Comparison of the efficacy of two insecticides for the management of Dactylopius opuntiae on prickly pear cactus in Lebanon and monitoring of the insecticides residues dissipation rates in fruits and cladodes

摘要

Environmental conditions and availability of new cultivated areas of prickly pear cactus in Lebanon appeared lately to befavourable for the survival and development of D. opuntiae which has become highly noxious. To thwart use of randomchemicals and broad spectrum pesticides by local farmers, efficacy of sulfoxaflor (Closer™ 240 SC, rate 0.179 kg a.i/ha) anddiflubenzuron (Dimilin® 25 W, rate 0.329 kg a.i/ha) was compared. Individual insecticidal solutions of each applied aloneor in mixing with mineral oil (spray oil 7E, rate 1.010 kg a.i/ha) on potted cladodes in laboratory conditions (T = 23 ± 4 ℃,RH = 58–63%) showed a sharp decrease in the number of individuals within colonies 48 h after treatment especiallyamong first- and second-instar larvae. Similarly, the same insecticidal solutions applied on separate plots in field conditions(T = 20–35 ℃, RH = 55–75%) according to the Good Agricultural Practices showed efficacious control of the pestdevelopment. D. opuntiae mortality mean percentage reached 80% and 72%, respectively, for sulfoxaflor and diflubenzuron96 h after treatment. The added mineral oil acted as a synergist and enhanced efficacy of both insecticides. Mortalitymean percentages increased to 92% and 88%, respectively. Insecticides residues content over time in fruits and cladodeswere afterwards monitored. Samples were harvested at 3 days interval and residues extracted by the QuEChERS methodand quantified by LC–MS. Dissipation rates after 30 days of treatment attained 70.8% and 80.6% in fruits and 98.5% and74.0% in cladodes, respectively, for sulfoxaflor and diflubenzuron. Half-life time varied accordingly and was higher forfruits treated with sulfoxaflor (14.20 days) than for those treated with diflubenzuron (11.18 days). On contrary, for cladodes,half-life time of the former (4.18 days) was lower than that of the latter (15.47 days). The addition of mineral oilinto the spray solution of the insecticides increased their persistency in the crop. Consequently, half-life times increasedand dissipation rates decreased. Findings of this study should enlarge the spectrum of chemical means for D. opuntiaemanagement and promote resilience of the crop. Analytical method applied for residues analysis should be useful forregistration of the insecticides on the crop and MRLs setting.