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Insects and other arthropods recorded from stored maize in western Ethiopia ABRAHAM TADESSE Entomology Section, National Maize Research Programme, Bako Research Centre, P.O.Box, 3, Bako/Shoa, Ethiopia (Received 22 April, 1995; accepted 27 October, 1995)
Code Number: CS96073
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ABSTRACT Surveys of species of arthropods on stored maize in western Ethiopia were conducted. Several species of arthropods were recorded. Among these, the Coleoptera Sitophilus spp., Tribolium spp., Carpophilus spp. and Cryptolestes spp., and Lepidoptera Sitotroga cerealella (Olivier), Ephestia cautella (Walker) and Plodia interpunctella (Hubner) were widespread and common. Several species of natural enemies of insect pests associated with stored produce were also recorded. It is necessary, therefore, that a nationwide survey be undertaken to determine the species of pests involved and the amount of losses inflicted by them in the various stored products in general and in stored maize in particular. Key Words: Insects, maize, pseudoscorpions resume Les etudes sur les especes d'artropodes etablies sur le ma•s en stock en Ethiopie de l' Ouest ont ete effectuees. Differentes especes d'arthropodes etaient enregistrees. Parmi elles, les Coleoptera Sitophilus spp., Tribolium spp., Carpophilus spp. et Cryptolestes spp. et Lepidoptera Sitotroga cerealella (Olivier), Ephestia cautella (Walker) et Plodia interpunctuella (Hubner) etaient largement repandus et communs. Differentes especes d'ennemies naturles des insectes associes avec les produits en stocks etaient egalement enregistrees. Ce qui montre qu' il pouvait etre important d'entreprendre des etudes au niveau national pour determiner les especes de ravageurs impliquees et les quantites de pertes provoquees par eux dans les differents produits en stocks en generale et le mais en particulier. Mots Cles: Insectes, mais, pseudoscorpions INTRODUCTION Maize (Zea mays L.) is the dominant food crop grown and stored by farmers in the Bako area of Ethiopia. Currently, the production and storage of maize is threatened by several insect pests. Compared with that in the field, loss in storage is finite since it cannot be reduced by compensatory growth of the crop. However, research information on stored products pests in general (Abate and Negassi, 1985) and thus on stored maize entomology, is meager in Ethiopia. The only available published information specific to stored products pests in this country is the survey work of Walker and Boxall (1974), although a short unpublished survey was also carried out by J.A. McFarlane in 1968 (Walker and Boxall, 1974). This survey was carried out to identify the species of arthropods associated with stored maize in Bako, an area between the administrative regions of Shoa and Wellega and located about 250 km west of Addis Abeba.
MATERIALS AND METHODS
The survey was conducted in August, 1989 and August, 1993 when there was grain in storage and when infestation and grain damage levels were most likely to be serious (6 to 8 months after storage). Survey sites were selected from both Shoa and Wellega administrative regions within the radius of up to 120 km from the Bako Research Centre (B.R.C.) (Table 1). A total of 20 sites were selected, and from each site, ten maize storage containers were sampled. Selection of sites, storage containers and samples were made at random. When a selected site or storage did not have maize the next site or storage was taken as a substitute. From each container, five samples, each consisting of 100g of grain, were taken. The samples were obtained from as many different parts of the various storage facilities as possible (top, sides, centre, bottom). Each sample was put in a sealed plastic-lined paper bag and was labelled with the necessary information (name and altitude of the site, sample number, date of sampling, storage time, etc.). The five samples obtained from the same storage were placed together in a cloth bag. In the laboratory, each sample of grain was sieved over a 2 mm mesh sieve and all fractions were examined. Insects were removed, counted and grouped according to order or genus and were preserved dry as pinned