Experiment A (trap color)

This experiment was conducted on a plantation of Dominico-Hartón plantains (Musa AAB), which was three years old and was located in the municipality of La Vega, Cundinamarca, Colombia (5°2’53.90” N and 74°18’30.80” W), at an altitude of 1,310 m a.s.l. in an area encompassing 2,000 m².

Traps that were 1.0 m long and 0.6 m wide were elaborated with polypropylene bags with three different colors: blue, white, and transparent. Toxic bait was placed inside, composed of ripe plantain (approximately 400 g), 5 g of insecticide powder (25 g kg^-1 of chlorpyrifos as the active ingredient), and 5 ml of water. Three treatments were implemented, one for each color, and the number of captured adults was counted every 7 d for 7 months. The traps were renewed every 7 d and placed randomly every 10 m on the perimeter of the plot. Each trap was tied 1 m above the ground between two plantain plants. There were seven repetitions for each treatment.

Experiment B (type of trap)

This experiment was developed on an 8-month-old plantation of Dominico-Hartón plantains, located in the municipality of La Vega (5°02’46.4” N and 74°18’58.4” W), at an altitude of 1,099 m a.s.l. and in an area of 1,000 m².

Based on the results obtained in Experiment A, the effectiveness of the best color trap (Color trap) was compared with the type of trap typically used by plantain producers (Artisanal trap) in the study area. The artisanal trap was elaborated with polyethylene containers (2.5 L soda bottles) with a base perimeter of 37.2 cm and a height of 38 cm. An opening that was 10 cm wide and 5 cm long was made in the containers 15 cm from the base to allow the entry of adult screwworms, and water and molasses were added at a 2:1 ratio (250 mL of water and 125 mL of molasses) as bait. The color trap was installed following the same methodology of Experiment A, except that it was attached to only one plant.

The captured screwworm adults were counted during the month. Trap renewal, counting periodicity, and number of repetitions were the same as in Experiment A. In addition, an analysis of the costs associated with the two types of traps was conducted.

Furthermore, to verify the taxonomic identity of the adult screwworms (T. atymnius), larvae were removed from the damaged plants and sent to the Colección Taxonómica Nacional de Insectos "Luis María Murillo" (CTNI) [National Taxonomic Collection of Insects] of the Corporación Colombiana de Investigación Agropecuaria (Agrosavia, C.I. Tibaitatá), where they were identified and deposited (catalogue number 187).

Climatic variables

In Experiment A, the average temperature and accumulated precipitation from April to October 2017 were recorded daily; these variables were included in the corresponding model.

Statistical analysis

In both experiments, a completely randomized design was used. Since the individual adult screwworms were recorded by counting (where excess zeros were evidenced), the data were analyzed using the following models: Poisson, negative binomial (NB), zero-inflated Poisson (ZIP), and zero-inflated negative binomial (ZINB). The best model was selected by comparing Pearson's chi-square, complete log-likelihood, Akaike information criterion (AIC), corrected AIC (AICc), and Bayesian information criterion (BIC) values of each model to choose the corresponding model for Experiment A. In Experiment B, AIC, and Schwarz Bayesian Criterion (SBC) were considered to select the best regression model. The screwworm individuals were considered the response variable; precipitation and temperature per month were the parameters in Experiment A.

For Experiment B, the parameters included trap type and capture week. The transparent color was taken as a benchmark in Experiment A to evaluate the effectiveness of the other colors because blue and white represented positive parameters in the regression model in contrast to the transparent color, which always demonstrated negative parameters (when it was not used as a reference point). In Experiment B, the color trap was taken as a reference point for the model because it represented a negative parameter. The parameters were considered significant when P<0.05. For the statistical analysis, Statistical Analysis System (SAS) 9.4 was used.

Experiment A (trap color)

The best fitting regression model was selected by comparing Pearson's chi-square (closer to 1) and the lower values in the complete log-likelihood criterion, AIC, AICc, and BIC (Tab. 1)

This allowed selection of the best model, namely, the ZINB model, which presented the best selection criteria values. It is important to note that the ZIP model was not selected because the negative of the Hessian was not a positive definite.

Based on the parameters estimated by the selected model, the blue and white color traps captured 2.84 (e^1.0443 = 2.84) and 1.38 (e^0.3220 = 1.38) more adult screwworms, respectively, than the transparent trap (Tab. 2), a finding that coincides with ^{Pérez (2013)}. Likewise, in studies conducted by ^{Goulson and Cary (1993)} and ^{Weiss (1997)} with blue, red, yellow, and white traps, they observed that blue traps captured up to eight different species of Lepidoptera. Furthermore, ^{Kočíková et al. (2012)} used traps of different colors to determine the effect of color on the behavior of butterflies (Lepidoptera: Hesperioidea and Papilionoidea). They discovered that white traps had higher captures followed by blue and violet ones. This finding could be related to peaks in the blue spectrum and the presence of UV and blue receptors in butterflies. ^{Taha et al. (2012)} found that blue sticky traps captured significantly more Lepidoptera adults, namely, T. absoluta (22.98%), than yellow sticky traps (13.99% of total adults), whereas there was no difference between the numbers captured by blue and green traps. The results of this study demonstrated that T. atymnius preferred blue to white, contrary to that reported for other Lepidoptera species, such as T. absoluta, which appeared to prefer white over blue (^{Tadele and Emana, 2017}).

