X-Ray Polarization of Solar Flares Measured with Rhessi

The degree of linear polarization in solar flares has not yet been precisely determined despite multiple attempts to measure it with different missions. The high energy range in particular has very rarely been explored, due to its greater instrumental difficulties. We approached the subject using the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study 6 X-class and 1 M-class flares in the energy range between 100 keV and 350 keV. Using RHESSI as a polarimeter requires the application of strict cuts to the event list in order to extract those photons that are Compton scattered between two detectors. Our measurements show polarization values between 2% and 54%, with errors ranging from 10% to 26% in 1 sigma level. In view of the large uncertainties in both the magnitude and direction of the polarization vector, the results can only reject source models with extreme properties.Comment: 26 pages, 11 figures, accepted for publication by Solar Physic

Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) in Cameroon: case study on its distribution, damage, pesticide use, genetic differentiation and host plants

Open Access JournalMaize farmers in sub-Saharan Africa recently experienced unusual damage in their farms, attributed to the fall armyworm (FAW) Spodoptera frugiperda (J. E. Smith). This pest was first recorded in Africa in 2016, but detailed information on its distribution and damage and farmer's response in invaded areas are largely lacking. In this study, we determined FAW distribution, genetic diversity, host plants, crop damage, and farmers' responses. S. frugiperda was recorded in the 10 regions of Cameroon. Average percentage of infested plants and damage severity (on a scale of 1 to 5) were lowest-20.7 ± 7.4% and 2.1 ± 0.1 respectively-in the Sahelian regions and greatest-69.0 ± 4.3% and 3.1 ± 0.1 respectively-in the Western Highlands. Altitude did not influence FAW incidence and severity and its larvae infrequently co-occurred with maize stemborers on the same plants, suggesting possible direct and/or indirect competition between the two groups of maize pests. In response to this new threat to maize production, farmers have opted for the application of synthetic pesticides. Although our experiments were not designed to determine pesticide efficacy, as parameters such as time since application were not considered, our observations suggest lack of a drastic effect on S. frugiperda infestations on maize. There were two haplotypes of FAW co-occurring in Cameroon corresponding to the rice and corn strains and separated by 1.7% sequence divergence, which does not support the existence of cryptic species. S. frugiperda larvae were also recorded on Sorghum bicolor (L.) Moench (10.6%), Solanum tuberosum L. (2.8%), Ipomoea batatas (L.) Lam. (1.9%), Saccharum officinarum L (0.8%), Phaseolus vulgaris L. (0.4%) and Gossypium hirsutum L. (1.9%). This study show that two strains are present in all agroecological zones in Cameroon, and probably in neighboring countries of central Africa sharing the same agroecologies. Management options should therefore consider the use of specific natural enemies and an informed decision of intervention based on strain capture and damage threshold, to avoid pesticide resistance that may arise from inadequate use of chemicals. Further studies should also be undertaken to assess the response of the two S. frugiperda strains to biopesticides and botanical insecticides

Geographic distribution and abundance of the Afrotropical subterranean scale insect Stictococcus vayssierei (Hemiptera: Stictococcidae), a pest of root and tuber crops in the Congo basin

Open Access Article; Published online: 01 Oct 2019Stictococcus vayssierei is a major pest of root and tuber crops in central Africa. However, data on its ecology are lacking. Here we provide an updated estimate of its distribution with the aim of facilitating the sustainable control of its populations. Surveys conducted in nine countries encompassing 13 ecological regions around the Congo basin showed that African root and tuber scale was present in Cameroon, Central African Republic, Congo, Democratic Republic of Congo, Equatorial Guinea, Gabon and Uganda. It was not found on the sites surveyed in Chad and Nigeria. The pest occurred in the forest and the forest-savannah mosaic as well as in the savannah where it was never recorded before. However, prevalence was higher in the forest (43.1%) where cassava was the most infested crop, compared to the savannah (9.2%) where aroids (cocoyam and taro) were the most infested crops. In the forest habitat, the pest was prevalent in all but two ecological regions: the Congolian swamp forests and the Southern Congolian forest-savanna mosaic. In the savannah habitat, it was restricted to the moist savannah highlands and absent from dry savannahs. The scale was not observed below 277 m asl. Where present, the scale was frequently (87.1% of the sites) attended by the ant Anoplolepis tenella. High densities (>1000 scales per plant) were recorded along the Cameroon–Gabon border. Good regulatory measures within and between countries are required to control the exchange of plant materials and limit its spread. The study provides information for niche modeling and risk mapping

Genetic Structure, Nestmate Recognition and Behaviour of Two Cryptic Species of the Invasive Big-Headed Ant Pheidole megacephala

info:eu-repo/semantics/publishe

Dominance hierarchy in colonies of Belonogaster juncea juncea (Vespidae: Polistinae)

