Methyl jasmonate (MeJA) is a phytohormone that has been used to artificially induce plant resistance against multiple arthropod herbivores. However, it is still uncertain whether MeJA can trigger pepper plant resistance against Myzus persicae (Sulzer) (Hemiptera: Aphididae) (green peach aphid, GPA). In this study, we assessed the effects of different concentrations (0, 0.008, 0.04, 0.2, 1.0, and 5.0 mM) of MeJA-treated pepper on the development and reproduction performance of GPA to identify an appropriate concentration for vigorous resistance enhancement. MeJA dose was applied on the pepper to investigate the changes in activities of protective enzyme (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD and polyphenol oxidase, PPO), detoxification enzymes (acetylcholinesterase, AchE; glutathione S-transferase, GSTs; cytocrome P450, CYP450, and carboxylesterase, CarE), and digestive enzymes (protease, PRO and amylase, AMY) in GPA. The results showed that all concentrations of MeJA-treated pepper significantly suppressed GPA performance, wherein 0.2 mM was the optimal concentration, as it presented the lowest intrinsic rate of increase (r_m), finite rate of increase (λ), and the highest population doubling time (Dt) values. Furthermore, the protective enzymes (SOD and CAT), detoxification enzymes (GSTs, CYP450, and CarE), and AMY activities increased significantly in MeJA-treated groups than the control group, while the POD and PPO activities were remarkly inhibited under 0.2 mM treatment. These findings indicate that exogenous spraying of 0.2 mM of MeJA significantly enhanced pepper resistance against GPA. The result of this study suggests MeJA application can be used as a promising strategy in integrative management of this insect pest.

Flavonoids are known to contribute to plant defense against herbivorous insects in a variety of systems, but their specific role in cassava (Manihot esculenta) resistance to the cassava mealybug (Phenacoccus manihoti) has remained unclear. Through expression profiling of nine flavonoid biosynthesis genes in high-resistance and high-susceptibility cassava varieties, chalcone synthase (CHS) was identified as the most differentially expressed candidate. Virus-induced gene silencing (VIGS) of CHS in the high-resistance variety C1115 led to a 67.5% reduction in CHS transcript levels, a 60.6% decrease in enzyme content, and a 29.7% decline in total flavonoid content. This was accompanied by the suppressed expression of downstream genes CHI and LAR. Silenced plants showed increased leaf damage and a higher pest index, effectively rendering the resistant phenotype susceptible. Furthermore, mealybugs feeding on these plants exhibited a 1.3-fold increase in their net reproductive rate. These results indicate that CHS-dependent flavonoid accumulation is one of the components required for resistance to P. manihoti in the high-resistance variety C1115, and identify CHS as a promising candidate target for marker-assisted breeding.