Distribution and Habitat in Mexico of Dactylopius Costa (Hemiptera: Dactylopiidae) and their Cacti Hosts (Cactaceae: Opuntioideae)

ECOLOGY, BEHAVIOR AND BIONOMICS

Distribution and Habitat in Mexico of Dactylopius Costa (Hemiptera: Dactylopiidae) and their Cacti Hosts (Cactaceae: Opuntioideae)

CK Chávez-Moreno^I; A Tecante^I; A Casas^II; LE Claps^III

^IDepto de Alimentos y Biotecnología, Facultad de Química, Univ Nacional Autónoma de México, México D. F., México

^IICentro de Investigaciones en Ecosistemas, Univ Nacional Autónoma de México, Morelia, Michoacán, México

^IIIINSUE - Instituto Superior de Entomología "Dr. Abraham Willink" Facultad de Ciencias Naturales e Instituto Miguel Lillo, Univ Nacional de Tucumán. San Miguel de Tucumán, Argentina

^{Correspondence}

ABSTRACT

The distribution pattern of species of the genus Dactylopius Costa in Mexico was analyzed in relation to the distribution of their host plants (subfamily Opuntioideae) to evaluate the specificity of the insect-host association. The distribution of Dactylopius currently recognized is narrower than that of its hosts and probably is not representative. Therefore, a broader distribution of the Dactylopius species in correspondence with those of their hosts was hypothesized. Insects and their hosts were collected and georeferenced in 14 states of Mexico from 2005 to 2007. The distribution areas, maps, and habitat characteristics of Dactylopius, Opuntia sensu stricto, Nopalea and Cylindropuntia were determined on the basis of field collections and examination of museum collections. This information was complemented with information from the exhaustive examination of microscope slides from a local insect collection, plants from local herbaria, and literature reviews. The current distribution of the genus Dactylopius and its hosts included 22 and 25 states of Mexico, respectively, and Dactylopius had a continuous distribution according to its hosts, broader than recognized hitherto. The new georeferenced records of the five Mexican Dactylopius species are reported. Insects with morphological characteristics of D. confusus combined with those of D. salmianus were identified, as well as insects with characteristics of D. opuntiae combined with those of D. salmianus. These records suggest that the number of local Dactylopius species could be higher than previously thought or that possible new processes of hybridization between native and introduced species may be occurring.

Keywords: Biodiversity, cactus, cochineal insect

Introduction

Insects of the genus Dactylopius Costa, the cochineals, and their cacti hosts Opuntia, Nopalea, Cylindropuntia and Grusonia, are endemic to the American Continent (Britton & Rose 1963, Bravo-Hollis & Sánchez-Mejorada 1978, Brummitt & Powell 1992, Anderson 2001). Interactions between these insects and cacti were known and profitably used for centuries by pre-Columbian Mesoamerican inhabitants for whom cacti were food and cochineals a source of dye (Casas & Barbera 2002, Chávez-Moreno et al 2009).

The genus Dactylopius includes nine species. Dactylopius coccus Costa, D. ceylonicus (Green), D. confusus (Cockerell), D. opuntiae (Cockerell) and D. tomentosus (Lamarck) have been reported for North America (Portillo 2005), whereas D. tomentosus (Lamarck), D. coccus Costa, D. ceylonicus (Green), D. confusus (Cockerell), D. opuntiae (Cockerell), D. austrinus De Lotto, D. confertus De Lotto, D. salmianus De Lotto, and D. zimmermanni De Lotto have been reported for South America (Diodato et al 2004, Portillo 2005). Before our study, the five North American species of Dactylopius had been reported in the states of Baja California, Coahuila, Estado de México, Jalisco, Oaxaca, Puebla and Veracruz, in a large number of hosts belonging to Opuntia, Cylindropuntia, and Grusonia (Mann 1969, De Lotto 1974, Piña 1977, MacGregor & Sampedro 1983, Pérez-Guerra & Kosztarab 1992, Portillo & Zamarripa 1992, Miller 1996, Portillo & Vigueras-Guzmán 2003a,b). These Dactylopius hosts had also been reported in several other regions in Mexico (Britton & Rose 1963, Bravo-Hollis & Sánchez-Mejorada 1978, Colunga et al 1986, González et al 2001, Bravo-Hollis & Scheinvar 2002, Guzmán et al 2003, Scheinvar 2004, Reyes-Agüero et al 2005) (see Online Supplementary Material 1).

