Helicoverpa armigera is an indigenous species in Africa and has been reported in the destruction of several crops in Benin. Management of H. armigera pest is mainly focused on the use of synthetic pyrethroids, which may contribute to resistance selection. This study aimed to screen the susceptibility pattern of field populations of H. armigera to deltamethrin in Benin. Relevant information on the type of pesticides used by farmers were gathered through surveys. Collected samples of Helicoverpa (F₀) were reared to F₁. F₀ were subjected to morphological speciation followed by a confirmation using restriction fragment length polymorphism coupled with a polymerase chain reaction (RFLP-PCR). F₁ (larvae) were used for insecticide susceptibility with deltamethrin alone and in the presence of the P450 inhibitor Piperonyl Butoxide (PBO). Deltamethrin and lambda-cyhalothrin were the most used pyrethroids in tomato and cotton farms respectively. All field-sampled Helicoverpa were found to be H. armigera. Susceptibility assays of H. armigera to deltamethrin revealed a high resistance pattern in cowpea (resistance factor (RF) = 2340), cotton (RF varying from 12 to 516) and tomato (RF=85) farms which is a concern for the control of this major polyphagous agricultural pest. There was a significant increase of mortality when deltamethrin insecticide was combined with piperonyl butoxide (PBO), suggesting the possible involvement of detoxification enzymes such as oxidase. This study highlights the presence of P450 induced metabolic resistance in H. armigera populations from diverse cropping systems in Benin. The recorded high levels of deltamethrin resistance in H. armigera is a concern for the control of this major agricultural pest in Benin as the country is currently embarking into economical expansion of cotton, vegetables and grain-legumes cropping systems.

The fall armyworm (FAW) Spodoptera frugiperda (Lepidoptera, Noctuidae) has now become an invasive pest of global concern. The pest was first detected in Central and Western Africa in early 2016. Sustainable management options explored by stakeholders during early FAW invasion in Africa included the use of biopesticides and biological control. The current study aimed to compare the susceptibility of FAW larvae to SfMNPV with the assumption that the virus isolated from FAW populations in Africa has higher virulence compared with an isolate from Argentina (SfMNPV-ARG). We also hypothesized that host plant plays a role in SfMNPV efficacy and that cannibalism mediates horizontal and vertical transmission of the virus. This work provides pioneering data on the virulence of the new SfMNPV isolate from Nigeria (SfMNPV-KA1), which proved more effective than its exotic counterpart from Argentina (SfMNPV-ARG). The host plant effect made a significant difference between maize and onion with more FAW death in the larvae fed with contaminated onion 5 days post treatment. The study demonstrates and discusses the effect of cannibalism on virus transmission.

From 2002 to 2004, three field trials were conducted in Senegal to compare the efficacy of a new biopesticide for grasshopper control, based on the entomopathogenic fungus Metarhizium anisopliae var. acridum Driver & Milner, with mixtures of this biopesticide and cyhalothrin, a widely used pyrethroid insecticide to control the Senegalese grasshopper Oedaleus senegalensis Krauss. The aim of these trials was to obtain a knockdown effect without compromising the environmental credentials of the biopesticide too much. During the first two trials, 50 ha (2002) and 25 ha (2003) plots were treated with Metarhizium at a rate of 50 g/ha, cyhalothrin at a rate of 40 g/ha, a mixture of Metarhizium at a rate of 25 g/ha and cyhalothrin at a rate of 20 g/ha. For the third trial in 2004, several mixtures of cyhalothrin at a rate of 10 g/ha and Metarhizium at dose rates of 6.25, 12.5 and 25 g/ha were prepared. These mixtures were compared with 50 g/ha of Metarhizium, 40 g/ha of cyhalothrin and 10 g/ha of cyhalothrin on 25 ha experimental plots. The volume application rate for all trials was 1 l/ha. The Metarhizium applications resulted in a slow but long-lasting reduction of grasshopper numbers. By contrast, cyhalothrin produced a rapid reduction, but grasshopper numbers re-increased a few days after application, except in 2003, when grasshopper densities in the surrounding areas were low. The mixtures caused a similarly fast reduction in grasshopper numbers, but this lasted throughout the 3 week post-application assessment period. These trials demonstrated that adding a low dose of a pyrethroid insecticide to a slow-acting biopesticide can increase the speed of population reduction, while retaining the latter's long-lasting effect. A bonus is that the price of the combination is lower than that of each product at the recommended dose rates. Since the insecticide is added at a low dose, its environmental impact is reduced compared with the full-dose insecticide only treatment.

