Prostephanus Truncatus in AFRICA: a REVIEW of BIOLOGICAL TRENDS and PERSPECTIVES on FUTURE PEST MANAGEMENT STRATEGIES

Prostephanus truncatus IN AFRICA: A REVIEW OF BIOLOGICAL TRENDS AND PERSPECTIVES ON FUTURE PEST MANAGEMENT STRATEGIES

B.L. MUATINTE, J. VAN DEN BERG1 and L.A. SANTOS2 Department of Biological Sciences, Faculty of Sciences, Eduardo Mondlane University, P. O. Box 257, Maputo, Mozambique 1Unit of Environmental Sciences, North-West University, Potchefstroom, Private Bag X6001, South Africa 2Department of Plant Production and Protection, Faculty of Agronomy and Forest Engineering, Eduardo Mondlane University, P. O. Box 257, Maputo, Mozambique Corresponding author: [email protected], [email protected]

(Received 12 February, 2014; accepted 18 August, 2014)

ABSTRACT

The pest status of the Larger grain borer, Prostephanus truncatus (Coleoptera: Bostrichidae), is higher in African countries than in Latin America, its region of origin. This pest reduces the storage period of maize grain and cassava chips in granaries of small scale farmers. This reduced storage period results from larval and adult feeding, with consequent shortening of the period these commodities are available for food and income generating sources. Depending on storage time, yield losses of up to 45 and 100% have been recorded for maize and cassava chips, respectively, in West Africa; while 62% yield losses have been reported in Mozambique. Since P. truncatus invaded Africa from approximately 1970, research mostly addressed its biology, ecology, dispersal and control methods. This review paper aims at evaluating P. truncatus pest status in Africa as a basis for designing pragmatic strategies for its control. Prostephanus truncatus pest status in Africa is high and the degree of infestation and damage vary between regions. The variation in pest status is due to climatic conditions, food sources, and degree of storage infra-structure development and efficacy of control methods. Prostephanus truncatus has established in 20 African countries. Its temporal and spatial dispersion is unpredictable and depends on ecological factors, maize and dry cassava trade routes, and availability of forest host plants. Development of sustainable integrated management strategies is a key to future successful management of this pest. Area-wide management strategies using the predator, Teretrius nigrescens, parasitoids, plant derived products and environmentally friendly insecticides is needed. Integrated management practices must be based on improved knowledge of P. truncatus population dynamics and its determining factors.

Key Words: Integrated pest management, maize, Mozambique

RÉSUMÉ

Le statut de la peste de dévoreur des grains, Prostephanus truncatus (Coleoptera: Bostrichidae), est plus élevé dans les pays africains que dans ceux d’Amérique Latine, sa région d’origine. Cette peste réduit la période de stockage des grains de maïs et de manioc dans des grainiers des petits exploitants. Ceci est dû à l’alimentation des larves et adultes, avec pour conséquence, l’écourtement de la période dont de ces produits devraient être disponibles pour nourriture et sources de génération des revenues. Dépendamment du temps de stockage, les pertes de rendement d’environ 45 et 100% ont été observées pour le maïs et le manioc, respectivement en Afrique de l’ouest; pendant que 62% de pertes de rendement ont été reportées au Mozambique. Depuis l’invasion de l’Afrique par P. truncatus aux environ de 1970, la recherche s’est en grande partie attablée sur sa biologie, écologie, propagation et méthodes de contrôle. Cette revue évalue le statut de la peste P. truncatus en Afrique pour comme base de conception des stratégies pragmatiques pour son contrôle. Le statut de la peste de Prostephanus truncatus est élevé en Afrique et les degrés d’infestation et dommage varient entre les régions. La variation du 238 B.L. MUATINTE et al. statut de cette peste est due aux conditions climatiques, sources d’aliments et, degré de développement des infrastructures de stockage et l’efficacité des méthodes de contrôle. Le Prostephanus truncatus s’est établi dans 20 pays africains. Sa propagation temporelle et spatiale est imprédictible et dépend des facteurs écologiques, les voies de commercialisation du maïs et manioc sec, et disponibilité des plantes hôtes dans des forets. Le développement durable des stratégies de gestion intégrée est une clé pour un succès futur de gestion de cette peste. Des stratégies de gestion utilisant le prédateur, Teretriusnigrescens, les parasitoïdes, les produits dérivés des plantes et des insecticides environnementalement viables sont nécessaires. Des pratiques de gestion intégrée doivent être basées sur l’amélioration des connaissances sur la dynamique des populations de P. truncatus et ses facteurs déterminants.