collections or in 75% alcohol. The different fractions of grain samples were reconstituted, re-bagged, and were held at room temperature to determine any internal infestation or parasitism. After about one month, these samples were re-examined and any emerged insects were recorded as previously. Based on their relative abundance in grain samples, the status of insects of each species was noted as being: very common (+++) when they were numerous and recorded from all samples; common (++) when they were few but recorded from all samples; uncommon (+) when they were few in number and recorded from some of the samples only; uncertain (-) when it was not possible to handle for counting (parasitic Hymenoptera); and unusual (?) when the species is not known as a pest of stored products and was recorded from one or two samples only. Samples of insects and other arthropods obtained during both inspection periods were sent to the C.A.B. International Institute of Entomology, England, for identification. The identified insect specimens were designated as C.A.B. International Institute of Entomology List No. 10431 Africa, Collection No. A. 20992. RESULTS AND DISCUSSION The species of arthropods recorded on stored maize are listed in Table 2. Twenty three species of Coleoptera, one of Diptera, six of Hymenoptera, three of Lepidoptera, one of Thysanura, and two species of the order Pseudoscorpionida (false scorpions) were identified. Among these, Coleoptera and Lepidoptera were the most common and widespread pests. The coleopterans Sitophilus spp., Tribolium spp., Carpophilus spp. and Cryptolestes spp. and the lepidopterans Sitotroga cerealella, Ephestia cautella and Plodia interpunctella were the dominant ones in maize grain samples. Gnathocerus cornutus, Oryzaephilus spp. and Rhizopertha dominica were found to be potential pests although their populations appeared to be low in the samples. Most of the pest species recorded were secondary pests attacking grains that have been broken or damaged by primary pests. Primary pests included Sitophilus spp., S. cerealella and R. dominica (TDRI, 1984). Species of Sitophilus weevils were the most common and perhaps the most destructive of all the insect pests recorded (Table 3). Both S. zeamais and S. oryzae were found attacking maize; however, S. zeamais was recorded from all the samples while S. oryzae was found only in three out of five (60%) samples. The ratio of S. zeamais to S. oryzae was 2.24: 1. Both species were recorded from samples obtained as a mixture of maize and sorghum or from samples of either maize or sorghum. However, samples of maize or sorghum obtained from the B.R.C. farm-store did not contain S. oryzae. Schmutterer (1971) did not indicate the occurrence of S. oryzae on either of these and other grains stored in the Bako area. He reported the severity of S. zeamais on both maize and sorghum in storage and showed a loss estimate of up to 80% in maize stored in unprotected silos. Sitophilus granarius, which is found at high elevations in Ethiopia, was not recorded during this survey from sites higher than 2300 m. McFarlane (1969) recorded S. granarius from altitudes at or above 2100 m while Walker and Boxall (1974) reported that this species was commonly found in Addis Abeba (> 2100 m) and was less common elsewhere. The bruchid, Zabrotes subfasciatus, was recorded for the first time in 1989 in Ethiopia from haricot bean (Phaseolus vulgaris L.) with which maize seeds were sparsely mixed in the B.R.C. farm-store. Walker and Boxall (1974) recorded the curculionid S. zeamais on haricot bean in Ethiopia. Zabrotes subfasciatus is one of the important bruchids attacking haricot beans and other pulses in Africa. It has been recorded from west, north and central Africa and Madagascar but not from Ethiopia or the Sudan and South Africa (Southgate, 1978). Abate, et al. (1982) did not mention the presence of this species in Ethiopia. However, during the present survey it was recorded as the only and most dominant bruchid attacking haricot bean (variety Mexican 142) grown and stored at B.R.C. Most of the species recorded are cosmopolitan pests in stored products. Carpophilus freemani, Cryptolestes ugandae, Oryzaephilus gibbosus and Palorus laesicollis are