Susceptibility of Mangifera indica (Sapindales: Anacardiaceae) cultivars to fruit flies (Diptera: Tephritidae) in 2 agroecological zones of Cameroon.

The Sudano-Sahelian and the high Guinea savannahs agroecological zones of Cameroon are suitable for the full development of tree crops, including mango. Unfortunately, fresh fruits exported to local and international markets are frequently rejected due to the presence of fruit fly larvae (Diptera: Tephritidae), resulting in drastic income losses and overuse of chemical control products. To promote sustainable management strategies, a 2-yr study (2020-2021) was conducted in 4 and 3 mixed orchards, respectively. Attacked mangoes showing signs of fruit fly damage were collected and taken to the laboratory to rear and identify fruit flies. Repeated grafting and agroclimatic differences were responsible for dissimilarities between the 2 zones, with 18 and 16 cultivars, respectively. From 2,857 attacked mangoes, 26,707 fruit flies belonging to 4 species were identified: Bactrocera dorsalis, Ceratitis cosyra, Ceratitis fasciventris, and Ceratitis anonae. Climate change was the factor determining the distribution of the 2 most important mango fruit flies: B. dorsalis was a wetland species (dominance/occurrence > 70%), while C. cosyra was a dry-land species (dominance/occurrence > 75%). Both species were responsible for high levels of infestations. Bactrocera dorsalis preferred 3 mango cultivars, namely Palmer and Smith in Zone 1, and Ifack 1 in Zone 2 (infestation > 20 individuals/100 g of mango). The host-plant spectrum of C. cosyra was modified by alternative host plants. Both C. fasciventris and C. anonae were rare. Findings from this study could guide researchers in the development of monitoring tools for fruit fly populations and, subsequently, in reducing the damage they cause to mangoes.

Response of cassava (Manihot esculenta Crantz) genotypes to natural infestation by scale insect pest Stictococcus vayssierei Richard (Hemiptera: Stictococcidae).

Cassava is mostly grown for its starchy roots, which ensure food security. However, it is heavily attacked by the African root and tuber scale (ARTS) Stictococcus vayssierei in Central Africa. This pest is a severe constraint to the production of cassava, food and income security for smallholder farmers. Crop resistance development through the selection of varieties with resistant traits against targeted pests is a promising approach to pest control. This study investigated cassava genotypes' response to natural infestation and determined their resistance levels against S. vayssierei. Six cassava genotypes (two local and four improved) were planted in a completely randomized block design with four replicates. Agronomic parameters and ARTS density were evaluated at 3, 6, 9 and 12 months after planting (MAP). Biochemical content was determined on the pith and cortex of 12 MAP aged tuberous roots. As a result, the improved Excel variety recorded the highest scale density per plant with 102.83 ± 4.14 ARTS/P at 9 MAP. At 12 MAP, high activity of total cyanide (69.18 ± 0.88 and 69.16 ± 1.44 mg/kg) and phenylalanine ammonia-lyase (0.142 ± 0.020 and 0.145 ± 0.010 ΔA/min/mg) were observed in the cortex of the tuberous roots of the improved varieties TMS 96/0023 and TMS 92/0057 which were colonized by the lowest ARTS density. The local variety (Douma) had a high content of total phenols (44.87 ± 1.15 µg/g) in the pith. It also produced the highest yield (23.8 ± 2.9 t ha-1). Varieties TMS 96/0023, TMS 92/0057 and Douma may be the most suitable varieties for the control of ARTS stress.

Tephritid Fruit Fly Species Composition, Seasonality, and Fruit Infestations in Two Central African Agro-Ecological Zones.

Bactrocera dorsalis and several Africa-native Ceratitis species are serious constraints to fruit production in sub-Saharan Africa. A long-term trapping and fruit collection study was conducted (2011-2016) in two contrasting agro-ecological zones (AEZs) of Cameroon to determine fruit fly species composition, seasonality, attraction to various lures and baits, and fruit infestation levels. Ten tephritid species from genera Bactrocera, Ceratitis, Dacus, and Perilampsis were captured in traps. Bactrocera dorsalis was the most dominant of the trapped species and persisted throughout the year, with peak populations in May-June. Ceratitis spp. were less abundant than B. dorsalis, with Ceratitis anonae dominating in the western highland zone and Ceratitis cosyra in the humid forest zone. Methyl eugenol and terpinyl acetate captured more B. dorsalis and Ceratitis spp., respectively than Torula yeast. The latter was the most effective food bait on all tephritid species compared with BioLure and Mazoferm. Bactrocera dorsalis was the dominant species emerging from incubated fruits, particularly mango, guava, and wild mango. Four plant species-I. wombolu, Dacryodes edulis, Voacanga Africana and Trichoscypha abut-were new host records for B. dorsalis. This study is the first long-duration and comprehensive assessment of frugivorous tephritid species composition, fruit infestations, and seasonality in Central Africa.