Mots Clés: Gestion intégrée de la peste, maïs, Mozambique

INTRODUCTION et al., 1997; Cugala et al., 2007; Chintzoglou et al., 2008), plant derived products (Tapondjou et The Larger grain borer, Prostephanus truncatus al., 2002; Smith et al., 2006) and biological control (Horn) (Coleoptera: Bostrichidae) was first by means of the exotic predator, T. nigrescens recorded in Africa in the Tambora region of (Richter et al., 1997; Holst and Meikle, 2003; Hell Tanzania in 1981 (Dunstan and Magazini, 1981) et al., 2006; Mahumane et al., 2009). and afterwards in Togo (Harnisch and Krall, 1984). Pest management strategies have been Since then, the Larger grain borer became a developed and include the use of several inert serious pest of stored maize and dry cassava; dusts (Golob, 1997), synthetic insecticides in reducing the storage period of these commodities combination with diatomaceous earth in granaries of small scale farmers. This reduction (Chintzoglou et al., 2008), and wood ash and results from larval and adult feeding, with entomopathogenic fungi (Smith et al., 2006). consequent shortening of the period these Despite the development of these control commodities are available for food and income practices, this pest continuously disperses and generating sources. This pest can also infest and causes severe damage to maize grain and dry cause damage to stored timber and timber cassava chips in granaries of small scale farmers products (Wright, 1984). in Africa. This paper reviews and discusses Several papers have been published about information on the pest status of P. truncatus, its the pest status of Larger grain borer in Africa dispersal since its introduction in Africa and prior to 2002; however, no assessment has been perspectives on future pest management done in this with reference to East Africa and strategies. Mozambique (Hodges et al., 1983; Hodges, 1986; Markham et al., 1991; Helbig et al., 1992; Hodges, Pest status. Prostephanus truncatus has become 1994; Birkinshaw et al., 2002). So, the question a serious pest of farm-stored maize and cassava can rightfully be asked: What is the current pest in Africa (Borgemeister et al., 1994; Borgemeister status of P. truncatus in Africa? Infestation and et al., 1998). The seriousness of P. truncatus resulting damage by P. truncatus is preceded by damage to stored maize grain and cassava chips spatial and temporal habitat invasion and varies considerably among countries. Infested colonisation by the pest. Dispersal of this pest is commodities are physically destroyed and influenced by its capability to survive on dry become unsuitable for human consumption and wood of several forest plant species (Helbig et trade (Richter et al., 1997) due to adults and larvae al., 1992; Nang’ayo et al., 1993; Nansen et al., boring and damaging maize grain and dry cassava 2002), predation by Teretrius nigrescens ships. High infestation levels result in (Coleoptera: Histeridae), as well as climatic accumulation of starch from insect metabolic conditions and availability of food sources excrements, fungal growth on stored produce and (Helbig, 1995; Hill et al., 2002; Hodges et al., 2003). build-up of detritus in storage facilities. Efforts to control the Larger grain borer largely The Larger grain borer was reported to cause involved the use of synthetic insecticides (Bekele losses in maize of nine percent over a five month Prostephanus truncatus in Africa 239 period in western Tanzania (Golob, 1988). Alternative food sources and forest plant species. Pantennius (1988) reported dry weight loss of up The Larger grain borer also infests and damages to 45% of maize grain after eight months of commodities other than maize and dry cassava storage in Togo. Gnonlonfin et al. (2008), also in chips. Wheat (Triticum aestivum Poaceae), rice Benin, investigated infestation and population (Oryzae sativa Poaceae), chickpea (Cicer dynamics of insects on stored cassava and yam arietinum Fabaceae), sweet potatoes (Solanum chips, and found that P. truncatus was more tuberosum Solanaceae), sorghum (Sorghum prevalent with up to 90.9% of individuals and bicolor Poaceae) and several leguminous crops 100% infestation in the Northern Guinea are some commodities that can host P. truncatus Savannah. Hodges et al. (1985) reported losses larvae and adults (Roux, 1999). up to 52.3% for fermented and 73.6% for Information on infestation and survival of P. unfermented cassava chips in Tanzania. This high truncatus on commodities, other than maize and level of damage was observed after a storage cassava, in Africa is scarce. The beetle damages period of only four months. In Ghana, this beetle stored timber and timber-derived products and reduced storability of cassava chips from a forest plant species. Infestation and survival of previously acceptable period of one year or more, P. truncatus in several host plant species has to between four and five months, with losses been reported by Makundi (1987) and Nang’ayo amounting to between 39 and 57% (Stumpf, et al. (1993) (Table 1). Jia et al. (2008) reported 1998). In Mozambique, Cugala et al. (2007) found that different grass, forbs and shrubs as well as that P. truncatus infestations in maize granaries forest tree species were hosts that facilitated resulted in losses of up to 59 and 62% in Manica survival of the lesser grain borer, Ryzopertha and Tete Provinces, respectively. Maize grain dominica F. (Coleoptera: Bostrichidae). Since storage periods in Tete were reduced from 10-12 members of the Bostrichidae are evolutionary, to 6-8 months. These authors argued that this typically wood borers, the latter authors reduction resulted from invasion of P. truncatus hypothesized that P. truncatus had the potential during the early 1980’s in the Mutarara district, to survive in several non-crop host plant species, Tete Province. Borgemeister et al. (1997) reported similar to that of R. dominica. increased losses of stored cassava chips since P. A survey done in the Herbaria of the truncatus was first reported in West Africa. Gueye Department of Biological Sciences, at Eduardo et al. (2008) reported up to 35% of stored maize Mondlane University showed that the plant grain loss caused by mixed infestations of P. species listed in Table 1 occur widely in truncatus and Sitophilus zeamais Motscholsky Mozambique. Herbarium records show that it has (Coleoptera: Curculionidae), Tribolium been collected in Manica, Barue and Guro districts castaneum (Herbst) (Coleoptera: Tenebrionidae) of Manica Province, Chibabava in Sofala and Rizopertha dominica (Fabricius) (Coleoptera: Province, Massingir district in Gaza Province, Bostrichidae) in Senegal. Mocuba district in Zambezia Province as well as Information on the exact quantities of maize in different forests and human settlements and cassava chips stored by farmers is scarce; (Senkoro et al., unpubl.). This finding suggests however, Helbig and Schulz (1996) estimated that that P. truncatus breeding and survival, 70% of the 120,000 to 150,000 metric tonnes of particularly in the natural forests of Mozambique, cassava produced annually in Togo was stored. are possible. However, no study has been done This information, as well as the market prices of to test this hypothesis. commodities is needed to enable a scientific Studies are needed to assess the role that estimate of the economic importance of the Larger wild host plant species play in the ecology of grain borer in Africa. Apart from the lack of this pest. Therefore, more research on distribution, sufficient appropriate storage infrastructure, the abundance, diversity and potential of local forest lack of sustainable and low-cost control methods plant species in hosting P. truncatus is needed. contribute significantly to high levels of damage This information can be used to predict temporal by P. truncatus to important commodities such and spatial colonisation and establishment of P. as maize and cassava. truncatus in different regions in Africa. Maize, 240 B.L. MUATINTE et al.

