Introduction

For decades the extraction of forest products, both timber and non-timber has sustained and maintained the economy of human communities in Mexico. Non-timber forest products (NTFP´s) are biological resources from natural forest areas, forest areas under management and other wooded areas (^{Peters, 1996}); include a variety of fruits, nuts, seeds, oils, spices, resins, gums, medicinal plants and other products (de ^{Beer and McDermott, 1989}). These play a vital role, as most are self-consumption and part of the informal productive economic system (^{Van Rijsoort, 2000}).

In northeastern Mexico 7.1% of the total population of Mexico are located, constituted by the states of Tamaulipas, Nuevo Leon and Coahuila, these being predominantly urban states. However, 15% of its population is engaged in the exploitation and extraction of different types of vegetation, such as oregano (Lippia graveolens Kunth), Damiana (Turnera diffusa Willd.), pequin pepper (Capsicum annuum var. aviculare [Dierb.] D'Arcy and Eashbaugh), palm leaves (Sabal mexicana Mart., Chamaedorea radicalis Mart., Brahea dulcis [Kunth] Mart.), mesquite pods (Prosopis juliflora [Sw.] DC.), ebony (Ebenopsis ebano Berland), laurel (Litsea glaucescens Kunth) (^{Medina et al., 1999}). Among wild plants from Tamaulipas, ^{Hernandez et al. (1991)} listed 610 useful species, of which 30% are edible.

However, ecological processes such as herbivorous caused by insects reduce the quality, quantity and plant price of products (leaves, stems, roots, flowers, fruits and seeds) which are often damaged totally or partially (^{Crawley, 1983}). Among the economically most important Hexapoda herbivores are Chrysomelidae, which are also bacteria vectors and phytopathogenic viruses. The beetles from the family Chrysomelidae comprise 37 000 species described worldwide, which are grouped into 13 subfamilies and more than 2 000 genera, this are herbivorous and are among the insect families most diverse and conspicuous associated to plants (^{Bouchard et al., 2011}).

Chrysomelidae are known as "turtles, wireworms, flea hoppers, pussies, beetles or mud balls" and are characterized by their oval or semi-oval body, slightly cylindrical or elongated, very convex generally bright and contrasting or metallic colors and small head mostly hypognathous. Antennae are long filiform or capitate, usually with eleven segments and inserted between the eyes and the base of the jaws. The legs are short and thin except for the tribe Alticini, its tarsal pseudotetramera formula, due to reduction of the fourth knuckle; the third knuckle is bilobed and pubescent below. Its length is variable from two to 20 mm (^{Morón and Terron, 1988}).

Most species are specific or have plant preferences as food, there are monophagous or more commonly oligophagus. The consumption is closely related to some plants (^{PérezContreras, 1999}). In many cases, Chrysomelidae feed on a group of related plants, and these patterns are often evident worldwide.

Some species of the Cassidinae subfamily are known as turtles or beetles turtles (^{Jolivet et al., 1988}). Most Cassidinae are specialized consumers (oligophagous). Cassidinae species are primarily associated to host plants of the Convolvulaceae, Asteraceae, Bignoniaceae, Boraginaceae, Lamiaceae and Solanaceae families (^{Jolivet and Hawkeswood, 1995}). Like many members from the Cassidinae, Plagiometriona clavata (Fabricius) subfamily seem to prefer plants from the Solanaceae family, including the genus Capsicum (^{Jolivet and Hawkeswood, 1994}) (Figure 1).

Figure 1 Number of species of Chrysomelidae associated to host plants families in Cañón La Libertad and Cañón del Novillo, Victoria, Tamaulipas. 

Biology and population dynamics of Chrysomelidae are poorly known. Their study has focused on a few species, mainly pests of agricultural crops like ladybug potato (Leptinotarsa decemlineata [Say]), wireworms (Diabrotica spp.), the arrocillo (Colaspis spp.) or fleahopper (Epitrix cucumeris [Harris]). Species of these genera are univoltine or multivoltine, and the number of generations per year depends on environmental conditions and food availability (^{García-Leaños and Marín-Jarillo, 2010}; ^{Pérez-Domínguez et al., 2010}).

The term pest has a markedly anthropocentric sense, since man applies it to everything that produces any damage. However, the notion of pest is associated almost exclusively to insects and other arthropods (^{Selfa and Anento, 1997}).

There are a number of factors that regulate insect populations and these can be seen in two variables. One is the biotic potential, i.e. the ability of a species to multiply without there being an opposing force to prevent it. Another, resistance to the environment (biotic and abiotic factors) is precisely the relationship between the two factors which indicates population abundance of a particular species.

To answer questions about possible potential pests of agricultural and forestry economic importance, it was consulted the specialized literature of prospective host that cause problems to economically important plant species that were recorded in the study area.

