al., 1983). The hemipteran Xylocoris flavipes has been observed as a predator of all three larval stages of P. truncatus in West Africa, however populations of the bug declined as pest numbers rose. It is believed that the conditions created by P. truncatus infestation are unfavourable to X. flavipes and hence this species probably does not play an important role in the control of the pest (Helbig, 1999).

Little is known about the relationship between P. truncatus and other organisms. Infestations of this beetle are found, together with those of other species, but P. truncatus is the predominant storage species in the dry conditions of Tanzania and Nicaragua. It has been demonstrated that P. truncatus is deterred from infesting grain in which the larvae of Sitophilus zeamais are developing and that this probably results from substances deposited on the grain surface by adult S. zeamais (Danho et al., 2000).

In a survey of the pest in Kenya, Odour et al. (2000) found that the entomopathogenic fungus Beauveria bassiana occurred on only 0.08 to 0.94% of the total insects collected. This is a low infection rate. Isolates of Beauveria, Metarhizium and Paecilomyces obtained in Ethiopia where all found to be virulent against P. truncatus although a total immersion bioassay was used so this result might have been anticipated (Kassa et al., 2002). The potential of Beauveria has been investigated in field trials designed to give a better understanding of how future research efforts can develop methods to make this fungus an effective means of control for P. truncatus (Meikle et al., 2001).

Means of Movement and Dispersal

Top of page P. truncatus is spread over longer distances almost entirely through the import and export of infested grain. Local dispersal is through the local movement of infested grain and by flight activity of the adult beetles themselves.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Land vehiclesCarried by national and international grain trade Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bulbs/Tubers/Corms/Rhizomes No No
Roots adults; eggs; larvae; pupae Yes No Pest or symptoms usually visible to the naked eye
True seeds (inc. grain) adults; eggs; larvae; pupae Yes No Pest or symptoms usually visible to the naked eye
Wood adults; eggs; larvae; pupae Yes No Pest or symptoms usually visible to the naked eye
Plant parts not known to carry the pest in trade/transport
Bark
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
Leaves
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) None
Crop production None
Environment (generally) None
Fisheries / aquaculture None
Forestry production None
Human health None
Livestock production None
Native fauna None
Native flora None
Rare/protected species None
Tourism None
Trade/international relations Negative
Transport/travel None

Impact

Top of page P. truncatus is a pest of maize and dried cassava roots after harvest in sub-Saharan Africa and also from time to time in Central America.

Infestations in maize may start on the mature crop in the field, i.e. when moisture content is at or below 18%. Weight losses of up to 40% have been recorded in Nicaragua from maize cobs stored on the farm for 6 months (Giles and Leon, 1975). In Tanzania, up to 34% losses have been observed after 3 months storage on the farm, with an average loss of 8.7% (Hodges et al., 1983). P. truncatus is a much more damaging pest when compared to other storage insects including Sitophilus oryzae, S. zeamais and Sitotroga cerealella, under similar conditions; maize losses due to these other species were 2-6, 3-5 and 2-5%, during a storage season in Zambia, Kenya and Malawi, respectively.

Losses caused by P. truncatus in dried cassava roots can be very high; the dried roots are readily reduced to dust by boring adults and a loss of 70% has been recorded after only 4 months of farm storage (Hodges et al., 1985). A group of 25 farmers from five villages in Togo sustained average cumulative losses of 9.7% after 3 months storage, this figure rose to 19.5% after 7 months (Wright et al., 1993).

Not all problems with this pest are restricted to farmers' granaries. In the early days after the arrival of P. truncatus in East Africa, countries with the pest found their maize exports banned. For example in 1987-88, it is estimated that Tanzania lost US$634,000 in export earning. This situation improved following efforts to upgrade phytosanitary procedures in the region but such procedures, involving fumigation, have their own continuing costs (Boxall, 2002).

A grain injury model for P. truncatus infesting farm-stored maize in West Africa has been developed at the International Institute of Tropical Agriculture. It can be used in conjunction with predictive models of pest population dynamics to guide the development of integrated pest management strategies (Holst et al., 2000a). The models are conveniently displayed, together with information on sampling routines, on a web site (<_http3a_ _www.agrsci.dk2f_plb2f_bembi2f_africa2f_project.htm="" xmlns="http://cabi.org/cet">).

A detailed review of the damage and loss caused by P. truncatus has been prepared by Boxall (2002). He considers loss of value, nutrition as well as impact at the national level, effect on international trade and modern methods of rapid loss assessment. In the early days after the arrival of P. truncatus in East Africa, countries with the pest found their maize exports banned. For example, in 1987-1988, it is estimated that Tanzania lost US$634,000 in export earning. This situation improved following efforts to upgrade phytosanitary procedures in the region but such procedures, involving fumigation, have their own continuing costs.

Environmental Impact

Top of page P. truncatus has no known environmental impacts.

Impact: Biodiversity

Top of page P. truncatus has no known effects on biodiversity.

Social Impact

Top of page P. truncatus infests the granaries of subsistence farmers and in sub-Saharan Africa the losses that result can be twice that caused by other storage pests. Subsistence farmers typically rely on their stored maize as food until the next maize harvest. The depredation of P. truncatus results in farmers having to purchase maize, or those farmers with more extensive stock will have no maize to sell. The pest is thus a threat to food security and to the livelihoods of poor people.

Detection and Inspection

Top of page Methods for detection and monitoring of P. truncatus has been reviewed in detail by Hodges (2002).

