Georg Goergen

Exchange of natural enemies of lepidopteran cereal stemborers between African regions.

Difficulties of identification of natural enemies of cereal stemborers for ‘redistribution’ in Africa are discussed. Tritrophic level studies on wild and cultivated habitats of borers and beneficial species are needed to judge the impact of a natural enemy species in the cropping system. Areas with low pest pressure which are climatically favorable for pest development may be selected for study. Based on the results of various countrywide surveys to map the relative importance of Sesamia calamistis Hampson, Eldana saccharina (Walker) and Busseola fusca (Fuller) in western Africa, recommendations are given for sites for tritrophic level studies. It is hypothesised that because maize is not always present in the field and because of its high susceptibility, natural biological control has to come from wild habitats. This emphasises the importance of the knowledge on the wild host-plant range. Survey results complemented with oviposition and life-table studies in the laboratory showed that, rather than being reservoirs for pests, most wild grass species act as trap plants causing mortalities of 100%. A comparison of light trap catches with pupae found on wild hosts and the scarcity of known wild hosts in areas with high pest pressure suggest gaps in our knowledge of the range of host plant species. Based on comparison of known natural enemy complexes in East and West Africa, the scelionid egg parasitoid Telenomus isis and an East African strain of the braconid larval parasitoid Cotesia sesamiae (Cameron) are proposed for redistribution against B. fusca and S. calamistis, respectively. Telenomus isis has never been reported from East Africa whereas C. sesamiae is common in East and southern Africa and scarce in western Africa, suggesting that C. sesamiae is probably not adapted to S. calamistis and B. fusca in this region.RésuméLes difficultés d’identification des ennemis naturels des foreurs des tiges de céréales pour leur ’redistribution’ en Afrique sont discutées. On a besoin d’études du niveau tritrophique sur les habitats sauvages et cultivés des foreurs et des espèces utiles pour juger de l’impact des espèces d’ennemis naturels dans le système cultural. Des régions à basse pression de ravageurs qui sont climatiquement favorables au développement de ces derniers, pourraient être choisies pour l’étude. Sur la base des résultats des différentes enquêtes à travers le pays pour dresser une carte de l’importance relative de Sesamia calamistis Hampson, Eldana saccharina (Walker) et Busseola fusca (Fuller) en Afrique de l’Ouest, des recommandations ont été formulées quant aux sites pour des études du niveau tritrophique. Une hypothèse a été avancée selon laquelle, du fait que le maïs n’est pas toujours présent dans le champ et à cause de sa haute susceptibilité, le contrôle biologique naturel doit provenir des habitats sauvages. Ceci met l’accent sur l’importance de la connaissance sur la circonscription territoriale de la plante hôte sauvage. Les résultats de l’enquête complétés par des études sur la ponte et la table de survie au laboratoire ont montré qu’au lieu d’être des réservoirs pour ravageurs, la plupart des herbes sauvages agissent comme des pièges, causant des mortalités à 100%. Une comparaison des captures au piège lumineux avec les pupes trouvées sur les hôtes sauvages et la rareté des hôtes sauvages connus dans des régions à haute pression de ravageurs suggèrent qu’il y a des lacunes dans notre connaissance sur la circonscription territoriale des espèces de plantes hôtes. Sur la base de la comparaison des complexes d’ennemis naturels connus en Afrique Orientale et Occidentale, le scélionidé parasitoïde de oeufs Telenomus isis et un biotype Est Africain du braconidé parasitoïde des larves Cotesia sesamiae (Cameron) sont proposés pour redistribution respectivement contre B. fusca et S. calamistis. Le fait que Telenomus isis n’a jamais été rapporté en Afrique Orientale tandis que C. sesamiae est commun en Afrique Orientale et Australe et rare en Afrique Occidentale suggère que probablement C. sesamiae n’est pas adapté à S. calamistis et B. fusca dans cette region.

