First comprehensive report of the resistance of Culex quinquefasciatus Say (Diptera: Culicidae) to commonly used insecticides in Riyadh, Saudi Arabia

Chemical composition and toxicity of commercial Mentha spicata and Eucalyptus citriodora essential oils on Culex quinquefasciatus and non-target insects

Current vector control strategies based on synthetic chemicals are not eco-friendly against non-target organisms; hence, alternative approaches are highly required. Commercially purchased oil of Mentha spicata (Spearmint) and Eucalyptus citriodora (Citriodora) were examined against the medical pest Cx. quinquefasciatus (Say) and their non-toxicity on the aquatic species was evaluated. Chemical screening with gas chromatography coupled with mass spectrometry (GC-MS) analysis revealed a total of 14 and 11 compounds in Citriodora and Spearmint oils, respectively, with the highest peak (%) at carvone (70.44%) and isopulegol (30.4%). The larvicidal activity on the fourth instar larvae of Cx. quinquefasciatus showed dose-dependent mortality and significance at a 100 ppm concentration 48 h post-treatment with Citriodora (76.4%, P ≤ 0.001) and Spearmint (100%, P ≤ 0.001). Additionally, the photomicrograph of the fourth instar larvae revealed significant physical abnormalities in the head and midgut tissues post-exposure to Spearmint and Citriodora oils. Moreover, the histological assay revealed severe damage in the epithelial cells and gut lumen 2 to 24 h post-treatment. The repellency percentage of adult Culex mosquitoes was prominent across both oils at 150 ppm 210 min post-exposure. Non-target toxicity on the aquatic predator showed both essential oils (Spearmint oil (17.2%) and Citriodora oil (15.2%)) are safer at the maximum treatment (200 ppm) compared to temephos (75.4% at 1 ppm). The in silico screening of phyto-compounds derived by both essential oils with BeeTox (online server) showed no contact toxicity to the honey bee Apis mellifera. Overall, the present research revealed that Spearmint and Citriodora essential oils and their active phyto-compounds were toxic to Cx. quinquefasciatus and harmless to the aquatic predator and honey bee.

Olfactory Learning Behavior and Mortality of the Honey Bee Apis mellifera jemenitica in Response to Pyrethroid Insecticide (Deltamethrin)

Honey bees are constantly threatened due to the wide use of pesticides. This study presents the effects of deltamethrin on the mortality, olfactory learning, and memory formation of the native Saudi bee Apis mellifera jemenitica. Topical and oral application of realistic field and serial dilutions of deltamethrin (250, 125, 62.5, and 25 ppm) caused significant mortality at 4, 12, 24, and 48 h posttreatment. Bee mortality increased with the increasing concentration of insecticide at all tested posttreatment times. Highest mortality was observed at 24 h and 48 h after both exposure routes. Food consumption gradually decreased with increasing concentration of deltamethrin during oral exposure. The LC50 of deltamethrin was determined at 12, 24, and 48 h for topical (86.28 ppm, 36.16 ppm, and 29.19 ppm, respectively) and oral (35.77 ppm, 32.53 ppm, and 30.78 ppm, respectively) exposure. Oral exposure led to significantly higher bee mortality than topical exposure of deltamethrin at 4 h and 12 h, but both exposure routes were equally toxic to bees at 24 h and 48 h. The sublethal concentrations (LC10, LC20, and LC30) of deltamethrin significantly impaired the learning during conditioning trials, as well as the memory formation of bees at 2, 12, and 24 h after topical and oral exposure. Thus, deltamethrin inhibits learning, and bees were unable to memorize the learned task.

First monitoring of resistance and corresponding mechanisms in the green peach aphid, Myzus persicae (Sulzer), to registered and unregistered insecticides in Saudi Arabia

Insecticides are widely used as the primary management strategy for controlling Myzus persicae, the devastating pest ravaging various vegetables, fruits, crops, and ornamentals. This study examined the susceptibility of M. persicae field populations to bifenthrin, fosthiazate, acetamiprid, spirotetramat, afidopyropen, and flonicamid while exploring the possible metabolic mechanisms of resistance. The study findings revealed that M. persicae field populations exhibited susceptible-to-moderate resistance to bifenthrin (resistance ratio (RR) = 0.94-19.65) and acetamiprid (RR = 1.73-12.91), low-to-moderate resistance to fosthiazate (RR = 3.67-17.00), and susceptible-to-low resistance to spirotetramat (RR = 0.70-6.68). However, all M. persicae field populations were susceptible to afidopyropen (RR = 0.44-2.25) and flonicamid (RR = 0.40-2.08). As determined by the biochemical assays, carboxylesterases were involved in the resistance cases to bifenthrin and fosthiazate, whereas cytochrome P450 monooxygenases were implicated in the resistance cases to acetamiprid. However, glutathione S-transferases were not implicated in the documented resistance of M. persicae field populations. Overall, the susceptibility of M. persicae field populations to flonicamid and afidopyropen-two unregistered insecticides in Saudi Arabia-suggests their potential as promising chemicals that can expand the various alternatives available for controlling this devastating pest. Although the detected moderate levels of resistance to bifenthrin, fosthiazate, and acetamiprid indicate a shift in the selection pressure of insecticides for M. persicae due to Saudi regulations, which have resulted in eventual obsolescence of conventional insecticides in favor of novel insecticides. Finally, rotational use of aforementioned insecticides can help in managing insecticide resistance in M. persicae.