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    The Effect of Temperature, Airflow, and Pest Morphology

    Greenberg     March 1, 2025 in News - 15 Minutes


    3.1. Morphometric Analysis of D. suzukii

    The total sample consisted of 572 SWD individuals, comprising 262 males and 310 females, used for the morphometric measurements. Differences in sample sizes between males and females are justified by the species’ sex ratio variation. The morphometric data were analyzed across a temperature range of 21.1 to 28.2 °C. To facilitate more detailed analysis, the data were divided into two temperature categories: ≤24.1 °C and >24.1 °C. This division aimed to balance the number of measurements within each range, with 24.1 °C serving as an approximate midpoint of the entire temperature interval.

    Table 1 presents values for thorax, abdomen, and total body lengths across the laboratory-reared SWD population, with measurements taken from both dorsal and lateral views. The table also differentiates between the two temperature ranges (≤24.1 °C, labeled as ↓T, and >24.1 °C, labeled as ↑T) and provides mean values for each group including overall means ( T ¯ ) for the entire temperature range (21.1–28.2 °C) to offer a comprehensive view of size variation under the full spectrum of conditions.

    The data indicate that females are larger than males, with the thorax being the largest body region (tagma) for both sexes. In the dorsal and lateral views, females have a larger thorax (1013 µm and 1050 µm) compared to males (907 µm and 918 µm). These measurements suggest a more developed thoracic structure in females, but the difference between the two views is not as pronounced, indicating a relatively symmetrical thorax shape, which is important when considering the selection of mesh hole shape.

    The abdomen of SWD exhibits clear sexual dimorphism, with females displaying larger dimensions than males in both dorsal and lateral views. In the dorsal view, the female abdomen measures 1001 µm compared to 894 µm for males, while in the lateral view, females measure 766 µm versus 660 µm for males. This suggests that females possess a broader and more developed abdominal structure, potentially linked to their reproductive role. In both sexes, the abdomen is wider than it is deep, indicating a more flattened geometric shape. However, its smaller size compared to the thorax makes this geometric characteristic less significant.

    The size differences between males and females are more pronounced in body length than in thorax and abdomen dimensions.

    The data also indicate a clear influence of temperature on the body dimensions of SWD, with individuals reared at lower temperatures (21.1–24.1 °C) exhibiting larger body sizes compared to those reared at higher temperatures (24.1–28.2 °C). This trend is consistent across both sexes and all measured traits (body length and thorax and abdomen dimensions). For example, the total body length of males and females is significantly larger in the lower temperature range, with males averaging 2350 µm and females 2804 µm at 21.1–24.1 °C, compared to 2180 µm and 2615 µm at 24.1–28.2 °C. Similarly, the thorax (both dorsal and lateral views) and the abdomen (dorsal view) decrease in size as temperature increases, with larger values recorded at the lower temperature range. However, abdomen height in the lateral view AL is unique in that only females show an increase in size with rising temperatures, while males experience a decrease.

    This reduction in size at higher temperatures is more pronounced in males. For instance, male thorax width in the dorsal view decreases from 964 µm to 842 µm between the lower and higher temperature ranges (a 12.7% reduction), while in females, it decreases from 1074 µm to 959 µm (a 10.7% reduction). A similar pattern is observed for thorax lateral measurements and abdomen dimensions.

    The two-way ANOVA results presented in Table 2 offer insights into how temperature (T) and sex influence the body dimensions of SWD, as well as whether there is an interaction between these two factors.
    According to the results shown in Table 2, both temperature and sex have highly significant effects on body length L, with very low p-values (<0.001) indicating strong evidence that both factors independently affect this trait. Specifically, sex has a much larger effect on body length (F = 384.05), confirming that females are significantly larger than males. However, the interaction between temperature and sex is not significant (p = 0.699), meaning that the effect of temperature on body length is similar for both sexes.

    Temperature and sex also significantly affect thorax width in the dorsal view TD, with both factors showing very low p-values (<0.001). Sex significantly influences thorax width TD, with an F-value of 237.80, while temperature also has a notable effect on this trait, with an F-value of 260.21. Similarly to body length, the interaction between temperature and sex is not significant (p = 0.624), indicating that the influence of temperature on this trait is consistent across males and females.

