The performance of six grain storage technologies for the control of insect pests in maize was evaluated over a 36-week (9-month) storage period. The six technologies used were: two ZeroFly® hermetic bag brands (laminated and non-laminated); Purdue Improved Crop Storage (PICS) bag; non-hermetic ZeroFly® bag; woven polypropylene (PP) bag containing maize grain treated with Actellic Gold® Dust (pirimiphos-methyl 1.6% + thiamethoxam 0.3%) and woven PP bag containing untreated grain. Each bag was filled with 50 kg maize grain and four replicates of each were set up. With the exception of the non-hermetic ZeroFly® bag, 50 live adults of the larger grain borer Prostephanus truncatus and of the maize weevil Sitophilus zeamais, were introduced into all the bags. Insects were not introduced into the non-hermetic ZeroFly® bag to assess its effectiveness in repelling infestation from outside. Parameters recorded were gas composition (oxygen and carbon dioxide) levels inside the bags; weight of flour generated by insect feeding activities; grain moisture level; live adult insect counts; grain damage and weight loss; grain germination rate and aflatoxin level. At termination, the plastic liners of the hermetic bags were examined for perforations. Results show that oxygen depletion and carbon dioxide evolution were faster in ZeroFly® hermetic compared to PICS bags. Throughout the 36-week storage trial, grain damage remained below 4% and weight loss below 3% in all the treatments except in the untreated PP bags in which it increased to 81.1 and 25.5%, respectively. The hermetic PICS, ZeroFly® and Actellic Gold dust-treated PP bags maintained grain germination at 60%, which was lower than the initial 90%, while in untreated control, it reduced to 4.7%. The mean aflatoxin levels fluctuated between 0.39 and 3.56 parts per billion (ppb) during 24 weeks of storage in all the technologies tested, which is below the acceptable maximum level of 10 ppb in maize. Based on the evaluation results, it can be concluded that hermetic PICS and ZeroFly® bags and woven PP bag with Actellic Gold dust-treated grain effectively protected stored maize grain from insect attack and weight losses. Appropriate strategies and mechanisms for the effective and efficient adoption of hermetic storage bag technology at scale would contribute towards global food security.

In biological control, successful establishment of a natural enemy species depends on its adaptability in the introduced range including its ability to re-establish desired ecological interactions with the pest. These are affected by genetic parameters hitherto largely unresolved in biological control. The larger grain borer (LGB), Prostephanus truncatus, an invasive species from meso-America, is the most important post-harvest pest of maize in Africa. We studied the genetic structure of Teretrius nigrescens, a predatory beetle previously released for the control of the pest in Africa, to test the hypothesis that establishment patterns were a result of ecotype–environment mismatch and to follow up on our earlier reports of distinct lineages of the predator. We studied 13 populations of T. nigrescens, using 16 polymorphic microsatellite markers. Five genetic populations with a hierarchical structure and significant isolation by distance were detected. The most diverse population was found in southern Mexico, consistent with earlier lineage coexistence observations. Populations introduced to Africa maintained genetic similarity to local geographic populations of their area of origin. The more successful Benin releases were also more genetically diverse. Loss of rare alleles and a higher frequency of existing private alleles in some populations indicated population expansions following bottleneck events. Sustainable biological control should accommodate pest and natural enemy species, and monitor genetic changes associated with introduction and release.

The larger grain borer Prostephanus truncatus Horn and the maize weevil Sitophilus zeamais Motschulsky are important pests of stored maize in the tropics, particularly where maize is stored on-farm with little control of moisture content and without use of pesticides. This study was undertaken to determine level of resistance among new experimental maize hybrids against P. truncatus and S. zeamais. Out of the 54 experimental hybrids tested, eight hybrids were resistant, six were susceptible and the remaining 40 hybrids were moderately resistant. Five hybrids showed considerable reduction in losses for both P. truncatus and S. zeamais (CKPH08013, CKPH08021, CKPH08003, CKPH08004 and CKPH08009), suggesting that they contained genes that confer resistance to the two pests. Low grain weight loss, powder production and low insect multiplication on resistant grains reduce the negative impact of the two beetle pests. Therefore, host plant resistance can be used as a vital component of an integrated pest management strategy against P. truncatus and S. zeamais.

