Direction of Dispersion of Cochineal (Dactylopius Coccus Costa) within the Americas

Article excerpt

Introduction

Cochineal (Dactylopius coccus Costa; Hemiptera: Dactylopidae) is a sessile parasitic insect living on cladodes of prickly pear (Opuntia ficus-indica Miller; Cactaceae) and has been used as a source of natural dyes in Mesomerica and the Andean area since pre-Columbian times. The insects were used as tribute during the Aztec Empire and the Spanish domination of America. The dry insect was the second export product of the Mexican viceroyalty after silver. In an attempt to break the Spanish monopoly, the culture of the insects and their host plants expanded around the world under the guidance of the British government (Mann 1969). As a result of those early introductions which were not backed by thorough scientific knowledge, several species of Opuntia became serious weed problems in Australia and South Africa. They were successfully controlled only in the 1930s after the introduction of their natural enemies including some species of the genus Dactylopius. Due to their commercial value and their use as agents of biological control, some species of the insect genus have expanded their original distribution ranges and are presently found in places as distant as the Canary Islands, Australia, South Africa, Botswana, Nepal, India and Sri Lanka.

Phylogenetic analysis provide the opportunity to evaluate with independent evidences different historical hypotheses about the origin and distribution of animals and plants (Brown & Lomolino 1998). The family Dactylopiidae has only one genus, Dactylopius, with nine species, all of them originated in America and specialized in Cactaceae of the genus Opuntia. D. tomentosus, D. confusus and D. opuntiae inhabit North America (New Mexico, Arizona, Texas and Mexico), while D, ceylonicus, D. austrinus, D. confertus, D. salmianus and D. zimmermanni inhabit South America (Andean zones of northeast Argentina, Bolivia and Paraguay). The remaining species, D. coccus, has a disjoint distribution and is present in both hemispheres, in Mexico and Peru (FIGURE 1). The origin of D. coccus is controversial. The earliest evidence of use of the insect as a source of dye was found in textiles from Paracas, Peru (Fester 1943; Yacovleff & Muelle 1934; Saltzman 1992), whereas evidence of cultivation and systematic exploitation of the insect were found in Tolteca settlements in Mexico (Pelham 1963; Brana 1964). Trading and coastal shipping between the Pacific Coast of the Andean area and Mesoamerica has occurred since 2200 BC and to southern Mexico since 1450 BC (Wolters 1999). Hence, it is likely that the presence of D. coccus both in Mexico and Peru is a consequence of introductions made with commercial purposes in pre-Columbian times. The aim of this study was to identify the hemisphere where the centre of origin of D. coccus is located, based on a phylogenetic reconstruction of the genus Dactylopius. The results of this first phylogenetic hypothesis could establish the direction (north-south or south-north) of the introduction of the insect and provide additional evidence of trading between pre-Columbian peoples.

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Methods

A data matrix containing 51 morphological, ecological and chromosomal characters of adult females of the nine species of the genus (TABLES 1 & 2) was constructed making use of published information. Cladistic analysis was performed using the PAUP 3.1 program (Swofford 1993). The dataset was run using multiple parsimony and multistate characters were treated as unordered (changes of states 1-2 or 2-1 have the same probability to occur) and did not receive additional weight. Unknown characters were treated as lost. Characters were polarized as to the plesiomorphic (0 = primitive) or apomorphic (1, 2, etc = derived) states, based on the methodology of outgroup comparisons (Maddison et al. 1984). Briefly, the method consists in the selection of an external group, usually the sister group (the taxon genealogically closest to the ingroup), and the comparison of character states between the outgroup and the ingroup, in order to decide which characters are plesiomorphic or apomorphic. …