Study sites

The study was carried out in two production systems in the state of San Luis Potosí, the first considered organic as it is duly certified through an officially recognized organization for this purpose (^{DOF, 2020}), called Casa Garambullo (CG), located in Peotillos, municipality of Villa Hidalgo (22° 29’54, 22488” north latitude and 100° 36’37, 36656” west latitude), at an altitude of 1 527 masl and the second characterized as an agroecological system, in the process of certification, located in La Virgin neighborhood in the municipality of Soledad de Graciano Sánchez, called Doña Mary (DM), of the Plantifor company (22° 11’27, 591” north latitude and 100° 57’2, 71368” west latitude) at an altitude of 1 853 masl. Both systems carry out the same practices (use of organic fertilizers, crop rotation, use of live barriers, maintenance of biodiversity, use of free pollination seeds, among others). The difference between the two is that in the organic system these practices have been carried out for more than three years, in contrast to the agroecological one.

Sampling of entomofauna in associated crops

The collection methods used were active and passive; the active method was by using an entomological net consisting of a metal ring of 0.3 m in diameter, handle of 1.5 m and using a white tulle-type fabric as material for the conical bottom bag and in the passive traps, water traps and sticky traps, which consisted respectively of a yellow plastic container with a capacity of 3 L with water, using 50 g of liquid soap to break the surface tension and increase the collection, and yellow plastic boxes of 0.25 x 0.25 m, fastened on two wooden poles previously installed on the ground at a height of 1.4 m (^{Ramírez et al., 2014}).

The capture of insects was carried out in lots cultivated with chard (Beta vulgaris) in development, squash (Cucurbita maxima) and corn (Zea mays), the latter two in conditions of development and postharvest, from mid-September to the first week of October 2019. The collections considered several points within the productive lots as shown in Figure 1. Due to logistical limitations, only four collections with an entomological net were carried out on September 11, 18, 25 and October 2, 2019, between 10:00 and 13:00 respectively, making 3 hits with the net on the vegetation, crossing the sowing bed according to the recommendations of ^{Coronado et al. (2015}).

Figure 1 Graphic representation of the delimitation made in the crops of chard, corn and squash, with the passive and active methods of capturing insects. 

Likewise, three collections with water traps were carried out following the methodology proposed by ^{Morón and Terrón (1988}), these traps were placed in the center of the polygons drawn for the evaluation of each crop; and finally the sticky traps were installed, from September 18 and 25 and October 2, to which vegetable oil was applied and, prior to the penultimate collection, synthetic oil was used (^{Mujica et al., 2007}; ^{Ruiz, 2010}), this type of trap is based on chromatic attraction and is considered for the monitoring of certain pests, whose color used is attractive to aphids and whiteflies (^{Qiu and Ren, 2006}). The insects captured by the net method were placed in airtight bags that contained a piece of cotton with formaldehyde. Those insects captured in the water traps were placed in glass containers with water and sealed.

The sticky traps removed in each collection were placed in airtight bags and were subsequently transferred to the entomology laboratory of the Faculty of Agronomy and Veterinary Medicine of the Autonomous University of San Luis Potosí, along with the specimens captured in the other two methods for their taxonomic identification by stereoscope and using the taxonomic keys by order and family (^{Gibb et al., 2006}; ^{Alonso, 2015}; ^{Aguirre and Barranco, 2015}; ^{Carles, 2015}; ^{García et al., 2015}; ^{Fernández and Pujade, 2015}), reported as beneficial or not, then placed in falcon tubes of 50 ml with 70% alcohol for their conservation, with the respective date and identification of the farm. For the identification, all insects collected in conditions to be observed were used.

Shannon and Simpson indexes

Once the count and subsequent identification of insects by order and families was made, the specific biodiversity was calculated through the ^{Shannon-Weaver index, (1964}) and the richness of organisms was measured based on the Simpson diversity index. For the calculation of the Shannon index, the following formula was used: H ′= -∑i=1spilog2pi Where: s= number of species (species richness); p_i= proportion of individuals of species; i= with respect to the total number of individuals (i.e., the relative abundance of species i); ni/N. Where: ni= number of individuals of species i; N= number of all individuals of all species.