TABLE 1. List of host plant species utilised by Prostephanus truncatus (modified from Makundi (1987) and Nang’ayo et al. (1993)

Forest plant species Family Plant part attacked Source

Acacia spp. Fabaceae Seed and wood Roux (1999) Commiphora africana Burseraceae Seed and wood Borgemeister et al. (1998), Roux (1999) Delonix regia Fabaceae Seed Helbig et al. (1992), Borgemeister et al. (1998) Leucaena spp. Fabaceae Seed Roux (1999) Prosopis spp. Fabaceae Seed Roux (1999) Spondias purpurea Anacardiaceae Seed and wood Ramirez-Martinez et al. (1994) Ficus exasperate Moraceae Seed Nang’ayo et al. (1993), Helbig and Schulz (1996), Kega and Warui (1983) Ceiba pentandra Bombacaceae Seed Hill et al. (2002) Lannea nigritana Anacardiaceae Seed and wood Nansen et al. (2002) Bursera fagaroides Burseraceae Seed Ramirez-Martinez et al. (1994), Helbig and Schulz (1996) Tectona grantis Verbenaceae Seed Borgemeister et al. (1998) Nansen et al. (2004) Sterculia tragacantha Sterculiaceae Seed and wood Helbig and Schulz (1996) cassava, wheat, sorghum, other commodities and individual variation is a key in dispersal ecology, forest host plants can play a role as food for P. linking movement behaviour and dispersal and truncatus colonisation and establishment on the population processes (Hawkes, 2009). From this African continent. approach some conceptual knowledge is generated: (i) a quantitative description of Prostephanus truncatus dispersal trends. The dispersal which fit distance data well and term dispersal as used here denotes population incorporates realistic assumptions about the redistribution, which results in a time and spatial underlying movement is necessary (Okubo and spread of a population as a consequence of Levin, 2002). This will not only improve the way individual movements (Tuchin and Omland, 1999). in which dispersal is described, but will also Dispersal is a crucial and functional variable of increase the understanding of movement population dynamics, since it is determined by mechanisms and link dispersal and population climatic factors such as temperature and humidity, dynamics. (ii) Movement between habitat wind speed, altitude and latitude. Dispersal is patches and breeding sites must be described as affected by environmental heterogeneity, for dispersal, quantitatively and qualitatively example food quantity and quality, its distribution different from the migration/movement occurring in time and space, disturbed and undisturbed within patches and which is aimed at foraging fields or habitats, and variations in topography, and finding of mating partners and refuges soil and biota within each field (Price, 1997; (Hanski, 1999; Fahrig, 2007). Here we review Huffaker and Gutierrez, 1999; Wellington et al., information on potential factors affecting P. 1999). Dispersal of insect individuals and species truncatus dispersal throughout Africa and can result from tritrophic metapopulation discuss potential ways of integrating information interactions, inter- and intra-specific competition and predicting further invasions and damage by for food, feeding and breeding habitats (Gutierrez, this pest. 1999). Broadly, dispersal of insects is based on ecosystem dynamics and processes (Price, 1997), Prostephanus truncatus spatial and temporal trophic complexity of insect communities dispersal. Prostephanus truncatus long- (Thompson and Althoff, 1999) and on insect- distance dispersal has been attributed to plant population and community interactions transport and trade of commodities, particularly (Nowierski et al., 1999). maize and dry cassava chips (Tyler and Hodges The dependence of dispersal on multiple 2002; Omondi et al. 2011). This could, in fact have factors has arisen from the assumption that insect been the means of transport of this pest from Prostephanus truncatus in Africa 241 Mexico and Central America to Africa (Markham (Table 2) show that the pest took approximately et al., 1991), possibly through shipments of 19 years to disperse and establish in nine infested maize grain (Harnish and Krall, 1984). countries in West Africa, 16 years in five countries Inter-country transport and trade of maize grain of Eastern and Central Africa, and 15 years in six and dry cassava chips, associated with lack of, countries of Southern Africa. These data are or inadequate quarantine regulations, measures rather empirical but biased due to uncertainty of and practices have been indicated as factors that the time of P. truncatus invasion in these lead to P. truncatus dispersal around Africa countries and due to the potential delay that may (McFarlane, 1988; Markham et al., 1991; Fadamiro, have occurred in public notification about the 1996; Tyler and Hodges, 2002;). occurrence and dispersal of the pest around Experiments on short-range flight ability of Africa. Bias can be deducted for example, from the Larger grain borer support the observations countries where information