afrotropical. Palorus laesicollis is especially common in Kenya and Ethiopia. Withius somalicus is one of the most common pseudoscorpions in eastern Africa (C.A.B. International Institute of Entomology, England, personal communication). Some of the insects recorded did not appear to be of importance as direct pests. They seem to be attracted by the microfungi associated with stored produce. Tenebroides mauritanicus is reported to be a cosmopolitan predator, and sometimes a minor pest in stored grain. (C.A.B. Inter. Inst. Entomol., pers. comm.,). Typhaea stercorea, Mycetophagus sp. and Drosophila spp. are likely to be mould feeders. Carpophilus sp. and Gonocephalum sp. are not usual pests of stored cereals and appeared to be new records. The root-feeding larvae of Gonocephalum sp. are sometimes field pests, and adults may scavenge dead plant or animal material. All species of insects recorded in the order Hymenoptera are natural enemies of pest species associated with stored products. The pteromalid Anisopteromalus calandrae is a well known cosmopolitan parasitoid of Coleoptera (and perhaps some Lepidoptera) associated with stored grain. Theocolax elegans, which has previously been treated under the name Choetospila elegans, is a cosmopolitan parasitoid of small beetles in stored grains. Holepyris syvanidis, sometimes known by the synonym Rhabdepyris zea, is a primary ectoparasitoid of various Coleoptera, including S. oryzae, T. confusum and Oryzaephilus surinamensis (Evans, 1978). Pteromalus and Eupelmus are large genera (100 - 200 spp.) with cosmopolitan distribution and attack a variety of hosts (Lepidoptera and Coleoptera). Antrocephalus spp. attack mostly Lepidoptera and they are known from the warmer regions of the Old World (C.A.B. Inter. Inst. Entomol., pers. comm.). Nationwide surveys should be carried out to determine the species of pests associated with stored produce in Ethiopia in general and with stored maize in particular. In addition, losses caused by the major pest species in the different types of stored produce should be determined. ACKNOWLEDGEMENTS
The 1989 survey data are part of a M.Sc. thesis submitted by the author to the Alemaya University of Agriculture, Dire Dawa, Ethiopia. Drs. T. Gebremedhin and M. Hulluka are acknowledged for their comments on the manuscript. Funding was provided by the Institute of Agricultural Research, Ethiopia. C.A.B International Institute of Entomology, England, identified the arthropod spp. and Dr. J. Smith of the University of Reading commented on the manuscript critically. REFERENCES Abate, T., Gebremedhin, T. and Ali, K. 1982. Arthropod Pests of Grain Legumes in Ethiopia: Their Importance and Distribution. Institute of Agricultural Research (IAR), Addis Abeba, Ethiopia. Abate, T. and Negassi, A. 1986. Current state of stored product pest management research in Ethiopia. In: A Review of Crop Protection Research in Ethiopia, Proceedings of the First Ethiopian Crop Protection Symposium. Addis Abeba, Ethiopia, 4-7 Feb. 1985. T. Abate, (Ed.), pp. 645-652. IAR., Addis Abeba, Ethiopia. Evans, H.E. 1978. The Bethylidae of America North of Mexico. Memoirs of the American Entomological Institute 27:1-332. McFarlane, J.A. 1969. A study of storage losses and allied problems in Ethiopia. ODNRI (TPS) report R40: Supplementary accounts of investigations. 67 pp + xii. Schmutterer, H. 1971. Contribution to the knowledge of the crop pest fauna in Ethiopia. Zeitschrift fur Angewandte Entomologie 67: 371-389. Southgate, B.J. 1978. The importance of the Bruchidae as pests of grain legumes, their distribution and control. In: Pests of Grain Legumes: Ecology and Control. Singh, S.R., van Emden, H.F. and AjibolaTaylor, J. (Eds.), pp. 219-229. Academic Press. London. Tropical Development and Research Institute (TDRI). 1984. Insects and Arachnids of Tropical Stored Products: Their Biology and Identification (A Training Manual). TDRI, Slough, England. 273 pp. Walker, D.J. and Boxall, R.A. 1974. An annotated list of the insects associated with stored products in Ethiopia, including notes on mites found in Harar province. East African Agricultural and Forestry Journal 39:330-333. Copyright 1996 The African Crop Science Society
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