    For the thorax in the lateral view TL, both temperature and sex are significant (p < 0.001), and there is now a significant interaction between temperature and sex (p = 0.003). This suggests that the effect of temperature on thorax size differs between males and females, with one sex being more sensitive to temperature changes than the other. Specifically, temperature has a greater influence on males, who exhibit a pronounced decrease in thorax size under higher temperatures compared to their lower temperature measurements.

    Regarding abdomen width in the dorsal view AD, temperature and sex significantly affect this tagma (p < 0.001), with no significant interaction (p = 0.861), suggesting that the size differences between males and females are stable across different temperatures.

    In contrast to the other traits, temperature does not have a significant effect on abdomen height in the lateral view AL (p = 0.706), while sex has a strong influence (F = 82.63, p < 0.001). There is a significant interaction between temperature and sex (p < 0.001), indicating that temperature affects males and females differently in this trait. Specifically, male abdomen height decreases slightly from 680 μm at lower temperatures to 638 μm at higher temperatures, while females exhibit an increase from 743 μm to 786 μm. This interaction suggests that the abdomen’s response to temperature changes is more complex in the lateral view, possibly due to sex-specific differences in abdominal development or function.

    The two-way ANOVA revealed significant effects of temperature, sex, and their interaction on several morphological traits of D. suzukii (Table 2). To further explore these differences, a Tukey’s HSD post-hoc test was conducted to compare the mean values of each trait between temperature levels and sexes. The results of these pairwise comparisons are summarized in Table 3.
    The Tukey HSD test revealed (Table 3) that both temperature and sex had a significant effect on all morphological traits of D. suzukii, except for AL when comparing the low and high temperature intervals. In this specific case, the difference in means was −11.3 µm, with an adjusted p-value of 0.365 (Table 3), indicating that the temperature range considered did not lead to significant changes in the lateral abdominal dimension.
    Given the significant interaction between temperature and sex detected using the two-way ANOVA (Table 2), a Tukey’s HSD post-hoc test was performed to assess pairwise differences between temperature–sex combinations for each morphological trait. The results of these comparisons are presented in Table 4.
    The Tukey HSD test assessing the interaction between temperature and sex showed significant differences in all morphological traits of SWD, except in four specific comparisons (Table 4). For each group (trait), the greatest differences are indicated by the absolute values in the third column (mean difference) of Table 4. No statistically significant differences were detected for TD, TL, AD, and AL when comparing females at high temperatures with males at low temperatures. This pattern suggests that, despite the overall influence of temperature and sex, the combination of these specific groups results in similar trait measurements, because females reared at high temperatures tend to be smaller and males reared at low temperatures tend to be larger. Figure 3 shows a series of frequency histograms with corresponding normal distributions, providing a comparative analysis of size distributions for key morphological traits of D. suzukii. The first row of histograms presents the overall size distributions of thorax (dorsal view, TD; lateral view, TL) and abdomen (dorsal view, AD; lateral view, AL) measurements across the entire temperature range (21.1–28.2 °C). The second row compares female size distributions across two temperature intervals: 21.1–24.1 °C (↓T) and 24.1–28.2 °C (↑T). Similarly, the third row illustrates the same comparison for male specimens.
    In the histograms (Figure 3) representing the body dimensions of SWD, clear effects of both temperature and sex are observed. Across all traits, females consistently exhibit larger sizes than males. The size difference between sexes is most pronounced in thorax dimensions, with females showing a tighter clustering around the mean, while males display more variability, particularly in thorax and abdomen lateral views.

    3.2. Geometrical Characteristics of Protective Nets

    Table 5 summarizes the geometric characteristics of the nine exclusion nets included in this study. The parameters considered include the thread density in both weft (ρx) and warp (ρy), hole dimensions (Lpx and Lpy), and the shape factor ψ (Lpx/Lpy), as well as the thickness of the threads in weft (Dhx) and warp (Dhy), mean hole surface area (A2D), mesh thickness (tt), and porosity (φ). The nets differ not only in their geometric properties but also in thread color (crystal, black, and green). Although thread color is not a variable studied in this research, it is included in the table due to its potential influence on some results.
    The geometric characteristics of the nine insect-proof nets selected for testing against SWD (Table 5) reveal important distinctions that may influence their effectiveness. The nets vary in thread densities (ρx × ρy), with values ranging from 5.6 × 5.7 to 9.6 × 10.0 threads cm−2. This variation, along with the thread thicknesses, directly affects the hole sizes (Lpx and Lpy), which range from 638 to 1407 μm in width and 742 to 1535 μm in length. The shape factor ψ (Lpx/Lpy) also differs, with some nets having more elongated holes (ratios as low as 0.600), while others have almost square holes (ratios close to 1.0).

