Insecticide-impregnated netting: A surface treatment for killing Lutzomyia longipalpis (Diptera: Psychodidae), the vector of Leishmania infantum

Abstract

The sand fly Lutzomyia longipalpis is the main vector of Leishmania infantum in Brazil. Synthetic male-produced sex/aggregation pheromone co-located with micro-encapsulated λ-cyhalothrin in chicken sheds can significantly reduce canine infection and sand fly densities in a lure-and-kill strategy. In this study, we determined if insecticide-impregnated netting (IN) could replace insecticide residual spraying (IRS). We compared numbers of Lu. longipalpis attracted and killed in experimental and real chicken sheds baited with pheromone and treated with a 1 m² area of either insecticide spray or netting. First, we compared both treatments in experimental sheds to control mortality established from light trap captures. We then compared the long-term killing effect of insecticide spray and netting, without renewal, in experimental sheds over a period of 16 weeks. Finally, a longitudinal intervention study in real chicken sheds compared the numbers and proportions of Lu. longipalpis collected and killed before and after application of both treatments. In Experiment 1, a higher proportion of males and females captured in IRS- and IN-treated sheds were dead at 24 h compared to controls (P < 0.05). No difference was found in the proportion of females killed in sheds treated with IN or IRS (P = 0.15). A slightly higher proportion of males were killed by IRS (100%) compared to IN (98.6%; P < 0.05). In Experiment 2, IN- and IRS-treated traps were equally effective at killing females (P = 0.21) and males (P = 0.08). However, IRS killed a significantly higher proportion of females and males after 8 (P < 0.05) and 16 (P < 0.05) weeks. In Experiment 3, there was no significant difference between treatments in the proportion of females killed before (P = 0.88) or after (P = 0.29) or males killed before (P = 0.76) or after (P = 0.73) intervention. Overall, initially the IN was as effective as IRS at killing female and male Lu. longipalpis in both experimental and real chicken sheds. However, the relative lethal effect of the IN deteriorated over time when stored under prevailing environmental conditions.

Keywords: (±)-9-methylgermacrene-B; Interceptor; Leishmania infantum; Lutzomyia longipalpis; Olyset plus; Sex-aggregation pheromone; α-cypermethrin; λ-cyhalothrin.

Graphical abstract

Fig. 1

Photographic images illustrating the chicken sheds and insecticide treatments used in experiments 1, 2 and 3. A Spray application of insecticide on wooden panels used in experimental chicken sheds in Experiments 1 and 2. B Insecticide-sprayed wooden panel placed in the real chicken shed in Experiment 3. C Specially constructed experimental chicken shed used in Experiments 1 and 2. D Insecticide-impregnated netting covered wooden panels in situ within in the experimental chicken shed used in Experiments 1 and 2. E Position of a pair of experimental chicken sheds located in household A used in Experiments 1 and 2.

Fig. 2

Number of female (top) and male (bottom) Lutzomyia longipalpis caught (left) and percentage dead (right) at 24 h in Hoover Pugedo suction traps. Data are superimposed over boxplots (median, 25–75% quantiles). Traps were placed next to real chicken sheds (“Control”) or in experimental chicken sheds treated with λ-cyhalothrin spray (“Spray”) or α-cypermethrin-impregnated netting (“Netting”). Different letters (a-c) indicate significant differences between treatments (pairwise Wilcoxon test, P < 0.05).

Fig. 3

Number of female (top) and male (bottom) Lutzomyia longipalpis caught (left) and percentage dead (right) at 24 h in Hoover Pugedo suction traps. Data are superimposed over boxplots (median, 25–75% quantiles). Traps were in experimental chicken sheds treated with λ-cyhalothrin spray (circles) or α-cypermethrin-impregnated netting (triangles). Different letters (a, b) indicate significant differences between percentage of sand flies killed between months (pairwise Wilcoxon test, P < 0.05). Asterisks indicate significant differences between treatments within months (pairwise Wilcoxon test: ∗P < 0.05; ∗∗P < 0.01; ∗∗∗P < 0.001; NS, not significant). No overall effect of month and treatment was found on numbers of female and male Lu. longipalpis caught (Kruskal-Wallis test).

Fig. 4

Change in number of female (top) and male (bottom) Lutzomyia longipalpis caught (left) and percentage dead (right) at 24 h in Hoover Pugedo suction traps. Data are superimposed over boxplots (median, 25–75% quantiles). Traps were in real chicken sheds treated with permethrin spray (“Spray”) or α-cypermethrin-impregnated netting (“Netting”). Asterisks indicate significant differences between treatments (Mann-Whitney U-test: ∗P < 0.05; ∗∗P < 0.01; ∗∗∗P < 0.001; NS, not significant). There was a significant overall effect of treatment on percentage of females killed (top right, Wilcoxon test, P < 0.05) but not males killed (bottom right, Wilcoxon test, P > 0.05).