The Shannon index, also considered an equity index, correlates abundance and richness of species and expresses the uniformity of abundance values across all species in the sample. It reaches values between 0, when there is a single species, and the Napierian logarithm of S, when all species are represented by the same number of individuals (^{Cámara and Díaz, 2013}). For the calculation of the Simpson index, the following formula was used: 1-∑i=1spi2 Where: s= is the number of species; p_i= is the relative abundance of species I; p_i= ni/Σni. Where: ni= number of individuals. D= Σpi² (dominance).

The distinction of the species with the highest value of importance without evaluating the contribution of the rest is considered based on the ^{Simpson index (1949}). It indicates the relationship between the richness or number of species and the abundance or number of individuals per species anywhere. The importance of the most dominant species is being strongly influenced in its calculation. Values close to 1 indicate the predominance of one or some species over others. As its value is inverse to equity, diversity can be calculated as diversity (D= 1- λ), which tells us that the closer to the value of 1, the greater the equity (^{Cámara and Díaz, 2013}).

Statistical data

The field data collected were sorted based on each trapping method. For the results of insect capture methods through entomological net, water traps and sticky traps, a two-way analysis of variance (Anova) with one replica was performed, followed by multiple comparisons with the Tukey test to test for significant differences (p< 0.05) between the type of traps used in both localities and the number of insects captured. For statistical analysis and graphical representation, the software Minitab19 and GraphPad Prism 9.0 were used respectively.

Climate data

Data on maximum, minimum temperatures and precipitation, but not relative humidity, were recorded in both localities during the time the study lasted through the application MeteoRed (version 6.8.3-free) in order to compare the behavior of the different insect populations based on climate information.

Insect capture

In the organic production unit CG, by means of an entomological net, 95 insects were captured in the selected crops, likewise, 84 insects were captured in the production unit DM, with the order Hymenoptera (Figure 2) being the most frequently collected in both localities. Based on the total number of individuals captured, the largest number of insects was collected in the chard crop with 32.60% and 44.05% in CG and DM respectively, with the family Formicidae being the one with the highest number of individuals. This type of sampling demonstrated efficiency in capturing adult insects.

Figure 2 Orders of insects most frequently captured by the entomological net method in Casa Garambullo and Doña Mary. A comparison of means between localities was made and a greater presence of insects of the order Hymenoptera was observed; there are no significant differences (p> 0.05) in the capture of this order in both farms. Error bars indicate a 95% confidence interval (CI). 

None of the crops sampled during the development of the study showed damages of economic importance in the two production units analyzed. ^{Duarte and Almirall (2020}) identified a high abundance of the family Formicidae (of the order Hymenoptera) through the association of crops that included chard, and mention that, although this family of insects presents a contribution as a biological controller, it must be taken into consideration that a high population of these insects could become a pest. On the other hand, ^{Campo et al. (2014}) mention that chard tends to present a high variety of insects, in addition to the fact that if this crop is associated, there would be a high diversity of natural enemies present in its environment.

The greatest capture of insects was achieved with the method of water traps, obtaining 1 202 in Casa Garambullo and 761 in Granja Doña Mary during the four weeks of study, being again the order Hymenoptera (Figure 3) the one that was most frequently observed in both farms. Of the total individuals, 39.6% and 33.51% were captured in the crops of corn in production and squash in postharvest in CG and DM, respectively. In both places, the family Vespidae was found in greater quantity. This method of collection is mostly used for flying insects (^{Hudson et al., 2020}).

Figure 3 Orders of insects most frequently captured by the method of water traps in Casa Garambullo and Doña Mary. A comparison of means in the collection of insects between localities was made and it was confirmed that there are significant differences (p< 0.05) in the capture of the order Hymenoptera in both farms. Error bars indicate a 95% confidence interval (CI). 

Within an agroecosystem, the presence of the family Vespidae has special relevance for the natural control of non-beneficial insects. ^{Lopez et al. (2013}) mention that this family acts as a natural controller of insects considered as a pest in corn; this arthropod acts as a controller of insects of the families Chrysomelidae, Cicadelidae, Noctuidae, Acrididae, found in a representative way in both study sites. In the same way, the family Vespidae can be associated as pollinators and predators of different pests in cucurbit crops (^{Dalló et al., 2018}).