    The thread thickness (Dhx and Dhy) shows relatively small variation, between 280 and 360 μm, with no clear correlation between thread thickness and hole size. This reflects a rigid design strategy by manufacturers, who do not consider the relationship between thread density and thread thickness to achieve the desired hole sizes while optimizing fabric porosity. Just as with hole sizes, thread thickness impacts the 2D surface area of the holes A2D, which varies significantly from 0.530 to 2.027 mm2. The thickness of the nets tt ranges from 370 to 568 μm, reflecting how tightly packed the weft and warp threads are. This thread tightness plays a crucial role in determining the real (3D) hole opening. However, this is an important parameter that manufacturers do not take into account at all. Additionally, the porosity (φ) ranges from 49.8% to 68.2%, indicating varying levels of air and light transmission. These factors are critical for both crop protection and maintaining adequate environmental conditions for plant growth.

    3.3. Efficacy of Protective Nets in Excluding D. suzukii

    The results of efficacy for each protective net are shown in Table 6. For each fabric, the results are provided for the temperature range between 20.4 and 25 °C (↓T), between 25 and 28.7 °C (↑T), and the entire temperature range ( T ¯ ). Each cell in this table consists of two values [ε (%); T (°C)]: efficacy and the temperature at which the trials were conducted. Each efficacy value is the mean of three repetitions performed for each air velocity level (0, 1.5, and 3 m s−1), and therefore, the temperature is also the mean of three sets of records. Consequently, the rows labeled T ¯ represent the average of six repetitions. Using the same logic, the sex ratios of the original sample introduced into the test device and the sample present in the second chamber of the device (the SWD sample that was able to pass through the mesh) are also presented.
    The efficacy of nets 1 and 2 (Figure 4) was very low under calm conditions, which is why tests at higher speeds were not conducted. Nets 6, 7, and 9 were fully effective against SWD at both high air velocities and high temperatures, while nets 3, 5, and 8 showed very high efficacy values. According to the results, hole widths around 700 μm are required (ψ = 0.792) to achieve very high protection against SWD, as is the case with mesh 8, which provides very high but not complete protection. Based on the results, a hole width of approximately 715 μm can be acceptable (nets 8 and 9) as long as the hole length is related to a shape factor not less than 0.8. Other interesting results are obtained with hole widths below 700 μm (nets 6 and 7), which allow for shape factors as low as 0.6–0.7, while improving porosity values above 53%.

    Nets 6 and 7 (completely effective) have hole widths below 700 μm and hole lengths around 1000 μm, with form factors ψ of 0.699 and 0.600, respectively. Net 9 (also completely effective) has a hole width of 715 μm and a pore length of 742 μm, with a form factor of 0.964. The design of nets 6 and 7 appears to be more suitable, as they provide complete protection against SWD and their porosity is higher than that of net 9, which will undoubtedly improve the crop conditions.

    Net 3 has larger hole dimensions (816 × 1333) µm2 compared to net 4 (778 × 1280) µm2. The form factors ψ of both nets are quite similar, 0.608 and 0.612, respectively. However, net 3 (with larger hole size) achieved better efficacy against SWD, which contradicts the logical expectation based on hole size alone. A difference between the two nets lies in the color of the threads: net 3 is made with crystal-colored threads, whereas net 4 has green threads. Therefore, thread color could be a relevant factor to consider in relation to the visual attractiveness of the net to this species.

    The results (Table 6) of the efficacy tests reveal notable patterns influenced by both temperature and airflow velocity. For tests performed within the lower temperature range (21.1–24.1 °C, ↓T), the efficacy values were significantly higher compared to those in the higher temperature range (24.1–28.2 °C, ↑T). For example, net 3 exhibited an efficacy of 100% at 23.8 °C under 0 m/s airflow and 91.0% at 25.4 °C, demonstrating the nets’ effectiveness in blocking the passage of insects at lower temperatures. In contrast, the efficacy decreased at higher temperatures, suggesting that D. suzukii may be more active (or smaller) and capable of passing through the nets as temperatures rise. We use the term “smaller” because higher temperatures are associated with smaller flies.