Characterization of actinobacteria associated with three ant-plant mutualisms.

Ant-plant mutualisms are conspicuous and ecologically important components of tropical ecosystems that remain largely unexplored in terms of insect-associated microbial communities. Recent work has revealed that ants in some ant-plant systems cultivate fungi (Chaetothyriales) within their domatia, which are fed to larvae. Using Pseudomyrmex penetrator/Tachigali sp. from French Guiana and Petalomyrmex phylax/Leonardoxa africana and Crematogaster margaritae/Keetia hispida, both from Cameroon, as models, we tested the hypothesis that ant-plant-fungus mutualisms co-occur with culturable Actinobacteria. Using selective media, we isolated 861 putative Actinobacteria from the three systems. All C. margaritae/K. hispida samples had culturable Actinobacteria with a mean of 10.0 colony forming units (CFUs) per sample, while 26 % of P. penetrator/Tachigali samples (mean CFUs 1.3) and 67 % of P. phylax/L. africana samples (mean CFUs 3.6) yielded Actinobacteria. The largest number of CFUs was obtained from P. penetrator workers, P. phylax alates, and C. margaritae pupae. 16S rRNA gene sequencing and phylogenetic analysis revealed the presence of four main clades of Streptomyces and one clade of Nocardioides within these three ant-plant mutualisms. Streptomyces with antifungal properties were isolated from all three systems, suggesting that they could serve as protective symbionts, as found in other insects. In addition, a number of isolates from a clade of Streptomyces associated with P. phylax/L. africana and C. margaritae/K. hispida were capable of degrading cellulose, suggesting that Streptomyces in these systems may serve a nutritional role. Repeated isolation of particular clades of Actinobacteria from two geographically distant locations supports these isolates as residents in ant-plant-fungi niches.

Patterns of species richness and diversity of insects associated with cucurbit fruits in the southern part of Cameroon.

Patterns of species diversity and community structure of insects associated with fruits of domesticated cucurbits were investigated from January 2009 to 2011 in three localities from two agroecological zones in the southern part of Cameroon. Rarefaction curves combined with nonparametric estimators of species richness were used to extrapolate species richness beyond our own data. Sampling efforts of over 92% were reached in each of the three study localities. Data collected revealed a total of 66 insect morphospecies belonging to 37 families and five orders, identified from a set of 57,510 insects. The orders Diptera (especially Tephritidae and Lonchaeidae) and Hymenoptera (mainly Braconidae and Eulophidae) were the most important, in terms of both abundance and species richness on the one hand, and effects on agronomic performance on the other. Values for both the species diversity (Shannon and Simpson) and the species richness indices (Margalef and Berger-Parker) calculated showed that the insect communities were species-rich but dominated, all to a similar extent, by five main species (including four fruit fly species and one parasitoid). Species abundance distributions in these communities ranged from the Zipf-Mandelbrot to Mandelbrot models. The communities are structured as tritrophic networks, including cucurbit fruits, fruit-feeding species (fruit flies) and carnivorous species (parasitoids). Within the guild of the parasitoids, about 30% of species, despite their low abundance, may potentially be of use in biological control of important pests. Our field data contribute in important ways to basic knowledge of biodiversity patterns in agrosystems and constitute baseline data for the planned implementation of biological control in Integrated Pest Management.

Repeated evolution of fungal cultivar specificity in independently evolved ant-plant-fungus symbioses.

Some tropical plant species possess hollow structures (domatia) occupied by ants that protect the plant and in some cases also provide it with nutrients. Most plant-ants tend patches of chaetothyrialean fungi within domatia. In a few systems it has been shown that the ants manure the fungal patches and use them as a food source, indicating agricultural practices. However, the identity of these fungi has been investigated only in a few samples. To examine the specificity and constancy of ant-plant-fungus interactions we characterised the content of fungal patches in an extensive sampling of three ant-plant symbioses (Petalomyrmex phylax/Leonardoxa africana subsp. africana, Aphomomyrmex afer/Leonardoxa africana subsp. letouzeyi and Tetraponera aethiops/Barteria fistulosa) by sequencing the Internal Transcribed Spacers of ribosomal DNA. For each system the content of fungal patches was constant over individuals and populations. Each symbiosis was associated with a specific, dominant, primary fungal taxon, and to a lesser extent, with one or two specific secondary taxa, all of the order Chaetothyriales. A single fungal patch sometimes contained both a primary and a secondary taxon. In one system, two founding queens were found with the primary fungal taxon only, one that was shown in a previous study to be consumed preferentially. Because the different ant-plant symbioses studied have evolved independently, the high specificity and constancy we observed in the composition of the fungal patches have evolved repeatedly. Specificity and constancy also characterize other cases of agriculture by insects.

