Developing Consensus Standard Operating Procedures (SOPs) to Evaluate New Types of Insecticide-Treated Nets

In response to growing concerns over the sustained effectiveness of pyrethroid-only based control tools, new products are being developed and evaluated. Some examples of these are dual-active ingredient (AI) insecticide-treated nets (ITNs) which contain secondary insecticides, or synergist ITNs which contain insecticide synergist, both in combination with a pyrethroid. These net types are often termed ‘next-generation’ insecticide-treated nets. Several of these new types of ITNs are being evaluated in large-scale randomized control trials (RCTs) and pilot deployment schemes at a country level. However, no methods for measuring the biological durability of the AIs or synergists on these products are currently recommended. In this publication, we describe a pipeline used to collate and interrogate several different methods to produce a singular ‘consensus standard operating procedure (SOP)’, for monitoring the biological durability of three new types of ITNs: pyrethroid + piperonyl butoxide (PBO), pyrethroid + pyriproxyfen (PPF), and pyrethroid + chlorfenapyr (CFP). This process, convened under the auspices of the Innovation to Impact programme, sought to align methodologies used for conducting durability monitoring activities of next-generation ITNs.

Effect of Treatment With 3-Octylthio-1,1,1-Trifluoropropan-2-One in the Diamondback Moth (Lepidoptera: Plutellidae) to the Toxicity of Diafenthiuron, Indoxacarb, and Bacillus thuringiensis

The diamondback moth, Plutella xylostella (L.), is a worldwide insect pest of cruciferous crops. Although insecticides have long been used for its control, diamondback moth rapidly evolves resistance to almost any insecticide. In insects, juvenile hormone (JH) is critically involved in almost all biological processes. The correct activity of JH depends on the precise regulation of its titer, and juvenile hormone esterase (JHE) is the key regulator. Thus, JH and JHE have become important targets for new insecticide development. Trifluoromethyl ketones are specific JHE inhibitors, among which 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP) has the highest activity. The interaction effects between pretreatment with or combination of OTFP and the insecticides diafenthiuron, indoxacarb, and Bacillus thuringiensis (Bt) were investigated in diamondback moth larvae to determine OTFP’s potential as an insecticide synergist. In third-instar larvae, both pretreatment and combination treatment with OTFP decreased or antagonized the toxicities of diafenthiuron, indoxacarb, and Bt at all set concentrations. In fourth-instar larvae, combination treatment with OTFP decreased or antagonized the toxicities of diafenthiuron and indoxacarb at all set concentrations. However, it increased or synergized the toxicity of Bt at lower concentrations despite the limited effect at higher concentrations. Our results indicated that the effect of OTFP on the toxicities of insecticides varied with the type and concentration, larval stage, and treatment method. These findings contribute to the better use of OTFP in diamondback moth control.

An unconventional use of piperonyl butoxide for managing the cotton whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae)

Bemisia tabaci (Gennadius) is a pest of global importance which resists many conventional insecticides. Novel strategies for control are required and these may incorporate compounds whose lethal and sublethal effects have gone unremarked. Although most commonly employed as an insecticide synergist, piperonyl butoxide alone was lethal to predominantly second instar nymphs of the cotton whitefly, B. tabaci at LC50s of between 60 and 600 ppm, depending on the strain. Formulated and technical material were similarly toxic and far more so than detergents. Some strains exhibited slight tolerance (c. 3–10 fold) but there was no correlation of this with the presence of known resistance mechanisms or enzyme banding patterns. Residues of piperonyl butoxide alone were toxic to adult B. tabaci at c. 2000 ppm which was similar to the toxicity of paraffin oil. Piperonyl butoxide also increased developmental times among B. tabaci nymphs at doses as low as 10 ppm and exerted a transient effect on oviposition. There was strong evidence that it did not reduce the feeding activity of insects surviving treatment. Such effects offer scope for incorporating this compound into resistance management programmes, especially in conjunction with natural enemies (e.g, parasitoids active specifically against immature hosts).