^{Tadele and Emana (2017)} discovered that, in greenhouse tomatoes, T. absoluta had a different attraction to several colors in the following decreasing order: white > blue > yellow > green > red. The maximum number of adults was captured with white sticky traps, followed by blue ones. The minimum number of adults was captured with red and green sticky traps. Furthermore, ^{Mahmoud et al. (2014)} found that T. absoluta adults exhibited a higher preference for white traps.

On the other hand, when the temperature increased, the adult insect captures increased by 6.26 times (e^1.8339 = 6.26, Tab. 2), as compared to the month with the lowest temperature. Likewise, when rainfall increased, the adult insect captures increased by 1.01 times (e^0.0056 = 1.01, Tab. 2).

Figure 2 shows that rain increased just before the experiment was initiated. Therefore, it would be expected that favorable conditions for insect development occurred in the period prior to trap setting. These results, together with the absence of control methods, led to higher captures at the beginning of the experiment. According to ^{Belalcázar (1991)}, screwworms are diurnal, are more active on sunny days, and fly in small groups 1 m above the ground. In June and July, there was a decrease in screwworm captures in response to trap installations in April and May, which reduced the insect population. Later, in August, there was an increase in screwworm captures that could be explained by high adult populations appearing in April and May whose offspring likely turned into adults by August.

Figure 2 Variation of screwworm individual captures using different color traps and rainfall changes in the study area from April to October 2017. Adult capture is represented as the average weekly count for each month. 

With low rainfall and temperature increases in June and July, it would be expected that the reproduction and activity of these insects would be favored (^{Londoño et al., 1991}), so the insect population in September and October would increase. However, the adult numbers during the low rainfall period was the lowest; the initial population might not have been enough to achieve a significant increase in the subsequent months. In addition, the trap installations decreased the chances for the reproduction and development of insects. In this regard, ^{Arboleda and Parra (2012)} found that the population indices of C. humboldti (Lepidoptera: Castniidae), considering the number of larvae and eggs per plant during a plantain plague in Buenaventura (Colombia), demonstrated a positive and significant relationship with precipitation; however, it demonstrated no significant relationship with relative humidity or with temperature.

According to ^{Urra (2016)}, rainfall could have either favorable or unfavorable effects on insects, depending on the type of insect, its development stage, and habits. The development rate of immature stages (egg, larva and pupa) fluctuates according to environmental temperatures within a range of 10-30°C although, for many species, a higher temperature is favorable, and warmer periods lead to premature larval development and, consequently, the rapid development of adult insects (^{Stefanescu et al., 2004}). In the current study, a temperature range of 21.3-22.1°C prevailed in the area where the experiments were performed.

^{Raupp (2006)} claimed that rain not only represented a direct threat of injury or death to butterflies but the fresh air associated with storms could also reduce temperatures below the thermal threshold for insect flight. Furthermore, cloudy skies limit the ability to collect the solar radiation necessary to fly (^{Roy and Asher, 2003}; ^{Raupp, 2006}).

Experiment B (type of trap)

By comparing the lowest values with AIC and SBC (Tab. 3), the best-fit regression model was selected, namely, the Poisson model, which demonstrated the best values for the selection criteria.

The comparison of the two trap types with Poisson modeling indicated that the most efficient trap for capturing screwworm adults was the artisanal trap, over the blue trap (Table 4). Based on the parameters estimated by the model, the artisanal traps captured 4.33 times (e^1.466337 = 4.33) more individual adult screwworms than the blue traps. ^{Lorya et al. (2002)}, considering the establishment of adult emergence periods and the population dynamics of Opsiphanes cassina Felder (Lepidoptera: Brassolidae), found the most effective traps for capturing adults of this species were those containing molasses bait.

It is important to note that, in this experiment, the plantain crops were in their vegetative growth stage, in contrast to the first experiment, where the plants were in their third productive cycle. ^{Tadele and Emana (2017)} stated that the effectiveness of a trap depends on when it was set in relation to the phenology of the crop. These authors discovered that the highest number of T. absoluta individuals captured in all tomato development stages (vegetative, flowering, and fruiting) was obtained with the white sticky trap, followed by the blue one.

The attractive odor of molasses is a more effective tool for monitoring and controlling insect populations from the integrated pest management perspective because adults are strongly attracted to carbohydrate and protein sources (^{Chinchilla, 2003}; ^{Rodríguez et al., 2009}). This phenomenon could explain why the artisanal trap was able to capture a greater number of screwworms. A traditional bait widely used successfully in trap studies in the neotropics is a mixture of ripe banana with sugarcane juice or molasses diluted in water; when fermented, it attracts butterflies that feed on fruits (^{Freitas et al., 2014}).

Table 5 shows the materials and the cost per unit (in USD cents) for manufacturing each trap type used in Experiment B. The cost of manufacturing the artisanal trap was 12% less than manufacturing the blue trap, making it more affordable for producers.

The artisanal trap displayed greater technical efficiency in catching T. atymnius adults, facilitating their implementation by plantain producers in the area. Additionally, this trap does not use agrochemicals, and the plastic bottle can be reused.