Permanent genetic resources added to Molecular Ecology Resources Database 1 February 2013-31 March 2013.

This article documents the addition of 142 microsatellite marker loci to the Molecular Ecology Resources database. Loci were developed for the following species: Agriophyllum squarrosum, Amazilia cyanocephala, Batillaria attramentaria, Fungal strain CTeY1 (Ascomycota), Gadopsis marmoratus, Juniperus phoenicea subsp. turbinata, Liriomyza sativae, Lupinus polyphyllus, Metschnikowia reukaufii, Puccinia striiformis and Xylocopa grisescens. These loci were cross-tested on the following species: Amazilia beryllina, Amazilia candida, Amazilia rutila, Amazilia tzacatl, Amazilia violiceps, Amazilia yucatanensis, Campylopterus curvipennis, Cynanthus sordidus, Hylocharis leucotis, Juniperus brevifolia, Juniperus cedrus, Juniperus osteosperma, Juniperus oxycedrus, Juniperus thurifera, Liriomyza bryoniae, Liriomyza chinensis, Liriomyza huidobrensis and Liriomyza trifolii.

Multi-locus phylogenies of the genus Barteria (Passifloraceae) portray complex patterns in the evolution of myrmecophytism.

The four species of the central African genus Barteria show variation in habitat and in degree of association with ants. Whereas B. solida, restricted to submontane forests, attracts opportunistic ants to extrafloral nectar, the three other species, found in lowland rainforests (B. fistulosa, B. dewevrei) and in littoral scrub (B. nigritana), possess stem domatia of varying shapes and degrees of specialisation, hosting either non-specific arboreal ants (B. nigritana, some B. dewevrei) or two large species of ants of the genus Tetraponera Smith, 1852 that are specific to some species of Barteria (B. fistulosa, some B. dewevrei). We aimed to investigate whether this variation represents an evolutionary trend toward increasing specialisation of mutualism or the reduction or loss of myrmecophytic traits. For this, we determined phylogenetic relationships within the genus using DNA sequences (primarily nuclear ITS) and microsatellite genotypes (11 loci) on a large sample of individuals, mostly from Cameroon and Gabon. The two types of markers support an initial dichotomy that groups B. dewevrei with B. nigritana and B. fistulosa with B. solida respectively. Within these pairs, species do not appear reciprocally monophyletic. At microsatellite loci, B. nigritana forms a clade embedded within B. dewevrei; and within both B. solida and B. fistulosa, geographical populations show levels of differentiation similar to that observed between populations of B. solida and B. fistulosa. Geographic distance alone does not account for genetic differentiation between species, which indicates reproductive isolation. Divergence in each of the two pairs implies evolutionary transitions in habitat and in myrmecophytism. Specialised mutualism with specific ant species of the genus Tetraponera has been lost in species found in more marginal habitats.

Plant-ants use symbiotic fungi as a food source: new insight into the nutritional ecology of ant-plant interactions.

Usually studied as pairwise interactions, mutualisms often involve networks of interacting species. Numerous tropical arboreal ants are specialist inhabitants of myrmecophytes (plants bearing domatia, i.e. hollow structures specialized to host ants) and are thought to rely almost exclusively on resources derived from the host plant. Recent studies, following up on century-old reports, have shown that fungi of the ascomycete order Chaetothyriales live in symbiosis with plant-ants within domatia. We tested the hypothesis that ants use domatia-inhabiting fungi as food in three ant-plant symbioses: Petalomyrmex phylax/Leonardoxa africana, Tetraponera aethiops/Barteria fistulosa and Pseudomyrmex penetrator/Tachigali sp. Labelling domatia fungal patches in the field with either a fluorescent dye or (15)N showed that larvae ingested domatia fungi. Furthermore, when the natural fungal patch was replaced with a piece of a (15)N-labelled pure culture of either of two Chaetothyriales strains isolated from T. aethiops colonies, these fungi were also consumed. These two fungi often co-occur in the same ant colony. Interestingly, T. aethiops workers and larvae ingested preferentially one of the two strains. Our results add a new piece in the puzzle of the nutritional ecology of plant-ants.

The cost of myrmecophytism: insights from allometry of stem secondary growth.

