Morphologie et abondance des stades de développement d’Ilyocoris cimicoïdes Linné 1758 (Heteroptera : Naucoridae) dans un lac anthropisé en zone tropicale (Cameroun)

Objectifs : Une étude conduite au laboratoire de Zoologie et de Biologie Générale de l’Université de Yaoundé I a porté sur l’écologie de la punaise aquatique Ilyocoris cimicoïdes Linné 1758 (Heteroptera : Naucoridae) prélevée dans le lac d’Obili (Yaoundé, Cameroun). Méthodologie et résultats : L’analyse physico-chimique montre que ce lac est dans un état eutrophe à hypereutrophe et ses eaux sont fortement chargées en matière organique. Les observations morphologiques et l’illustration des stades de développement ainsi que l’étude de leurs fluctuations numériques montrent que I. cimicoïdes à six stades post-embryonnaires parmi lesquels cinq sont larvaires. La taille des individus augmente de la larve de 1er stade jusqu’au stade adulte. Les stades larvaires d’I. cimicoïdes se distinguent les uns des autres par la présence ou l’absence du ptérothèque, la forme de la marge postérieure du mésotergum et la taille relative du ptérothèque par rapport à la base du mésotergum. Conclusions : L’abondance des stades de développement d’I.cimicoïdes est influencée par la saisonnalité et l’évolution de certaines variables physico-chimiques. Les larves pullulent pendant la saison sèche et les oeufs et adultes pendant la saison des pluies.Mots clés : Pollution aquatique, morphologie, développement, Ilyocoris cimicoïdes.  Objectives : A study conducted at the Laboratory of Zoology and General Biology, University of Yaoundé I focused on the ecology of aquatic bug Ilyocoris cimicoides Linnaeus 1758 (Heteroptera : Naucoridae) taken from Lake Obili (Yaoundé, Cameroon). Methodology and Results: The physico-chemical analysis showed that this lake is in a eutrophic state and its waters are heavily loaded with organic matter. Morphological observations and illustration stages of development and the study of their digital fluctuations show that I. cimicoides, has six post-embryonic stages of which five are breeding. The sizes of individuals increase the first stage larva to adult. Larval stages of I.cimicoides are distinguished from each other by the presence or absence of pterotheque, the shape of the posterior margin and mesotergum pterotheque relative size with respect to the base of mesotergum. Conclusions : Abundance stages of development I. cimicoides is influenced by seasonality and the evolution of certain physico-chemical variables. Larvae swim in the dry season and eggs and adults during the rainy season.Keywords : Water Pollution, morphology, development, Ilyocoris cimicoides

Phytiatrie et fonction du phytiatre en phytoprotection

La phytiatrie est une branche de la phytoprotection dont la définition est peu claire, variable et très confuse dans la littérature. Dans cet article dont les données sont issues de sources secondaires, nous essayons de : (1) clarifier la définition des mots phytiatrie et phytiatre ; (2) préciser le contenu d’une formation de base en phytiatrie ; (3) proposer une organisation de la fonction de phytiatre. Le phytiatre (médecin de la plante), s’occupe de la gestion des maladies, des agresseurs et des traumatismes des plantes. La phytiatrie se distingue clairement de la phytopathologie, science qui étudie les maladies des plantes causées par les microorganismes et les facteurs environnementaux. Le phytiatre a des connaissances en phytopharmacie, mais n’est pas un phytopharmacien. Le diplômé en phytiatrie doit être capable d’analyser et de comprendre les exigences de la phytoprotection afin de développer et de proposer des solutions adéquates, dans un contexte de protection de l’environnement. Le grade de phytiatre devrait être réservé aux ingénieurs en phytiatrie, aux titulaires d’un Master ou d'un Doctorat / Ph.D en phytiatrie. Une meilleure structuration des formations en phytiatrie et de la fonction de phytiatre, peut contribuer à une meilleure prise en charge des affections des plantes dans les systèmes de production en Afrique. English title: Phytiatrics and function of the phytiatrist in plant protection Abstract Phytiatrics is a branch of Phytoprotection whose definition is unclear, variable and very confused in the literature. In this article, whose data come from secondary sources, we try to: (1) clarify the definition of phytiatrics and phytiatrist; (2) specify the content of basic training in phytiatrics; (3) propose an organization of the function of phytiatrist. The phytiatrist (plant medical doctor) deals with the management of plant diseases, pests and trauma. Phytiatrics is clearly distinguished from phytopathology which is the science that studies plant diseases caused by microorganisms and environmental factors. The phytiatrist has knowledge in phytopharmacy, but is not a phytopharmacist. The graduate in phytiatrics must be able to analyze and understand the requirements of phytoprotection in order to develop and propose adequate solutions, in a context of environmental protection. The rank of phytiatrist should be reserved for engineers in phytiatrics, holders of a Master’s degree or a doctorate in phytiatrics. A better structuring of training in phytiatrics and the function of phytiatrist can contribute to better management of plant ailments in plant production systems in Africa. Keywords: plant, disease, aggressors, training, phytiatrist

Temperature-dependent phenology of the parasitoid Fopius arisanus on the host Bactrocera dorsalis

