Fumigant toxicity and repellency of Citrus limetta (L.) peel essential oil on four coleopteran stored product pests

    In this research, fumigant toxicity and repellency of essential oil of sweet lemon, Citrus limetta fruit peels were investigated against sawtoothed grain beetle Oryzaephilus surinamensis, rice weevil Sitophilus oryzae, lesser grain borer, Rhizopertha dominica and confused flour beetle, Tribolium confusum. In fumigant toxicity assays, in addition to common bioassays and probit analysis of the data, two indices of effective concentration and mortality were used for evaluating the essential oil efficacy. In the first method, the minimum concentrations that caused effective mortality (over 90%) were determined against the four pests. In the second one, two constant concentrations; low (0-50% mortality) and high (50-100% mortality) were tested to evaluate different susceptibility of these four insects. Repellency of the essential oil was estimated by applying four concentrations; 0.1, 0.2, 0.41 and 0.83 μl/cm². LC₅₀ values were 208.9, 248.99, 328.66 and 257.212 μl/L air for the pests, respectively, demonstrating the more sensitivity of sawtoothed grain beetle. In the assays of the concentration as an index, estimated concentrations for the species were 600 (100% mortality), 625 (95% mortality), 700 (100% mortality) and 375 µl/L air (92.5% mortality), respectively. In the assays of the mortality as an index, the low concentration (175 µl/L air) caused 42.5±13.1, 20±0, 15±6.4 and 12.5±9.4% mortality and the high concentration (350 µl/L air­) caused 72.5±4.7, 65±6.5, 52.5±8.5 and 72.5±8.5% mortality, respectively. The mean repellencies of four concentrations at three hours after treatment were 61.6±15.9, 49.9±9.6, 48.3±16 and 83.3±4.1%, respectively. The results of this research revealed the average efficacy of citrus lemon peels essential oil for controlling these coleopteran stored products pests.