The invasive larger grain borer Prostephanus truncatus (Horn) is the most important pest of farm-stored maize in Africa. It was introduced into the continent from Mesoamerica in the late 1970s and by 2008 had spread to at least 18 countries. Classical biological control using two populations of the predator Teretrius nigrescens Lewis achieved long-term and cost effective control in warm-humid areas, but not in cool and hot-dry zones. The present study investigated the phylogenetic relationships between geographical populations of the predator. Ten populations of T. nigrescens were studied using randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR), sequence analysis of mitochondrial Cytochrme oxydase 1 (mtCOI) gene and ribosomal internally transcribed spacers (ITS) 1, 5.8S and ITS2. The mtCOI variation revealed two clades associated with geographical regions in Central America. It also reveals a significant isolation by distance between populations and considerable genetic shifts in laboratory rearing. RAPD-PCR did not reveal any potential SCAR diagnostic markers. The ITS variation mainly involved insertions and deletions of simple sequence repeats even within individuals. This study reveals the existence of two different mitochondrial lineages of the predator, associated with the geographical origin of populations distinguishable by fixed mutations on the mtCOI gene. The populations of T. nigrescens released in Africa belonged to two different clades from Meso America, namely south (released in West Africa) and north (released in eastern Africa). However, more polymorphic markers are required to clarify the observations in demographic time scales.

The study sought to confirm reports by farmers and agricultural extension personnel of Prostephanus truncatus (Horn) attacking harvested maize in Mashonaland West and Mashonaland Central provinces of Zimbabwe and to map out, using pheromone trap catch data, the distribution of the pest in the country. A survey of 296 respondents confirmed the presence of P. truncatus in five districts of the provinces. Some respondents reported that the first few sightings of the pest were in 2005 or earlier, while the majority mentioned the 2006/2007 storage season. The map showed a more concentrated distribution of P. truncatus in the northern part of the country moving further inland towards the central and eastern parts of Zimbabwe, indicating possible spread of the pest from the neighbouring countries Zambia and Mozambique. The results of the study indicate legitimate concerns over food security with respect to stored maize grain and seed. The occurrence of P. truncatus in the country has serious implications on training of extension agents and packaging of extension messages that need to be disseminated to the farming community to reduce the impact of the pest. This is the first evidence-based and official documented report of P. truncatus occurrence in Zimbabwe.

Information on longevity and on the effect of ageing on pheromone signalling in Bostrichidae infesting stored products is important because pheromones play a crucial role in mediating aggregation by the species in storages. The longevity of starved and unstarved Prostephanus truncatus (Horn) and Rhyzopertha dominica (Fabricius) were determined at 28±1°C, 65±2% RH and L12:D12 cycle. Additionally, the effects of ageing on rate of pheromone emission were investigated in R. dominica by comparing emission rates of the aggregation pheromones Dominicalure-1 (DL1) and Dominicalure-2 (DL2) released by adult males ranging from 4, 8, 12, 24 and 48 weeks of age. Mean survival time of starved male and female P. truncatus was 8.6±0.6 and 9.1±0.4 days, respectively. Starved R. dominica males lived for 5.7±0.2 days, and females for 4.7±0.1 days. However, mean survival times were not significantly different for starved males vs. females of either species. Mean survival time of unstarved male and female P. truncatus was 27.5±2.0 and 18.0±3.3 weeks, respectively, and for unstarved male and female R. dominica was 26.1±2.8 and 16.7±2.9 weeks, respectively. Difference in mean survival times of unstarved males vs. females in both P. truncatus and R. dominica were significant. Between species, no significant difference was observed in mean survival time between unstarved males of P. truncatus or R. dominica, nor between females of both species. Rate of pheromone emission in R. dominica was higher when the insects were relatively young (4, 8 and 12 weeks old), but declined by almost 55% in treatments where the insect were at about 24 or 48 weeks old, suggesting that recruitment potential of R. dominica might reduce substantially as the insects age.

The effects of egg clutch size on development and survivorship of the larger grain borer, Prostephanus truncatus (Horn) (Col.: Bostrichidae) on maize were measured in the laboratory using single grains of the white maize variety, TZSR-W, at 30 ± 2°C and 70 ± 5% RH. Varying numbers of P. truncatus eggs (1, 2, 4, 8, or 16) were introduced into a hole drilled into a single maize grain. Destructive sampling was used at regular intervals to obtain data on immature developmental parameters, the location of immatures within the grain and the weight and sex of any emerged adults. First instars fed mainly on the floury endosperm tissue whereas the second and third instars preferred the germ tissue. Mortality due to competition was highest in first instars. At high initial densities (> 4 per kernel), some P. truncatus larvae reduced competition by moving out of the grain. A maximum of 6 adults emerged from a single grain. The mean number of adults that emerged per grain for initial egg densities of 8 and 16 were 3.3 and 3.5, respectively. Prostephanus truncatus adult weight at emergence was not significantly influenced by initial egg density except in the case of clutch size 16. The sex ratio of emerged adults was also unaffected by competition, and was always 1:1. Complete developmental period within grains ranged between 28 and 32 days.

