Diatraea tabernella is recorded for the first time in the Cauca River Valley of Colombia. Even though there has been no information on the status of D. tabernella in Colombia for almost a century, its recent appearance creates concern about its potential economic importance by virtue of its abundance and distribution in the northern region of the Cauca River Valley. Descriptions of the pupae and the male genitalia of D. saccharalis, D. indigenella, and D. tabernella are given, together with a key to aid in the identification of Diatraea species in the region. Also information and perspectives on biological control of D. tabernella are presented.
Diatraea spp. borers are considered among the most damaging of sugarcane (Saccharum spp. L; Poales: Poaceae) pests in the Americas (White et al. 2001). Under the conditions of the Cauca River Valley of Colombia, the economic losses caused by Diatraea spp. are estimated at 143 kg of sucrose per each percent of bored internodes (Gómez et al. 2009). In Colombia there are 6 species of Diatraea, e.g., D. lineolata (Walker), D. tabernella (Dyar), D. saccharalis (F), D. indigenella (Dyar & Heinrich), D. rosa (Heinrich) and D. busckella (Dyar & Heinrich) (Bleszynski 1969; Gaviria 1990). However, in the Cauca River Valley, the main sugarcane producing area of Colombia, D. saccharalis and D. indigenella axe the only Diatraea borers that attack sugarcane (Gómez & Lastra 1995; Cadena 2008).
In 2012, growers of the northern area of the Cauca River Valley reported infestations of Diatraea larvae that did not match the morphological characteristics of D. saccharalis and D. indigenella. In Oct 2012 we visited an infested field on a farm near the municipality of Cartago (N 4° 43′ 33.416″ W 75° 57′ 53.384″) and observed the attack on a 2 month-old crop with a level of ‘dead hearts’ of < 20% infested shoots. Observations were made on larvae, pupae, and adults in the laboratory of the Colombian Sugarcane Research Center (CENICAÑA). The species was identified as Diatraea tabernella (Dyar), and voucher specimens were deposited in the Entomological Museum of the Universidad del Valle, Cali, Colombia, (females, 24325; males, 24326 MUSENUV).
Some effort has been made to use larval characteristics to distinguish among Diatraea species. For instance, Linares & Bastidas (1996) suggested the use of the dorsal meso-thoracic shield as a way to distinguish among the species of Diatraea in Venezuela. However, the same authors mentioned that this character is not reliable when larvae are collected from the field. Additionally, Riley & Solis (2005) highlighted the great difficulties of separating species of Diatraea using immatures. The pupal stage provides more elements to distinguish between some species. For instance, the cephalic horns in the pupa of D. saccharalis are pointed at the end (ridge-like) (Fig. 1A), in D. indigenella they are dull and rounded at the end (Fig. 1B), whereas in D. tabernella they are rounded as in D. indigenella, but shorter (Fig. 1C). In the adult stage, the differences are more pronounced and the hind tibia of the males of D. tabernella each have a large tuft of blackish hairs that are absent in D. saccharalis, D. indigenella, and all other species of Diatraea reported in Colombia (Bleszynski 1969). Following descriptions suggested by Bleszynski (1969), the 3 species found in the Cauca River Valley can be distinguished using the male genitalia and more specifically the lateral tegumenal lobes. In D. saccharalis the lateral tegumenal lobes are large and broadly rounded (Fig. 2A), in D. indigenella, these are proportionately narrow and tapering (Fig. 2B), whereas in D. tabernella these are somewhat similar to those of D. saccharalis, but much narrower (Fig. 2C).
THE FOLLOWING KEY BASED ON THE MALE GENITALIA MAY BE USED FOR SPECIES RECORDED THUS FAR IN THE CAUCA RIVER VALLEY OF COLOMBIA:
1. Lateral tegumenal lobes narrow and tapering (Fig. 2B) D. indigenella
—. Lateral tegumenal lobes broad and rounded (Fig. 2A, C) 2
2. Lateral tegumenal lobes broadly rounded (Fig. 2A) D. saccharalis
—. Lateral tegumenal lobes narrow, longer than broad (Fig. 2C) D. tabernella
Diatraea tabernella has been reported in Panamá, Nicaragua, Costa Rica, and Honduras (Box 1931; Bleszynski 1969). Although it has been recorded in Colombia since 1914 (Box 1931), this is the first time it has been observed in the Cauca River Valley attacking sugarcane. According to Box (1931), the species was first reported in Colombia along the Magdalena River; however, specifics concerning the locality were not provided. Also, D. tabernella was noted near the municipality of Condoto, Department of Chocó, not far from the locality where D. tabernella was collected in Cartago. Later, Box (1959) mentioned that D. tabernella was a major pest in Panama, a dominant species in Costa Rica, but in Colombia its status was thus far unknown. According to Badilla (2002), D. tabernella is the most important and widely distributed pest of sugarcane in Costa Rica, where D. saccharalis and D. guatemalella (Schaus) are also present (Badilla & Solís 1984). In Panamá, Bennett (1971) suggested that D. tabernella was economically more important than D. saccharalis. Rodriguez et al. (2004) mentioned that in some areas of Panamá where D. tabernella predominates, the damage can exceed 2.5% of bored internodes, the established nominal damage threshold.
PERCENT DISTRIBUTION AND FREQUENCY OF ENCOUNTER OF DIATRAEA SPECIES AND PARASITISM BY LYDELLA MINENSE ON LARVAE COLLECTED FROM 25 SUGARCANE FARMS IN THE NORTHERN CAUCA RIVER VALLEY OF COLOMBIA (N = 81 LARVAE).
Additional surveys for larvae from the northern area of the Cauca River Valley resulting in collecting larvae from 25 different farms located between the municipalities of Viterbo (Department of Caldas) and La Unión (Department of Valle del Cauca). Approximately 75% of the larvae collected were D. tabernella, and this species was present in more than 75% of the sites visited (Table 1). Additionally, the percent parasitism by Lydella minense (Townsend) (Diptera: Tachinidae) was smaller than that observed in D. saccharalis (Table 1), indicating the need to consider various pest management approaches for this new pest. In Costa Rica, the introduction of Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) has been used effectively against D. tabernella (Badilla 2002). However, in Panamá the level of parasitism following massive releases of C. flavipes has not resulted in the reduction of the damage by D. tabernella, and the percent parasitism has not been greater than that of Billaea claripalpis (Wulp) (Diptera: Tachinidae) (Rodríguez et al. 2004). Although the potential economic importance of D. tabernella remains to be determined in the Cauca River Valley of Colombia, its detection in that region generates questions as to the relative economic importance in comparison to the other 2 species already present. A coordinated effort among farmers and CENICAÑA to monitor the distribution of D. tabernella in the whole Cauca River Valley should constitute an important first step in a series of studies on this pest and its management. Additionally, it is noteworthy that the taxonomic status of the Diatraea species has not been adequately updated, and it warrants further study as the sugarcane crop is expanding in Colombia in projects not only related to sucrose, but to energy, and ethanol production as well.