Studies by De Lotto (1974) and Pérez-Guerra & Kosztarab (1992) described the distribution of Dactylopius in Mexico, although they were mainly focused on taxonomic and ethno-biological aspects of the insects. Some reports (e.g., Pérez-Guerra & Kosztarab 1992, Portillo & Zamarripa 1992, Miller 1996) are catalogs or check lists of Dactylopius species and the states where they are localized, with scarce data about the features of their habitats (Pérez-Guerra & Kosztarab 1992, Miller 1996), with the most systematic, detailed report being the catalog of Mexican coccids of the family Dactylopiidae by MacGregor & Sampedro (1983). However, the distribution of host plants of the genera Opuntia, Grusonia and Cylindropuntia reported until now is wider than that of the insects (see Online Supplementary Material 2). However, information available on Dactylopius and their hosts lack precise descriptions of their distribution pattern and characteristics of their habitats.

Therefore, we aimed to determine the distribution pattern of Dactylopius in Mexico in relation to the distribution of Opuntia, Grusonia and Cylindropuntia, describing the main features of their habitats (altitude, vegetation, soil and climate). Our investigation was based on the hypothesis that the distribution of Dactylopius currently recognized is not representative and should be broader in correspondence with the distribution of their host plants and in accordance with the complex climate and biogeography of Mexico.

Material and Methods

A database for comparing the distribution areas of Dactylopius and their hosts was constructed based on: (1) an exhaustive literature review, (2) a meticulous examination of 262 specimens of opuntioids at Herbario Nacional de México (MEXU) and Herbario del Instituto de Botánica de la Universidad de Guadalajara (IBUG), (3) an examination of 367 microscope slides of Dactylopius at Colección Nacional de Insectos - Instituto de Biología, Universidad Nacional Autónoma de México (CNI-IB-UNAM) and (4) collected samples (see Online Supplementary Material 1-3). A geographic information system was constructed through ILWIS 3.3 mapping the geographic location of Dactylopius and their hosts data from our database.

Sampling area

To identify the interacting species and gather information on their distribution, species of cochineals and their hosts were sampled in the area enclosed between 98º and 104º northern latitude and 18º and 23º western longitude, comprising the states of Aguascalientes, Mexico City, Guanajuato, Hidalgo, Jalisco, Estado de México, Michoacán, Morelos, Oaxaca, Puebla, Querétaro, San Luis Potosí, Tlaxcala, Veracruz and Zacatecas. This area was chosen because it was considered to be the main reservoir of host species of Dactylopius.

Field collection of specimens

Dactylopius from 208 insect populations in 120 localities of 14 states of Mexico within the sampling area were collected on February, May to June and September 2005; April to June 2006 and February and November 2007. The number of collected samples was variable (from 25 to 100 specimens) depending on the size of the population. Male and female insects at different stages of development were collected. In the plants where insects were present in different portions of the same host, insects were collected separately from each portion. Samples were preserved in 70% ethanol. Samples of Dactylopius and their hosts were collected from wild populations, production and research centers, and urban and rural zones. Cladodes of Opuntia, Nopalea and Cylindropuntia were collected in triplicate for propagation. Specimens of Dactylopius were vouchered in the Hemiptera collection of CNI-IB-UNAM. Host plants, Opuntia, Nopalea and Cylindropuntia were vouchered in the area of desert-zone plants of the living collection of the Botanical Garden at the Centro de Investigaciones en Ecosistemas (CIEco-UNAM).

