The fall armyworm (FAW), Spodoptera frugiperda is a real threat to food security. It is able to totally destroy the cereal crops in a country. It can cause famine in Sub-Saharan Africa where cereals are subsistence crops. Reported in Africa in 2016, the FAW succeded to colonize 47 countries in one year. Its migration capacities wich are of around 100 km per night can allow it have fully infest a country like Senegal (ca 200 000 km²) in less than a week. The FAW is very difficult to fight because resistant to several insecticides. Invasive species often invade a new environment without their natural enemies, which promotes their multiplication and damage to crops. To estimate the generation number per year and evaluate the impact of biological control of indigenous natural enemies on the FAW, larvae were collected in maize fields and monitored in the laboratory. The results show that the development cycle of S. frugiperda takes 25 days on average, that is to say fifteen (15) generations per year. The study confirms the presence of three species of native natural enemies, a nematode Hexamermis sp. and two Hymenopterans Chelonus sp. and Campoletis sp. detected for the first time in West Africa on FAW larvae. The overall parasitism rate is 25.8%. These native natural enemies are a very promising means of control against FAW populations. The introduction of agricultural techniques to promote the maintenance and the proliferation of the FAW auxiliaries is an alternative to the use of pesticides.

Biotic factors (including insect pests) constrain field-grown tomato production in Senegal. However, little information is available on the identity and life system of key pests. The objectives of this study were to: (i) update key pest records of field-grown tomato in the central vegetable-producing area along the northern coast of Senegal, known as the Niayes area; (ii) map their spatial and temporal incidence and (iii) understand insecticide use by growers to control the pests. A total of 98 tomato fields distributed in three zones along a north–south transect in the Niayes area were monitored over four crop cycles from 2012 to 2014. As expected, the tomato fruitworm Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) was the most destructive pest with an occurrence of 92% in sampled fields (90/98) and up to 38% damaged fruits in one field at the time of sampling. The proportion of damaged fruits did not differ among zones, but was significantly higher in the early dry season compared to the late dry season. The invasive tomato leafminer Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) was detected in 53% of sampled fields (52/98), mainly in the south of the Niayes area in the late dry season. Because of their ability to adapt to unstable environment and insecticides, this insect pest assemblage is a new challenge that farmers have to deal with while decreasing their use of broad-spectrum insecticides.

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Monitoring of the evolution of insecticide resistance in the field is crucial to prevent pest control issues. The present study was conducted to assess insecticide resistance status of the fruitworm, Helicoverpa armigera (Hübner) (Lepidoptera, Noctuidae), the most destructive pest of field-grown tomato in Senegal. A sample of 11- 15 field populations were monitored for their susceptibility to abamectin, deltamethrin, and profenofos, using a standard leaf-dip bioassay method. Resistance ratios ranged from 1- to 30-fold to abamectin (4/15 populations with RR>10), 7- to 112-fold to deltamethrin (11/12 populations with RR>10), and 1- to 29-fold to profenofos (3/11 populations with RR>10). This indicates that resistance evolution to deltamethrin was widespread among field populations of H. armigera. However, an increasing trend of resistance to deltamethrin was observed from the South to the North of Niayes. Susceptibility to abamectin and profenofos was generally high but showed that resistance might be evolving within some populations. In addition, signs of cross-resistance to abamectin were detected, suggesting possible metabolic resistance mechanisms already selected in pyrethroid-resistant populations. The recorded high levels of pyrethroids resistance are a concern for the control of H. armigera in Senegal as the country is being currently embarking into economic expansion of tomato cropping systems. © 2020 International Formulae Group. All rights reserved. Keywords: Insecticide resistance, pyrethroids, avermectins, OPs, Helicoverpa armigera, West Africa

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