on P. truncatus on long-distance dispersal reported above. For occurrence is still scarce or unknown, while such instance, Farrell and Key (1992) used a mark- a country may be located within a region where release-recapture technique and showed that pest establishment have been confirmed for a long over a 24 hour period, P. truncatus could fly in a period of time. directed manner to a pheromone source in an The long temporal differences in public upwind direction for 50-100 m from the release notification about P. truncatus between, for point. Distances of 250 to 340 m were the maximum example two neighbouring countries, can also distances of flight reported by Rees (1990) and skew this estimate. However, this overview can Farrell and Key (1992) for Larger grain borer flight contribute to knowledge of the general picture of towards a pheromone source over a 72 hr period. the total time period of its invasion and Pike (1993), however, considered P. truncatus as establishment on the African continent, and its a fairly strong flier, after observations that beetles potential and future negative impacts, if in tethered flight under laboratory conditions appropriate pest management measures are not could fly 25 km over a period of 45 hours. taken. Information on the levels of pest These findings demonstrate that the Larger infestation, damage, distribution and density in grain borer is capable of dispersing by flight. relation to characteristics of the invasion area, However, no evidence exists that flight time period could provide improved estimates of P. truncatus in natural environments lasts as long or involves establishment periods and rate of dispersal on such distances as described above (Farrell, 2000). the continent. In addition, individual insect movements and, hence dispersal, can be hindered by physical Role of host commodities and forest host plant barriers such patch forest density, mountains, species. The role of host commodities in dispersal hills and seasonal or permanent flowing rivers. of this pest has been widely reported (Hodges et From field and empirical observations in Manica al., 1983; Hodges, 1986; Markham et al., 1991; Province in Mozambique, it can be assumed that Hodges 1994; Helbig et al., 1995; Borgemeister et frequent and seasonal forest fires can kill insects al., 1997; Stumpf, 1998; Roux, 1999; Farrell, 2000; and physically destroy their habitats, and hence Cugala et al., 2007; Gueye et al., 2008). inhibit their capability for flight and temporal Birkinshaw et al. (2002) found a significant dispersal at population level. Prostephanus correlation between trap catch and infestation of truncatus in- and inter-country invasion and stored maize and other products by P. truncatus. dispersal time period and distance is a subject of These results show that pheromone-baited traps much discussion since it could provide an estimate are effective tools for measuring dispersal of P. of dispersal speed of the pest under different truncatus populations. Fadamiro and Wyatt environmental conditions. (1995) indicated that large numbers of pests Approximately, 20 African countries are resulting in significant degradation of food affected by P. truncatus and estimates based on resources could prompt dispersal of P. truncatus. years of public notification of P. truncatus Scholz et al. (1998) came to similar conclusions occurrence in the respective countries in Africa when studying P. truncatus flight initiation and 242 B.L. MUATINTE et al. 5 2 2 1 1 2 2 1 2 2 1 1 1 5 1 9 4 10 19 19 16 ears Y Africa ogo Africa T America and anzania and Kenya ogo and Burkina Faso ogo and Benin Guinea and Senegal Central Nigeria and Niger T Mozambique and Malawi Pukina Faso and Nigeria T T Guinea Conakry and Bissau Malawi and Zambia Benin and Guinea Conakry Namibia and Mozambique Guinea and Ghana Kenya and Burundi Zambia and Namibia Mozambique and South Zimbabwe and South Burundi and Rwanda Rwanda and Uganda between two neighbouring countries (years) Estimated dispersal and establishment time period 1) . (1991) . (2010) et al Africa. Modified after Schulsen (1996) and Farrell (2000) (unpublished) (2008) et al . (2007) (1996) . (1992) et al. et al. et al et al. et al Harnish and Krall (1984) Dunstan and Magazini (1981) Munthali (1992) Anon. (1986) Gueye Kega and Warui (1983) Milimo and Munene (1993) Adda Kalivogui and Much (1989) Dick and Rees (1989) Pike Schulten (1987) Larsen (1998) Aman Bosque-Perez Bonzi and Ntambabazi (1993) Cugala Roux (1999), Giliomee (201 Nyagwaya Opolot and Odong (1999) Reference , Dosso, Gaya Area olta region aveta district abora district ogo border Lomé area T Karonga district Mono region Vélingara Boydo T Nakonde district Niamey Fouta Djallon region Oyo and Ogun states V Gisuru market Northern Namibia Bissau region T Kigali Mutarara district Kruger Park Northern Zimbabwe Busia district invasion, dispersal and establishment time periods in