Identification of species of Dactylopius, Opuntia, Nopalea, and Cylindropuntia

Dactylopius specimens were identified using the taxonomic keys of De Lotto (1974), Pérez-Guerra & Kosztarab (1992) and de Haro & Claps (1995). The technique of de Haro & Claps (1995) was used to prepare 153 microscope slides with four to eight insects per slide. Slides were observed under a light microscope (Olympus BX45, Olympus, Japan) coupled to a CDD camera (High Performance Pro-Series UTV 0.5 XC, model 1E08849, Japan) connected to a personal computer (Blue Code, Pentium IV). The captured images were analyzed with the program IPwin 32 (Image Pro version 4.5.1 XProf 22, 2000, for Windows 1998). The identity of Opuntia, Nopalea and Cylindropuntia was corroborated by comparisons to the literature (Britton & Rose 1963, Bravo-Hollis & Sánchez-Mejorada 1978, González et al 2001) and to specimens from the herbaria MEXU and IBUG. Some specimens were assigned their common name due to their morphological complexity.

Environmental database

The database included the following fields: the name of the insect species, host (portion of the plant where the insect was found), place of collection, i.e., the locality and state, geographic coordinates of localization, i.e., latitude, longitude and altitude, collection date and information reference. The data from our fieldwork, including new records, vegetation and soil types, were inserted into the previously generated database in a boldface typeset. The keys and descriptions of Peel et al (2007) were used to characterize the weather of the studied area.

Results

Dactylopius

The information from our database constructed from literature reviews, examination of opuntioids at MEXU and IBUG, observation of microscope slides of Dactylopius at CNI-IB-UNAM and collected samples, was used to draw the distribution maps of Dactylopius and their hosts of the genera Opuntia, Nopalea, Cylindropuntia and Grusonia (Fig 1). Specimens of the five Dactylopius species were collected: 175 of D. ceylonicus, 575 of D. coccus, 675 of D. confusus, 1200 of D. opuntiae and 200 of D. tomentosus (Fig 1). Our field observations are shown for each species (details of each species are given in the Online Supplementary Materials 1-3). As shown in Fig 2a, it was possible to obtain a larger number of records of populations with one or two species of insects and some other populations with three and four Dactylopius species and one state with the five species.

Dactylopius ceylonicus

The distribution of this species and its hosts is shown in Fig 1a. This species had been previously reported in six states of Mexico; on O. fuliginosa (Piña 1977) in Jalisco, on O. ficus-indica in Jalisco (MacGregor & Sampedro 1983) and Veracruz (Piña 1977), on Opuntia sp. in Estado de México, Morelos, Oaxaca, Veracruz (MacGregor & Sampedro 1983), Hidalgo (Piña 1977, MacGregor & Sampedro 1983) and Jalisco (MacGregor & Sampedro 1983, Portillo & Vigueras-Guzmán 2003a). Additionally, in this investigation, D. ceylonicus was collected for the first time in Mexico City and Hidalgo on O. ficus-indica and Cylindropuntia imbricata, respectively (Fig 1a). Like the rest of dactilopids, the cottony-white thin layer covering the insect's body characterizes this species.

Insect specimens were collected during April to June on the top portion of their hosts, on ripe cladodes of Opuntia with more than three levels of cladodes and on the areoles of prickly pears, in living fences with scarce vegetation and regosol. In November, D. ceylonicus was collected on the root nodules of Opuntia sp., in wild populations where xerophilous thickets and arenosol predominate. The presence of the insect is scarce without perceptible damage to its host. Specimens of this species collected in this work were localized within the previously reported altitude range of 950 m to 2650 m above sea level.