    Regarding airflow velocity, the efficacy measurements varied with different airflow velocities (0, 1.5, and 3.0 m/s). For example, in net 3 at ↓T, the efficacy was 100% at 0 m/s but dropped to 86.0% at 3.0 m/s. In the case of net 4, the efficacy decreased significantly when the air velocity increased from 1.5 to 3 m s−1, and this is one of the fabrics with the greatest thickness tt (566 μm). This trend is consistent across most nets, indicating that increased airflow velocity may facilitate the passage of D. suzukii, potentially due to increased pressure or turbulence disrupting the nets’ barrier protection.

    The sex ratios of the initial samples compared to those that crossed the nets indicate a trend towards a reduction in the number of females that successfully traversed the exclusion barriers. For example, the initial ratios show that females were consistently more prevalent (e.g., ratios like 1:1.12 and 1:1.24), while the ratios of those that crossed the nets indicate a decline in the proportion of females, such as 1:0.89 and 1:0.82 for nets 7 and 9, respectively. The selective permeability of the nets favors the passage of smaller males, leading to a shift in the sex ratio among those that successfully cross.

    A multiple regression analysis was conducted to assess the influence of the variables involved in the experimental design on the efficacy of the insect-proof meshes. External variables, such as air velocity and temperature, and mesh-related variables, including hole width Lpx, hole length Lpy, mesh thickness tt, and shape factor ψ, have been considered. The results from this initial attempt to model the influence of the variables on the efficacy of the protective meshes showed an R2 = 0.855 and indicated that neither hole length Lpy and mesh thickness tt nor the shape factor Lpx/Lpy had a significant influence on mesh efficacy, with p-values (0.627, 0.932, and 0.393, respectively) exceeding 0.05. However, we know from other studies [70] and from the results of this work (see the results for nets 8 and 9) that hole length Lpy is an influential variable in the efficacy of exclusion nets. Nonetheless, the experimental design of this study did not aim to investigate this factor specifically, in part due to the limited commercial availability of meshes, which made it impossible to control other geometric variables while varying Lpy. Therefore, the analysis was repeated excluding these variables, and the results are presented in Table 7.
    This multiple linear regression explains 84.7% of the variability in mesh efficacy due to air velocity u, air temperature T, and hole width Lpx. Considering that mesh efficacy can only vary between 0 and 100 (when expressed as a percentage), we express the result of the linear regression model as shown below.

    ε u , T , L p x = 0 , i f − 1.64 u − 0.97 T − 0.15 L p x + 226.98 < 0 − 1.64 u − 0.97 T − 0.15 L p x + 226.98 , i f 0 ≤ − 1.64 u − 0.97 T − 0.15 L p x + 226.98 ≤ 100 100 , i f − 1.64 u − 0.97 T − 0.15 L p x + 226.98 > 100

    We do not find it coherent to conduct an ANOVA with the temperature intervals to support the results of the multiple regression analysis, as the experimental reality is that the temperature varied continuously between 20.4 and 28.7 °C. Therefore, establishing a low and high temperature range serves the purpose of presenting results and understanding the phenomenon but does not align with the true nature of the ANOVA analysis. However, the air velocities u are categorized (0, 1.5, and 3 m s−1), and thus, in this case, the ANOVA analysis is appropriate. The data from this analysis support the results obtained in the multiple regression analysis and highlight the influence of air velocity on efficacy values (F-value = 6.818 and p-value = 0.002).

    To analyze whether the means of the air velocity groups show statistically significant differences, we performed a Tukey’s test, the results of which are presented in Table 8. Significant differences are observed between the 0 and 1.5 m s−1 groups (and, of course, between the 0 and 3 m s−1 groups as well). However, the analysis does not allow us to reject the null hypothesis of equal means between the 1.5 and 3.0 m s−1 groups, which may have important practical implications.

    The greatest impact on efficacy appears to occur when moving from zero velocity (0 m s−1) to a moderate velocity (1.5 m s−1). Beyond this point, further increasing the velocity (up to 3 m s−1) does not lead to significant differences in efficacy, although the general trend observed in the regression model remains negative (efficacy decreases as air velocity increases). As previously mentioned, mesh 4 is an exception to this trend, revealed by the Tukey analysis, as in this case, there is a drastic drop in efficacy when the velocity increases from 1.5 to 3.0 m s−1. Perhaps the combination of hole width (Lpx = 778 μm), length (Lpy = 1280 μm), the shape factor (Lpx/Lpy = 0.608), and net thickness (tt = 566 μm) creates a confluence of factors that leads to this drastic drop in efficacy.



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    Antonio J. Álvarez www.mdpi.com

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