Africa 1984 1981 1991 1986 2007 1983 1993 1994 1988 1992 1989 1984 1998 1988 1991 1993 1999 1999 2005 1997 ear of first report Africa Y Africa estern Prostephanus truncatus

Africa ABLE 2. Estimated otal dispersal period in Eastern and Central otal dispersal period in Southern otal dispersal period in W anzania ogo Country T Eastern and Central Africa T West Africa T T T Southern Africa Malawi Benin Senegal Kenya Zambia Niger Guinea Conakri Nigeria Ghana Burundi Namibia Guinea Bissau South Burkina Faso Rwanda Mozambique Zimbabwe Uganda T Prostephanus truncatus in Africa 243 flight activity in Benin. These authors observed volatiles or any synergism between pheromones that flight initiation depended on changes in the and food volatiles. These authors suggested that numbers and sizes of beetle populations in a given the male aggregation pheromone was the only area, as well as on breeding site availability and known long-range semiochemical involved in P. suitability. truncatus dispersal and host selection. Host Reduction in food resources and quality can plant selection, infestation and successful directly determine initiation of P. truncatus breeding by P. truncatus are subjects of research dispersal in closed commodity granaries, where importance since increased knowledge in this field the concentration of maize or cassava can be high could lead to predicting habitat invasion and and become reduced over time. However, in open colonisation by this beetle in Africa. The use of environments such as forest habitats, the stable isotope carbon and nitrogen marker occurrence, distribution and diversity of host- methods (Hood-Nowotny and Knols, 2007; plant species (food), as well as its shortage and Mahrrof and Phillips, 2007) may also be suitable quality seem to determine the initiation of Larger for determining host plant-insect interactions. grain borer dispersal. Therefore, variation of plant Research on forest host plants as well as biomass concentration, caused by deforestation insect-commodity interactions previously and seasonal large-scale forest fires, can focussed on the role of these substrates as food hypothetically influence dispersal initiation by sources that provide nutritional requirements for P. truncatus. growth, development, reproduction and energy The capacity of the Larger grain borer to flow, rather than insect movements which lead to utilise forest plant species as a resource for its dispersal. survival and dispersal has been published by several workers (Makundi, 1987; Nang’ayo et al., Role of host plant resistance. Varietal resistance 1993; Helbig et al., 1995; Jia et al., 2008). Nang’ayo of host commodities or host suitability of forest et al. (2002) studied the potential of P. truncatus plant species for P. truncatus are factors that could feed and breed on native and agroforestry trees also affect P. truncatus dispersal. Arnason et al. and shrubs, and reported that 27 out of 84 tree (1992) investigated the role of phenolics in species supported the breeding of P. truncatus resistance of maize grain to P. truncatus and S. under laboratory conditions. Breeding success zeamais, and found that variety-specific phenolic varied widely between tree species and showed compounds influenced the suitability of grain for no trends with regard to systematic position of the development of the former pest. Kumar (2002) species or wood hardness. These results suggest performed a series of infestation, selection and that the determining factors, mostly secondary inbreeding experiments over four generations of metabolites for forest host plant species maize land races and observed that the S3 maize exploitation by P. truncatus, should be further grain showed a high level of resistance against P. investigated. In addition, laboratory experiments truncatus. on insect-host plant interactions should be This resistance was evident from low powder conducted, particularly on searching, selection, production caused by pest damage, relative to acceptance and preference behaviour, as well as the susceptible control, as well as the small sizes kairomones involved in the process. of individuals developing on the resistant grains. Scholz et al. (1997) investigated P. truncatus This result suggested that antibiosis could be host-finding behaviour and concluded that the mechanism of resistance operating within the kairomones, specifically those emitted by mature S3 progenies of selected land races. Tefera et al. maize ears, and probably by dried cassava (2011), in Kenya, evaluated 54 hybrids and found functioned as short range attractants. eight to be resistant and 40 to be moderately Prostephanus truncatus long-range responses resistant to P. truncatus and S. zeamais. This and, hence, its primary attraction to stored finding suggested that resistant hybrids commodities could not be demonstrated. contained genes conferring maize grain to be However, Fadamiro et al. (1997) observed the resistant either through antixenosis or antibiosis, absence of P. truncatus upwind flight to food resulting in reduced grain weight loss and powder 244 B.L. MUATINTE et al. production; and subsequently, an overall development and life-history trait adaptation to reduction in the impact of the two pests. However, environmental conditions. in laboratory and field experiments, Meikle et al. Climate directly affects the propensity of (1998) concluded that maize kernel hardness and insects to disperse through flight. Research on physical ear characteristics, such as husk the effect of pheromones as a factor driving P. extension and number of leaves might not play a truncatus flight activity and dispersal has been role in plant resistance to P. truncatus. done since Cork et al. (1991) identified and The heterogeneity in chemical and structural synthesized the male beetle aggregation composition of plants, together with inter-plant pheromone. This development resulted in the variation prevents herbivorous insects from fully monitoring of flight activity of the Larger grain exploiting their host plants (Schoonhoven et al., borer in several countries. Laboratory research 1998). Evidence of this is supported by several has demonstrated the positive response of P. authors (Berenbaum and Zangerl, 1992; Olckers truncatus towards synthetic pheromone sources and Hulley, 1994). It is, therefore, suggested that (Fadamiro et al., 1996; Smith et al., 1996). Tigar et future research addresses identification and al. (1993) investigated the period of effective possible use of feeding deterrents in host attraction of P. truncatus to synthetic commodities and in forest host plant species. pheromones over a 33-day period and observed Such information will contribute to better that the highest number of beetles was caught understanding of the mechanisms of P. truncatus- between 8 and 14 days after traps were put out. host plant interactions and, hence, identify certain These authors also highlighted