Dactylopius coccus

Its pulverulent white cover and a size larger than the rest of the species of the genus distinguish D. coccus. The distribution of this species and its hosts is shown in Fig 1b. It had been reported in five states of Mexico on N. cochenillifera, O. atropes (Portillo & Zamarripa 1992, Portillo & Vigueras-Guzmán 2003a,b), O. ficus-indica, and O. jaliscana (Portillo & Vigueras-Guzmán 2003a). In Jalisco on N. cochenillifera (Piña 1977, Miller 1996), O. ficus-indica (Piña 1977, MacGregor & Sampedro 1983), O. pilifera (Piña 1977), O. hyptiacantha and O. tomentosa (MacGregor & Sampedro 1983, Pérez-Guerra & Kosztarab 1992, Portillo & Vigueras-Guzmán 2003a,b). On O. ficus-indica in Oaxaca and Puebla (Mann 1969), on Opuntia sp. in Puebla, Veracruz (MacGregor & Sampedro 1983), Hidalgo (Piña 1977, MacGregor & Sampedro 1983), and Oaxaca (MacGregor & Sampedro 1983, Pérez-Guerra & Kosztarab 1992); another hosts, O. crassa, O. fuliginosa, O. megacantha, O. streptacantha and O. undulata in unspecified localities (Portillo & Vigueras-Guzmán 2003b), within the altitude range of 1250 m to 2200 m. In this study, D. coccus was collected from February to June, in research and production centers: Tlapanochestli in Santa María Coyotepec, Oaxaca; Nopaltepec A.L.P.R. in Nopaltepec, Estado de México and Campo Carmín S.P.R. de R.L. in Tetecalita, Morelos, where the species O. ficus-indica is used as the main host for culturing and processing the insect. Additionally, specimens were collected in localities close to those centers. The presence of D. coccus in wild localities of Estado de México, Mexico City on O. ficus-indica and O. streptacantha and in San Luis Potosí on O. ficus-indica, O. robusta spp. larreyi and O. tomentosa is reported here for the first time. The most frequent habitat of these cochineals was formed by intensive cultures of O. ficus-indica, on rain-watered lands with the presence of nopale where the types of soil included vertisol, calcisol, xerosol, regosol, leptosol, and foezem, within the previously reported altitude range of 1654 m to 2845 m.

Dactylopius confusus

The distribution of this species and its hosts is shown in Fig 1c. The species had been previously reported in 11 states of Mexico, on O. fuliginosa in Jalisco (Portillo & Vigueras-Guzmán 2003a), on O. pumila in Oaxaca (Pérez-Guerra & Kosztarab 1992), on Opuntia sp. in Chihuahua (Mann 1969), Estado de México, Guanajuato, Guerrero, Hidalgo, Jalisco, Mexico City, Oaxaca, Puebla, San Luis Potosí, Tamaulipas (MacGregor & Sampedro 1983) and Morelos (MacGregor & Sampedro 1983, Pérez-Guerra & Kosztarab 1992); another hosts are G. grahamii, C. imbricata, C. kleiniae, C. leptocaulis and C. tunicata (Mann 1969), within the altitude range of 1100 m to 2200 m. In this work, examination of the morphological characteristics of specimens of D. confusus species resulted in two separate groups, designated here as D. confusus and D. confusus biotype 1, whose descriptions are as follow.

Dactylopius confusus - description

Insects with the typical morphology of this species were designated by this name (De Lotto 1974, Pérez-Guerra & Kosztarab 1992). They were collected from April to June, on O. ficus-indica in Mexico City, Hidalgo, Morelos and Puebla and on O. ficus-indica and on O. fuliginosa, O. jaliscana, O. joconostle, O. spinulifera, and O. streptacantha in Jalisco. Their presence in the states of Veracruz on Opuntia sp. and Zacatecas on O. hyptiacantha, O. phaeacantha and O. streptacantha is reported here for the first time. Our field observations show that D. confusus grows mainly on the cladodes of tree and shrub cactus forms and on their prickly pear fruits in a predominantly desert habitat with scarce vegetation and arenosol, within the altitude range of 1200 m to 2547 m, which is higher than the previously reported altitude.

Dactylopius confusus biotype 1 - description

Insects with the morphological characteristics diagnosed for D. confusus (De Lotto 1974, Pérez-Guerra & Kosztarab 1992) combined with characteristics corresponding to the D. salmianus species were designated with this name. It is worth mentioning that D. salmianus has been reported only for South America (De Lotto 1974, Pérez-Guerra & Kosztarab 1992, de Haro & Claps 1995), without reports of its presence in Mexico. Insects were collected in the states of Hidalgo, Morelos, Puebla and San Luis Potosí on O. ficus-indica and Tlaxcala on Opuntia spp. and C. tunicata; additionally, D. confusus and D. confusus biotype 1 were collected in the states of Morelos cohabiting on the same host, O. ficus-indica.

