Synthetic and Natural Insecticides: Gas, Liquid, Gel and Solid Formulations for Stored-Product and Food-Industry Pest Control

Abstract

The selective application of insecticides is one of the cornerstones of integrated pest management (IPM) and management strategies for pest resistance to insecticides. The present work provides a comprehensive overview of the traditional and new methods for the application of gas, liquid, gel, and solid physical insecticide formulations to control stored-product and food industry urban pests from the taxa Acarina, Blattodea, Coleoptera, Diptera, Hymenoptera, Lepidoptera, Psocoptera, and Zygentoma. Various definitions and concepts historically and currently used for various pesticide application formulations and methods are also described. This review demonstrates that new technological advances have sparked renewed research interest in the optimization of conventional methods such as insecticide aerosols, sprays, fumigants, and inert gases. Insect growth regulators/disruptors (IGRs/IGDs) are increasingly employed in baits, aerosols, residual treatments, and as spray-residual protectants for long-term stored-grain protection. Insecticide-impregnated hypoxic multilayer bags have been proven to be one of the most promising low-cost and safe methods for hermetic grain storage in developing countries. Insecticide-impregnated netting and food baits were originally developed for the control of urban/medical pests and have been recognized as an innovative technology for the protection of stored commodities. New biodegradable acaricide gel coatings and nets have been suggested for the protection of ham meat. Tablets and satchels represent a new approach for the application of botanicals. Many emerging technologies can be found in the form of impregnated protective packaging (insect growth regulators/disruptors (IGRs/IGDs), natural repellents), pheromone-based attracticides, electrostatic dust or sprays, nanoparticles, edible artificial sweeteners, hydrogels, inert baits with synthetic attractants, biodegradable encapsulations of active ingredients, and cyanogenic protective grain coatings. Smart pest control technologies based on RNA-based gene silencing compounds incorporated into food baits stand at the forefront of current strategic research. Inert gases and dust (diatomaceous earth) are positive examples of alternatives to synthetic pesticide products, for which methods of application and their integration with other methods have been proposed and implemented in practice. Although many promising laboratory studies have been conducted on the biological activity of natural botanical insecticides, published studies demonstrating their effective industrial field usage in grain stores and food production facilities are scarce. This review shows that the current problems associated with the application of some natural botanical insecticides (e.g., sorption, stability, field efficacy, and smell) to some extent echo problems that were frequently encountered and addressed almost 100 years ago during the transition from ancient to modern classical chemical pest control methods.

Keywords: IPM; aerosol; baits; diatomaceous earth; essential oils; fumigation; impregnated nets; insecticides; nanoparticles; spray.

Figure 1

The selection and efficacy of a particular insecticide formulation is affected by a complex interplay between multiple factors that include insecticides, environment (temperature, humidity, crop, structure of stores, technology), workplace and environmental safety and technological constraints, and pests (species, stage, resistance, targeted route of entry into the insect body, etc.).

Figure 2

Gases and vapors. (A) Historic biocide (disinsection/disinfection) flame heat evaporator; (B) historic heat electric evaporator; (C) modern electric pyrethroid evaporator for Diptera control; (D) example of insecticide (pyrethroids/naphthalene) evaporation tablets (“mothproofers”); (E) pressed sublimation block of paradichlorobenzene; (F) large CO₂ tank station for controlled atmospheres; (G1) dichlorvos (DDVP) in a porous evaporator matrix; (G2) application of DDVP evaporation strips supplied in aluminum packages; (H) hypoxic storage bag from a composite foil–modified/controlled atmosphere; (I) fumigation chamber—controlled atmosphere; (J) nitrogen generator unit—controlled atmospheres; (K) fumigation circulation loop—piping with blower (x-ventilator); (L) metal vertical silo complex for N₂ controlled atmospheres in the Czech Republic; (M) concrete horizontal storage complex for CO₂ controlled atmospheres in China; (N) cylinders with N₂ for controlled atmospheres; (O1) thermal speed-box for releasing phosphine from magnesium phosphide plates; (O2) phosphine gas generator from solid phosphides; (P) two cylinders for the coupled release of compressed ethane dinitrile (EDN) gas + gray cylinder with N2 inert propellant; (Q) cylinders and piping for releasing compressed phosphine (PH₃) gas mixed with inert CO₂ gas; (R) cylinders and piping for releasing compressed sulfuryl fluoride (SF) into a freight container sealed by plastic sheets/tarpaulins; (S1) spray-nozzle for hydrogen cyanide (HCN) application; (S2) cylinders for the release of compressed HCN gas; (S3) lines and piping network for the application of EDN and HCN gases; (T1–T3) solid phosphide tablets for PH₃ gas release; (T2,T3) bottle (with inert atmosphere) and traditional can tube-type metal packages for phosphide tablets and pellets; (T4) automatic applicator of phosphide round tablets/pellets into grain moving on conveyors; (T5) chain of phosphide-containing bags for PH₃ slow release into a stored commodity; (T6) application of PH₃-generating phosphide tablets into grain mass by a metal hollow spear-probe applicator; (U) fumigation under tarpaulin/fumigation sheets; (V) release of HCN from liquid HCN-soaked discs after removal from hermetic metal cans; (W) quarantine application of compressed methyl bromide (MeBr) from a cylinder container placed on a weight-scale to measure the accurate dosage (photographs (A–W): V. Stejskal; R. Aulicky, T. Vendl).

