Essential oils (EOs) are alternatives to synthetic insecticides used to control aphids that attack brassica species. However, the effects of species such as the Brazilian pepper tree (BPEO) Schinus terebinthifolius (Raddi), lemon eucalyptus tree (LEEO) Eucalyptus citriodora (Hook), and citronella grass (CGEO) Cymbopogon winterianus (Jowitt) on these organisms, as well as on beneficial insects, has been poorly studied. This work was aimed to evaluate the activity of BPEO, LEEO, and CGEO, at concentrations of 0.5% and 1%, on aphids Brevicoryne brassicae (Linnaeus) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) applied on leaf discs and/or cabbages, as well as the chemotaxic effects on its natural enemy Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae). The results showed that the essential oil of C. winterianus had a higher mortality rate for B. brassicae (100%) (0.5%, 48 h) and M. persicae (98.99%) (1%, 48 h). The average number of aphids (both species) found on cabbage leaf discs treated with 0.5% and 1% of the three essential oils (separately) was always lower than those found on leaf discs treated with water. Essential oils at 1% presented significantly higher mortality rates for B. brassicae and M. persicae than the control treatment. Females of D. rapae were attracted to plants of green cabbage with essential oil (0.5%) of S. terebinthifolius, but did not respond to E. citriodora and were significantly responsive to plants sprayed with water when contrasted with those in the presence of C. winterianus oil.

Taro leaf blight caused by Phytophthora colocasiae affects plant health and is a major threat to taro culture in Cameroon. Chemical fertilizers used often harm the ecosystem. Plant growth-promoting rhizobacteria (PGPR) are better alternatives that increase plant growth promotion and suppress phytopathogens. In the present study, a total of 67 fluorescent Pseudomonas spp. was characterized by 17.91, 5.97, and 4.47% populations of P. fluorescens, P. chlororaphis, and P. putida, respectively, among the most represented. More than 36% of bacteria showed antagonistic potential through the production of both diffusible and volatile compounds. Some of them (03) exhibited antagonistic activity in dual culture against P. colocasiae with a diameter greater than 13 mm. These rhizobacteria produced a significant amount of siderophore, IAA, SA, HCN, protease, lipases, and cellulases. For the pot experiment, treatment by Pseudomonas significantly increased the enzymatic activity involved in the resistance of taro, such as peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL). The two antagonists also increased plant growth parameters of taro such as chlorophyll, plant height, shoot length, total leaf surface, fresh root biomass, and fresh leaf biomass. These findings showed that fluorescent Pseudomonas have an intriguing and undeniable potential in the fight against P. colocasiae, which could lead to the development of a biopesticide in the future.