Successful control of Triatoma dimidiata with residual application of a microencapsulated formulation of pirimiphos-methyl (Actellic 300CS) in southeast Mexico

Triatoma dimidiata, the main vector of Trypanosoma cruzi throughout South Mexico and Central America, infest domiciles and peridomestic ecotopes of rural and semi-rural communities. This study reports the effect of the residual application of the organophosphate pirimiphos-methyl in a microencapsulated formulation (Actellic 300CS) for the control of intradomiciliary and peridomestic T. dimidiata in the community of Tekik de Regil (hereafter Tekik) in Yucatan, Southeast Mexico. From March to October 2022, a two-arm, unblinded entomological trial was performed in Tekik. Timed Manual Collections (TMC) characterized house and peridomicile infestation by T. dimidiata prior (baseline) and after the residual spraying (RS) (post-intervention) of a microencapsulated formulation. A total of 120 premises were surveyed (60 positive and 60 negative for T. dimidiata), randomly allocated 1:1 to treatment (RS with Actellic 300CS) and control (no RS) arms. Monthly post-spraying entomological surveys (May-October) with TMC were carried out in a random sample of ten houses from each arm. We analyzed the association between the treatment and post-intervention infestations using chi-square contingency tables. The estimated efficacy of the intervention with the 95% Confidence Intervals (CI) was calculated with the efficacy formula, using the Odds Ratio (OD) calculated from a binomial Generalized Linear Mixed Model (GLMM) from the positive premises in the baseline survey and post-intervention, using time as a random effect. Domestic infestations post-intervention were only detected in the control group (2/60 houses, 3.3%). Cumulative peridomestic infestation was significantly higher in the control arm (31.7%; 19/60) compared to the treatment arm (11.7%; 7/60) (X2 = 0.007, p < 0.01). The cumulative 6-month estimated efficacy of the intervention (% reduction in treatment versus control arm) was 65% (95% CI: 14%-79%). A single application of Actellic 300CS reduced T. dimidiata infestations by more than 60% for up to 6 months and provides evidence of an alternative formulation suitable for triatomine control in Mexico.