Our field observations and records show that these insects promote changes in the color of cladodes and fruits, and when the insects are closely gathered at the trunk-stem and stem-fruit joints, these parts are damaged and may detach from the main plant body. Our data also show that D. confusus biotype 1 develops mainly on the cladodes of ripe tree or bush plants and prickly pear fruits in the urban zones and production cultures of Opuntia and on rain-watered lands in wild habitats where xerophilous thickets growing on arenosol and calcisol predominate. The insects were localized within the altitude range of 1654 m to 2773 m.

Dactylopius opuntiae

The distribution of this species and its hosts is shown in Fig 1d. This species has the greatest number of records for the genus; it had been reported in 20 states of Mexico, on 17 species of Cactaceae. D. opuntiae on N. cochenillifera, N. karwinskiana, O. atropes, O. ficus-indica, O. jaliscana, O. megacantha, and O. undulata in Jalisco (Portillo & Vigueras-Guzmán 2003a); on O. robusta in Hidalgo and Veracruz (MacGregor & Sampedro 1983); on N. cochenillifera in Mexico City (Pérez-Guerra & Kosztarab 1992); on N. cochenillifera, O. ficus-indica and O. tomentosa in Oaxaca (MacGregor & Sampedro 1983); on Nopalea sp. in Michoacán (Piña 1977, Pérez-Guerra & Kosztarab 1992), Oaxaca and Tamaulipas (MacGregor & Sampedro 1983); on Opuntia sp. in Baja California, Durango, Estado de México, Michoacán, Oaxaca (MacGregor & Sampedro 1983, Pérez-Guerra & Kosztarab 1992), Morelos, Tamaulipas (Pérez-Guerra & Kosztarab 1992), Aguascalientes, Chiapas, Chihuahua, Mexico City, Guerrero, Hidalgo, Nayarit, Nuevo León, Puebla, Querétaro, Veracruz, Zacatecas (MacGregor & Sampedro 1983) and Jalisco (MacGregor & Sampedro 1983, González et al 2001); another hosts O. vulgaris (Pérez-Guerra & Kosztarab 1992), O. engelmannii, O. fuliginosa, O. hyptiacantha, O. leucotricha, O. macdougaliana, O. streptacantha (Mann 1969); within an altitude range of 25 m to 2678 m. Examination of the morphological characteristics of the insects of the species D. opuntiae resulted in two separate groups, designated here as D. opuntiae and D. opuntiae biotype 1, described as follows.

Dactylopius opuntiae - description

Insects with a typical morphology of this species (De Lotto 1974, Pérez-Guerra & Kosztarab 1992) were designated by this name. They were collected from February to September, on O. hyptiacantha in Aguascalientes, on O. tomentosa in Mexico City and Estado de México, on O. hyptiacantha, O. jaliscana, O. joconostle, O. megacantha, O. robusta, O. streptacantha, O. tomentosa, and Opuntia sp. in Jalisco, on O. robusta spp. larreyi in Puebla and on O. albicarpa, O. hyptiacantha, O. robusta, O. robusta spp. larreyi, and cultivars of O. robusta spp., O. streptacantha, O. streptacantha ssp. aguirreana Bravo and several cultivars in San Luis Potosí; in these localities and in Michoacán it was also collected on O. ficus-indica, on O. joconostle, O. phaeacantha and O. streptacantha in Zacatecas and on Opuntia sp. in Veracruz. Additionally, specimens and records of D. opuntiae in the states of Guanajuato and Tlaxcala on O. ficus-indica and O. streptacantha and O. tomentosa, respectively, are reported here for the first time.

Insects of this species develop on any portion of the plant, the cladodes, fruits, flower calyx and trunk, during any stage of host development. This is the most aggressive species of the genus; its development and invasive growth in the host plant promote changes in the color of the cladodes and fruits, the detaching of the cladodes and fruits when the insect grows on cladode-cladode, cladode-flower and cladode-fruit joints, and even death when the insects damage the trunk. The collected specimens were localized in all types of vegetation, soil and climates already reported for this genus, within an altitude of 750 m to 2845 m, which is higher than that reported by several sources.

