Laboratory evaluation of particle size, food contamination, and residual efficacy of pyrethrin + methoprene aerosol

Abstract

Efficacy of aerosol applications of pyrethrin+methoprene was assessed through emergence of morphologically-normal adults exposed as larvae and through a developmental index. Concrete arenas were treated with aerosol droplets (particles) averaging 2µm or 16µm, food material was placed on the arenas at 1-8 weeks post-treatment, and 3-4-week-old larvae of one of four stored product insect species placed on the arenas at the same time. No exposed Lasioderma serricorne (DeGeer) larvae reached the adult stage at either particle size, though they developed further when exposed residual deposits of the 2 µm aerosol particles compared to residual deposits of 16 µm particles. No exposed larvae of either Tribolium confusum Jacqueline duVal or Trogoderma variabile (Ballion) reached the adult stage when exposed to residues of the 16 µm particles, but most of the larvae exposed to the 2 µm residues completed development. Exposed Dermestes maculatus (DeGeer) larvae completed development to the adult stage after exposure to both particle sizes, indicating low susceptibility to methoprene residues. When food material in the arenas was also treated with the two particle sizes and bioassays conducted using only larvae of L. serricorne, T. confusum, and T. variable, results were similar to those described above. In a final experiment, only the 16 µm particle size aerosol was used to treat arenas with or without food, with arenas without food having it added one day after treatment. At 1-8 weeks post-treatment, the food was transferred to new untreated arenas and food was replaced in the arenas originally treated with aerosol. Bioassays were conducted using only larvae of T. confusum and T. variabile. The food material blocked deposition of the aerosol on the arenas or absorbed some of the residues, indicating transference of the methoprene residues from the treated surfaces onto the food.

Case Study: A Practical Application of an Aerosol Treatment in a Commercial Mill

“…Eight out of the 20 locations had complete adult recovery after a week. The ability of affected adult T. confusum to recover as observed in this study is consistent with previous research [5,6,8,10]. The affected state, or knockdown as it is sometimes termed, is a transitional category from which individual insects may survive or die, with the outcome likely related to the dosage of insecticide received [8].…”

“…Aerosol particle size is a critical factor affecting the efficacy of insecticides, since smaller droplets tend not to settle onto surfaces or impinge on the insect cuticle. For example, laboratory testing in a continuous flow chamber has demonstrated how larger particle sizes of 16 µm were more effective than smaller particle sizes of 2 µm at preventing Tribolium confusum Jacquelin du Val, confused flour beetle, and Trogoderma variabile Ballion, warehouse beetle, development from the larval to the adult stage [6]. Particle size also impacts movement of particles within a structure, with larger droplets traveling shorter distances than smaller droplets.…”

“…Given that most of the population is hidden during a treatment, aerosols most likely contribute to population reduction through residual persistence of the IGR component that is combined with pyrethrin. Exposures of late state larvae of Lasioderma serricorne F., the cigarette beetle on concrete arenas treated with a pyrethrin and methoprene formulation, resulted in no adult emergence of those exposed larvae, even after 8 weeks post-exposure [6].…”

Mobility of Stored Product Beetles after Exposure to a Combination Insecticide Containing Deltamethrin, Methoprene, and a Piperonyl Butoxide Synergist Depends on Species, Concentration, and Exposure Time

“…Our data show a temporary effect in adult movement, which may be desirable, as the inclusion of a neurotoxic agent along with methoprene slows down the exposed adults without terminating the exposure. As methoprene acts on the immatures, the inclusion of an adulticide, such as deltamethrin, is expected to cause adult mortality [24][25][26][27]. For instance, Athanassiou et al [28] used a combination of methoprene with natural pyrethrum, and found that all the exposed psocid individuals were dead in a very short interval, an effect that was apparently due to the presence of natural pyrethrum and not to methoprene.…”

Effect of Diet, Photoperiod and Host Density on Parasitism of <i>Anisopteromalus calandrae</i> on the Tobacco Beetle and Biological Parameters of the Parasitoid

“…Due to damage caused by these insects, the difficulty of controlling them, and because many species, such as L. serricorne, have already acquired resistance to insecticides [5], new alternatives aimed at minimizing economic losses and controlling pests efficiently become necessary, as is the case of biological control with the use of parasitoids [6].…”