An Assessment of Steinernema rarum as a Biocontrol Agent in Sugarcane with Focus on Sphenophorus levis, Host-Finding Ability, Compatibility with Vinasse and Field Efficacy

In Brazil, countless insect species attack and damage sugarcane (Saccharum officinarum L.), which is an extremely important crop since it is planted on more than 10 million hectares. Among these insects, the sugarcane billbug, Sphenophorus levis (Coleoptera: Curculionidae), is of great importance as the larvae open tunnels in the rhizome of the plant, causing high damage and losses. This insect is attracted mainly to vinasse, which is the liquid fraction generated from the alcohol production and discarded onto the sugarcane fields for fertigation. Toward a novel control method for S. levis, the native entomopathogenic nematode Steinernema rarum (Pam 25) was compared with S. carpocapsae (IL 1) and Heterorhabditis bacteriophora (HBEN01) in respect to their ability to search for larvae of two insect hosts (Galleria mellonella and S. levis) within the cane rhizome. The selected nematode S. rarum was also assessed for rate effects, its survival in vinasse and field efficacy to control sugarcane pests S. levis, Hyponeuma taltula (Lepidoptera, Erebidae) and Leucothyreus alvarengai (Coleoptera: Melolonthidae). Steinernema rarum exhibited superior virulence to G. mellonella and S. levis larvae inserted into the cane rhizomes (75–78% mortality) compared to S. carpocapsae (30–53%) and H. bacteriophora (18–28%). Vinasse affected S. rarum when infective juveniles were suspended in the liquid compost for more than 6 h but did not affect the nematode when kept on the straw and soil treated with the compost. Steinernema rarum tested at 1–3 × 108 infective juveniles/ha on the sugarcane field caused 74.1, 56.3 and 50.6% control of S. levis, L. alvarengai and H. taltula, respectively.