|Wilson, L -|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2012
Publication Date: April 20, 2012
Citation: White, W.H., Wilson, L.T. 2012. Feasibility of using an alternative larval host and host plants to establish Cotesia flavipes (Hymenoptera: Braconidae) in the temperate Louisiana sugarcane ecosystem. Environmental Entomology. 41(2):275-281. Interpretive Summary: Caterpillars of the sugarcane borer moth are the most important insect pest of sugarcane in Louisiana. In the temperate climate that sugarcane is grown in Louisiana it is difficult for biological control organisms to consistently obtain a density sufficient to impact sugarcane borer populations before economic injury occurs. Attempts to introduce exotic beneficial insects to assist native beneficial insects have generally been met with failure. Cold temperatures and lack of synchrony among the pest, the sugarcane crop, and effective overwintering sites is generally thought responsible for this failure. We investigated the feasibility of using alternative hosts and hosts plants to overcome these problems. Evaluations in the laboratory and greenhouse suggested that weeds around sugarcane fields could be used as overwintering habitat and another species of borer associated with some of these could serve as an alternative host thereby overcoming some of the ecological barriers for exotic beneficials. However, when these systems were evaluated in the field, they proved to be inadequate. Mass rearing and releases of beneficials seems the only workable solution, but this approach would not be cost effective and therefore not practical.
Technical Abstract: Although successfully introduced and established in sugarcane fields around the world, attempts to establish Cotesia flavipes (Cameron) (Hymenoptera: Bracondiae) in the temperate sugarcane fields of Louisiana as a parasitoid of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae) have been unsuccessful. A series of experiments were conducted investigating the feasibility of using alternative larval hosts and host plants to overcome those ecological barriers preventing its establishment. Using cages we evaluated C. flavipes ability to search for D. saccharalis in young cane without above-ground internodes. Parasitism by C. flavipes at this stage of plant growth was 30%. Apparently sugarcane borer larvae move about the developing shoots redistributing themselves thus becoming vulnerable to parasitism by C. flavipes; however, restricting a large number of parasitoids within the cages may have inflated this value. The use of Diatraea evenescens Dyar (Lepidoptera: Crambidae) as an alternative host for C. flavipes was additionally investigated. C. flavipes was reared for five generations without any indication of diminishing fitness as measured by days to parasite pupation and average clutch weight. However, there was a significant reduction in percent parasitism, cocoon weight, and percent emergence when C. flavipes parasitized D. evenescens as compared to D. saccharalis. The gross reproductive rate (R0) for C. flavipes parasitizing D. evenescens was 25% less than when D. saccharalis was the host. Greenhouse studies suggested that, in general, there was little difference in parasitism of sugarcane borer on johnsongrass, Sorghum halepense (L.), and vaseygrass, Paspalum urville Steud. However, when these plants were established in refuge plots near a sugarcane field, we found that johnsongrass, vaseygrass, and two energy canes to be poor hosts for D. saccharalis as after three years of infesting and monitoring we only recovered one parasitized D. saccharalis larvae within the johnsongrass refuge. Although D. evenescens readily established in vaseygrass, these larvae were also found inaccessible to C. flavipes. We concluded from these studies that establishing C. flavipes in the southern Louisiana sugarcane agroecosystem remains an unlikely prospect at this time, and although augmentative releases are justified the cost of this practice is prohibitive.