Un nouvel insecte ravageur majeur du sorgho, Poophilus costalis au Togo: degats et methodes de lutte

Le changement climatique est source de nouvelles conditions favorables à la prolifération des ravageurs. Depuis 2001, une espèce émergente, Poophilus costalis (Walker) (Hemiptera: Cercopidae), cause de sérieux dégâts aux cultures de sorgho au Togo. Des prospections ont été faites dans 75 champs de sorgho de la Région des Savanes au Togo en 2012 pour évaluer la densité de P. costalis et l’importance de ses dégâts. Par ailleurs, des bioessais ont été réalisés pour étudier la sensibilité du ravageur aux bioinsecticides Extrait de Graines de Neem (EGN), spinosad et abamectine et aux insecticides de synthèse cyperméthrine, carbofuran et chlorpyrifos éthyle. Les prospections ont montré que les attaques de P. costalis ont été fortes dans les préfectures de Tandjoaré, Cinkassé et Tône avec des densités respectives de 65, 56 et 39 individus sur 20 plants de sorgho. Les densités étaient faibles dans la préfecture de l’Oti (19 individus/20 plants) et modérées dans celle de Kpendjal (29 individus/20 plants). Comparés à l’Oti, Les indices de dégâts (ID) de P. costalis étaient forts (ID ≥ 2) à Tandjoaré, Cinkassé et Tône et modérés à Kpendjal (ID ≤ 2). Les bioessais ont montré que les insecticides EGN, chlorpyrifos éthyle et cyperméthrine ont été plus toxiques à P. costalis que spinosad, carbofuran et abamectine. Au vu de ces résultats, l’étude doit se poursuivre pour mettre au point une méthode de lutte intégrée incluant l’utilisation de l’EGN contre P. costalis. Mots clés: Changement climatique, Poophilus costalis, bioinsecticide, insecticide de synthèse, lutte intégré

Biological control of cassava green mite with exotic and indigenous phytoseiid predators—effects of intraguild predation and supplementary food

Published online: 10 March 2005Intraguild predation, one aspect of predator–predator interaction, has received in recent years increasingly greater attention because of mounting evidence of the impact of predator–predator interactions on the structure of ecological communities and biological pest control. In laboratory experiments, we determined if intraguild predation occurs between Typhlodromalus manihoti and Euseius fustis, two phytoseiid mite predators of the cassava green mite Mononychellus tanajoa on cassava in Africa, and if the level of intraguild predation is affected by the availability of the primary prey, M. tanajoa, and maize pollen as alternative non-prey food. In the laboratory, the two predators attacked and killed heterospecific larvae but they did so only when prey mites and alternative food (maize pollen) were absent or scarce. On a diet of intraguild prey alone, the two predator species survived for several days but failed to reproduce. Addition of abundant levels of M. tanajoa and maize pollen increased survival and reproduction of the two predator species and reduced intraguild predation to very low levels. We then determined, on whole plants in pot experiments in a screenhouse, the effect of maize pollen (an alternative food) on the interactions between the two predator species and the impact of predator–predator interactions on suppression of M. tanajoa population densities. In single predator species treatments, both E. fustis and T. manihoti significantly reduced M. tanajoa densities; but surprisingly, E. fustis appeared to be superior to T. manihoti. The co-presence of the two predators on the same cassava plant resulted in similar suppression of M. tanajoa population densities, but greater suppression of M. tanajoa compared with T. manihoti alone, regardless of presence or absence of maize pollen. The presence of the two predator species together reduced their respective abundance compared with single predator species treatments. Addition of maize pollen, however, significantly increased densities of the generalist predator E. fustis, in both single and two predator species treatments; and tilted the balance of the interactions between the two predator species in favour of E. fustis. The findings of our research underscore the role of generalist predators like E. fustis in the suppression of M. tanajoa populations on cassava, and the potential role of alternative non-prey food in altering the interactions between co-occurring predators sharing the same primary prey (by favouring the generalist predators), and the effect of these interactions on suppression of population densities of the shared primary prey

Females as intraguild predators of males in crosspairing experiments with phytoseiid mites

Published online: 15 May 2013Studies on intraguild interactions between phytoseiid species have shown that intraguild predation occurs and is most commonly manifested as adult females of one species feeding on juveniles of another. Whether such intraguild interactions can also occur between adult females of one species and adult males of another, is not known. Herein, we report on intraguild interactions between adults of the two sexes in cross-pairing experiments involving three related phytoseiid species (Neoseiulus paspalivorus, N. baraki and N. neobaraki) that are potential candidates for controlling the coconut mite Aceria guerreronis, a serious pest of coconut palms in tropical countries. For comparative reasons, the experiments were repeated with larvae instead of males, and with only males or only females of two different species together. In the presence of an ample supply of prey, females of N. neobaraki never fed on individuals of their own species, yet appeared to be very aggressive against males, as well as larvae of the other two phytoseiid species. They also fed on females of N. paspalivorus, but rarely on females of N. baraki. Males of N. neobaraki did not suffer mortality when together with females of either of the two other phytoseiid species. Males of N. baraki did not suffer predation from females of N. paspalivorus, but males of N. paspalivorus suffered some mortality (15 %) from N. baraki females. Larvae of each of the three species were vulnerable to intraguild predation by heterospecific adult females, except for N. neobaraki larvae when together with N. baraki females. The absence or presence of intraguild predation is largely explained by the size ratios of the individuals that were put together: large individuals feed on smaller ones, but never the reverse. For each sex, size declines in the following order: N. neobaraki > N. baraki > N. paspalivorus. Moreover, for each species, females are larger than males and males are larger than larvae. Strikingly, however, females did not kill males and larvae of their own species. We propose that niche competition between related phytoseiid species is not only determined by intraguild predation on heterospecific larvae, but also by imposing great mortality on males from the intraguild prey because phytoseiid females being pseudo-arrhenotokous require insemination to produce offspring of both sexes