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

Abstract

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.

Keywords: Saudi Arabia: toxicity; honey bee; insecticide; learning; lethal concentration; memory.

Figure 1

Wooden cage (15 × 15 × 5 cm: L × H × W). (A) Front side with Plexiglass; (B) back side of cage with mesh.

Figure 2

Plastic containers for the toxicity bioassay. (A) Syringes—W for water, S for sugar; (B) meshes installed on each side of container for proper ventilation.

Figure 3

Mortality (%) of Apis mellifera jemenitica after topical application of deltamethrin. Different letters indicate significant differences among the tested concentrations at each timeframe.

Figure 4

Mortality (%) of Apis mellifera jemenitica after oral administration of deltamethrin. Different letters indicate significant differences among the tested concentrations at each timeframe.

Figure 5

Food consumption (%) of Apis mellifera jemenitica during oral intake of deltamethrin. Different letters indicate significant differences among the tested concentrations.

Figure 6

Probit analysis graph for lethal and sublethal concentrations of deltamethrin at 24 h posttreatment: (a) topical (b) oral exposure.

Figure 7

Mortality of Apis mellifera jemenitica after topical and oral exposure to deltamethrin (a) 4 h posttreatment, (b) 12 h posttreatment, (c) 24 h posttreatment, and (d) 48 h posttreatment; (e) aggregate mortality after topical and oral exposure. Asterisks represent a significant difference between the mortality of bees after topical and oral exposure at each single concentration attribute (p < 0.05, t test).

Figure 8

Proboscis extension response (PER) of Apis mellifera jemenitica after exposure to deltamethrin through the topical route: (a) learning trials, (b) memory formation test. The asterisk indicates significant differences between the control and deltamethrin-treated groups of bees (Fisher’s exact test/χ² test; * p < 0.05).

Figure 9

Proboscis extension response (PER) of Apis mellifera jemenitica after exposure to deltamethrin through the oral route: (a) learning trials, (b) memory formation test. The asterisk indicates significant differences between the control and deltamethrin-treated groups of bees (Fisher’s exact test/χ² test; * p < 0.05).