The aim of this study was to identify Chrysomelidae species associated to timber and non-timber forest resources in the Cañon del Novillo and la Libertad, Victoria, Tamaulipas, Mexico.

Materials and methods

The study area is located in the central part from the state of Tamaulipas: Cañón of "La Libertad" located between 23° 46' 34" north latitude and 99° 13' 21" west longitude, and Cañón del Novillo located between 23° 42' 19" north latitude and 99° 13' 31" west longitude, from the municipality of Victoria. The climate in the area is semi-warm humid with summer rains. The average annual temperature is 24 °C and annual precipitation ranges from 717.3 to 1058.8 mm. For field work 20 quadrants of 20 x 10 m (200 m²) were selected, in the Cañon de La Libertad five quadrants for pine-oak forest at an elevation between 540 and 560 masl and five quadrants for lowland deciduous ranging between 380 and 405 masl, and in the Cañon Del Novillo five quadrants for pine-oak with an elevation between 710 and 580 masl and five quadrants for lowland deciduous between 510 and 520 masl, for a year collection, from February 2012 to January 2013, preferably from 9:00 to 17:00 h.

The collection of specimens was obtained mainly on herbaceous and shrub vegetation in accordance with phytophagous habits of Chrysomelidae (^{Jolivet, 1988}), and the collection was reinforced by 50 insect net strokes per quadrant. The usual tools and techniques used in entomology were applied: insect net, sheet or inverted umbrella and direct collection. Adult beetles hosts were recorded in the field, and comprise the plants on which insects were observed feeding, and photographs to complement the observations were taken. In Figure 2a and b, shows P. clavata in adult and larval stage feeding on piquin pepper leaves, these observations fell within a quadrant located in the vegetation of low deciduous forest at an elevation of 390 masl in Cañon La Libertad.

Figure 2 a) Adult of Plagiometriona clavata, b) Larva of P. clavata feeding on leaves of piquin pepper (Photo: I. Martínez-Sánchez). 

The research was carried out in two vegetation types, low deciduous and pine-oak forest preferably in remote undisturbed areas from anthropogenic activities, it is possible that species of agricultural and economic importance may be present but in low numbers.

Results and discussion

A total of 119 examples, 81 examples for Cañón de Libertad and 38 for Cañón del Novillo were obtained; a total of 26 species belonging to five subfamilies and 24 genera of Chrysomelidae (Table 1) associated with 18 host plant families were recorded (Table 2). The Cassidinae subfamily recorded the highest species diversity with 12 species, followed by Galerucinae with six and with fewer Chrysomelinae and Cryptocephalinae with three species each, in last place Eumolpinae with two species (Table 1). According to vegetation type, 16 species for deciduous forest and 15 for pine-oak in Cañon La Libertad, while Cañón del Novillo has six species for deciduous forest and 11 for oak pine, it is worth mentioning that of the 26 species recorded in the study area, eight species are unique for deciduous forest, nine species are unique for pine-oak forests in both Canons and nine Chrysomelidae species shared the two vegetation types. The largest number of species was for the Cassidinae subfamily with 46.15% of the total collection and Galerucinae with 23.07%, in a similar work from ^{Sánchez- Reyes et al. (2015)} recorded for Cañón de la Peregrina 157 species, of which Galerucinae obtained 49% of the collected species, while Cassidinae with 20%, totally opposite to our work.

The difference of results in species found in these studies may be due to environmental factors such as favorable weather conditions at collection time in a given year and the physical work, number of strokes on shrub vegetation, 200 net strokes, for Sánchez-Reyes over 50 for this work where in most collections the direct technique (manual) on plants was used. In another study in the Sierra de San Carlos within the same state of Tamaulipas, ^{Sánchez-Reyes et al. (2014)}, captured a total of 290 examples of Chrysomelidae, again they found that most species found correspond to Galerucinae subfamily (43.24%), again there is difference with species diversity for this work, with respect to the vegetation in this work a greater species diversity (39) in the oak forest and (5) species for deciduous forest were recorded. Compared to this work pine-oak forest recorded (18) species and (17) Chrysomelidae species associated with deciduous forest.

The Fabaceae family has the highest number of associated insects with eight species of Chrysomelidae, contrary to the work from ^{Gavrilović and Ćurčić (2013)} who reported that Asteraceae was one of the best represented families with 11 host species of Chrysomelidae in the Province of Vojvodina, Serbia; on the other hand ^{Aslan and Gök (2006)} report that Asteraceae was from the five families with the highest number of hosts with 65 Chrysomelidae species recorded in Turkey. ^{Aslan et al. (2009)} found in Antalya, Turkey that Asteraceae family dominated in 5% of host plants for Chrysomelidae from the shrub layer, very similar to that found in this study with 5.4%.

