Bioactivity of vegetable oils to Orthezia praelonga (Hemiptera: Sternorrhyncha: Orthezidae) and selectivity to its predator Ceraeochrysa caligata (Neuroptera: Chrysopidae)

Abstract

Vegetable oils are abundant in oleaginous plants and they can be an alternative for the pest control in integrated management systems. Fatty acids present in these oils are bioactive to pests and they can be an alternative to the use of insecticides suggested to crops of citrus. Although these oils are of natural origin, the impact on beneficial species must be widely evaluated. Here, we evaluated the toxicity and repellency of crude oils of cotton, palm, soybean and coconut to a key citrus pest, Orthezia praelonga (Hemiptera: Sternorrhyncha: Ortheziidae), and its selectivity to Ceraeochrysa caligata (Neuroptera: Chrysopidade). Bioassays of concentration-mortality were performed under laboratory conditions and lethal concentrations of oils were estimated on O. praelonga adult females were estimated. Additionally, the repellent effect of each oil to the LC₅₀ and LC₈₀ was evaluated after 1.24, and 48 h. The four vegetable oils showed toxicity to O. praelonga: cotton LC₅₀ = 1.92 μl/ml, palm oil LC₅₀ = 2.54 μl/ml; soybean LC₅₀ = 3.18 μl/ml and coconut LC₅₀ = 5.02 μl/ml; and its selectivity to C. caligata was verified (CLs₅₀ >80 % alive). Repellent effects of cotton oil (LC₅₀ = 1.92 μl/ml, LC₈₀ = 5.99 μl/ml), and palm oil (LC₈₀ = 10.22 μl/ml) were demonstrated for one hour of exposure. In contrast, the soybean oil (LC₈₀ = 12.50 μl/ml) repelled O. praelonga after 24 and 48 h of exposure. Results of toxicity, repellence and selectivity show the cotton, palm, and soybean oils as the most suitable for the control of O. praleonga.