A cotton field was used to set up an arena trial for investigating the dose transfer of oil-based ultra-low-volume sprays of Metarhizium anisopliae (Metchnikoff) Sorokin to the cotton bollworm Helicoverpa armigera (Hübner). Two doses of conidia (75 and 50 g/ha, being 3.75 × 1012 and 2.5 × 1012 conidia/ha, respectively) formulated in 2 litres (70:30, kerosene–peanut oil) were applied using a Berthoud ‘Micro Ulva’ to three groups of larvae of cotton bollworms positioned in three rows downwind of a single spray line. Both the distribution of the droplets and the effect of direct contact with spray droplets were quantified. The mean number of droplets decreased from 416 ( ± 60) droplets per cm2 (line 1; 0.4 m) to 45 ( ± 36) droplets per cm2 (line 3; 5 m). To achieve 50% mortality, >10 and >13 days were necessary for 75 and 50 g/ha, respectively. From day 15, the difference in mortality rates was significant between the two treatments. At line 3 (5 m), at 12 days after application, the mortality rate reached 52% for 75 g/ha and 47% for 50 g/ha. The results are discussed in view of optimizing the application of the biopesticides.

Optimisation de l'application du Metarhizium anisopliae var. acridum sur le criquet puant, Zonocerus variegatus (Orthoptera: Pyrgomorphidae) - Volume 25 Issue 4 - O.K. Douro Kpindou, C. Gbongboui, R. Badou, E. Paa-Kwessi, J.B. Ackonor, J. Langewald

A socio-economic study was executed in South East Niger to determine the conditions under which a novel mycopesticide based on the fungus Metarhizium flavoviride could be introduced for locust and grasshopper control as a possible alternative reducing the use of synthetic chemicals. From the interviews, all farmers estimated locusts and grasshoppers to be one of three major pests. The survey revealed that 93.8% of the farmers conduct collective pesticide applications. About 45.5% of the farmers received support from the brigades, at least once. The remaining farmers (54.5%) were not assisted by the brigades due to a lack of pesticides. Farmers estimate that the choice of any pesticide greatly depends upon its knock-down ability (57.5%) or the numbers of cadavers found after a treatment (42.5%). Most farmers (82%) consider the government to be responsible for locust and migrant grasshoppers control. On average, farmers were willing to pay US$ 1.00 per ha per year, to protect their crops. Une enquête a été réalisée en vue d'étudier les conditions socio-économiques et techniques dans lesquelles serait introduit un mycopesticide pour remplacer les produits chimiques utilisés contre les criquets. De cette étude il ressort que pour les gens enquêtés, les sauteriaux constituent un des trois principaux ravageurs de cultures. La lutte anti-acridienne se fait de manière collective (93,8% des cas) et 45,5% des paysans enquêtés affirment avoir bénéficié d'au moins une assistance de la brigade phytosanitaire du village. Les autres (54,5%) n'avaient pas pu en bénéficier à cause du manque de pesticides. Un pesticide est choisi en fonction de sa rapidité à tuer les criquets pour 57,5% des agriculteurs, et son efficacité (le nombre de cadavres observés après un traitement) pour 42,5% d'entre eux. La majorité (82%) des agriculteurs considèrent le traitement contre les acridiens comme une responsabilité du gouvernement. Les paysans pourraient en moyenne consentir 1 $ US par ha/an, pour la protection de leurs cultures.