Introduction

Agricultural activity satisfies human needs, but food is the one that requires a bigger surface and causes greater territorial impacts (^{López and Llorente, 2010}). The industrialization of export crops for livestock feed and the growing demand for the production of biofuels have strengthened monoculture farming; however, this has a negative impact on health, ecosystem integrity, and food quality (^{Holt-Giménez and Patel, 2009}). Monoculture specialization has various consequences, including the frequent and abundant use of agrochemicals related to environmental problems and the increase of insect infestations (^{Gliessman, 1998}). The knowledge about the environmental, social and cultural impact of certain agricultural practices has led us to consider that changing towards a sustainable agricultural model is necessary (^{Gliessman, 2002}; ^{Sarandón, 2002}).

According to ^{Muñoz (2004)}, the best known aspect of the agroecological food production is the substitution of agrochemicals with less pollutant and aggressive practices. ^{Martínez (2002)} propose an ecological approach to agriculture, using a new theoretical framework to analyze agricultural processes. ^{Koohafkan and Altier(2010)} show models to promote biodiversity, support output without agrochemicals, and promote ecological integrity. Agroecological production systems are biodiverse, resilient, energy efficient, socially fair, and they make up a strategy for energy, production, and food sovereignty (^{Gliessman, 1998}). Pest control in agroecological farming is carried out by means of practices that contribute to keeping low the population of harmful organisms. Therefore, control is preventive and occurs before the pest manifestation (^{Villalobos, 1995}).

The preparation for sowing and the raking of the plots has a double purpose: besides preparing the plot for the sowing, the larvae and the pests are eliminated from the soil where they live, such as pre-pupae and motionless pupae, which are more sensitive to predators (birds); the desiccation by temperature and the overwhelming action of the tools of cultivation; this reduces the populations’ annual and biannual cycle. ^{Aragón et al. (2001)} consider that the species’ identity and their life cycle is a key point to establish the adequate time to prepare the plot for sowing or raking. Later, ^{Aragón et al. (2008)} proposed collecting adult Melolonthidae, using light traps in agricultural plots, since this reduces the number of adults in the crops and, in consequence, the larvae population.

Owing to the increase of human population and the increasing demand for agricultural products, the Food and Agriculture Organization of the United Nations (FAO), the World Health Organization, and the National Academy of Science (NAS) are interested in crops with appropriate nutritional and protein values that meet the food needs of the global population, like amaranth (A. hypochondriacus L.), which is one of the most promising pseudocereals for human consumption.

Amaranth stands out due to its high content of lysine and other amino acids, proteins, vitamins and minerals, such as calcium (^{Mapes et al., 1997}); in addition, it adapts to different conditions (agricultural, altitude, climate, and soil type). Amaranth is an important source of jobs for the agricultural, industrial, commercial, and services sectors; it also provides earnings to the farmers and, therefore, an increasing number of producers are interested in growing amaranth in Mexico (^{Hernández and Herrerías, 1998}).

More than 70% of the amaranth sowing in Mexico is carried out in the state of Puebla, with an average output of 1.4 Mg ha^-1, using conventional handling (^{SIAP, 2014}). Amaranth crops are invaded and harmed by insect infestations, such as beetles (Melolonthidae), colaspis larvae (Colaspis sp.), cucumber beetles (Diabrotica balteata; Chrysomelidae), wireworms (Agriotes sp.; Elateridae), and fall armyworms (Spodoptera sp.; Noctuidae). The most abundant species which cause the greatest harm to the root system include the white grub complex, made of larvae of the Phyllophaga, Diplotaxis, Macrodactylus, Paranomala, and Cyclocephala genera which, along with borer and defoliator insects, are responsible for 65% of those losses (^{Aragón and Tapia, 2009}). According to ^{Aragón and López-Olguín (2001)}, ^{Aragón et al. (2004} and ²⁰⁰⁵⁾, and ^{Pérez-Torres et al. (2005)}, this complex is one of the most important phytosanitary problems that this crop faces.