BACKGROUND AND AIMS: Plant defence traits against herbivores incur production costs that are usually difficult to measure. However, estimating these costs is a prerequisite for characterizing the plant defence strategy as a whole. Myrmecophytes are plants that provide symbiotic ants with specialized nesting cavities, called domatia, in exchange for protection against herbivores. In the particular case of stem domatia, production of extra wood seems to be the only associated cost, making this indirect defence trait a particularly suitable model for estimating the cost of defence. METHODS: Measurements were made of growth pattern and cumulative production cost of domatia over secondary growth in the myrmecophyte Leonardoxa africana subsp. africana, whose internodes display both a solid basal segment and a hollow distal part (the domatium), thus allowing paired comparison of investment in wood. KEY RESULTS: Previous studies showed that 'overconstruction' of the hollow part of internodes during primary growth is needed for mechanical support. In this study, it is shown that the relationship between the woody cross-sectional area of the solid and hollow parts of internodes is negatively allometric at the beginning of secondary growth and nearly isometric later on. Thus, in hollow stems, the first phase of slow secondary growth compensates for the 'overconstruction' of the ring of wood during primary growth. Moreover, the cumulative production cost of a domatium (estimated as the additional volume of wood required for a hollow stem compared with a solid one) is very high at the beginning of secondary growth and then quickly tends to zero. CONCLUSIONS: Making domatia incurs high costs early in ontogeny, costs that are then amortized later in development of stems and of individual plants. Characterizing ontogenetic variation of the net cost of this peculiar defence mechanism will help us build more accurate theoretical models of resource allocation in myrmecophytes.

The diversity of ant-associated black yeasts: insights into a newly discovered world of symbiotic interactions.

Based on pure culture studies and DNA phylogenetic analyses, black yeasts (Chaetothyriales, Ascomycota) are shown to be widely distributed and important components of numerous plant-ant-fungus networks, independently acquired by several ant lineages in the Old and New World. Data from ITS and LSU nu rDNA demonstrate that a high biodiversity of fungal species is involved. There are two common ant-fungus symbioses involving black yeasts: (1) on the carton walls of ant nests and galleries, and (2) the fungal mats growing within non-pathogenic naturally hollow structures (so-called domatia) provided by myrmecophytic plants as nesting space for ants (ant-plant symbiosis). Most carton- and domatia-inhabiting fungi stem from different phylogenetic lineages within Chaetothyriales, and almost all of the fungi isolated are still undescribed. Despite being closely related, carton and domatia fungi are shown to differ markedly in their morphology and ecology, indicating that they play different roles in these associations. The carton fungi appear to improve the stability of the carton, and several species are commonly observed to co-occur on the same carton. Carton fungi commonly have dark-walled monilioid hyphae, colouring the carton blackish and apparently preventing other fungi from invading the carton. Despite the simultaneous presence of usually several species of fungi, forming complex associations on the carton, little overlap is observed between carton fungi from different ant species, even those that co-occur in nature, indicating at least some host specificity of fungi. Most fungi present on carton belong to Chaetothyriales, but in a few samples, Capnodiales are also an important component. Carton fungi are difficult to assign to anamorph genera, as most lack conidiation. The domatia fungi are more specific. In domatia, usually only one or two fungal species co-occur, producing a dense layer on living host plant tissue in domatia. They have hyaline or light brown thin-walled hyphae, and are commonly sporulating. In both carton and domatia, the fungal species seem to be specific to each ant-plant symbiosis. Representative examples of carton and domatia ant-fungus symbioses are illustrated. We discuss hypotheses on the ecological significance of the Chaetothyriales associated with ants.

Plant-ants feed their host plant, but above all a fungal symbiont to recycle nitrogen.

In ant-plant symbioses, plants provide symbiotic ants with food and specialized nesting cavities (called domatia). In many ant-plant symbioses, a fungal patch grows within each domatium. The symbiotic nature of the fungal association has been shown in the ant-plant Leonardoxa africana and its protective mutualist ant Petalomyrmex phylax. To decipher trophic fluxes among the three partners, food enriched in (13)C and (15)N was given to the ants and tracked in the different parts of the symbiosis up to 660 days later. The plant received a small, but significant, amount of nitrogen from the ants. However, the ants fed more intensively the fungus. The pattern of isotope enrichment in the system indicated an ant behaviour that functions specifically to feed the fungus. After 660 days, the introduced nitrogen was still present in the system and homogeneously distributed among ant, plant and fungal compartments, indicating efficient recycling within the symbiosis. Another experiment showed that the plant surface absorbed nutrients (in the form of simple molecules) whether or not it is coated by fungus. Our study provides arguments for a mutualistic status of the fungal associate and a framework for investigating the previously unsuspected complexity of food webs in ant-plant mutualisms.

