White et al.: L. dorsalis (F.): Candidate biological control agent of the sugarcane borer 261 LEPTOTRACHELUS DORSALIS (COLEOPTERA: CARABIDAE): A CANDIDATE BIOLOGICAL CONTROL AGENT OF THE SUGARCANE BORER IN LOUISIANA W. H. WHITE1, T. L. ERWIN2 AND B. J. VIATOR3 1USDA, ARS Sugarcane Research Unit, 5883 USDA Road, Houma, LA 70360 2Hyper-diversity Group, Department of Entomology, MRC-187, National Museum of Natural History, Smithsonian Institution, Washington, P.O. Box 37012, DC 20013-7012 3Calvin Viator, Ph.D. and Associates, LLC, Labadieville, LA 70372 ABSTRACT Following registration and the wide-spread use of insect growth regulators (e.g. tebufeno- zide and novaluron) for control of sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), in Louisiana, larvae of the ground beetle, Leptotrachelus dorsalis (F.) (Cole- optera: Carabidae, have become more abundant in sugarcane fields. In a survey of the 18 parishes growing sugarcane in Louisiana, L. dorsalis was found in 8 (44%) of those parishes. The highest number of beetles occurred in a field where 10% of the stalks sampled were harboring larvae. Laboratory studies revealed a developmental period of 37 d from egg de- position to adult emergence. Three larval instars were identified with the first 2 lasting 5 d, and the third instar requiring 17 d. In a voracity study, larvae were found to consume on average 798 first instar sugarcane borer larvae per ground beetle larva. Seventy-five percent of those sugarcane borer larvae were consumed by third instar beetle larvae. Field surveys suggest that adults migrate into sugarcane fields when above-ground internodes form on the sugarcane stalk (June) and increase in numbers thereafter. All 3 instars of the beetle can be found in sugarcane fields during the critical period of Jun to Sep when sugarcane is subject to economic injury by sugarcane borer. If L. dorsalis are abundant in fields during establish- ment of second generation sugarcane borer, our data suggests they are capable of holding the average season-long damage at or below 10% bored internodes. This level of damage is the recognized economic injury level for sugarcane borer in Louisiana. Our study indicates that L. dorsalis is a good candidate for continued research on augmentative releases as a strategy to increase beetle numbers in sugarcane fields early in the growing season and thus enhance their efficacy as predators of sugarcane borer larvae. Key Words: Diatraea saccharalis, fire ants, habitat manipulation, augmentative release, predators RESUMEN Con el registro y amplio uso de los reguladores de crecimiento de insectos (por ejemplo tu- bufenozida y novalurón) para el control del barrenador de la caña, Diatraea saccharalis (F.) (Lepidoptera: Cambidae) en Louisiana, las larvas del escarabajo de tierra, Leptotrachelus dorsalis (F.) (Coleoptera: Carabidae), han aparecido recientemente en los campos de caña de azúcar. En un sondeo de los 18 municipios que siembran caña de azucar en Louisiana, se encontró L. dorsalis en 8 (44%) de los municipios. Se encontró el mayor número de escara- bajos en un campo donde habian larvas en el 10% de los tallos muestrados. Los estudios de laboratorio revelaron un período de desarrollo de 37 dias desde la deposición de los huevos hasta la emergencia de los adultos. Se identificaron tres estadios larvales; cada uno de los 2 primeros estadios duró 5 días, y el tercer estadio duró 17 días. En el estudio sobre vora- cidad, las larvas depredadoras consumieron un promedio de 798 larvas del primer estadio del barrenador de la caña de azúcar por cada larva del escarabajo de tierra. Setenta y cinco por ciento de estas 798 larvas del barrenador de la caña de azúcar fueron consumidas por el tercer estadio de las larvas del escarabajo de tierra. Los estudios de campo sugieren que los adultos migran hacia los campos de caña de azúcar cuando se forman los entrenudos de los tallos de caña de azúcar encima la superficie de la tierra (en junio) y luego aumentan en número. Se puede encontrar los tres estadios de larvas del escarabajo en los campos de caña de azúcar durante el período crítico de junio hasta septiembre cuando la caña de azúcar está sujeta a pérdidas económicas hechas por el barrenador de caña de azúcar. Si L. dorsalis es abundante en los campos durante el establecimiento de la segunda generación del barrena- dor de caña de azúcar, nuestros datos indican que son capaces de mantener el promedio del daño hecho por el barrenador por toda la temporada igual o menos de 10% de los entrenudos perforados. Este nivel de daño es reconocido como el umbral de daño económico hecho por 262 Florida Entomologist 95(2) June 2012 el barrenador de la caña en Louisiana. Nuestro estudio indica que L. dorsalis es un buen candidato para continuar investigaciones sobre el incremento de liberaciones como un estra- tegia para aumentar la cantidad de escarabajos en los campos de caña de azúcar de manera temprana en la temporada del cultivo, asi mejorando su eficacia como depredadores de las larvas del barrenador de la caña. Beneficial arthropods provide