Poaceae and Verbenaceae families showed fewer Chrysomelidae, in this case four associated species were recorded; while for Bignoniaceae and Convolvulaceae families three species were found. Asteraceae and Solanaceae had two species. Finally with a single species Acanthaceae, Asclepidaceae, Boraginaceae, Cucurbitaceae, Euphorbiaceae, Fagaceae, Flacourtiaceae, Malvaceae, Pinaceae, Salicaceae and Vitaceae families were recorded (Figure 1).

The Cassidinae subfamily recorded the highest number of families (8) of host plants being this also the most diverse in species within the study area, where Poaceae, Fabaceae, Convolvulaceae and Bignoniaceae had the highest frequency of species association from Cassidinae; as mentioned by ^{Jolivet (1988)}, these plant families have the largest number of hosts for adult Chrysomelidae. Table 2 shows a list of Chrysomelidae species associated to timber and non-timber species in the two vegetation types; also species collected per canyon and species shared by both canyons.

All species found were collected in preserved areas, but not ruling out the possibility that any of these can be a potential pest if there was a crop close, since it has the ability to fly in search of food.

Chrysomelidae species recorded, Plagiometriona clavata proved to be the most agriculturally important for piquin pepper of the region (Capsicum annuum var. Aviculare Dierb.) (Figure 2). According to herbivory caused by larvae and adults found on the plant, this could be an original host for the life cycle of the beetle, this species may become a pest of importance to wild populations of piquin pepper, as reported by ^{Tejas et al. (2011)} for Baja California Sur.

It is important to note that Chrysomelidae densities were influenced by the prevailing climate in the collection period, since 2012 was an atypical year with respects to previous years; the average temperature of the study area ranges from 18 to 24.3 °C and average annual rainfall from 717.3 mm to 1 058.8 mm with a climate hot humid (A) C (w0) climate with summer rains (^{Almaguer-Sierra 2005}), but these canyons according to its topography and vegetation have its own microclimate of up to 2 °C less with respect to temperature outside of the canyons, this makes that any temperature rise above the average will produce destabilization, water stress and sometimes death of animals and plants species that are sensitive to significant changes in temperature.

In 2012 the high temperatures of up to 40 °C in the months of April and May in Cañón de La Libertad and 44 and 42 ° C for May and June, respectively in Cañón del Novillo. Another environmental factor that had an effect on the low population density not only of Chrysomelidae but other arthropods was the lack of rain during almost all the seasons which in turn slowed down growth and development of vegetation in the rainy season, the annual average precipitation (2012) in Cañón del Novillo was 104 mm and 660 mm for the Cañón de La Libertad, did not even reach the 717.3 mm which is the lowest annual rainfall in the area.

Conclusions

In Cañón de la Libertad and Cañón del Novillo, Tamaulipas, 24 genera and 26 species of Chrysomelidae were recorded, being the most abundant in individuals Galerucinae subfamily, these data are consistent with the work of ^{Sánchez-Reyes et al. (2014}; ^{2015); Niño (2005)} conducted in Tamaulipas, where Galerucinae subfamily was the most abundant in total collection of Chrysomelidae.

Gynandobrotica lepida was the most representative with 17.6% (21) examples, followed by Xanthonia sp. with 15.1% (18) examples both species found in both canyons.

Of the 26 species found in the two canyons, (8) were found only in deciduous vegetation, while for pine-oak were recorded (9) species, and also (9) species shared by both plant communities. It is possible that these species because of its ability to fly and travel long distance may find them in different types of vegetation where have not been recorded before, especially polyphagous species.

As already mentioned, one of the main factors influencing the distribution of Chrysomelidae is the presence of host plant, because its diversity is determined directly by the diversity of plants present in a zone (^{Baselga and JiménezValverde, 2007}).

Fabaceae family had the highest amount of Chrysomelidae associated with eight species, followed in order of importance Poaceae and Verbenaceae (4); Bignoniaceae and Convolvulaceae (3); Asteraceae and Solanaceae (2); and families with a single species Acanthaceae, Asclepiadaceae, Boraginaceae, Cucurbitaceae, Euphorbiaceae, Fagaceae, Flacourtiaceae, Malvaceae, Pinaceae, Salicaceae and Vitaceae. Alagoasa bipunctata, Gynandobrotica lepida, Heterispa vinula, Brachycoryna pumila, Centralaphthona fulvipennis and Xantonia sp. have a broader distribution range on the two vegetation types by having available host plants where they can complete their life cycle.

For the first time in Tamaulipas was recorded Plagiometriona clavata associated to wild piquin pepper (Capsicum annuum var. aviculare).