Mamadou Diatte

Tuta absoluta Meyrick (Lepidoptera: Gelechiidae): a new threat to tomato production in sub-Saharan Africa

In sub-SaharanAfrica, vegetable crops are an essential component of sustainable development, with a significant contribution to food security and nutritional balance, but also an important source of income for resource-poor growers, especially in urban and peri-urban areas (FAO 2012). However, a major constraint to growing field horticultural crops is the reduction in yield and quality caused by insect pests by direct feeding or as plant disease vectors (James et al. 2010; Ekesi et al. 2011). Chemical control is the main control strategy implemented by growers to cope with insect pests (Ngowi et al. 2007; Grzywacz et al. 2010). Extensive and sometimes inappropriate use of chemical insecticides to control insect pests increases production costs and negatively impacts food safety (residues), human health and environment, especially biodiversity and beneficial arthropods (Desneux et al. 2007; Biondi et al. 2012). The implementation of effective and ecologically-sound integrated pest management (IPM) strategies is needed to develop sustainable vegetable production.

Parasitoid control of the tomato fruitworm, Helicoverpa armigera, in smallholder farmer fields in Senegal

ABSTRACT In Africa, Helicoverpa armigera (Hübner) (Lepidoptera, Noctuidae) is a key pest of cotton and vegetable crops, particularly tomato. Alternatives to insecticides to control this pest are needed such as conservation biological control. However, knowledge on the diversity and ecology of naturally occurring enemies of H. armigera is limited. A two-year field survey was conducted in a set of tomato farmer fields in the main vegetable-growing area in Senegal (Niayes) to assess the spatial and seasonal occurrence of indigenous parasitoids of H. armigera, and to evaluate the effect of insecticide use on biological control efficiency. No parasitoid emerged from H. armigera eggs. Incidence of larval parasitoids was generally moderate (20%) but highly variable (0%–100%) among fields, independently of host abundance, and negatively affected by the number of insecticide applications. Larval parasitism was largely dominated by the larval parasitoid Meteorus laphygmarum Brues (Hymenoptera, Braconidae), but a positive correlation was found between specific richness or Shannon diversity index of the parasitoid community and parasitism rate. This study is a first step toward development of research and extension programs for conservation of natural enemies in the framework of integrated management of the tomato fruitworm in Senegal.

Dynamique des parasitoïdes larvaires de Helicoverpa armigera (Lepidoptera : Noctuidae) dans la zone des Niayes au Sénégail

La lutte biologique contre les ravageurs necessite une connaissance de la dynamique des ennemis naturels. Cette etude a pour objectifs d’etudier la distribution spatio-temporelle des especes de parasitoides de H. armigera dans la zone des Niayes et d’evaluer l’impact de la phenologie de la tomate et du stade larvaire sur ces parasitoides. Environ 1965 larves ont ete collectees dans 62 parcelles de tomate dans la zone des Niayes entre 2012 et 2014. La periode de culture influe sur le parasitisme du a Apanteles SP. Les attaques du parasitoide sont moins elevees en premiere partie de saison seche, sur le premier cycle de culture suivant immediatement la fin de la saison des pluies (0,5%) qu’en deuxieme partie de saison seche (5,1%). En fonction de la zone, le parasitisme du a M. laphygmarum et a Apanteles SP. Est plus important dans les zones Centre et Sud que dans la zone Nord. Le stade phenologique n’influe pas sur le parasitisme de H. armigera . Les premiers stades larvaires (L1, L2, L3 et L4) sont plus parasites que les derniers stades (L5 et L6). Ces resultats contribuent a mieux comprendre le potentiel regulateur des parasitoides de H. armigera et leurs importances dans des strategies de gestion integree. Mots cles: Parasitoides, Helicoverpa armigera , tomate, dynamique, lutte biologique, Senegal.

Spatial and temporal incidence of insect pests in farmers' cabbage fields in Senegal

In Senegal, damage caused by insect pests is a major obstacle to seasonal stability and an increase in cabbage production. Little is known about the spatial and temporal distribution of cabbage pests, which makes the design of management recommendations to small-scale farmers challenging. The objectives of this study were to: (i) evaluate the status of insect pests observed in cabbage farmers’ fields; (ii) give information on the spatial and temporal distribution of key pests and (iii) assess the effect of temperature, insecticide applications, and host crop abundance on their incidence. Atotal of 116 cabbage fields were monitored for insect pests and related damage over four crop cycles, from October 2012 to May 2014, in the main vegetable producing area of Senegal (Niayes). The diamondback moth Plutella xylostella (L.) was by far the most important pest present in all the fields and with high levels of incidence (37.1% infested plants), particularly in the latter part of the dry season in the South of Niayes (50% infested plants). The cabbage webworm Hellula undalis (F.) was mainly observed in the early dry season in the south of Niayes, with an incidence of up to 12.5% infested plants. More surprising was the detection of the tomato fruit worm Helicoverpa armigera (Hübner), with damage of up to 9.4% of cabbage heads. The incidence of sucking pests such as whiteflies Bemisia tabaci (Gennadius), or aphids (including Lipaphis pseudobrassicae (Davis, 1914), Myzus persicae (Sulzer) or Brevicoryne brassicae (L.)) was generally low. The incidence of P. xylostella increased significantly with the number of insecticide applications, indicating that control deployed by growers was ineffective. The incidence of H. undalis did not depend on the number of insecticide applications, but significantly increased with host crop abundance and decreased with temperature. This study is a first step towards developing alternative pest management strategies in the framework of sustainable vegetable production systems.