The study was conducted during the 2024 cotton-growing season at two experimental sites in Côte d’Ivoire representing contrasting agroecological conditions. The first site was the cotton research station of the National Agricultural Research Center (CNRA) in Bouaké, located in the central cotton basin. The second site was Nambingué, a small research station in the northern cotton-producing zone used by CNRA to repeat field experiments under hotter and drier far-northern conditions. The two sites were selected deliberately because previous surveys in Côte d’Ivoire showed clear geographic differences in the abundance and damage caused by major cotton pests, including jassids [2][5]. Bouaké and Nambingué therefore provided a relevant contrast for testing whether treatment efficacy remained stable under different pest-pressure profiles and environmental backgrounds.

The cotton variety CI-128 (Gossypium hirsutum), developed by CNRA, was used in all trials because it is adapted to local production conditions and is routinely used in agronomic and plant-protection evaluations in Côte d’Ivoire, allowing insecticidal performance to be assessed against a representative crop background [10]. Pest assessments were designed to test the field spectrum expected from the proposed formulation. The monitored pests therefore included the invasive jassid Amrasca biguttula, the whitefly Bemisia tabaci, and the bollworms Helicoverpa armigera and Earias spp., which together represent important components of the cotton pest complex in the study zones [4][5]. Because recent outbreaks have made A. biguttula the dominant species within the local jassid complex in Côte d’Ivoire, special attention was given to its abundance and damage, whereas the other pests were included to determine whether the formulation could also contribute to broader pest management under field conditions [2][3].

Five treatments were evaluated: an untreated control, three doses of a binary formulation containing nitenpyram (200 g/L) and pyriproxyfen (150 g/L) applied at 375, 500, and 750 mL/ha, and a reference insecticide combining acetamiprid (64 g/L) and spinetoram (56 g/L) applied at 250 mL/ha (Table 1). The three rates of the test formulation were selected to compare field efficacy over a low-to-high dose range and to identify the rate associated with the most consistent response under local conditions. The acetamiprid + spinetoram treatment was included as a positive control because it represents an insecticidal standard already used in cotton protection programs and provided a benchmark for comparison under the same field conditions.

A randomized complete block design with four replicates was used at each site. Each block contained the five treatments randomly assigned to elementary plots. As shown in Figure 1, each elementary plot measured 10 m × 9.6 m (96 m²) and consisted of 12 rows spaced 0.80 m apart, each 10 m long. This layout provided a sufficiently large, treated area while preserving internal rows for assessment and reducing border interference between adjacent plots. Three foliar applications were made at 14-day intervals beginning 45 days after sowing, a crop stage corresponding to active vegetative development and the period when early jassid colonization becomes agronomically important in local cotton systems. This schedule was selected to assess treatment effects during the period when sucking-pest pressure usually increases. Treatments were applied with a calibrated backpack sprayer fitted with a constant-pressure system and a horizontal boom. A spray volume of 60 L/ha was maintained for all applications because the trial was conducted over a relatively narrow crop-development window and the same delivery conditions were required for all treatments and sites. Under these conditions, the fixed spray volume was intended to standardize treatment comparisons rather than optimize canopy coverage at each growth stage. Before each application, sprayer output was checked to verify that the target dose per hectare was delivered accurately, and the equipment was thoroughly rinsed between treatments to avoid cross-contamination.

Table 1. Insecticidal treatments evaluated in the study.

Figure 1. Arrangement of elementary plots.

Pest assessments were conducted one day before each application (T − 1) and at 3 and 7 days after treatment (T + 3 and T + 7, respectively) to document pre-treatment infestation levels and short-term treatment effects. Thirty plants per plot were sampled along the diagonal of each plot following the method of Nibouche et al. [11], as previously applied in cotton pest surveys in Côte d’Ivoire [2]. The main response variables were jassid abundance and jassid damage. For the dominant jassid, adults were counted on five well-developed terminal leaves per sampled plant, and a plant was recorded as damaged when at least one terminal leaf showed characteristic hopperburn symptoms. Adults of Bemisia tabaci were counted to assess activity on another major sucking pest. Larvae of Helicoverpa armigera and Earias spp. were counted by whole-plant inspection to assess activity on fruit-feeding Lepidoptera.

