Fumigant Toxicity of Essential Oils against Frankliniella occidentalis and F. insularis (Thysanoptera: Thripidae) as Affected by Polymer Release and Adjuvants

Abstract

Frankliniella occidentalis is among the most economically significant pests of greenhouse crops, whose resistance to conventional insecticides has created demand for biopesticides such as essential oils. We assessed the fumigant toxicity of linalool against F. occidentalis, F. insularis, and Solanum lycopersicum. Thrips were fumigated with polyacrylamide hydrogels containing either (R)-linalool, (S)-linalool, racemic linalool, or a binary mixture of (R)-linalool with one of twelve adjuvants (i.e., peppermint, cedarwood, neem, clove, coconut, jojoba, soybean, olive, α-terpineol, 1,8-cineole, trans-anethole, or (R)-pulegone). Solanum lycopersicum seedlings were exposed to (R)-linalool or a mixture of (R)-linalool and peppermint oil via conditioned hydrogels or foliar spray. For F. insularis, (R)-linalool was more toxic than (S)-linalool, with LC50 values of 11.7 mg/L air and 16.7 mg/L air, respectively. Similarly for F. occidentalis, (R)-linalool was more toxic than (S)-linalool, with LC50 values of 29.0 mg/L air and 34.9 mg/L air, respectively. Peppermint oil and α-terpineol were the only synergists, while the other adjuvants exhibited varying degrees of antagonism. All seedling treatments demonstrated phytotoxicity, but symptoms were most severe for foliar sprays and mixtures containing peppermint oil. While hydrogels conditioned in linalool may be a favorable substitute to conventional insecticides, the cross-resistance demonstrated herein indicates that expectations should be metered.

Identification of Terpenoid Compounds and Toxicity Assays of Essential Oil Microcapsules from Artemisia stechmanniana

“…A. stechmanniana essential oils against F. occidentalis were performed by fumigation that was described in a previous study, with some modifications [ 27 ]. The tested concentrations of essential oils also had five concentrations: 1.02, 2.05, 4.10, 8.20, and 16.40 mg/mL, with acetone as the solvent.…”

Gel Carriers for Plant Extracts and Synthetic Pesticides in Rodent and Arthropod Pest Control: An Overview

“…In terms of various higher taxa groups of target pest organisms, highly sorptive pesticide hydrogels have been formulated not only as insecticides but also as fungicides [ 39 , 40 , 41 ] and herbicides [ 42 , 43 , 44 , 45 ]. Apart from pesticide synthetic compounds, hydrogels were suggested as a formulation matrix for natural compounds [ 46 ] and bioagents [ 47 ]. The natural-based formulations may be potentially employed in situations in which biocontrol is required, such as in some types of organic farming systems.…”

“…Mechanisms of improving essential oil stability include various encapsulation techniques of natural substances by formulating them as nano- and microemulsions [ 131 ], microspheres [ 132 ], and nanoparticles [ 133 ]. The use of highly sorptive hydrogels may also provide higher and longer activity of essential oils applied as pesticides and repellents [ 46 , 98 , 134 ].…”

“…Essential oils (EOs) formulated in hydrogels may be used as natural-based pesticides (acting as contact pesticides, fumigants, or baits) for the direct control of pests. For example, Gharbi and Tay [ 46 ] conducted a series of fumigation assays to assess the vulnerability of two species of pest thrips ( Frankliniella occidentalis and F. insularis ) to fumigation with EOs released from hydrogel formulation. The tested EOs included either (R)-linalool, (S)-linalool, racemic linalool, or a binary mixture of (R)-linalool with one of twelve other essential oils.…”

“…However, it is questionable what application of these types of gel formulations will find practical use due to increasingly stringent registration measures against these and possibly other groups of neurotoxic pesticide compounds. Thus, a more optimistic outlook for agricultural pest control seems to be in the development of gel formulations as carriers of microbial bio-agents [ 47 ], natural botanical insecticides (plant extracts, essentials oils) [ 46 ], natural repellents, and gel-based lures for the controlled release [ 132 ] of pheromones applied as pheromone mating disruptors [ 37 , 145 , 146 ] within the framework of IPM strategy. Gels and other polymers (especially biopolymers) then also have good prospects as carriers of environmentally acceptable impregnating agents (e.g., borates) for structural/construction wood protection [ 111 , 147 , 148 , 149 ].…”