Bactrocera invadens (Diptera: Tephritidae), a New Invasive Fruit Fly Pest for the Afrotropical Region: Host Plant Range and Distribution in West and Central Africa

ABSTRACT In 2003, the invasive fruit fly Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) (Drew et al. 2005), of possible Sri Lankan origin, has been detected in the East and about 1 yr later in West Africa. In regular surveys in Benin and Cameroon covering 4 yr, samples from 117 plant species across 43 families have been obtained. Incubation of field-collected fruits demonstrate that in West and Central Africa (WCA) B. invadens is highly polyphagous, infesting wild and cultivated fruits of at least 46 species from 23 plant families with guava (Psidium spp.), mango (Mangifera spp.), and citrus (spp.), and the wild hosts tropical almond (Terminalia catappa L.), African wild mango (Irvingia gabonensis (Aubry-Lecomte) Baill.), and sheanut (Vitellaria paradoxa C.F.Gaertn.) showing the highest infestation index. B. invadens occurs in 22 countries of WCA with new records for Angola, Central African Republic, the Congo, DR Congo, Equatorial Guinea, Gabon, Gambia, Guinea Bissau, Mali, Mauritania, Niger, and Sierra Leone. Overall, the pest has spread across a North-South distance of ≈5,000 km representing a contiguous area of >8.3 million km2 within WCA. B. invadens has adapted to a wide range of ecological and climatic conditions extending from low land rainforest to dry savanna. Because of its highly destructive and invasive potential, B. invadens poses a serious threat to horticulture in Africa if left uncontrolled. Moreover, the presence of this quarantine pest causes considerable restrictions on international trade of affected crops.

Seasonal Fluctuations of Noctuid Stemborer Egg Parasitism in Southern Benin with Special Reference to Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and Telenomus spp. (Hymenoptera: Scelionidae) on Maize

Parasitism of noctuid stemborer eggs was assessed in monthly surveys in maize fields in southern Benin, from May 1995 to October 1996, and on alternative hosts, i.e. wild grasses, during the dry season from November 1995 to February 1996. Sesamia calamistis was the most prevalent stemborer species, accounting for 98% of the larvae identified from subsamples reared on ear pieces. Egg batch densities ranged between 0.02-0.15 per plant, with lowest densities found during high rainfall periods. 77% of all egg batches were found to be parasitized The egg parasitoids were the scelionids Telenomus busseolae, T. isis , and the trichogrammatid Lathromeris ovicida , accounting for 55.6, 41.6 and 2.8% of total counts, respectively. Parasitism increased in the course of the cropping season and reached peaks of 92 and 86% during the second growing season of 1995 and 1996, respectively. This coincides with the time when farmers have planted a second crop and during a stage when the plants were most attractive and susceptible to S. calamistis attacks. During the dry season, relatively high parasitism was found on maize and wild grasses in inland valleys, and it was concluded that those habitats play an important role in stabilizing the system for both the pest and its natural enemies. As a result, in the Dahomey Gap, which includes parts of Benin, Togo and Ghana, S. calamistis is usually not of economic importance. Although T. busseolae is ubiquitous in Africa, T. isis was only reported from West Africa, including Cameroon. It is recommended that the geographic range of T. isis should be expanded and include East and Southern Africa, where another host, Busseola fusca , is the most important noctuid stemborer pest on cereals.

Arthropod diversity in Lama forest reserve (South Benin), a mosaic of natural, degraded and plantation forests