Fopius arisanus (Sonan), an egg-pupal parasitoid of numerous fruit fly species, was recently introduced into Africa for the control of the Oriental fruit fly, Bactrocera dorsalis (Hendel). In this study, life-table data of F. arisanus were generated under laboratory conditions at six constant temperatures (15, 20, 25, 30, 28 and 35 °C; 75% RH, L12:D12 photoperiod) and under variable conditions in a screenhouse on B. dorsalis. Several non-linear functions were fitted to model species development, mortality, longevity and oviposition using the Insect Life Cycle Modeling (ILCYM) software. The established phenology models were stochastically simulated at variable temperatures to estimate the life table parameters. Fopius arisanus completed development from egg to adult at all the temperatures tested except at 35 °C. Mean developmental time from egg to adult was inversely proportional to the temperature. The minimum temperature threshold (Tmin) from egg to adult was 8.15 °C, while the maximum temperature threshold (Tmax) was estimated at 34.2 °C. The optimal temperature for immature stages survival was predicted for 20-30 °C. The optimum fecundity estimated was 251 eggs/female at 22 °C. Following the stochastic simulations under natural conditions of the selected agro-ecological zones, it appears that the Humid Forest with Bimodal Rainfall provides a suitable thermal condition for potential population growth of F. arisanus. The present study shows the importance of temperature on the demographic parameters of F. arisanus. Implications of present findings on the biological control of B. dorsalis under climate change scenarios is discussed

Independent Recruitment of a Flavin-Dependent Monooxygenase for Safe Accumulation of Sequestered Pyrrolizidine Alkaloids in Grasshoppers and Moths

Several insect lineages have developed diverse strategies to sequester toxic pyrrolizidine alkaloids from food-plants for their own defense. Here, we show that in two highly divergent insect taxa, the hemimetabolous grasshoppers and the holometabolous butterflies, an almost identical strategy evolved independently for safe accumulation of pyrrolizidine alkaloids. This strategy involves a pyrrolizidine alkaloid N-oxygenase that transfers the pyrrolizidine alkaloids to their respective N-oxide, enabling the insects to avoid high concentrations of toxic pyrrolizidine alkaloids in the hemolymph. We have identified a pyrrolizidine alkaloid N-oxygenase, which is a flavin-dependent monooxygenase, of the grasshopper Zonocerus variegatus. After heterologous expression in E. coli, this enzyme shows high specificity for pyrrolizidine alkaloids of various structural types and for the tropane alkaloid atropine as substrates, a property that has been described previously for a pyrrolizidine alkaloid N-oxygenase of the arctiid moth Grammia geneura. Phylogenetic analyses of insect flavin-dependent monooxygenase sequences suggest that independent gene duplication events preceded the establishment of this specific enzyme in the lineages of the grasshoppers and of arctiid moths. Two further flavin-dependent monooxygenase sequences have been identified from Z. variegatus sharing amino acid identities of approximately 78% to the pyrrolizidine alkaloid N-oxygenase. After heterologous expression, both enzymes are also able to catalyze the N-oxygenation of pyrrolizidine alkaloids, albeit with a 400-fold lower specific activity. With respect to the high sequence identity between the three Z. variegatus sequences this ability to N-oxygenize pyrrolizidine alkaloids is interpreted as a relict of a former bifunctional ancestor gene of which one of the gene copies optimized this activity for the specific adaptation to pyrrolizidine alkaloid containing food plants

Larviciding intervention targeting malaria vectors also affects Culex mosquito distribution in the city of Yaoundé, Cameroon

Although Culex species are considered to be equally affected by control measures targeting malaria vectors, there is still not enough evidence of the impact of interventions such as larviciding on the distribution of these mosquito species. The present study assessed the impact of a larviciding trial targeting malaria vectors on Culex mosquito species in the city of Yaoundé, Cameroon. A cluster randomized trial comparing 13 treated clusters and 13 untreated clusters was implemented. Data were collected at baseline and during the larviciding intervention, from March 2017 to November 2020. The microbial larvicide VectoMax G was applied once every 2 weeks in the intervention areas. Adult mosquitoes were collected using CDC light traps in both intervention and non-intervention areas and compared between arms. Globally, larviciding intervention was associated with 69% reduction in aquatic habitats with Culex larvae and 36.65% reduction of adult Culex densities in houses. Adult Culex densities were reduced both indoors (35.26%) and outdoors (42.37%). No change in the composition of Culex species was recorded. The study suggests a high impact of larviciding on Culex mosquito species distribution. The impact of the intervention can be improved if typical Culex breeding habitats including pit latrines are targeted

Abundance and life cycle of Zonocerus variegatus (Orthoptera: Pyrgomorphidae) in the humid forest zone of southern Cameroon

Weekly captures from January 2000 to January 2002 enabled us to study the abundance and life cycle of the variegated grasshopper, Zonocerus variegatus (Orthoptera: Pyrgomorphidae), in the humid forest zone of Southern Cameroon. We found that Z. variegatus was present throughout the year in the forest reserve and the human‐influenced zones of Yaounde and Mbalmayo in two univoltine populations, which had unequal abundance and durations. The separation of the two populations was clearer in the Yaounde and Mbalmayo developed zones than in the Mbalmayo forest reserve (undeveloped zone). The abundance of Z. variegatus varied according to the post‐embryonic stage, sex, year and season. Hatching and coupling took place during the dry and rainy seasons, whereas oviposition occurred only in the rainy season. In Cameroon, the type of life cycle of Z. variegatus observed in the humid forest zone of the south is different from that of the “Sudanian and Sahelian” zones

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