the possibility of habitat types/host plant communities that are results being influenced by rainfall, temperature, vulnerable to pest invasion and colonisation. wind and trap positioning. Nang’ayo (1996) in Kenya, Borgemeister et Role of climate conditions. Climate conditions al. (1998) in southern Benin, Birkinshaw (1998) in which favour abundance, diversity and suitability Ghana, Hodges et al. (1998) and Scholz et al. of food sources have been suggested as driving (1998) in Togo and Benin, found that the use of factors for the continuous dispersal of P. pheromone traps for P. truncatus dispersal truncatus in Africa (Hodges, 1986; Farrell, 2000). studies skewed surveyed populations by sex, Giles et al. (1996) in Kenya and Borgemeister et because 60-70% of captured insects were females. al. (1997) in Benin found that the numbers of In addition, trap captures arrested more young beetles trapped by means of pheromone traps individuals because they were more active fliers varied seasonally and annually, signifying (Fadamiro et al., 1996; Scholz et al., 1997). Despite weather or climate effects. these disadvantages, pheromone-baited traps At individual level, body temperature is the became the most effective method for studies on most basic variable determining rates such as P. truncatus flight activity and abundance and growth, development, feeding, fecundity and its relationship with climate and other insect mortality (Wellington et al., 1999). environmental variables. Birkinshaw et al. (2004) Prostephanus truncatus completes its life cycle and Hodges et al. (2004) improved and optimised in about 25-27 days at the optimum temperature pheromone lures and trapping methodology to of 32 o C and relative humidity of 70-80% under address the skewing of P. truncatus trap catches laboratory conditions on maize grain (Hodges, by sex and age. 1982; Subramanyan and Hagstrum, 1991). Adults Scholz et al. (1997) showed that live for at least 4 months (Guntrip et al., 1996) commencement of infestation of maize by P. excluding the effect of predators or other natural truncatus was prompted by releases of the male enemies and exogenous factors that can cause aggregation-pheromone, late in the storage unpredicted death. The life-history of the Larger season. Since the initiation of invasion of grain borer has been widely studied (Shires, 1980; granaries is a logical consequence of dispersing Howard, 1983; Li, 1988). The capability of insects beetle populations, it is deductible that to disperse mainly by flight is generally pheromone release by males plays an important determined by the success of their individual role in pest dispersal to maize storage facilities. It Prostephanus truncatus in Africa 245 is also possible that pheromones may play a role seasonal trends of larger grain borer flight in the dispersal of beetles from granaries into behaviour in Kakamega in western Kenya and forest environments. Mombasa in coastal lowlands of the same country, but it was inaccurate in highland regions. Besides Modelling and multivariate analysis of flight the availability of stored grain, the influence of activity. Multivariate analysis has been used to climate factors, altitude, latitude and solar design models and to predict P. truncatus flight radiation on accuracy of prediction models activity, as well as for estimating likely subsequent should be considered. population outbreaks and infestation of maize and The question can, therefore, be asked: “Will cassava chips in granaries. Meikle et al. (1998) in models that accurately predict P. truncatus flight Benin designed a simulation model for P. activity and, hence, spatial and temporal dispersal truncatus and concluded that temperature become a reality in future, and will it be possible affected development and flight activity more or to use these on a large scale?” The positive less linearly; whereas the effect of humidity answer to this question is more theoretical than appeared to be non-linear. Nansen et al. (2001) practical, because variations in climate patterns investigated the response of P. truncatus flight and environmental variables such as habitat activity to environmental variables in Benin and patches, topography, solar radiation, wind speed concluded that day length, minimum relative and host-plant species, host commodities and humidity, and minimum temperature were the most habitat connectivity vary significantly at local important variables explaining P. truncatus trap and regional level. These factors complicate the catches. This result provided some improvement development of a model for which development on early attempts to predict catches. relies on large investment in resources, as well as Hodges et al. (2003) in Ghana, examined the time consuming. Simultaneous, large-scale spatial relationship between climatic variables, seasonal and temporal surveys needed to collect data for and annual variations in P. truncatus trap catches. use in model development. It, therefore, seems These authors then developed a rule-based more appropriate that models be developed at model, a useful tool to predict years of higher P. country or regional level. truncatus flight activity and to estimate the pest status in certain regions. Predators and parasitoids. Several studies on the Current models for P. truncatus flight activity impact of Teretrius nigrescens on P. truncatus are sketchy in some aspects. The day length have been conducted. These studies mostly based-model of Nansen et al. (2001), which highlighted the importance of the predator to defined day length as the most important variable suppress pest population density in granaries or for predicting flight activity was able to accurately forests (Helbig and Schulz, 1996; Richter et al., predict trap catch data between the latitudes of 6 1997; Holst et al., 2003; Schneider et al., 2004; to 9o N, but the model was inaccurate in northern Hell et al., 2006). The subject of P. truncatus Benin (10o N) (Hodges et al., 2003). This rule- biological control is of our further concern. based model, works well under a range of The direct effect of the predator on pest conditions in which P. truncatus is likely to be a population dynamics, specifically on flight serious pest. However, it has to be tested under activity patterns and dispersal is mostly more extreme conditions and in different unexplored. Borgemeister et al. (1997) observed environments. It was also found to be difficult to that peaks of T. nigrescens flight activity were set the scale (calibrate) for trap catches in areas correlated with precipitation; whereas those of P. where previous data were scarce or unknown. In truncatus were only weakly related to addition, the scale of the rule-based model was precipitation. The latter study on the influence seen to wrongly estimate host-plant suitability of seasonal and weather factors on annual flight and the impact of predators and parasitoids on