The genus Diabrotica has over 400 described species [1], the majority of them neotropical, but only 7 species, plus six subspecies, are considered agricultural pests in the Americas [2]. Of these, only three species are considered agricultural pests in South America: D. speciosa (Germar) with subspecies speciosa and vigens, D. balteata (LeConte), and D. viridula (F.) (Figure 1). The genus Diabrotica is divided into three species groups: virgifera, fucata, and signifera [3,4]. However, studies on South American virgifera group species suggest that these groups are not as well defined as previously thought [5,6]. D. speciosa and D. balteata are in the fucata group, which is the group with the largest number of species. The species in this group that have been studied are polyphagous both as adults and during the larval stage. Another characteristic of the North American pest Diabrotica of the fucata species group is that they overwinter as adults and lack resistant stages to deal with harsh climatic conditions [2]. D. viridula is in the virgifera group, the same clade of the Northern, Western, and Mexican corn rootworms (Diabrotica barberi, Diabrotica virgifera virgifera, and Diabrotica virgifera zeae, respectively). The larvae of the North American species in the virgifera group feed exclusively on Poaceae [7], although the host range has been observed or tested for only a few of the species in the group [8]. The North American pest species in the virgifera species group are univoltine, or sometimes semivoltine, and possess diapausing eggs that allow them to overwinter in temperate climates or survive dry seasons in the subtropics [9,10], both situations during which the adult cannot find sustenance or survive the extreme conditions.

D. speciosa is distributed throughout South America, from agricultural patches in the temperate Patagonian steppes to the tropics, with the exception of Chile, and up to altitudes of over 2500 m above sea level [2,11] (Figure 2). It is the best studied Diabrotica species in South America due to its impact on many crops. The adult has over 132 recorded host species, in 24 different plant families [11, and literature therein]. Larval hosts are not as well known, but D. speciosa has at least five confirmed larval hosts: maize (Zea mays L.), wheat (Triticum spp.), Johnsongrass (Sorghum halepense Persoon), peanut (Arachis hypogaea L.), and potato (Solanum tuberosum L.). Another four plant species hosted full development in the laboratory [11,12,13,14,15]. However, the fact that larvae can develop on plant species in four families of three different orders suggests that there could be many more larval hosts that simply have not been discovered because of the hypogeous habit of the larva.

D. speciosa is documented in most crops in South America, but is considered mainly a horticultural pest as an adult, and a pest of potato, maize, and peanuts as larva [11,13,16]. Yet these generalizations are not without exceptions. In Brazil, this species is considered a pest of maize as a larva, and a minor pest as an adult as well [17,18]. It is also regarded as an important pest of potato during both the adult and larval stages, although this depends heavily on the cultivar [19]. In addition, the adult is also regarded as an important pest of seedlings and young plants of some extensive crops, such as soybeans, beans (Phaseolus vulgaris), cotton, sunflower, maize, tobacco, wheat, and canola [20,21,22], and, curiously, of table grapes [23] (Table 1).

 

D. balteata is found from subtropical North America through Central America and Caribbean islands including Cuba, Hispaniola, and Puerto Rico, to South America, although its distribution in South America is limited to Venezuela and Colombia [2,24], where it can occur at altitudes ranging from 0 to 2000 m [25]. However, there is insufficient data to infer species distribution patterns in either country. The adult of D. balteata also has an extremely wide range of host plants, as it has been documented on over 140 plant species [26]. There is a more conservative estimate of 50 species in 23 families, with a preference for plants in the Cucurbitaceae, Rosaceae, Fabaceae, and Brassicaceae [27]. The D. balteata adult is considered a pest on squash (Cucurbita spp., Cucurbitaceae), several bean species (P. vulgaris, Glycine max, Mucuna pruriens, and Vigna unguiculata, Fabaceae), lettuce (Lactuca sativa, Asteraceae), sugar cane (Saccharum officinarum, Poaceae), and potato [28]. Adults are also implicated in the transmission of the tomato brown rugose fruit virus (Tobamovirus, ToBRFV) to P. vulgaris [29], and other viruses of P. vulgaris and calapo (Calopogonium mucunoides Desv.) [30,31]. Larval damage is reported only from Colombia, where this species is known to attack beans, but as considered a minor problem [32], maize, on which it can be locally problematic [33,34], and peanuts, on which it is considered among the 10–12 worst pests in Colombia [35] (Table 1). It is considered a pest of sweetpotatoes in North America. The fact that these hosts are also from three families in three orders suggests that there could be many more larval hosts as well. In addition, phylogenetic studies indicate D. speciosa and D. balteata are sister clades [37].

D. viridula is distributed from Mexico to northern Argentina, and apparently absent in Uruguay and Chile (Figure 3). Like D. balteata, its distribution is primarily tropical and subtropical. The D. viridula adult is considered a minor pest of beans in Peru [39], while the larva is considered locally important on maize in Central America and Peru [40]. In greenhouse tests, both the larvae and the adults of this species were able to transmit maize chlorotic mottle virus (MCMV) to maize, and they are assumed to be one of its vectors in the field [41]. D. viridula is also assumed to be an important, albeit new, pest of maize roots in Argentina, Paraguay, and Brazil [11,42], but its damage cannot be differentiated from that of D. speciosa. Studies to clarify what proportion of the damage is owed to each species (e.g., collections of larvae directly in the field) have not been done. The larva has been found feeding on maize roots only, and in the laboratory, it developed successfully on wheat as well, but not on any of the species tested from outside the Poaceae, suggesting it is stenophagous during the larval stage [2,43]. As an adult it is polyphagous, albeit reduced to fewer hosts than D. speciosa and D. balteata, as it has been recorded only on 21 plant species in the Poacae, Cucurbitaceae, and Asteraceae [11] (Table 1). Yet, similarities with the North American species in the virgifera group end here, as D. viridula eggs do not diapause. 

Evidence indicates that the three South American pest Diabrotica overwinter as adults, are multivoltine, and do not have diapausing eggs. A reproductive diapause has been observed for D. speciosa, at least for the populations from the temperate and higher subtropical areas, but the fact that it could be overridden by manipulating temperature and light hours suggests it may not exist in the lower latitudes [44].

3. Control of South American Diabrotica