Thermal response and horizontal transmission of cameroonian isolates of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae – Candidates for microbial controls of the banana root borer Cosmopolites sordidus

Beauveria bassiana and Metarhizium anisopliae are two promising microbial agents for biopesticides development against the banana root borer Cosmopolites sordidus. In this study, germination, mycelial growth, and sporulation of six local Cameroonian isolates of those two species were assessed under seven different thermal conditions (13, 15, 20, 25, 29 33, and 37 °C) to select thermo-tolerant isolates. The Transmission potential of the thermo-tolerant isolates was determined at 25 ± 1 °C by dipping adult weevils in conidial suspensions (3.2 × 108) conidia/ml and mixing these with uninoculated weevils in different proportions (0, 10, 30 and 50%), in groups of 30, and assessing the spread of the mycosis within the group over 35 d of co-incubation. Incubation temperature and isolates significantly affected germination, mycelial growth and conidial production. All isolates had large thermal tolerance ranges (13–33 °C) except MIITAC6.4.2 (20–29 °C). Horizontal transmission resulted in mortality of non-inoculated weevils from 4.63 ± 1.77 to 53.3 ± 11.9%. The isolate BIITAC6.2.2 exhibited high auto-dissemination potential and high conidia yield in cadavers. These results demonstrate the potential use of these isolates for biopesticides development against C. sordidus in Central Africa

Productivity and resistance of okra (Abelmoschus spp.) to the cotton aphid Aphis gossypii glover (Hemiptera: Aphididae) under tropical conditions

Aphis gossypii Glover (Hemiptera: Aphididae) is among major arthropods causing significant damage to okra in the tropics. Resistant varieties could reduce aphid infestation and increase productivity. This study was carried out to identify aphid-resistant and high yielding okra accessions for management of the pest. Eleven farmers’ varieties and four aphid-resistant accessions from AVRDC were evaluated at its Nkolbisson station in Yaounde, Cameroon. Field screening was done to determine resistance to aphids, days to 50% anthesis and days to 50% commercial maturity. Aphid data was expressed as the area under infestation pressure curve and subjected to statistical analysis based on mean (m) and standard deviation (S.D.). Crop cycle and yield data were subjected to analysis of variance. Accession ‘VI033824’ was the most resistant to aphids (474 ± 41.9 per leaf) with yield 0.76 ± 0.26 t/ ha whereas the yield of the highly susceptible Babungo (1519.8 ± 0.0 aphids) was 1.33 ± 0.07 t/ha, 75.5% higher that the yield of the only resistant variety. Abelmoschus esculatus was less attacked (601.4 ± 60.0 aphids) by aphids than Abelmoschus caillei (826.0 ± 71.6 aphids; df = 1, 41; Pr {>Chi} = 0.037). The yield of A. caillei species were higher (1.26 ± 0.14 t/ha) than A. esculentus species (0.43 ± 0.08 t/ha; df = 1, 41; Pr {>Chi} = 0.0002). Hence, varieties with resistance, tolerance to aphids and earliness could be incorporated into integrated pest management of aphids and enhance productivity of okra

Spatio‐temporal partitioning and sharing of parasitoids by fall armyworm and maize stemborers in Cameroon

Biological invasion is a global concern with species deployed out of native range, the most recent in Africa being the invasion by fall armyworm (FAW) Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae). One of the most mentioned ecological consequences is the capacity of invaders to change native communities' structure. Busseola fusca Fuller (Lepidoptera: Noctuidae) has long been the most destructive pests of maize in Africa. Few or no studies have attempted to look at the interaction between FAW and native maize pests over a cropping cycle for sustainable management. Maize trials were established over two cropping cycles in Cameroon to investigate the nature of such interactions and eventual sharing of parasitoids. FAW incidence decreased with maize growth, while the reverse was observed for stemborers. Few cases of co‐occurrence were recorded at the later maize growth stage. There was a clear indication that FAW infestation was associated with vegetative stages, while stemborers were associated with reproductive stages. Only FAW eggs were found on abaxial and adaxial leaf surfaces, while only stemborer eggs were inside leaf sheaths. Similarly, while larvae of both groups were found in maize whorl and on ears, only FAW larvae were found in closed tassels, while only stemborers were found inside stems. These results are in favour of segregation in time and space in plant colonization by native and invasive pests, which may limit competition and exacerbates damage if no control is provided. The same egg, larval and pupal parasitoids respectively Telenomus remus, Cotesia icipe and Procerochasmias nigromaculatus emerged from isolated FAW and B. fusca eggs, larvae, and pupae. The sharing of parasitoids by both species provides a unique opportunity for augmentative biocontrol

A preliminary analysis on the effect of copper on Anopheles coluzzii insecticide resistance in vegetable farms in Benin.