Diversity and spatial distribution of vectors and hosts of T. brucei gambiense in forest zones of, Southern Cameroon: epidemiological implications.

Host and vector distribution of Trypanosoma brucei gambiense was studied in relation to habitat types and seasons. Six (19.35%) of the 31 mammal species recorded in Bipindi were reservoir hosts. Cercopithecus nictitans was confined to the undisturbed forest and the low intensive shifting cultivation zones, while Cephalophus monticola, Cephalophus dorsalis, Cricetomys gambianus, Atherurus africanus and Nandinia binotata occurred in all the habitat types. As for vectors of human African trypanosomiasis (HAT), Glossina palpalis palpalis, was the most abundant (99.13%) among tsetse fly species. It occurs in all biotopes with its highest density recorded in the village-adjacent forest. The village-adjacent forest is therefore the most risky transmission zone for HAT mainly during the short rainy season when G. palpalis palpalis' density is highest (2.91); while, the high and low intensive shifting cultivation zones are the most important contact zones between humans, G. palpalis palpalis and wild mammals in all seasons.

Influence of habitat and seasonal variation on wild mammal diversity and distribution with special reference to the Trypanosoma brucei gambiense host-reservoir in Bipindi (Cameroon).

To evaluate the role of wildlife in the resurgence and perenisation of human African trypanosomiasis (HAT), we investigated the influence of habitat and seasonal variations on the diversity and spatial distribution of wild mammals, with special reference to those recognised as potential host-reservoirs of Trypanosoma brucei gambiense in Bipindi (southwestern Cameroon). To achieve this, we carried out transect surveys in four habitat types over two years. A total of 31 mammal species were recorded, of which 14 occurred in the undisturbed forest, 9 in cocoa plantations, 11 in farmlands and 11 in village-adjacent gallery forests. Among them, six species (Cephalophus monticola, Cephalophus dorsalis, Atherurus africanus, Cricetomys emini, Nandinia binotata and Cercopithecus nictitans), known as reservoir hosts of T. b. gambiense, occurred in all kinds of habitats suitable or unsuited to Glossina palpalis palpalis and in all seasons. These species are the most involved in the transmission cycle (human being/tsetse flies/wild animals). Cercopithecus cephus, Miopithecus talapoin and Heliosciurus rufobrachium host Trypanosoma brucei spp.; however, only C. cephus does not occur permanently in the suitable habitat of G. palpalis palpalis. In general, some species (C. monticola, Tragelaphus spekei and C. emini) showed a slight density increase from the long dry to the heavy rainy season within the undisturbed and farmland habitats, and a slight decrease within cocoa plantations and village-adjacent forests in the same period. The density of A. africanus increased greatly from the long dry season to the heavy rainy season in the undisturbed forest while, the density of primates in this habitat decreased slightly from the long dry season to the heavy rainy season. These variations indicate a permanent movement of wild mammal reservoir or feeding hosts from one biotope to another over the seasons. Thryonomys swinderianus needs to be investigated because it occurs permanently in the suitable habitat of G. palpalis palpalis and Potamochoerus porcus for its genetic similarities to domestic pigs, favourable feeding hosts of G. palpalis palpalis.

Ant-plants and fungi: a new threeway symbiosis.

Symbioses between plants and fungi, fungi and ants, and ants and plants all play important roles in ecosystems. Symbioses involving all three partners appear to be rare. Here, we describe a novel tripartite symbiosis in which ants and a fungus inhabit domatia of an ant-plant, and present evidence that such interactions are widespread. We investigated 139 individuals of the African ant-plant Leonardoxa africana for occurrence of fungus. Behaviour of mutualist ants toward the fungus within domatia was observed using a video camera fitted with an endoscope. Fungi were identified by sequencing a fragment of their ribosomal DNA. Fungi were always present in domatia occupied by mutualist ants but never in domatia occupied by opportunistic or parasitic ants. Ants appear to favour the propagation, removal and maintenance of the fungus. Similar fungi were associated with other ant-plants in Cameroon. All belong to the ascomycete order Chaetothyriales; those from L. africana formed a monophyletic clade. These new plant-ant-fungus associations seem to be specific, as demonstrated within Leonardoxa and as suggested by fungal phyletic identities. Such tripartite associations are widespread in African ant-plants but have long been overlooked. Taking fungal partners into account will greatly enhance our understanding of symbiotic ant-plant mutualisms.