This study represents the first systematic contribution of Apioninae in a tropical rainforest in the state of Tabasco. We report 33 apionid species for the SM, representing 96.9% of the fauna for Tabasco, in accordance with that reported by (Alonso-Zarazaga 2004; Jones et al. 2012), 19% for Mexico (Alonso-Zarazaga 2004), and 0.05% for the world (Oberprieler et al. 2007). Of the 33 species, only 15% were determined to species level, and 85% at the genus or morphospecies level, due to the limited information, ecological and biological studies, in addition to the absence of taxonomic keys, or represent undescribed taxa.
Comparing our richness with other faunal studies of Apioninae in Mexico, we observed that the richness of apionids in the SM is low compared to that recorded in the northeast of the country in the state of Tamaulipas with 51 species (Jones et al. 2012), to that documented in the Sierra de Huautla, in the state of Morelos with 89 morphospecies (Castro-Martínez 2019), and to the 29 species reported for the state of Queretaro (Jones and Luna-Cozar 2007). The species N. cretaceicolle and Chrysapion chrysocomun occur in both the SM and El Cielo Biosphere Reserve, and C. chrysocomun occurs in the SM and Sierra de Huautla (Castro-Martínez 2019).
These species represent 6.1% of the total fauna for the SM and have a very wide distribution according to the literature. N. cretaceicolle is distributed in Mexico in the states of Tamaulipas and Guatemala. C. chrysocomun is distributed in Mexico in the states of Chiapas, Morelos, San Luis Potosí, Tabasco, and Veracruz, with additional records in Guatemala, Honduras, El Salvador, and Panama (Alonso-Zarazaga 2004; Castro-Martínez 2019; Jones et al. 2012). Trichapion and Coelocephalapion were the most species-rich genera for the SM. According to Jones et al. (2009) and Castro-Martínez (2019), these genera are the ones that register the highest richness and distribution for the country, since they have a Nearctic or Neotropical affinity (Alonso-Zarazaga and Lyal 1999), so their presence in the SM and in studies conducted in other regions could be attributed, indicating that these genera may be generalist in their habits, exploiting different types of vegetation and food resources.
Most of the species were present during the dry season in April and May, coinciding with what was reported in the study by Jones et al. (2012). In this season, low rainfall and high temperature were documented, which may coincide with the greater availability of resources, since the dry season includes the spring, and this is the season that records the highest flowering and seed production in plants, resulting in food resources for apionids. Similarly, in this season, apionids can be found in their adult stage, on various plants that are not considered their reproductive hosts, and consequently occupy all available habitats in ecosystems (Alonso-Zarazaga 2004; Jones et al. 2012). In addition, the dry season provides an ideal temperature or climate for dispersal and establishment in the middle (shrubs and low branches) and low (herbs) strata, which could cause the greatest presence of these beetles and the greatest record or collection in the SM.
The rainy and norths seasons were the ones with the lowest richness. These stations registered climatic factors such as abundant rain, low temperature and high wind intensity; these environmental variables are very important because they limit the distribution of organisms in natural ecosystems (Janzen 1987).
In addition to the above, there are other biological factors that influence the presence or absence of many beetles during the climatic seasons. First, due to environmental conditions, many Apioninae are in a larval stage during the humid and rainy seasons, and therefore the record of adults was less. With the onset of rains, the production of shoots, leaves and branches of plants increases, which represents a greater availability of food for the developing immatures (Alonso-Zarazaga 2004; Jones et al. 2012; Novotny and Basset 1998; Ribeiro-Costa 2013; Wolda 1978). In addition, the literature mentions that some species of Apioninae use and form galls on branches at the beginning of the rainy season (Vergara-Pineda et al. 2015). Similarly, the increase in foliage during the rainy and norths seasons provides greater refuge and shelter for apionids, reducing the likelihood of collecting individuals by beating the vegetation.
The differences recorded in the presence of apionids by sites with sun or shade exposure may be due to site conservation, fragmentation, food availability, microclimatic conditions and land use, as well as the increase in cultivated land (Hallmann et al. 2017; Rainio and Niemelä 2003; Sánchez-Bayo and Wyckhuys 2019). The sites presented different characteristics, the shaded sites concentrated the highest density of plants, species characteristic of the rainforest: trees over 30 meters high, palms, ferns and little grass. In contrast to the sites exposed to the sun, where the vegetation was fragmented, consequently the lower stratum was composed of grasses, and these sites are used for crops or monocultures, in addition, in these sites the use of herbicides is not controlled.
The most important environmental factors in the distribution of species richness and abundance at sites in the SM were Altitude, Relative humidity, Dew point temperature, Temperature, Wind speed, and Barometric pressure (B.P). Previous studies indicate that Apioninae tend to occupy sites with high elevation (Obregón-Zúñiga 2013). Similarly, the distribution of these beetles could be related to the strong relationship that occurs between Apioninae and their host plants, in the same way that occurs with insects of the family Chrysomelidae, where climatic and microclimatic effects provide a set of temporal resources that cause changes in community structure and, therefore, in species composition and abundance (Flinte et al. 2011; Şen and Gok 2016).
The richness estimates suggest that it is necessary to apply a greater collection effort for the curves to reach the asymptote and consequently document the true richness of Apioninae in the SM. Furthermore, because Apioninae have very diverse host plants and can be found not only on leaves, branches, flowers and seeds, but also in leaf litter and plant fruits, it is necessary to use not only vegetation beating, but also different collection methods to complete the sampling and allow a better representation of these beetles in the ecosystems. For example, leaf litter collection (Jones and Luna-Cozar 2007), seed collection (De la Cruz-Pérez et al. 2013), gilled branch collection (Jones and Luna-Cozar 2007; Vergara-Pineda et al. 2015), and direct collection on flowers and fruits (Arcaya et al. 2020).
This study provides new biological and ecological information on the subfamily Apioninae, a group of weevils that has been poorly studied. However, more studies on this group of insects are needed to determine the geographic distribution, associations, and to clarify important aspects on ecology, systematics, and control, since some species are considered pests in many ecosystems, agroecosystems, and agriculture.