The use of agrochemicals in vegetable production could influence the selection for insecticide resistance in malaria vectors. Unfortunately, there is a dearth of information on the potential contribution of agrochemicals to insecticide resistance in Anopheles mosquitoes breeding on vegetable farms in southern Benin. A Knowledge, Attitudes and Practices study was conducted with 75 vegetable farmers from Houeyiho and Seme to determine the main agrochemicals used in vegetable production, and the concentration and frequency of application, among other details. Mosquitoes and breeding water were sampled from the farms for analysis. Bioassays were conducted on mosquitoes, while breeding water was screened for heavy metal and pesticide residue contamination. Lambda-cyhalothrin was the main insecticide (97.5%) used by farmers, and Anopheles coluzzii was the main mosquito identified. This mosquito species was resistant (30-63% mortality rate) to λ-cyhalothrin. It was also observed that 16.7% of the examined breeding sites were contaminated with λ-cyhalothrin residues. Furthermore, copper contamination detected in mosquito breeding sites showed a positive correlation (r = 0.81; P = 0.0017) with mosquito resistance to λ-cyhalothrin. The presence of copper in λ-cyhalothrin-free breeding sites, where mosquitoes have developed resistance to λ-cyhalothrin, suggests the involvement of copper in the insecticide resistance of malaria vectors; this, however, needs further investigation

Towards the development of sustainable control options for the African root and tuber scale on cassava in Central Africa : understanding the biology and ecology of the tending ant "Anoplolepis tenella" (Hymenoptera: Formicidae)

Anoplolepis tenella Santschi is an afrotropical ant widely distributed in the forest zones of Central Africa. It is the most frequent species associated with the African root and tuber scale (ARTS) Stictococcus vayssierei (Hemiptera: Stictococcidae), an afrotropical insect that infests a wide range of root and tuber plants, particularly cassava. Present evidence supports the hypothesis that the scale needs the ant to remove its honeydew secretions, as the scale would otherwise drown in its own secretions. Therefore developing effective management options to reduce ARTS infestations, requires adequate understanding of the biology and ecology of A. tenella and its impact on ARTS life cycle and ecology. Therefore, we carried out study on the distribution and abundance of A. tenella and thereby co-occurring ant species in mixed-crop fields, fallow and forest which are the dominant vegetation type in southern Cameroon. We also assessed some of the factors that could explain the observed distribution. Results indicated highest species richness in the forest. Anoplolepis tenella abundance, density and activity was affected by vegetation type, season and a set of abiotic parameters among which are air temperature and relative humidity. Its abundance was higher in mixed-crop fields, while it was and either absent or rare in the lowland where coincidently S. vayssierei was also absent. These results indicate that human activities reduce ant diversity and offer new nesting niches or food sources to ants which could explain the proliferation of species like A. tenella. Among other factors affecting the ant’s distribution are plants producing nectar and extrafloral nectaries and honeydew producers among which S. vayssierei. The distribution of these plants and honeydew-producing insects significantly differed between vegetation types, hence the difference in ant composition. Network analysis of the ant-hemipteran matrix showed high specialization index at individual level for A. tenella and S. vayssierei. We couldn’t demonstrate the dispersal of the scale by air currents or through phoresis on A. tenella founding queens. However, through a dispersal experiment in a screenhouse, we demonstrated the active role of A. tenella workers in the transport and dissemination of scale crawlers within and between cassava plants. In an effort to control ant colonies under laboratories condition, Boric acid-sucrose solution showed a significant reduction of A. tenella population within six weeks. These results demonstrate that control of S. vayssierei in crop fields is contingent on reductions in the densities of its associated ant A. tenella

Transport and dispersal of Stictococcus vayssierei (Homoptera, Stictococcidae) by Anoplolepis tenella (Hymenoptera, Formicidae)

