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 functional response and some predation parameters of the predators Alloeocranum biannulipes Montrouzier & Signoret (Hemiptera: Reduviidea) and Teretrius nigrescens Lewis (Coleoptera: Histeridae) were evaluated at five different densities of larvae and pupae of Dinoderus porcellus Lesne (Coleoptera: Bostrichidae) with the aim to understand their roles in the biological control of this major pest of stored yam chips. Experiments were performed in petri dishes at 25 ± 1 °C, 60 ± 10% RH, and a photoperiod of 12:12 (L:D) h in a controlled temperature room. Both predators showed Type II of functional response with respect to larvae, determined by a logistic regression model. However, T. nigrescens significantly killed more larvae of D. porcellus compared with A. biannulipes. This behavior, however, changed to a linear functional response (Type I), when pupae of D. porcellus were offered to both predators, possibly because of their immobility. In addition, there was no significant difference between T. nigrescens and A. biannulipes in terms of the killed pupae. Parameters of the Holling disc equation for both predators were estimated. Estimated handling time on larvae of D. porcellus for T. nigrescens and A. biannulipes was 0.254 and 0.677 h and the rate of searching efficiency was 0.289 and 0.348 h-1, respectively. Results indicated that T. nigrescens was a more suitable candidate for augmentative release for D. porcellus control than A. biannulipes. However, semifield studies are required to draw firm conclusions.

Jatropha curcas is an oleaginous plant whose seed yield is low. The present study aimed at evaluating is pests associated with J. curcas. In regards to the densities, Denticera near divisella density was obtained 0.85 larvae per plant in J. curcas in sole farming and 0.70, 0.61, 0.85 larvae respectively when intercropped with casava, maize and cowpea. When J. curcas was intercropped with cassava Stomphastis thraustica was the most encountered species with a density of 1.28 larvae per plant while 0.61 larvae density was encountered for intercropped with maize and 0.27 larvae density with cowpea against 0.43 larvae in mono culture. For J. curcas with maize, Aulacophora africana was the most abundant species with a density of 0.47 adult per plant. In the case of J. curcas with cowpea. D. nr divisella had the highest density of 0.85 larvae per plant. It was also shown that the grain yield of J. curcas depends of intercrop. The yields were from 591.75 ± 109.25kg / ha; 431.75 ± 92.50kg / ha; 252.50 ± 51.50kg / ha; 89.50 ± 43.00kg/ha respectively in pure farming of J. curcas, Jatropha intercropped with maize, cowpea or cassava respectively. Therefore, it is important to choose intercropping to reduce the density of pests in Jatropha crop.