Arthropod assemblages were examined in Lama forest reserve, a protected area situated in the Dahomey gap, southern Benin, composed of plantations, degraded forest and remnants of natural forest. The objectives were to compare assemblages in relation to forest type and use, to elucidate the value of forest plantations for biodiversity conservation and to identify indicator species for specific forest habitats. Arthropods were collected over an 11-month period, using standardized sets of traps (pitfall, emergence, Malaise and flight intercept traps). Nine different habitats were studied, including natural and degraded forest, forest plantations (Tectona grandis and Senna siamea) of different age, and isolated forest fragments. Our analysis focused on detritivorous and xylophagous arthropods but also included ground beetles and heteropterans, totalling 393 species. We found no differences in species richness among natural and degraded forest habitats in the centre of the reserve (Noyau central). Outside of the Noyau central, species richness was highest in old teak plantations and isolated forest fragments and lowest in young teak and fuelwood plantations. Detrended correspondence analysis (DCA) separated three main groups: (1) natural forest, (2) degraded forest and young plantations, and (3) old plantations and isolated forest fragments. Multiple regression of DCA scores of the first two axes on environmental variables identified one natural and three disturbance-related predictors of arthropod assemblages in Lama forest: soil type (texture), canopy height, naturalness (proportion of Guineo-Congolian plant species) and understorey vegetation cover. We identified 15 indicator species for six different forest habitats. The highest numbers were found in abandoned settlements and old teak plantations. β-diversity was similar among the three DCA ordination groups (degraded forest excluded). Values for β-diversity were relatively high, suggesting that all major forest habitats contribute significantly to regional species pools and should therefore be protected. To enhance arthropod diversity, we propose that management practices in Lama forest should aim to encourage the development of species-rich understorey vegetation of the Guineo-Congolian phytogeographical region.

First Report of Outbreaks of the Fall Armyworm Spodoptera frugiperda (J E Smith) (Lepidoptera, Noctuidae), a New Alien Invasive Pest in West and Central Africa

The fall armyworm Spodoptera frugiperda is a prime noctuid pest of maize on the American continents where it has remained confined despite occasional interceptions by European quarantine services in recent years. The pest has currently become a new invasive species in West and Central Africa where outbreaks were recorded for the first time in early 2016. The presence of at least two distinct haplotypes within samples collected on maize in Nigeria and São Tomé suggests multiple introductions into the African continent. Implications of this new threat to the maize crop in tropical Africa are briefly discussed.

Saproxylic beetle assemblages on native and exotic snags in a West African tropical forest

The management of dead wood is crucial to the conservation of saproxylic beetles, species dependent on dead wood. This holds for both natural forest and tree plantations. However, the importance of dead wood in tropical forest ecosystems is not yet well understood. The present study investigates saproxylic beetle assemblages of native and exotic standing dead trees (snags). The study was conducted in semi-deciduous protected forest and tree plantations of the Lama Forest Reserve in Benin, West Africa. The snag beetle fauna was sampled for a total of 12 weeks during one year, using trunk window traps. As a control an equal number of live trees was sampled to distinguish saproxylic and non-saproxylic beetles. Mean snag beetle species richness, relative abundance and the number of singletons, species sampled only once, per snag were similar among native and exotic snags. The total number of snag beetle species and beta-diversity of snag beetle assemblages were higher for native than for exotic snags, reflecting high heterogeneity in habitat quality among snags in natural forest. It is concluded that snag beetle assemblages were influenced mainly by the forest system, semi-deciduous forest vs plantations. With regard to dead wood management, retention or creation of snags in semi-deciduous forest, as well as in plantations, can enhance and preserve the diversity of the saproxylic beetle fauna.

Seasonal Abundance of Mango Fruit Flies (Diptera: Tephritidae) and Ecological Implications for Their Management in Mango and Cashew Orchards in Benin (Centre & North)

ABSTRACT We report the results of a large-scale (six orchards) and long-term (5-yr) study on seasonal population fluctuations of fruit flies (Diptera Tephritidae) in mango (2005–2009) and cashew (2007–2009) orchards in the Borgou Department, Benin. During the five consecutive years of mango fruit fly monitoring, 25 tephritid species were captured including three species of Bactrocera, 11 of Ceratitis, and 11 of Dacus, which is represented by 2,138,150 specimens in mango orchards. We observed significant differences in Bactrocera dorsalis (Hendel) counts between “high” and “low” mango production years from 2005 to 2008 but not in Ceratitis cosyra (Walker) counts. The native species, C. cosyra, the most abundant species during the dry season, peaked beginning of May, while the exotic species, B. dorsalis, the most abundant species during the rainy season, peaked in June. Preliminary results underlined the role of nine species of wild hosts and seven species of cultivated ones around mango orchards that played an important role in maintaining B. dorsalis in this Sudan zone all year round. The presence of C. cosyra stretched over 9 mo. During the first 14 wk of tephritid monitoring on cashew orchards situated near mango orchards, most flies (62%) were captured in traps positioned in cashew orchards, showing the strong interest of an early fly control on cashew before the mango season. According to these results, in the Sudan zone, effective and compatible control methods as proposed by the IPM package validated by the West African Fruit Fly Initiative project against mango fruit flies are proposed for a large regional tephritid control program in same zones ofWest Africa.