Figure 3

Liquids (A) Portable aerosol thermal fogging in food industry silos; (B) vehicle-carried cold aerosol applicator; (C) cold aerosol container pressurized with propellant; (D) cold ULV aerosol application in a store; (E) barrier treatment—fluid insecticide-soaked sponge door mat; (F) baits—fluid carrier with attractant toxicant or genetic disruptor (dsRNA encapsulated with liposome carriers); (G) spray nozzle with device for its attachment to grain conveyor belts; (H) mobile compressor and sprayer for grain protectant application; (I) dual injection spray/aerosol device; (J) visualization of spray protectant applied on grain moving on a conveyer belt; (K) visualization of spray/aerosol protectant application on falling grain; (L) band barrier or spot spray treatment; (M) spray barrier treatment of transport pallets; (N) broadcast spray of walls; (O) insecticide brushing; (P) insecticide sponging; (Q) dip application of insecticide protectant on the surface of dried fish; (R) multipoint treatment of grain moving on covered conveyer belts (piping is visible; spray nozzles hidden inside covered equipment); (S) wall-mounted compressor, insecticide tank, and piping for grain treatment located at the bottom of a grain silo (photographs (A–S): V. Stejskal; R. Aulicky, T. Vendl).

Figure 4

Gels and foams. (A,B) Insecticide foams can be applied on vertical and horizontal surfaces; (C) foam injected into cracks and crevices and voids; (D–F) gel and/or foam bait for ants, cockroaches, and flies, respectively; (G) bait administered in a plastic resistant box; (H) foams and gels that can be applied from ready-to-use pressurized containers; (I) gel bait application into cracks and crevices using injection guns; (J) detail of protective gels applied on ham directly or on ham nets; (K) ham surface gel protection against mites; (L) detail of a plastic tube gel or foam injector (photographs (A–L): V. Stejskal; R. Aulicky, T. Vendl).

Figure 5

Solids. (A) Historical hand-pumped piston-gun: it was modified either for the application of aerosols (“Flit-gun”/“Fly-tox”) or as a sprayer or duster for the application of insecticide deposits; (B) application of baits in solid crystalloid form (sugar); (C) pelleted baits in bulk formulation; (D) granular baits enclosed in protective boxes; (E) duster container with a perforated lid applicator; (F) manual application of botanical ash/dust by low-income rural farmers; (G) duster container with an injection lid applicator; (H) visualization of barrier dusting; (I) ignition-activated smoke generator; (J) water-activated (chemically activated) smoke generator; (K) dust admixed with grain with the help of motorized or manually rotated drums; (L) seed treatment (dressing/coating and coloring with a warning dye); (M,N) various forms of dressed, coated, and colored seeds; (O) visualization of an admixture of grain kernels with solid traditional (fresh or dried parts of plants, e.g., neem) and new (tablets, granules, sachets) formulations of botanical insecticides; (P) visualization of a triple-layer hermetic bag with incorporated insecticide; (Q) visualization of a pest control net with incorporated insecticide; (R) solid granulated bait (left) and its slurry form (right); (S) solid inert dust (left) and its slurry form (right); (T) insecticide-/repellent-incorporated packages (photographs (A–T): V. Stejskal; R. Aulicky, T. Vendl).

Figure 6

(A,B) Various types of manual applications of inert dusts for surface and subsurface grain treatment in horizontal stores; (C,D) two types of motorized blenders for surface and subsurface grain treatment in horizontal stores (ASAG-Beijing); (E) one purpose-built automatic dust applicator machine (ASAG-Beijing); (F) surface and subsurface manual application with the help of an automatic dusting machine; (G) application of dust on the wall of a horizontal store with the help of a dusting machine; (H) broadcast structural treatment of an empty store with inert dust; (I,J) surface of empty storage wickerwork baskets treated using inert dust or ash; (K) visualization of the layer treatment of maize cobs using diatomaceous earth dust; (L) grain stored in drums treated using botanical ash; (M) dust applicator for continual grain treatment on a conveyor belt inside a silo building (ASAG-Beijing); (N) short-term outdoor storage of commodities treated using botanical ash. Note: Photographs (A–H) were kindly provided by Prof. Dr. Cao Yang and Prof. Dr. Yanyu Li (Academy of National Food and Strategic Reserves Administration, ANFSRA and ASAG Beijing) solely for the purpose of this review (photographs (I–N): V. Stejskal; T. Vendl).