The larvae of agricultural crops are not fully understood; therefore, identifying species and studying this complex’s eating habits in every region is necessary to solve the problem (^{Pinzón, 2006}). In addition, making a diagnosis is necessary in order to find out the infestation degree, from sowing to harvesting, with the aim of developing actions to handle the pest and to find out its ecological importance. The problems created by the white grub complex in each region depend on the handling and the weather conditions. The species that live in the amaranth crops in the agricultural zone of San Jerónimo Coyula, Atlixco, Puebla are unknown, although the farmers declare that these pests cause losses.

The aim of this research was to evaluate the agroeconomical handling of the white grub complex associated with amaranth, a handling that farmers can affords and which effectively increases the grain output, without causing environmental damage.

Materials and methodology

The study was carried out in the 2012 and 2013 agricultural cycles, in San Jerónimo Coyula, Atlixco, at an altitude of 1903 m. In order to determine the species density of the white grub complex, larvae samples were taken in a 32 800 m² plot, when the amaranth stumps from the previous agricultural cycle (November 2012 and February 2013) were still there. To take the samples, three 310 meter-long transects were traced, with a 20 m separation between them; 20 sample sites were selected along each one, and they had 15 m separations between them. A 30x30x30 cm cube of soil was obtained from each site, and the larvae were manually separated from them.

The collected larvae were placed in plastic containers and were taken for analysis to the Entomology lab of the Agroecology Center of the Instituto de Ciencias of the Benemérita Universidad Autónoma de Puebla (CENAGRO-ICUAP). In the lab, the larvae were separated in accordance with the morphological characters proposed by ^{Morón (1986)}. Thirty percent of the collected population was fixed in Pampel’s fluid; 4 d later, they were transferred to a 70 % alcohol solution (^{Morón and Terrón, 1988}) and then they were identified according to the dichotomous keys proposed by ^{Morón (1986)} and ^{Aragón et al. (2005)}.

The remainder of the population was kept alive, in 500 mL polyethylene containers, with soil from the site of collection, inside a brood chamber, with a 26±2 °C temperature and a 70(10 % relative humidity, in order to verify its taxonomic identity and to determine the larvae-adult ratio. Adults were left in the same recipients for a month, until they reached their sexual maturity. The dichotomous keys for the Coleoptera:

Scarabaeoidea fauna proposed by ^{Morón (1986}; ¹⁹⁹⁴⁾ were used to corroborate the larvae-adult identity and the taxonomic identification of the adults. Larvae and adults were added to the CENAGRO collection.

In order to carry out an agroecological handling of the white grub complex, amaranth was planted, during the agricultural cycle 2013, in the study plot where the diagnosis was made; the plot was divided in three sections: 1) an 8000 m² treatment section; 2) a 16 800 m² barrier; and 3) a 8000 m² control section. With the purpose of destroying the larvae and the pupae in the treatment section, the soil was prepared for sowing to a depth of 30 cm, on February 25, 2013, and on April 22, 2013; in both cases third stage larvae and pupae were found; they were exposed to the effect of their natural predators and solar irradiance; in addition, to catch and recover the beetles, a mercury light trap with a sheet (with its own portable generator) was placed in the plot, and it turned on from 8:00 pm to 10:00 pm. The samples were taken in the adults’ flight season, from April 27 to June 30. The taxonomic determination of the adults was made with the keys proposed by ^{Morón (1986}; ¹⁹⁹⁴⁾ and they were compared with the collections of CENAGRO-ICUAP’s Entomology lab.

The effectiveness of agroecological handling in the larvae population density was detected by means of the systematic soil sampling in the treatment and control sections; 100 amaranth plants and 30x30x30 soil samples were randomly taken from each sections. Sampling was carried out during February 2014. White grub complex larvae were identified using the same methodology that was used for diagnosis. Statistical analysis included a comparison test between two independent samples, in order to evaluate if there was any difference (p≤0.05) between the number of larvae in the treatment and the control sections.