a significant borer larvae. Fuller & Reagan (1988) reported proportion of the season-long control of the sug- that the dominant canopy-dwelling carabid in an arcane borer, Diatraea saccharalis (F.) (Lepidop- experiment comparing sugarcane borer predation tera: Crambidae), in Louisiana with the bulk of in sweet sorghum and sugarcane was L. dorsalis. this control (90%) resulting from predation by the Again, we presume these authors were reporting red imported fire ant,Solenopsis invicta (Buren) L. dorsalis adults. They reported higher L. dorsa- (Hymenoptera: Formicidae) (Hensley 1971). The lis numbers where fire ants were excluded with balance of biological control comes from an ar- a soil application of the persistent insecticide ray of species representing numerous predatory chlordane. Insecticides were not used to control arthropod taxa (Negm & Hensley 1967). Sugar- sugarcane borer in their study thereby permit- cane borer larva parasitoids and egg parasites ting L. dorsalis the opportunity to become well are less abundant with only Lixophaga diatraeae established. (Townsend) (Diptera: Tachinidae), Alabagrus Specimens of L. dorsalis have been collected stigma (Brullé) (Hymenoptera: Braconidae), and from most states of the eastern US including Kan- Trichogramma sp. (Hymenoptera: Trichogram- sas and South Dakota and eastward including the matidae) presently established (White et al. Province of Ontario, Canada. Outside of the US 2004). In many agroecosystems, insecticides have specimens have been collected from Barbados, had a profound impact on the presence and abun- Cuba, and Hispaniola. (Smithsonian Institution dance of beneficial insects (Hensley et al. 1961). database of Western Hemisphere Carabidae). In This has certainly been the case for the Louisiana Barbados, L. dorsalis, was reported as a predator sugarcane industry where the use of insecticides of the sugarcane thrips, Fulmekiola serrata (Ko- began with the botanical compound ryania and bus) (Thysanoptera: Thripidae) (Peck 2009). the inorganic compound cryolite, advanced to the Knowledge of the immature stages of L. dorsa- organochlorines and then organophosphates, was lis is lacking. It was not until our laboratory suc- then followed by the pyrethroids, and currently cessfully reared a larva to the adult beetle that the the insect growth regulators (IGR) (Hensley 1971; identity of what was thought to be a new insect Rodriguez et al. 2001). The IGR tebufenozide, an in Louisiana sugarcane fields was determined ecdysone agonist causing precocious incomplete to be L. dorsalis. The objectives of this research molting in some lepidopterans (Retnakaran et were: 1) to determine the seasonal abundance al. 2001), was first labeled in Louisiana for sug- and distribution of L. dorsalis (adults and larvae) arcane borer control in 1997. Labeling tebufe- within the Louisiana sugarcane agroecosystem, nozide for sugarcane ushered in an era of green 2) to acquire information on the life stages of the chemistry for the Louisiana sugarcane agroeco- beetle, and 3) quantify predation during the criti- system apparently having a profound impact on cally important time of Jun through Sep when the the abundance of arthropod predators in the field sugarcane borer is considered an economic pest of (Hensley 1971). One species that we hypothesize sugarcane in Louisiana (Hensley 1971). has benefitted from this new chemistry is the ground beetle Leptotrachelus dorsalis (F.) (Co- MATERIALS AND METHODS leoptera: Carabidae). With a reduction in use of broad spectrum insecticides for sugarcane borer Adult Distribution and Abundance in Sugarcane Fields control, the larvae of this beetle are now able to exploit the sugarcane ecosystem and can be an From 3 to 25 Aug 2004 we conducted a state- important predator of larvae of the sugarcane wide survey for L. dorsalis in those parishes where borer. sugarcane is cultivated in Louisiana. One hundred The earliest reference of this ground beetle in fields from 18 parishes were surveyed. As the area Louisiana sugarcane was by Negm & Hensley in sugarcane cultivation varied in each parish, the (1969), but these authors do not indicate if the number of fields surveyed also varied; the num- specimens they reported were adults or larvae. ber surveyed per parish ranged from 1-13. Each We presume they were adults because the larval field was approximately 8 km distance from one stages of this species have not been described another. A random sample of 40 stalks were chosen (Erwin and White, in prep.). They did, however, from each field and searched for both adult and report that the L. dorsalis specimens were ob- immature L. dorsalis. Our search of a stalk did not served feeding on sugarcane borer eggs. No ref- include a search of tunnels within stalks. Labora- erence was made of them feeding on sugarcane tory observations suggests that large D. sacchara- White et al.: L. dorsalis (F.): Candidate biological control agent of the sugarcane borer 263 lis larvae, fourth and fifth instar, are too large for that are nearing release to sugarcane farmers for L.