Pesticide resistance in Plutella xylostella (Lepidoptera: Plutellidae) populations from Togo and Benin

Published online: 17 August 2016The diamondback moth, Plutella xylostella (L.) is the major insect pest of cabbage crops in Togo and Benin. For control, farmers very often resort to spraying chemical insecticides at high dosages with frequent applications. Bioassays were carried out on three populations of P. xylostella, two from Togo (Kara and Dapaong) and one from Benin (Cotonou), to assess their level of susceptibility to currently used insecticides. A reference strain of P. xylostella from Matuu in Kenya was used as a control. In the laboratory, three insecticide representatives of different chemical families (deltamethrin, chlorpyrifos ethyl and spinosad) were assayed against third instar larvae of P. xylostella. Results revealed that P. xylostella populations from Dapaong, Kara and Cotonou were more resistant to deltamethrin (13 to 59-fold at LC50 level, 149 to 1772-fold at LC90 level) and chlorpyrifos ethyl (5 to 15-fold at LC50 level, 9 to 885-fold at LC90 level) than the reference strain. Spinosad was more toxic to P. xylostella populations than the other insecticides with LC50 and LC90 values less than 1 μg/ml and 15 μg/ml, respectively. However, the population from Cotonou appeared significantly more resistant to spinosad compared to the reference strain. These results are discussed in the light of developing an integrated pest management strategy for reducing the selection pressure of spinosad

Parasitoid complex of fall armyworm, spodoptera frugiperda, in Ghana and Benin

Open Access Journal; Published online: 21 Jan 2020The fall armyworm, Spodoptera frugiperda, a moth originating from the American continent, has recently invaded most African countries, where it is seriously threatening food security as a pest of cereals. The current management methods rely heavily on the use of synthetic insecticides but there is a need for more sustainable control methods, including biological control. Surveys were conducted in two West African countries, Ghana and Benin, to determine the native parasitoid complex and assess parasitism rates of S. frugiperda. Samples of S. frugiperda eggs and larvae were collected in maize fields located in 56 and 90 localities of Ghana and Benin, respectively, from July 2018 to July 2019. Ten species were found parasitizing the pest, including two egg parasitoids, one egg–larval, five larval and two larval–pupal parasitoids. The two most abundant parasitoids in both countries were two Braconidae: the egg‐larval parasitoid Chelonus bifoveolatus and the larval parasitoid Coccygidum luteum. Parasitism rates were determined in three Ghanaian regions and averages varied from 0% to 75% between sites and from 5% to 38% between regions. These data provide an important baseline for the development of various biological control options. The two egg parasitoids, Telenomus remus and Trichogramma sp. can be used in augmentative biological control and investigations should be conducted to assess how cultural practices can enhance the action of the main parasitoids, C. luteum and Ch. bifoveolatus, in the field. Understanding the parasitoid complex of S. frugiperda in Africa is also necessary before any development of classical biological controls involving the introduction of parasitoids from the Americas

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