In order to determine the connection of soil factors that regulate the population of white grub species, soil samples were laid on paper, and were kept 48 hours in the shade, before being put through a sieve with 2 mm holes. The following elements were evaluated: 1) pH, using a potentiometer in a watery suspension (1:2); 2) texture, using a Bouyoucos hydrometer; and 3) organic matter, using the Walkley-Black method. Additionally, the effect on amaranth production of the preparation for sowing and adult collection with the light trap (agroecological handling) was determined. With this purpose, production was determined in 100 plants, from the treatment, control, and barrier sections, randomly chosen before harvest (measured in kg, and kg per ha^-1 output was calculated).

Results were analyzed with ANOVA and a Tukey test (p≤0.05), using the Statgraphics Centurion XVI statistics software (^{Statgraphics, 2010}), and a 95 % trust level.

Results and discussion

In the soil sampling carried out before the sowing (November 2012-Feburary 2013), 203 third stage Paranomala larvae and 33 larvae from unidentified genera were detected. After the preparation for sowing was carried out, 31 Paranomala and 8 Strigoderma larvae were detected, with a 0-8 larvae gap per rootball. This result showed that the number of larvae diminished by 80.93% as a result of the said preparation process.

The nocturnal flight of Melolonthidae was recorded in 32 collection activities, carried out between May 9 and June 22 (Figure 1); most of them were registered on May 30 (677 adult specimens). Paranomala foraminosa was the first species to appear; it began its flight on May 9; its maximum abundance was recorded on May 15 and May 30 (29 and 28 individuals, respectively); afterwards, it gradually diminished, and its activity stopped on June 21. This species was found during the collection period, except for rainy and windy days. These results match the findings of ^{Castro-Ramírez et al., (2004)} who pointed out that Melolonthidae do not fly under adverse environmental conditions.

Figure 1 Variation of melolonthidae adults captured in the agricultural zone of San Jerónimo Coyula, Atlixco, México. 

Overall, 2591 adult specimens from 32 species were collected, including 13 genus and 7 Scarabaeoidea subfamilies; 78.1 % of the species were represented by few specimens (<15) (Table 1). The specific richness and abundance of species in this study contrast with the findings of ^{Aragón et al., (2008)}, in a maize crop at Santa Cruz Alpuyeca, Puebla; these researchers collected 91 486 specimens, from 19 species out of 14 genus, 6 subfamilies, and four families, using black fluorescent lamps (20W). The results also differed from those documented by ^{Lugo-García et al. (2011)}, who collected 61 198 adult specimens, using a 20W black fluorescent funnel trap, in a maize crop, at Sinaloa, and which belonged to 8 species, seven genus, and four subfamilies; in the last case, despite the abundance of individuals, the richness of species was low, in comparison with the variety found in our study.

Table 1 List of species and relative abundance of Coleopteora: Lamellicordia found in San Jerónimo Coyula, Atlixco, México (20013). 

In the Melolonthidae species of the white grub complex, the Ph. ilhuicaminai, Ph. ravida, P. foraminosa, Cyclocephala lunulata, C. borealis, S. aloeus, and D. bífida adult females showed positive phototaxis (Table 2). This result matches the findings of ^{Castro-Ramírez et al. (2003)} and ^{Aragón et al. (2008)}, who pointed out that the positive phototaxis of Phyllophaga ravida females stood out in collecting activities carried out using light traps. More males were found in Ph. setifera; only one male represented Phyllophaga sp., Ph. martinezpalaciosi, Ph. obsoleta, Ph. balsana, and Paranomala atomograma; in contrast, Macrodactylus mexicanus, Paranomala sticticoptera, P. undulata, P. denticollis, Ligyrus sallei, Hybosorus illigeri, and Ataenius sp. were only represented by one female. This may mean that not all species are attracted to mercury light traps and that using only light traps for collections is a relevant factor, since these may only attract one sex.

