Nanoencapsulated deltamethrin combined with indoxacarb: An effective synergistic association against aphids

Abstract

Widespread pesticide use for decades has caused environmental damage, biodiversity loss, serious human and animal health problems, and resistance to insecticides. Innovative strategies are needed to reduce treatment doses in pest management and to overcome insecticide resistance. In the present study, combinations of indoxacarb, an oxadiazine insecticide, with sublethal concentrations of deltamethrin encapsulated in lipid nanocapsules, have been tested on the crop pest Acyrthosiphon pisum. In vivo toxicological tests on A. pisum larvae have shown a synergistic effect of nanoencapsulated deltamethrin with a low dose of indoxacarb. Furthermore, the stability of deltamethrin nanoparticles has been demonstrated in vitro under different mimicking environmental conditions. In parallel, the integrity and stability of lipid nanoparticles in the digestive system of aphid larvae over time have been observed by Förster Resonance Energy Transfer (FRET) imaging. Thus, the deltamethrin nanocapsules/indoxacarb synergistic association is promising for the development of future formulations against pest insects to reduce insecticide doses.

Keywords: Acyrthosiphon pisum; indoxacarb; nanoencapsulated deltamethrin; pest control; synergistic association.

Fig. 1. Toxicity of indoxacarb and deltamethrin on A. pisum larvae. Aphids were fed orally with artificial diet containing indoxacarb (A) ranging from 10⁻⁸ to 10⁻³ M or deltamethrin (B) ranging from 10⁻⁸ to 10⁻⁴ M. Mortality rate was assessed 48 hr and 72 hr after intoxication. Smooth lines represent the fit through the mean data according to the Hill equation. Data are means±S.E.M. (n=4–15).

Fig. 2. Toxicity of deltamethrin/indoxacarb association on A. pisum larvae. Comparative mortality rates produced by indoxacarb (10⁻⁷ to 10⁻⁵ M) tested alone and indoxacarb associated with deltamethrin at 10⁻⁷ M at 48 hr (A) and 72 hr (B). Data are means±S.E.M. (n=4–13). ns: not significant p>0.05.

Fig. 3. Toxicity of LNCs on A. pisum larvae. Comparative mortality rates produced by different concentrations (8.5 to 8500 µg/mL) of LNCs at 48 hr (A) and 72 hr (B). Data are means±S.E.M. (n=4–11).

Fig. 4. Lipid nanocapsules fate in A. pisum larvae. Fluorescence microscopy analysis over time in A. pisum larvae after 24 hr ingestion of FRET-LNCs at 850 µg/mL. FRET and DiI signals were observed using excitation wavelength of 561 nm. The excitation wavelength for acceptor DiD was 640 nm. For FRET and DiD signals, the emission wavelengths were between 663 and 738 nm. The emission wavelengths of DiI signal were between 570 and 620 nm. All sets of images were acquired with the same conditions. Scale bar: 500 µm.

Fig. 5. Impact of encapsulation on deltamethrin (deltamethrin-LNCs) toxicity on A. pisum larvae. Comparative mortality rates produced by deltamethrin alone and deltamethrin-LNCs at 10⁻⁸ M and 10⁻⁷ M at 48 hr (A) and 72 hr (B). Data are means±S.E.M. (n=4–14). ns: not significant p>0.05; ***p<0.001.

Fig. 6. Toxicity of deltamethrin-LNCs/indoxacarb association on A. pisum larvae. Comparative mortality rates produced by indoxacarb (10⁻⁷ to 10⁻⁵ M) tested alone and indoxacarb associated with deltamethrin-LNCs 10⁻⁷ M at 48 hr (A) and 72 hr (B). Data are means±S.E.M. (n=4–13). ns: not significant p>0.05; *p<0.05; **p<0.01; ***p<0.001.

Fig. 7. Comparison of indoxacarb toxicity associated with deltamethrin-LNCs or PBO/deltamethrin on A. pisum larvae. Comparative mortality rates produced by deltamethrin 10⁻⁷ M/indoxacarb 3×10⁻⁶ M, deltamethrin 10⁻⁷ M/indoxacarb 3×10⁻⁶ M associated with PBO at 1 mg/mL and deltamethrin-LNCs 10⁻⁷ M/indoxacarb 3×10⁻⁶ M at 48 hr and 72 hr. Data are means±S.E.M. (n=4–6). ns, not significant p>0.05; *p<0.05; **p<0.01.