Dactylopius opuntiae biotype 1 - description

Insects with typical morphological characteristics of D. opuntiae (De Lotto 1974, Pérez-Guerra & Kosztarab 1992), combined with characteristics corresponding to the species D. salmianus, were designated by this name. Unlike the species D. confusus and D. opuntiae, the species D. salmianus has a thinner and elongated body and the structures of the setae and pores are more elongated and more separated or dispersed over the insect body (De Lotto 1974, Pérez-Guerra & Kosztarab 1992). This insect was collected from February to September, on O. atropes, O. ficus-indica and Opuntia sp. in Guanajuato, C. tunicata in Jalisco, on O. albicarpa, O. ficus-indica, O. streptacantha and cultivars of O. streptacantha spp. in San Luis Potosí and on O. ficus-indica in Tlaxcala. Additionally, D. opuntiae and D. opuntiae biotype 1 were collected on O. ficus-indica in Mexico City and Michoacán cohabiting on the same host, O. ficus-indica. It was noticed that D. opuntiae biotype 1 was less aggressive than D. opuntiae. It develops mainly on cladodes and fruits and the aerial parts of its hosts. Dactylopius opuntiae biotype 1 was found in urban zones and production cultures of Opuntia, on rain-watered lands, in wild habitats where xerophilous thickets and other cacti growing on arenosol predominate, within an altitude range of 1663 m to 2773 m.

Dactylopius tomentosus

The distribution of this species and its hosts is shown in Fig 1e. No records for this species exist at CNI-IB-UNAM. In the literature, it is reported in eight states of Mexico; on C. acanthocarpa (Pérez-Guerra & Kosztarab 1992) and O. megacantha (MacGregor & Sampedro 1983) in Baja California, on N. karwinskiana in Oaxaca (Piña 1977, MacGregor & Sampedro 1983), on Cylindropuntia sp. in Jalisco (Portillo & Vigueras-Guzmán 2003b), Chihuahua, Oaxaca (Pérez-Guerra & Kosztarab 1992, Portillo & Vigueras-Guzmán 2003a), Guanajuato and Nuevo León (MacGregor & Sampedro 1983), on Opuntia sp. in Baja California (MacGregor & Sampedro 1983, Pérez-Guerra & Kosztarab 1992), Coahuila, Mexico City, Guanajuato, Nuevo León and Oaxaca (MacGregor & Sampedro 1983), within the altitude range of 0 to 2500 m. Dactylopius tomentosus was collected from April to November, on O. atropes in Guanajuato and on C. tunicata in Hidalgo on species of the genera Opuntia and Cylindropuntia, within the previously mentioned altitude range. The insects develop exclusively on the cladodes of their hosts and their tiny size makes them almost imperceptible. They do not damage or promote changes in the plant and develop in a desert habitat where xerophilous thickets predominate, on vertisol and arenosol. The presence of spiders was frequently observed with this species.

Opuntia, Nopalea and Cylindropuntia

Our fieldwork revealed the presence of Dactylopius only on the genera Opuntia and Cylindropuntia (see Online Supplementary Material 3) . The species of hosts identified and recorded were: Opuntia ficus-indica (variants and cultivars), O. streptacantha (variants and cultivars), O. robusta (variants and cultivars), O. tomentosa, O. albicarpa (cultivar), O. joconostle, O. hyptiacantha, O. jaliscana, O. phaeacantha, O. megacantha, O. fuliginosa, O. spinulifera, O. atropes, Cylindropuntia imbricata and C. tunicata and in 20 cultivars. Insects were not found on some of the hosts previously reported in the literature (Online Supplementary Materials 1 and 3). For instance, we collected the species Nopalea cochenillifera, N. karwinskiana and N. auberi in Jalisco without observing the presence of the insects during our complete period of fieldwork.

Dactylopius was mostly found on tree and shrub cactus forms. The parts of the plant where the insect was localized were mainly the areoles of cladodes and fruits and the stem commissures, during the months of April to June (aerial cycle) and the rest of the year on the root nodules (latency period). The insects were collected only in Mexico City and Estado de México, in their aerial cycle throughout the year on O. ficus-indica. Fifty-three species and varieties of opuntiods were vouchered in the living collection of the desert zone plants of the Botanical Garden at CIEco-UNAM.