Laboratory experiments on the role of humidity, density and species of prey were conducted in order to better understand the ecology of Teretriosoma nigrescens Lewis (Coleoptera: Histeridae), a predator introduced into West Africa to control the larger grain borer, Prostephanus truncatus. Developmental time of T. nigrescens was very similar among individuals exposed to 30,40, 70 and 90% relative humidity at 30°C, although survivorship varied. At optimal temperature and humidity larvae fed only first-instar Sitophilus zeamais as prey took longer to develop and weighed less at emergence, than those raised on first-instar P. truncatus. Larvae feeding on Tribolium castaneum took longer to develop with only 10% surviving to the adult stage. None of the larvae offered Gnatocerus maxillosus as prey survived. In an analysis of prey consumption rates, no T. nigrescens larvae survived on one P. truncatus first-instar larva per day; 50% survived on two per day, and almost 90% survived on five larvae per day. In an analysis of density effects on T. nigrescens reproduction and survivorship, there was no difference in the number of Fl offspring at T. nigrescens:P. truncatus ratios of 15:300,30:300,60:300 or 90:300, suggesting that the lowest predator: prey production ratio was the most efficient one.

Three designs of pheromone-baited flight trap for the larger grain borer, Prostephanus truncatus (Horn) were compared in a daily-trapping trial in Ghana. Japanese-beetle (JB)-type traps, composed of a funnel surmounted by a cross-vane, captured two to three times more beetles than delta- and box-type sticky traps, which are currently the most commonly used designs. Japanese beetle traps have now been adopted by the Ghana National Trapping Network for P. truncatus. The higher efficiency of the JB traps has led to the discovery of the borer in two important maize-growing areas which had previously recorded zero catches using sticky delta-type traps. Analysis of correlation between replicates suggested that JB traps were the most consistent of the three trap designs (r = 0.88). The mode of entry of P. truncatus adults into different trap types, which may explain variations in catches from the different traps, is discussed.

Various wood species used for granary or crib construction were tested for their susceptibility to Prostephanus truncatus (Horn), a new stored grain pest in Benin found in 1984. Ten of the widely used wood species were chosen after survey in infested zones. Wood samples were dried in the oven (60°, 72 hr). They were reduced to 20 cm length, with diameter 2.0–2.6 cm and moisture content varying from 11.1–12.7%, respectively. Wood densities ranged from 0.455–0.999 g/cm−3. Fifty adult insects (<7 days old) were released into the middle of a sample made up of the 10 wood species for free-choice assays and 20 insects per wood species in no-choice tests. Four replicates were set up for each category. After 45 days of exposure at a temperature of 20–35°C and 60–90% r.h., data related to number of Insects that had penetrated each wood, number of larvae, and length of tunnelling were assessed. From the overall data analysis, Elaeis guineensis Jacq. and Holarrhena floribunda (G. Don) appeared least susceptible. Tectona grandis L., Fagara xanthoxyloides Lam., Azadirachta indica A. Juss and Mallotus oppositifolius (Geisel). Mull. Arg. were the more susceptible wood species.

Since it was first reported in Tanzania in 1981 the Larger Grain Borer (LGB) has spread from a small area in the northwest of the country to 17 of the 20 regions. Only in the extreme south, along the Mozambique border, has the pest not been found. It has also become established in Kenya, Burundi, Togo and Benin.

LGB can cause very high weight loss in farm stored maize and dried cassava, commodities on which it is able to breed. After 5 months storage during the dry season in western Tanzania, mean losses of 9% were found, a much higher level than losses of less than 1% which would be expected in LGB-free areas in East/Central Africa.

Application of 0.5% permethrin dust at 2.8 ppm provides excellent protection against LGB when applied to loose maize grain for 1 year. However, the storage of shelled maize predisposes towards the development of Sitophilus species which can result in high losses being sustained. A “cocktail” of permethrin and pirimiphos-methyl, applied at 3.3 and 17.7 ppm respectively, successfully controls all storage pests and is currently being used in an extensive control campaign in Tanzania.

A multi-donor funded control and containment campaign, co-ordinated by FAO, has been in operation in Tanzania since 1984. The programme is comprised of a training element for agricultural staff and several field extension campaigns which assist with insecticide distribution and with dissemination of information to farmers. The primary objectives of the programme are to reduce farm storage losses and to contain LGB within the areas it is now found. In some regions, where LGB is relatively isolated, attempts are being made to eradicate it.

Pheromones have been successfully used on a large scale for control of pink bollworm, Pectinophora gossypiella, by mating disruption in Egypt and Pakistan using various slow release formulations. Similar formulations are being developed for control of other cotton bollworms, Earias insulana and E. vittella. Small-scale trials are in progress to evaluate pheromone formulations for control of sugar-cane borers, Chilo sacchariphagus and C. auricilius in Mauritius and India, and the tropical warehouse moth, Ephestia camelia, as a pest of stored cocoa in Brazil. Traps baited with the pheromone of the African armyworm, Spodoptera exempta, have been extensively used in Eastern and Southern Africa as the basis of a forecasting system of pest incidence.

Traps baited with the synthetic aggregation pheromone of the larger grain borer, Prostephanus truncatus, have been developed and are in use in E and W Africa for detection and monitoring of this pest of stored grain.