Dispersal can be a crucial factor affecting fitness in insects. We conducted a series of experiments and observations with the aim of determining the dispersal mode of the African root and tuber scale Stictococcus vayssierei, a pest on cassava in the Congo Basin. We monitored the main options of dispersal that occurred in scale insects: wandering of first-instar nymphs (crawlers), active dispersal by ant workers, phoresis on colony-founding queen ants, and passive dispersal by wind. Results showed that A. tenella workers are actively involved in the transport and dissemination of scale crawlers. When ants were excluded, crawlers could move by themselves for a short distance to find the host plant. In the presence of ants, crawlers were transported by ant workers for longer distance across the bridge and established on scale-free plants. Scales transport increased with the duration of the experiment and ant density. Neither a case of phoresis nor dispersal by wind was recorded, suggesting that passive dispersal is rare. These results outline the active role of A. tenella workers in the dispersal of immature stages of S. vayssierei in Southern Cameroon and have implication in the management of the scale on cassava

Ant Diversity in Dominant Vegetation Types of Southern Cameroon

Ants have been shown as particularly affected by land disturbance through deforestation and conversion of forest to agriculture. The effect of land use change on ant diversity in the Congo Basin is not well known. We conducted intensive sampling along a gradient of increasing vegetation disturbance to test the effect of habitat disturbance on ant diversity and Functional Groups composition. Sampling was conducted in 30 plots (5 study sites × 3 habitat × 2 plots/habitat), replicated six times in 1 year. In each plot, ants were monitored with pitfall traps, quadrats and baits. We recorded 237 ant morphospecies grouped in 10 subfamilies and 43 genera. Myrmicaria opaciventris was the most abundant species followed by Anoplolepis tenella. Forest had greater ant diversity compared with fallows and mixed-crop fields. Functional groups were dominated by Opportunists, followed by Omnivorous Arboreal Dominants and Generalized Mymicinae. Their composition was not affected by the disturbance, but occurrence of Specialist Predators decreased with increasing disturbance. Occurrence of Generalized Myrmicinae, Opportunists and Subordinate Camponotini increased with disturbance. These results indicate that forest conversion into mixed-crop fields reduce ant diversity. It can also increase abundance of species with generalized diet that predominates where stress and disturbance limits other ants

How plants and honeydew-producing hemipteran insects affect ant species richness and structure in a tropical forest zone

Extrafloral nectaries (EFNs) and hemipteran honeydew are often discussed as two alternative mechanisms encouraging ant visitation in mutualistic ant–plant relationships, but little is known about the processes that generate distribution pattern in species-rich insect communities. A case study on the interaction between ants, EFN-bearing plants and hemipterans was investigated along a gradient of increasing disturbance from regenerated forest to mixed crop field. Ants, EFN-bearing plants and hemipterans sampling was conducted in these vegetations during the wet and the dry seasons in five locations. Results showed that partitioning of ant species between season and vegetation was significantly different from random. High specialization index was observed in hemipterans/plants and ant/hemipterans interactions. Low specialization index was observed between ants and EFN-bearing plants mainly in the mixed crop field. Ant species were mostly found in non-aggressive co-occurrence at nectar sources. At the species level, specialization index was high for Anoplolepis tenella (0.86 ± 0.06) and also for its associated hemipterans Stictococcus vayssierei (0.97 ± 0.02). This association is detrimental to food crop especially cassava. These results outline the effect of vegetation and food source on the structure of the ant assemblage and interaction in tropical forest zone

Species Richness, Density, Activity, and Composition of Ground-dwelling Ants in the Humid Forest Zone of Southern Cameroon: Role of vegetation Cover and Abiotic Factors

The destruction of natural habitats is among the major factors responsible for the decrease in species diversity and distribution. This study focused on the effect of vegetation and its interaction with the season on ant species richness, density, activity, and composition in the three dominant habitats - forest, fallow, and mixed crop field - prevailing in southern Cameroon. Ants were sampled using two sampling techniques -pitfall trap and quadrat - in fallows, forest, and mixed crop fields from May 2007 to April 2008. Average ant species richness did not differ between fallow and forest, but the number of species in both habitats was higher compared with mixed-crop field. Species richness was also higher during the short dry season compared with other seasons. Species density was higher in mixed-crop field and in the long dry season. Species activity was similar in the three habitats, but it was higher during the long-wet season. Species richness, activity, and density were lower at low altitude. Vegetation and season affected the composition of ant species, but not the interaction between the two factors. The highest dissimilarity index was observed between mixed crop-field and forest while between seasons, it was between the short-wet and the long dry season. These results suggest that vegetation cover and abiotic factors interact to determine the distribution, density, activity, and composition of ant species. Identifying key drivers among environmental factors could help to understand the response of species to the variation of those factors in the context of climate change