P. patterns of P. truncatus and T. nigrescens did truncatus populations. not show clear direct cause-effect relationships A model based on climatic factors, designed between the predator-prey population by Omondi et al. (2011), accurately predicted fluctuations. Omondi et al. (2011) monitored P. 246 B.L. MUATINTE et al. truncatus and T. nigrescens flight activity in applied since the pest invaded Africa (Golob and Kenya and observed that the prediction model Hanks, 1990; Meikle et al., 1999; OEPP/EPPO they used did not allow for assessment of the Bulletin, 2012). Ritcher et al. (1998) investigated impact of the pests density because it relied on the efficacy of dust-formulated insecticides in direct effect of temperature, humidity and traditional maize granaries, and found that precipitation and also excluded availability of pyrethroids, particularly deltamethrin, effectively stored maize grain. Some research on monitoring controlled the Larger grain borer in West Africa. P. truncatus trap catches, after T. nigrescens The use of inert dusts, particularly releases have been made, showed no or only small diatomaceous earths, has widely been tested and numerical differences in pest density and flight applied against P. truncatus in Africa. Barbosa et activity compared with periods prior to al. (1994) reported that precipitated and fumed establishment of the predator (Giles et al., 1996; silicas were effective in causing mortality of adult Hill et al., 2003). It was also observed that T. P. truncatus. Stather et al. (2004) evaluated two nigrescens did not reduce the abundance of pest commercially enhanced diatomaceous earth populations in Guinea and Sudan savannas in products (DE), admixed with grain commodities West Africa (Nansen et al., 2001; Schneider et and concluded that these could be effective and al., 2004). persistent for the control of storage pests, A decrease in numbers and eventual total especially of the larger grain borer. The use of absence of predator populations was observed a inert dust by small scale farmers can be a few months after their release in the western sustainable alternative to conventional chemical highlands of Kenya was also observed (Omondi insecticides. However, cost-effectiveness of et al., 2011). The theory of stable equilibrium processing DE products from raw material is a (Hoddle, 2003) may explain the variation observed matter of high concern, and the development of in insect population densities as observed for T. such products remains a challenge. nigrescens and P. truncatus. Hypothetically, the The efficacy of plant derived products for large-scale and periodical use of pheromone control of P. truncatus has been widely sticky traps that attract and kill both the Larger investigated. Locally available plant materials grain borer and the predator can gradually reduce have been traditionally used by rural farmers in the numbers of T. nigrescens. The aim of pest Nigeria (Poswal and Aka, 1991), Botswana (Jackai management is to reduce pest numbers. However, and Daust, 1986; Bila, 1996), Zambia and Tanzania reduction of T. nigrescens populations in the (Berger 1994), and in Mozambique (Mapilele et process reduces the effectiveness of the predator al., 1996; Segeren, 1993; Muatinte unpubl.). Bekele and hence, its dispersal. Berryman and Gutierrez et al. (1997) found dry ground leaves and oils of (1999) reported that predators can indirectly limit Ocimum kenyense (Lamiaceae) to be repellent and or regulate dispersal of their prey through toxic against S. zeamais and R. dominica in regulation of population density. Kenya. Tapondjou et al. (2002) in Cameroon tested leaf powder and essential oils of CURRENT STATUS OF MANAGEMENT Chenopodium ambrosioides L. IN AFRICA (Chenopodiaceae) against the Bruchidae, Callosobruchus chinensis, C. maculatus and Integrated Pest Management (IPM), as defined Acanthoscelides obtectus, the curculionids, S. by Kogan (1998) is the combined use of host zeamais and S. granarius, and P. truncatus. These plant resistance, biological control, cultural researchers found C. ambrosioides products to control and chemical control in order to keep pest provide effective protection of stored products. populations below economic injury levels. This However, further research is needed to determine approach to pest management is discussed below seasonal variability of the active ingredient, with reference to P. truncatus. effective dosages and appropriateness for use by rural small scale farmers. Chemical control. Based on the use of fumigants The use of plant derived products, especially such as phosphine and methyl-bromide has been essential oils and powders with repellent, toxicant Prostephanus truncatus in Africa 247 or antifeedant properties, represents a possible The use of sticky pheromone traps in way forward in development of IPM strategies monitoring programmes of P. truncatus flight against P. truncatus. The use of these products activity can hypothetically lower the predator against storage pests is increasingly being density in areas where populations are newly investigated in Africa and worldwide (Bouda et established, or when the numbers are still low, al., 2001; Tapondjou et al., 2005; Rajendran and since they can stick and kill T. nigrescens together Sriranjini, 2008; Nukenine et al., 2010; Silva et al., with the pest. Inundated and augmented releases 2012). of the predator can increase its abundance, followed by increased efficacy in controlling P. Biological control - use of predators. Biological truncatus in natural environments. Bucket funnel control with the use of the predator, T. nigrescens traps, which are suitable for capturing both P. has become one of most promising alternatives truncatus and the predator without causing for the control of P. truncatus in Africa. The mortalities, have the advantage that individuals effectiveness of T. nigrescens in suppressing of the latter can be released back into granaries population numbers of P. truncatus has been of the wild. demonstrated under laboratory conditions. Hymenopteran parasitoids have been Helbig (1995) in Togo investigated maize grain suggested for control of P. truncatus. Helbig damage under near-traditional storage conditions (1998) in Benin found that Anisopteramalus and reported that damage was reduced by calandrae (Howard) (Hymenoptera: approximately 23% in the presence of the predator Pteromalidae) was more effective in controlling after nine months of storage. Holst et al. (2003) P. truncatus under laboratory conditions than in Benin developed a simulation model based on Teocolax elegans (Westwood) (Hymenoptera: life-table data and found that T. nigrescens Pteromalidae). The latter species showed more significantly reduced population growth of P. promise than Cerchysiella sp. (Hymenoptera: truncatus and the non-target, S. zeamais. Encyrtidae), Pediobius furvus (Gahan) In field experiments, Richter et