Vegetation, soil and weather

Dactylopius and their hosts develop on diverse types of vegetation; xerophilous thickets, and tropical dry, tropical deciduous and coniferous forests, in which insects share habitats with columnar cacti (Stenocereus spp.), pirul (Schinus molle), huizache (Acacia spp.), izotes (Yucca spp.) and maguey (Agave spp.). They can also be found in pine-oak forests, natural grasslands with or without weed vegetation, living collections and intensive cultures of nopale in monocultures or in association with rain-watered lands, home gardens, orchards, ornamental plants, and fragmented and anthropogenic lands. Likewise, the types of soil included arenosol, vertisol, calcisol, xerosol, leptosol and foezem.

As shown in Fig 2, the distribution of Dactylopius and their host included different climate types, which according to Köppen-Geiger's climate classification are BSh, BSk, and BWh for xerophilous thickets and natural grasslands, and Cfa, Cfb, Cwa, Cwb and Cwc for tropical dry, tropical deciduous, temperate coniferous and pine-oak forests and Aw and Am for tropical savannah (Peel et al 2007). BSh, BSk, and BWh correspond to arid to semiarid dry climates, where precipitation is less than the evapotranspiration potential, i.e., a hydric deficit, and annual temperatures lie around 18°C. Cfb, Cf, Cwa, Cwb, and Cwc indicate warm and humid climates, where the average temperature is 10°C in the warmest months, between 0 to 18°C in the coldest months and Aw y Am where precipitation of the driest month is below and above 100 MAP/25 respectively according to Peel et al (2007). As indicated by our data, the distribution of Dactylopius matches the distribution of their cacti hosts, but it is wider than previously reported (Fig 2).

Species associated with the genus Dactylopius

In this work, the recorded species of Dactylopius were found sharing hosts with ants (Hymenoptera: Formicidae), the lady beetles Chilocorus sp. and Hyperaspis sp. (Coleoptera: Coccinellidae), spiders (Araneae), the weaver worm Laetilia coccidivora (Lepidoptera: Pyralidae), the needle worm Symherobius sp. (Neuroptera: Hemerobidae) and undetermined beetles.

Discussion

Our research shows that the five species of Dactylopius have a continuous distribution broader than previously reported. The insects are localized in correspondence with their hosts in different ecosystems of the northern and central plateau and southeastern regions of Mexico (Fig 2), Dactylopius hosts are distributed within an altitude of 0 to 3900 m, which is higher than the Dactylopius distribution altitude which is in the range of 0 to 2845 m. Our fieldwork made it possible to recognize localities where one species of Dactylopius is present on one or different hosts or shares hosts with different species of Dactylopius, or where two, three and four species of insects coexist (Fig 2a). According to our data, the distribution area of the host species Opuntia, Nopalea and Cylindropuntia, is broader than previously recorded for Dactylopius (Fig 2b), what suggests that these insects can be found distributed over a larger area, in correspondence with their hosts. Opuntia ficus-indica was the most common and most widely distributed host.

Insects of the genus Dactylopius and their cacti hosts Opuntia, Nopalea, Cylindropuntia and Grusonia, are endemic to the American Continent (Britton & Rose 1963, Bravo-Hollis & Sánchez-Mejorada 1978, Brummitt & Powell 1992, Anderson 2001). The distribution of Dactylopiidae in this continent has been divided into Nearctic and Neotropical regions. Dactylopius opuntiae, D. coccus, D. ceylonicus, D. confusus, and D. tomentosus are considered Nearctic and Neotropical, whereas D. austrinus, D. confertus, D. salmianus and D. zimmermanni are considered Neotropical (Rodríguez & Niemeyer 2000, Portillo 2005).

Our study shows that in Mexico the five species of Dactylopius and their hosts are localized mainly in arid and semiarid climates, where they have diversified, i.e. they are present in different hosts and localities. This distribution corresponds to the xeric areas. Additionally, the five Dactylopius species identified and recorded in Mexico are also present in South America, i.e. taxa with Nearctic Andean affinities diversified in Mexico. Studies of diverse species present in Mexico indicated that when species are present in the xeric area, have diversified there and have affinities with South American taxa, their geographic distribution can been considered as Neotropical and Nearctic distribution pattern (Llorente-Bousquets et al 1996). Therefore, from previous reports together with our records presented here on the distribution of the genus Dactylopius in North America, specifically in Mexico, it can be said that the distribution of this genus comprises the Nearctic and Neotropical regions and a portion of the Mexican transition zone (Morrone & Llorente 2003, Morrone 2004, 2005, Portillo 2005).