Data were first examined for distributional assumptions. Because normality and homoscedasticity were not satisfied, nonparametric analyses were used. Site effects were first assessed to determine whether pest pressure differed between Bouaké and Nambingué. Because the two locations represented contrasting agroecological conditions and showed significantly different baseline pest abundance, treatment effects were then analyzed separately within each site rather than pooled across locations. This approach was adopted to avoid masking treatment responses under site-specific pest-pressure profiles and to keep the interpretation of treatment effects directly linked to each field context. For each plot and response variable, post-treatment observations from the three application cycles were pooled by averaging the T + 3 and T + 7 assessments after each spray, resulting in one plot-level mean based on six post-treatment observations. These plot-level means were then used as the analytical units for treatment comparisons within each site. Pre-treatment observations collected at T − 1 were used only to check baseline comparability among treatments before spraying and were not included in the post-treatment efficacy means. Kruskal-Wallis tests were used to compare treatments for each response variable, and when significant differences were detected (p < 0.05), multiple comparisons were performed to separate homogeneous groups. Analyses were conducted using the agricolae package in R [12], and seasonal dynamics were visualized with ggplot2 [13] in R version 4.4.2 [14]. Because the same plots were assessed repeatedly over time and were nested within blocks and sites, a mixed-effects modelling framework would provide a more complete assessment of treatment, time, site, and interaction effects. However, given the distributional characteristics of the present data and the objective of providing a field-efficacy comparison under site-specific pest-pressure conditions, nonparametric analyses were retained. This limitation is acknowledged in the interpretation of the results.

The monitored pest complex differed significantly between the two study sites, confirming that Bouaké and Nambingué represented contrasting field contexts for evaluating the spectrum of the tested formulation. Nambingué showed the highest infestation levels of Bemisia tabaci, Helicoverpa armigera, and jassid damage, whereas Bouaké recorded higher abundance of the dominant jassid and higher densities of Earias spp. (Table 2). All pest parameters differed significantly between sites (p < 0.01), indicating that the field performance of the formulation had to be interpreted against two distinct pest-pressure profiles rather than under a single homogeneous infestation context.

Table 2. Mean abundance of monitored pest parameters at Bouaké and Nambingué, with associated Kruskal-Wallis test statistics.

Means followed by different letters are significantly different according to the Kruscal-Wallis test at 5% significance level.

At Bouaké, most treatment differences were driven by the response of the dominant jassid, which represented the clearest signal within the monitored pest complex. All three doses of the nitenpyram-pyriproxyfen formulation significantly reduced jassid abundance and jassid damage (p < 0.001) relative to both the untreated control and the acetamiprid + spinetoram reference treatment. Mean jassid densities ranged from 16.80 to 19.63 individuals per 30 plants in the treated plots, compared with 47.23 in the untreated control and 52.68 in the reference treatment (Table 3). Jassid damage followed the same pattern, remaining below one infested plant per 30 plants in all nitenpyram-pyriproxyfen treatments, whereas it exceeded 10 plants in the control and reference plots. By contrast, no significant treatment effects were detected at this site for Bemisia tabaci, Helicoverpa armigera, or Earias spp. (p > 0.05), indicating that, under Bouaké conditions, the contribution of the formulation was essentially confined to management of the dominant jassid.

Table 3. Mean pest parameters at Bouaké according to insecticidal treatment, with associated Kruskal-Wallis test statistics.

Means followed by different letters are significantly different according to the Kruscal-Wallis test at 5% significance level.

At Nambingué, the strongest treatment effect was again observed on the dominant jassid, although this site also showed a detectable response in whiteflies. Significant treatment effects were observed for both jassid abundance and jassid damage (p < 0.05). The highest jassid densities occurred in the untreated control (24.84 individuals per 30 plants), followed by the acetamiprid + spinetoram treatment (15.47 individuals per 30 plants), whereas all doses of the nitenpyram-pyriproxyfen formulation significantly reduced infestations, with the 750 mL/ha dose resulting in the lowest level (3.05 individuals per 30 plants) (Table 4). Treatment effects were also significant for Bemisia tabaci, with the 375 mL/ha dose producing the lowest adult densities and the untreated plots showing the highest infestation. In contrast, no significant treatment effects were detected for Helicoverpa armigera or Earias spp., confirming that under Nambingué conditions the formulation contributed mainly to the management of sucking pests and did not provide meaningful control of the monitored fruit-feeding Lepidoptera.