al. (1997) (Hymenoptera: Eulopidae) and species of observed that infestation by P. truncatus in Bethylidae family. Helbig (1999) reported that the granaries decreased after introduction of T. predatory bug, Xylocoris flavipes (Reuter) nigrescens in Benin. The number of P. truncatus (Heteroptera: Anthocoridae), was not effective individuals was reduced by 93%, while damage in controlling P. truncatus in traditional maize to grains was reduced by approximately 40% in granaries in Southern Togo. the presence of the predator. Schneider et al. Although the above studies do not show (2004) in Benin and Togo, found that P. truncatus large scale impact of T. nigrescens on P. truncatus, numbers caught in traps decreased steadily after biological control holds potential and is most introduction of T. nigrescens during 1992. likely the only strategy that could have Augmented releases of T. nigrescens done sustainable impact on the African continent, if by Hell et al. (2006) for Larger grain borer control predator populations adapt and establish. in cassava chips in Benin, resulted in reduction Investigations into parasitoid-pest interactions of cassava chip losses by 5 and 11% after one in both natural and granary environments must and five months of storage, respectively. be intensified. In addition to this, the potential Contrastingly, Mahumane et al. (2009) in Manica synergism between the predator and parasitoids, Province, Mozambique, reported that T. as well as other biological interactions are nigrescens had no impact on P. truncatus numbers subjects for further research to better understand two years after it was released. However, the and exploit the role that natural enemies could predator had established and dispersed to new play in management of P. truncatus. localities.Generally, the studies mentioned above The use of entomopathogenic fungi (EPF) and indicate that T. nigrescens can impact on P. fungus-derived products constitutes another truncatus numbers, indicating its usefulness for tool for use in biological control of stored product control of this pest. pests. Odour et al. (2000) reported the presence 248 B.L. MUATINTE et al. of the entomopathogenic fungus, Beauveria such as forests and agro-ecosystems (Scholz et bassiana (Balsamo) Vuillemin (Hyphomycetes) al., 1998). However, attraction of T. nigrescens on pests of stored maize in Kenya and highlighted using synthetic pheromone of P. truncatus was it as a potential control agent. Hertlein et al. not observed by Hodges and Dobson (1998) in (2011) reviewed the use of Spinosad against laboratory experiments. This fact is contrary to storage pests, including P. truncatus and reported the finding that T. nigrescens can fly or walk (Rees to be effective against R. dominica, T. castaneum, et al. 1990) into traps baited with synthetic T. confusum and Oryzaephilus surinamensis (L.) pheromones of P. truncatus, but stresses the (Coleoptera: Silvanidae). This insecticide is hypothesis from Steward-Jones et al. (2004) that reduced-risk derived by fermentation of the soil there may be other compound cues involved in actynomycete, Saccharopolyspora spinosa this predator-prey interaction. Mertz & Yao (Bacteria: Actinobacteridae) (Chintzoglou et al., 2008; Hertlein et al., 2011). Integrated pest management (IPM). The However, its large scale use under small scale combined use of several control methods for P. grain storage conditions requires further truncatus in granaries of small scale farmers in investigation. Africa has been widely investigated. Tyler and Hodges (2002) recommended implementation of Use of semiochemicals. Information on the phytosanitary measures, particularly quarantine economic impact of using semiochemicals to inspection of large-scale traded maize, cassava protect stored products from insect pest and other P. truncatus host commodity products. infestation, especially whether these provide However, these authors considered that stopping effective, control is scarce. However, mass P. truncatus long-term dispersal around Africa trapping using sex pheromones is potentially was unrealistic. useful despite the fact that their efficacy depends Some of the promising approaches towards on trap design and possible saturation of traps, effective IPM for P. truncatus comprises of the particularly under conditions of high pest application of Spinosad combined with densities. Another disadvantage is single sex diatomaceous earth (Chintzoglou et al., 2008; attraction and the possible effects of Vayias et al., 2009; Kavallieratos et al., 2010), inappropriate positioning of traps, maintenance insect-resistant maize and biological control using of traps in the field, and possible immigration of T. nigrescens (Bergvinson et al., 2011). The individuals towards traps from outside the study application of wood ash, combined with conidia areas (Cox, 2004). of the fungus B. bassiana, as suggested by Smith Moreover, feeding or oviposition stimulants et al. (2006), as well as the use of hermetic bags have been used, especially to improve the efficacy (Groote et al., 2013) hold potential for the control of insecticides and biocontrol agents.Laboratory of the larger grain borer. research results of Steward-Jones et al. (2004; Research on integration of several methods 2007) showed strong evidence of the existence for the control of the Larger grain borer in Africa of a high concentration of compounds in P. has, to a large extent, been done. Integrating truncatus dust that acts as a contact kairomone effective technologies and getting farmers for the predator T. nigrescens. involved in evaluating them under real conditions The results from the above studies explained in order to develop sustainable IPM strategies the predator-prey arrestment mechanism between remains a challenge. T. nigrescens and P. truncatus that occurs at close range such as in granaries and conventional maize CONCLUSION storage facilities. Additionally, these findings complement the known attraction of T. nigrescens The pest status of the Larger grain borer in Africa to by P. truncatus male aggregation pheromone. is high. Continuous monitoring should be done This attraction towards P. truncatus aggregation at local and national level to determine pest pheromone, results in T. nigrescens flight from presence. This pest continues to disperse within significant long distances in open environments and between African countries. Research on Prostephanus truncatus in Africa 249 factors influencing its population dynamics (Ayobangira) as source of repellents, should be done and monitoring programmes toxicants and protectants in storage against implemented at international, regional, national three major stored product insect pests. and local levels. Modelling of P. truncatus Journal of Applied Entomology 121:169-173. population dynamics should be done to predict Berenbaum, M. and Zangler, A.R. 1992. 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