Dominance behaviours and the structure of the dominance hierarchy in colonies of Belonogaster juncea juncea are described. The frequency of these behaviours was recorded for each individual by noting "all occurrences of rare behaviours". Among the dominance behaviours recorded, the most frequent was "grappling," which represents 69.8 % of the total number of dominance interactions observed. The overall frequency of dominance behaviours was 0.4 ± 0.36 and 2.99 ± 1.97 per hour per individual in pre- and post-emergence colonies, respectively. The data were submitted to the Appleby test, which shows the hierarchy's highly significant level of linearity. The a female showed the highest frequency of dominance interactions and initiated 81.5 % and 48.8 % of the total dominance interactions observed in pre- and post-emergence colonies, respectively. A weekly record of the frequency of dominance interactions throughout the biological cycle shows that this frequency was highest before or immediately after the disappearance of the dominant female. The most aggressive dominance behaviour (falling fights) was observed only during the weeks after the dominant's departure. This behaviour is thus involved in the establishment of the hierarchy and not in its maintenance, which is accomplished by means of less aggressive behaviours

Parisitisme des Loranthaceae sur lavocatier (Persea americana, Lauraceae) dans la region de Yaounde (Cameroun)

In Cameroon, parasitism by Loranthaceae is a limiting factor of the avocado tree cultivation as well as the many diseases and pests which have been better studied. Inventories were carried out in the agroecosystems of five localities around Yaounde, Cameroon. In each one of these localities, all the avocado trees likely to produce and located within a perimeter 2000 m×50 m were observed and characterized by the circumference of the trunk, the number of tufts of Loranthaceae present on the tree and of the taxon of the parasite. Avocado trees are primarily parasitized by three species of Loranthaceae. Parasitism rates (43.30-69.44%) varied significantly among the five localities of the zone studied. In addition, in each locality, this rate of parasitism varied to a significant degree according to the various classes of trunk circumference. The average number of tufts of Loranthaceae by tree was also significantly different according to locality. On a given locality scale, the variables 'average tuft number by tree' and 'trunk circumference' appeared correlated. In the absence of parasitic specificity, control has to be carried out on all the potential host species. While waiting for the avocado tree parasitism by Loranthaceae to be taken into account in the search for resistant cultivars, it is advised to control these phanerogams by carrying out a manual destruction of the tufts

Record of new host plants associated to the invasive mealybug species Paracoccus marginatus Williams and Granara de Willink (Hemiptera: Pseudococcidae) in the Center and Littoral regions of Cameroon.

Published online: 07 Jan 2021The papaya mealybug (PM) is a known notorious polyphagous insect pest of many plant species and has always been found associated with a new host/s in newly invaded areas. This pest recently invaded West and Central Africa. Surveys were conducted randomly from July 2014 to May 2018 to determine the host range of this pest in the Center and Littoral regions in Cameroon. Plants infested by PM were recognized by the presence of black sooty mould, leaf deformation and/or chlorosis. A standard infestation scale was used to evaluate the infestation level on each plant. After collection, infested plants were pressed, dried and identified at the national Herbarium. A total of 52 plant species (only one undetermined) belonging to 23 families were found infested by PM associated with other mealybug or with two species of mealybugs with a percentage of (79.2%, N = 75) and (20.8%, N = 75) respectively. Two plant families (out of 23 identified) and 18 plant species (out of 52 infested) were reported as host plants for the first time. The Euphorbiaceae, Malvaceae and Solanaceae are the most infested families. In addition to plant species from its native zone (tropical America), PM has established new associations with plants from tropical Africa. Carica papaya and ten additional plants were categorized as favored hosts of P. marginatus. These results will be very useful to develop appropriate management options for PM in West and Central Africa

Transport and dispersal of Stictococcus vayssierei (Hemiptera, stictococcidae) by Anoplolepis tenella (Hymenoptera, formicidae)

Published online: 30 July 201

Insect pests incidence and variations due to forest landscape degradation in the humid forest zone of southern Cameroon: farmers perception and need for adopting an Integrated Pest Management strategy

Group surveys were conducted in five villages in each of the three resource-use zones of the humid forest zone of Southern Cameroon, to assess insect pests’ incidence and the variation due to forest landscape degradation in the agricultural production systems. 389 farmers were interviewed. The results show that: (1) In annual crop systems, insect pests in general rank together with vertebrate pests and diseases amongst the most important agronomic constraints. No differences were found between the intensification zones, except for weeds, which appeared to be a greater constraint in the slightly degraded area. Within the insect pest, the greatest damage to crops according to farmers originated from borers and scales, followed by variegated grasshopper. Only the termites showed a difference between zones - the problem being greatest in the high-degraded areas. (2) In the young perennial crop systems, all the categories of agronomic constraints were equally important. Within the insect pest, mirids were identified as the greatest constraint, followed by borers and caterpillars. There were more variations in the responses according to zones compared to annual crops. Termites and scales were relatively more important in the high-degraded area. In term of control strategy, we recommended an integrated pest management