Fabien Hountondji

Host specificity of the cassava green mite pathogen Neozygites floridana

Tests were conducted on the hostspecificity of a Brazilian isolate of thefungus Neozygites floridana, a potentialbiological control agent for the cassava greenmite, Mononychellus tanajoa, in Africa.Five insect and two mite species, mostly fromthe cassava agroecosystem, were evaluated forsusceptibility to N. floridana, namelyEuseius concordis, E. citrifolius, Phenacoccus herreni, Stethorus sp., Aleurothrixus aepim, Apoanagyrusdiversicornis, and Bombyx mori.Individuals of each species were exposed tocapilliconidia (the infective stage of thefungus). None of the tested individuals wasfound with hyphal bodies (the vegetative stageof the fungus), whereas 73 to 94% of thecassava green mites in the controls becameinfected. Non-germinated capilliconidia were,however, found attached to several individualsin most species. N. floridana appears tobe safe for exportation. Further evaluation ofits performance against M. tanajoa inAfrica is therefore desirable.

Racocetra beninensis from sub-Saharan savannas : a new species in the Glomeromycetes with ornamented spores

A new fungal species is described under the epithet Racocetra beninensis (Racocetraceae, Glomeromycota). It forms white to creamy-white, globose to sub-globose (sometimes oval) glomerospores terminally on sporogenous Cells. Spores measure 195-335 mu m diam and have two spore walls: a three-layered outer wall and a three-layered inner wall. The Outer spore surface is ornamented with rounded wart-like projections that measure 0.9-2.8 x 0.9-3.8 mu m and are spaced (2.2-)4.0-11.0 mu m apart. The germination shield that forms on the outer surface of the inner wall is multiple-lobed (6-10 lobes) and (sub-)hyaline or occasionally yellowing with age. The lobes regularly bear a single germ tube initiation. The fungus differs from other Racocetra species by spore size and color, ornamentation type, and outer spore wall staining reaction. It has been frequently recovered from sites under natural vegetation and newly cultivated or post-harvest yam (Dioscorea spp.) fields in the sub-Saharan Sudan and Guinea savannas of Benin (West Africa).

Effects of formulated imidacloprid on two mite pathogens, Neozygites floridana (Zygomycotina: Zygomycetes) and Hirsutella thompsonii (Deuteromycotina: Hyphomycetes)

Neozygites floridana (Weiser & Muma) Remaudière & Keller and Hirsutella thompsonii Fisher are important fungal pathogens of mites on cassava in Benin. Bioassays were conducted to evaluate the influence of four concentrations (50, 100, 200 and 500 ppm) of a water-dispersible formulation (Gaucho 70 WS) of imidacloprid on the conidial germination of these two fungi. Imidacloprid significantly reduced the germination of primary conidia and formation of infective capilliconidia in N. floridana. In contrast, imidacloprid concentrations of 100 ppm and above increased conidial germination in H. thompsonii. Another bioassay was conducted to evaluate possible synergism between imidacloprid and H. thompsonii in the mortality of the cassava green mite, Mononychellus tanajoa (Bondar). Hirsutella thompsonii alone and in combination with imidacloprid both killed around 95% of the mites after five days. In contrast, the mortality of mites treated with imidacloprid alone was close to that of untreated mites, which was around 30% on the fifth day after treatment.RésuméNeozygites floridana (Weiser & Muma) Remaudière & Keller et Hirsutella thompsonii Fisher sont des champignons pathogènes des acariens du manioc au Bénin. Des essais ont été conduits afin d’évaluer l’influence de quatre différentes concentrations (50, 100, 200 et 500 ppm) de la formulation en poudre hydrosoluble de l’insecticide imidacloprid sur la germination des conidies des deux champignons. Les résultats prouvent une action spécifique de l’imidacloprid sur chacun’des deux champignons. La germination des conidies primaires et des capilloconidies de N. floridana est significativement affectée, alors que chez H. thompsonii, le pourcentage de germination est significativement plus élevé aux plus fortes concentrations. Vu ces résultats, de nouveaux essais ont été entrepris pour évaluer une éventuelle synergie de l’imidacloprid et de H. thompsonii pour lutter contre l’acarien vert du manioc, Mononychellus tanajoa Bondar. Comparativement au traitement à l’imidacloprid seul, la mortalité est significativement plus élevée chez les acariens traités avec H. thompsonii seul ou avec la combinaison imidacloprid-H. thompsonii. L’efficacité entre ces deux derniers traitements est comparable.

Incidence of tarsonemid mites on Cocos nucifera L. (Arecaceae) from Oman with description of a new species of Nasutitarsonemus Beer and Nucifora (Acari: Tarsonemidae)

Coconut is an important crop grown in the coastal plain of the Dhofar region, south-eastern Oman, on the edge of the Arabian Peninsula desert. It holds a particular place in the landscaping of the region and is also of great interest for the production of coconut drinking water. One of the main pests of coconut in this region is the coconut mite (Aceria guerreronis Keifer). In surveys conducted to understand the dynamics of that mite and its association with other arthropods, the incidence of tarsonemid mites was determined. Steneotarsonemus furcatus de Leon was the most commonly found tarsonemid on fruits as well as on growing tips of coconut seedlings, always at low levels. A few representatives of an undescribed tarsonemid species were also found. That new species is here described as Nasutitarsonemus omani Lofego and Moraes, sp. nov. A key to the species of this little-known genus is provided.

Olfactory responses of Maruca vitrata (Fabricius) larvae to reproductive parts of different varieties of cowpea, Vigna unguiculata (L.) Walp.

Preferences of Maruca vitrata (Fabricius) (Lepidoptera: Pyralidae) larvae to flowers, flower buds and pods of three different varieties of cowpea (IT 82E-666, IT 82D-716 and Botokpoyi) were studied in the laboratory using a four-branched olfactometer. For each plant part, fourth instars of M. vitrata were individually exposed to a set of three odours obtained from the cowpea varieties with pure air serving as the control. Movements of the larvae in the exposure chamber were followed at two levels of choice. Results from the first level of choice showed that the attractiveness of a particular plant part to M. vitrata larvae was not significantly influenced by variety. At the second level of choice a weakly significant preference was found for flowers (P = 0.1218) compared to pods (P = 0.7530) and flower buds (P = 0.6172). In all cases, no significant difference was found between the control (pure air) and the varieties.RésuméL’étude des préférences larvaires de Maruca vitrata aux fleurs, aux boutons floraux et aux gousses de trois différentes variétés de niébé (IT 82E-666, IT 82D-716 et Botokpoyi) a été faite au laboratoire à l’aide d’un olfactomètre à quatre bras. Pour chaque organe, des larves de quatrième stade ont été individuellement soumises aux odeurs des trois différentes variétés en plus de l’air pur qui a servi de témoin. Le déplacement de chaque larve a été suivi et deux niveaux de choix ont été établis: un premier choix et un choix définitif. Au niveau du premier choix, les résultats ont montré une absence de différence significative entre les variétés pour tous les organes: boutons floraux (P = 0.8260), fleurs (P = 0.8662) et gousses (P = 0.5724). Au niveau du choix définitif également, aucune différence significative n’était observée aussi bien pour les gousses (P = 0.7530), pour les boutons floraux (P = 0.6172) que pour les fleurs (P = 0.1218). Aucune différence significative n’était aussi observée entre le témoin (air pur) et les variétés dans tous les cas.