By means of the method of yellow sticky traps, during the three samples in the farm Casa Garambullo and Granja Doña Mary, 460 and 373 individuals were collected respectively, with the orders Hemiptera and Thysanoptera being the most frequently found in both farms (Figure 4). In the postharvest squash crop, in both farms, the largest number of captured insects was found with 36.96% and 37.27% in CG and DM respectively, with the families Aleyrodidae, Aphididae, Thripidae and Aeolothripidae being observed most frequently in both farms.

In a study conducted by ^{Díaz et al. (2020}) in squash, the efficacy of yellow sticky traps in the control of Bemisa tabaci belonging to the family Aleyrodidae, vector of the squash curly leaf virus (SLCV), was reported. Likewise, ^{Corrales (1995}) mentions that several species of Thysanoptera have been found in vegetables, including squash; however, within biological control, to keep a low population of these pest insects, it can be done with the presence of the family Eulophidae of the order Hymenoptera as mentioned by ^{Loomans et al. (1997}), which were identified at both study sites.

Figure 4 Orders of insects captured with sticky traps in Casa Garambullo and Doña Mary. Through the comparison of means, a greater presence is observed in the capture of non-beneficial insects of the order Hemiptera and Thysanoptera, there are no significant differences in the capture of these orders (p> 0.05) in both farms. Error bars indicate a 95% confidence interval. 

As for the total number of insects captured in the organic CG and agroecological DM production units, it was found that, with the captures with entomological net, it was possible to collect 58.95% and 57.14% of beneficial insects respectively; likewise, from the water traps, despite the fact that a greater number of insects were captured, only 52.83% and 54.27% were identified as beneficial in both organic and agroecological production units respectively, finally through the sticky traps, 16.09% and 15.55% insects considered beneficial were captured in CG and DM (Table 1).

Organic agriculture is a driver of the abundance of species of natural enemies as stated by ^{Muneret et al. (2019}) and it could be inferred that, based on the data obtained in the capture of beneficial insects with water traps and entomological net, their abundance is inversely proportional to the non-beneficial insects captured in both farms (organic and agroecological).

Species diversity in both production units

The Shannon-Weaver index has been the most used to measure the diversity of entomofauna. In ecology, diversity refers to the diversity of species, expressing the number of populations and their relative abundances (^{Segnini, 1995}). For its part, from the Simpson index, the relationship between richness or number of species and the abundance or number of individuals per species anywhere is indicated (^{Moreno, 2001}).

Considering the total number of insects captured through the three established collection techniques, the following orders of beneficial insects were identified: Hymenoptera, Coleoptera, Hemiptera and Diptera in Casa Garambullo and Doña Mary, being the families Vespidae, Apidae, Syrphidae, Eulophidae, Crabronidae, Formicidae, Cynipidae and Coccinellidae the ones identified in greater quantity in both farms.

As for the indices of specific biodiversity, these were low H’: 1.33 and 1.26 in the organic and agroecological production units respectively (Table 2), considering a high range of specific biodiversity when they oscillate between 2 and 3 as stated by ^{Pla (2006}) and ^{Gelambi (2018}).

In the calculations made from the Simpson index, a low dominance among insect species was obtained in the Casa Garambullo and Doña Mary farms (D= 0.25 and D= 0.21 respectively), however, there was a high diversity of species in both farms 1 - D= 0.75 and 0.79 respectively (Tables 3 and 4). If the diversity of species is 1 or close to 1, it is considered high, as mentioned by ^{Brito et al. (2007}). The latter could be linked to changes in temperature and precipitation (Figures 5 and 6) since climate is an element that affects insect populations. Climatic variables influence the survival and duration of insect life cycles, causing variations in the number of individuals captured (^{Hodgson et al., 2011}).

Figure 5 Climograph of the municipality of Villa de Hidalgo where the maximum temperature 30 °C, minimum temperature 11 °C and precipitation from September 11 to October 3, 2019, are indicated. 

Figure 6 Climograph of the municipality of Soledad de Graciano Sánchez where the maximum temperature 29 °C, minimum temperature 8 °C and precipitation from September 11 to October 03, 2019, are indicated. 

The richness and diversity of insects is directly linked to biotic and abiotic factors. Although the offspring is high, arthropod mortality is high and variable, some authors emphasize that biodiversity is being affected by habitat and climate (^{Fox, 2013}).