The biogeographical region of Mexico is of special interest because of its geological, geographical and biotic complexity (Llorente-Bousquets et al 1996). In this area the characteristics of cultural importance and biotic diversity converge due to the genetic richness generated in an enormous variety of climates (Fig 2), in areas with irregular-surface topography where man has selected and promoted the variation of species, in this case O. ficus-indica (Reyes-Agüero et al 2005) and D. coccus (Portillo 2005). The main outcome of this is the presence of a great richness of hosts species, of diverse geographical affinities and ages, that have been proposed to include lineages evolved in situ during the Cenozoic (Llorente-Bousquets et al 1996, Anderson 2001) and the existence of many ecosystems with mixtures of flora and fauna of different origins, whose evolution in this area has allowed them to differentiate from each other (Fig 2). Llorente-Bousquets et al (1996) propose that in the case of insects all this has configured a hybrid biota comprising principally boreal and austral native lineages.

On the other hand, Southwood (1973) suggested that in Hemiptera the abundance of insects associated with plants was proportional to plant recent abundance. According to our observations in the collecting sampling area, this is the case of Dactylopius which is associated with their cacti hosts in several localities, for instance in Jalisco, San Luis Potosí and Mexico City (Fig 2).

The distribution of Dactylopius in Mexico is continuous, maintains correspondence with the host plants and is broader than previously known. Within the studied area, localized between 98° to 104° northern latitude and 18° to 23° eastern longitude, comprising the states of Aguascalientes, Mexico City, Guanajuato, Hidalgo, Jalisco, Estado de México, Michoacán, Morelos, Oaxaca, Puebla, Querétaro, San Luis Potosí, Tlaxcala, Veracruz and Zacatecas, and extending mainly from the northern and central plateau to the southeast of Mexico. These zones are characterized by xerophilous thickets, and temperate coniferous and pine-oak forests, with a wide variety of soils (arenosol, vertisol, calcisol, xerosol, regosol, leptosol and feozem), climates ranging from arid to semiarid dry to warm and humid, within the altitude range of 0 to 2845 m. This work provides new georeferenced records about the five species of Dactylopius and their hosts not reported previously, further describing the distribution areas of the insects.

The presence of species of Dactylopius with different morphological characteristics cohabiting in the same locality on different portions of the same host was reported here for the first time. Insects with morphological characteristics of D. confusus and D. opuntiae blended with characteristics of D. salmianus, named here as D. confusus biotype 1 and D. opuntiae biotype 1, respectively, were identified in this work for the first time. This suggests the presence of new species not yet studied or the possibility of interspecific hybridization between the identified species. It could be also the product of polymorphism or polyphenism within the Dactylopius species. Polymorphism implies having multiple alleles of a gene within a population, usually expressing different phenotypes, while polyphenism implies the existence of a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions (Southwood 1973). However, the presence of these characteristics should be the object of further studies.

Acknowledgments

We are grateful to Dr. Léia Scheinvar (IB-UNAM) for her support with identification of the species of cactaceae and her valuable suggestions and comments to carry out this work. We also thank Dr. J. Jesús A. Fuentes-Junco (CIEco-UNAM) for his support to produce the maps. We appreciate financial support from CONACYT (grant 2002-CO1-0544) and PAPIIT, UNAM (project IN219608). C.K. Chávez-Moreno acknowledges Programa de Posgrado en Ciencias Biológicas-UNAM and the scholarships granted by CONACYT and DGEP-UNAM. Thanks are also given to the reviewers for their useful comments.

Received 09 October 2009 and accepted 21 June 2010

Edited by Angelo Pallini - UFV

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Publication Dates

• Publication in this collection
  14 Mar 2011
• Date of issue
  Feb 2011

History

• Received
  09 Oct 2009
• Accepted
  21 June 2010