Flight traps, such as funnel, delta or wing traps baited with the male-released aggregation pheromone of P. truncatus, are highly effective for monitoring this species. These traps should be placed at least 100 m from stores, which contain maize or dried cassava, or from the standing maize crop to avoid attracting the beetles to these food sources. A detailed leaflet giving recommendations on the use of pheromone traps to monitor P. truncatus has been prepared by Hodges and Pike (1995). For long-term, routine trapping programmes in both East and West Africa the Japanese beetle flight-trap baited with P. truncatus pheromone is now the method of choice while pheromone baited Delta traps, made from cardboard, are used in short-term programmes.

The risk of stores becoming infested by P. truncatus is known to be related to the number of P. truncatus that are flying (Birkinshaw et al., 2002). There are big variations both within and between years in the numbers of beetles taking flight. In many locations this difference between years is noticeable by the extent to which farmer's stores become infested, i.e. there are good and bad years. A computer-based model has been developed that uses climate data to predict P. truncatus flight activity and in this way it can predict the years when P. truncatus infestation will be bad (Hodges et al., 2003).

Monitoring for the presence of P. truncatus in farm maize stores themselves is difficult because the pest is not attracted to its pheromone when present on its food. A sequential sampling plan for inspecting stores in West Africa has been described by Meikle et al. (2000). Compton and Sherington (1999) have described a rapid method for estimating the weight losses caused by P. truncatus to maize cobs.

Prevention and Control

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Chemical Control

The most effective method of controlling P. truncatus in maize is to admix a dilute dust insecticide. P. truncatus is highly susceptible to synthetic pyrethroid insecticides such as permethrin and deltamethrin. However, these insecticides are relatively ineffective against other storage pests such as Sitophilus spp. and Tribolium castaneum, which occur in the same pest complex and are more susceptible to organophosphorus insecticides. Both types of insecticide are applied in order to control the whole complex (Golob et al., 1985; Golob and Hanks, 1990). Combinations such as pirimiphos-methyl and permethrin, deltamethrin and pirimiphos-methyl or fenitrothion and fenvalerate have been used successfully to protect farm-stored grain. Fumigation with phosphine is very effective in large-scale stores.

Recent laboratory and field studies have shown that unless inert dusts are applied at very high rates, they are not particularly effective against P. truncatus. However, good control can be achieved when they are mixed with insecticides or soil bacteria metabolites such as Spindeba (Stathers, 2003).

For a detailed review of chemical, physical and cultural methods for the control of P. truncatus, see Golob (2002).

Biological Control

Detailed reviews on the control of P. trunctus by the predator Teretrius nigrescens have been published by Meikle et al. (2002) and Borgemeister et al. (2003). Initial releases of T. nigrescens were in Togo in 1991 and in Kenya in 1992. In both countries it became well established and spread. Subsequently, there have been predator releases in Benin, Ghana, Tanzania and Malawi. Only in the case of Tanzania does it appear that there has been any difficulty in the predator becoming quickly and easily established. However, despite the successful introductions, there are still regular outbreaks of P. truncatus and farmers still suffer losses. It has been concluded by Holst et al. (2000b) that T. nigrescens does not offer a good example of classical biological control but as the predator is able to reduce the density of the pest it is considered that it has, nevertheless, a role to play in integrated pest management.

Cultural Control and Sanitary Methods

Good store hygiene, especially the removal of infested residues and the selection of only sound material for storage, can play an important role in limiting infestation by P. truncatus. The use of resistant cultivars may also reduce the severity of an infestation, although much work remains to be done on the mechanisms of resistance.

References

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Adda C; Borgemeister C; Meikle WG; Markham RH; Olaleye I; Abdou KS; Zakari MO, 1996. First record of the larger grain borer, Prostephanus truncatus (Coleoptera: Bostrichidae), in the Republic of Niger. Bulletin of Entomological Research, 86(1):83-85; 11 ref.

Anon, 2004. Mozambique Food Security Update. December 2004. (http://www.fews.net/centers/files/Mozambique_200411en.pdf.

APPPC, 1987. Insect pests of economic significance affecting major crops of the countries in Asia and the Pacific region. Technical Document No. 135. Bangkok, Thailand: Regional Office for Asia and the Pacific region (RAPA).

Arnason JT; Gale J; Conilh de Beyssac B; Sen A; Miller SS; Philogene JR; Lambert DH; Fulcher RG; Serratos A; Mihm J, 1992. Role of phenolics in resistance of maize grain to the stored grain insects Prostephanus truncatus (Horn) and Sitophilus zeamais (Motsch). Journal of Stored Products Research, 28(2):119-126

Back EA; Cotton RT, 1938. Stored Grain Pests. Farmers' Bulletin No. 1260 (revised). Washington DC, USA: US. Department of Agriculture.

Bell RJ; Watters FL, 1982. Environmental factors influencing the development and rate of increase of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) on stored maize. Journal of Stored Products Research, 18(3):131-142

Birkinshaw LA; Hodges RJ; Addo S, 2004. Flight behaviour of Prostepahanus truncatus and Teretrius nigrescens demonstrated by a cheap and simple pheromone-baited trap designed to segregate catches with time. Journal of Stored Products Research, 40:227-232.

Birkinshaw LA; Hodges RJ; Addo S; Riwa W, 2002. Can 'bad' years for damage by Prostephanus truncatus be predicted?. Crop Protection, 21(9):783-791; 23 ref.

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