An illustrated identification key to four different species of adult Dinoderus (Coleoptera: Bostrichidae), commonly attacking dried cassava chips in West Africa.

Bostrichids of the genus Dinoderus are commonly found as pests of dried cassava chips in West Africa. An illustrated key facilitating the identification of the four most frequent African species, i.e. D. bifoveolatus (Wollaston), D. minutus (Fabricius), D. porcellus Lesne, and D. oblongopunctatus Lesne is presented.

Genetic structure and origin of Busseola fusca populations in Cameroon

The cereal stem borer Busseola fusca Fuller (Lepidoptera: Noctuidae) is a species endemic to sub‐Saharan Africa. It is a major pest of maize and cultivated sorghum, the main cereal crops on the African mainland. Previous studies using mitochondrial markers revealed the presence of three clades of haplotypes (W, KI, KII) among B. fusca populations. Previous preliminary studies based on a few B. fusca individuals collected from three localities within the Guineo‐Congolian rain forest in Cameroon demonstrated a matching with clade KII, a fairly surprising result because the putative centre of origin of that clade is located 3 000 km away in East Africa. To check this finding, 120 individuals of B. fusca covering several Cameroonian sites belonging to both Guineo‐Congolian rain forest and Afromontane vegetation mosaics were collected. Comparison of cytochrome b sequences using the same marker revealed low mitochondrial diversity (h = 0.483 ± 0.054, π = 0.073 ± 0.061%). Moreover, molecular diversity in the Guineo‐Congolian rain forest zone was lower than that in Afromontane vegetation, which is therefore thought to be the likely starting point for the colonization of other zones in Cameroon. The study showed a moderate but significant structuring between populations (ΦST = 0.034, P<0.001) as well as within and among the two Cameroonian phytogeographical groups considered (ΦSC = 0.000 and ΦCT = 0.051, respectively, both P<0.001). Nested clade phylogeographic analysis indicated that all Cameroonian clades with significant geographical associations were interpreted as a phenomenon of contiguous range expansion. All results suggest that the Cameroonian population of B. fusca is relatively recent and originates from the recent geographical expansion of clade KII.

A second New World hoverfly, Toxomerus floralis (Fabricius) (Diptera: Syrphidae), recorded from the Old World, with description of larval pollen-feeding ecology

Recently (2013-2014), several hoverfly specimens from two localities in Benin and Cameroon (West and Central Africa) were caught from a species that we could not identify using existing identification keys for Afrotropical Syrphidae. Specific identification as Toxomerus floralis (Fabricius) was accomplished using morphology and various Neotropical identification keys. Corroboration of this identification was made by sequencing of the standard COI barcode region and a subsequent BLAST-IDS in BOLD that revealed a 100% sequence similarity with Toxomerus floralis from Suriname (South America). Species identification was further supported by sequencing parts of the nuclear 18S and 28S rRNA genes. The species is widespread in Togo, Benin, Nigeria and Cameroon, and eggs, larvae and adults are abundant at several localities. Yet, the full extent of its geographic distribution within tropical Africa remains to be determined. This is only the second known established introduction of a non-African hoverfly species in the Afrotropics. Interestingly, the larvae of the species have been reported as predators of Aphididae and Delphacidae but we found them to be pollenivorous, which is a rare feeding mode within the subfamily Syrphinae. Moreover, it is the only known Syrphinae species of which the larvae feed on pollen from two plant species from different families (Cyperaceae and Orobranchaceae). This example illustrates how DNA barcoding may allow a fast and accurate identification of introduced species.