More females were collected than males (60.4% vs. 39.6%); therefore, this will have reductive repercussions in the larvae population in the next cycle. In this regard, ^{Aragón et al. (2005)} pointed out that each oviposit female lays 18-23 eggs on the ground. However, ^{Méndez-Aguilar et al. (2005)} stated that taking into account the abundance of females with regard to males is not enough to determine the effect of the kind of collection. Therefore, in order to make a diagnosis of agricultural important species and their ratio, capture methods must be combined, in order to optimize a response from most species.

A sampling carried out in February 2014, has proven the effectiveness of agroecological handling in the soil’s larvae population. Ninety-four white grub larvae were found in the treatment section. Based on larvae development, adults collected, and their identification, the following number of larvae was found: 3 Ph. brevidens, 7 Ph. ilhuicaminai, 11 Paranomala hoepfneri, 13 P. affinis binotata, 32 P. foraminosa, 9 Paranomala sp., and 19 Diplotaxis sp. Meanwhile, 323 larvae were found in the control section, including: 7 Ph. brevidens, 5 Ph. ilhuicaminai, 16 Strigoderma costulipennis, 29 Paranomala hoepfneri, 4 P. affinis binotata, 168 P. foraminosa, 36 Paranomala sp., and 58 Diplotaxis sp. Not all Melolonthidae species have positive phototropism, such as the case of the Strigoderma genus, which, according to ^{Alcázar-Ruiz et al. (2003)} and ^{Morón et al. (1997}, ¹⁹⁹⁸⁾ is likely diurnal, and probably P. affinis binotata also.

The comparison test between two independent samples showed a significant difference between the number of larvae in the treatment and control sections (p<0.001). The number of larvae per rootball had a 0-9 range in the control area, and a 0-3 range in the treatment area. Of all the adults captured, Ph. ilhuicaminai and P. foraminosa matched the number of larvae collected; therefore, they belong to the white grub complex associated with amaranth crops in San Jerónimo Coyula.

Paranomala was the richest genus. ^{Morón (1983)} pointed out that the larvae of this genus have optional rhizophagus habits, and that they seem only to feed on roots in soils with scarce organic matter, when they are facing inter or intra-specific competition. There may have been a problem in the plot caused by this optional genus which dominates the edaphic Melolonthidae samples. Therefore, understanding the feeding habits of the white grub complex species is necessary, because some studies mistakenly generalize the Phyllophaga genus species as a pest, when in fact a genus and species complex may be present (some of which may have potentially-damaging rizophagus habits), while others (with saphrophagus habits) are actually beneficial for soil conservation (^{Ramírez-Salinas et al., 2001}).

The soil’s 7.3 pH was optimum for plant growth. The organic matter content in the cultivated plot was very low (0.31 %), mainly owing to the intense cultivation and high-density crop rotation in the plot, which leave behind very few residues because they are extracted to be used as stubble for livestock. The soil had a high permeability level (sand: 82 %; slime: 12 %, and clay: 6 %) with regard to water and nutrients (washed-away and inert soils).

Since the Paranomala genus includes the most frequent and abundant species found in the samples collected in San Jerónimo Coyula, and that organic matter is very scarce in the area under study, the larvae likely feed from roots and consequently harm them.

The production of amaranth seeds was different (p≤0.05) in each section (Table 3). The treatment section had a greater production (26.79 %), compared with the control, which showed a lower production (p≤0.05) than the treatment and the barrier.

Handling the white grub complex with cultural practices, within a sustainable agricultural framework, has the benefit of increasing the output, without using chemical products. These practices are healthy alternatives for humans, are beneficial for the environment, and improve biodiversity, due to their minimal impact. Agroecological treatments, such as the one employed in this study, may be repeated in other sites.

Conclusions

Preparing the land for sowing and collecting adult Melolonthidae with light traps during their flight season is a green and inexpensive alternative that reduces the larvae population of the white grub complex. Farmers from San Jerónimo Coyula, Puebla, use it as an alternative to increase the grain output per hectare. The integrated, non-pollutant control of white grub in amaranth increased the output by one third with regard to the control section.