Leafminer and Leafminer Parasitoid Incidence on Selected Weeds in South Florida

Abstract

The leafininer Liriomyza trifolii Burgess (Diptera: Agromyzidae) is a serious pest of celery in Florida. L. sativae (Blanchard), a morphologically similar species which has many hosts in common with L. trifolii, was once considered a pest of Florida celery but no longer affects this crop (Leibee 1984). Both species are attacked by the same parasitoid complex (Johnson & Hara 1987). L. sativae and L. trifolii occur on many weed hosts in south Florida (Stegmaier 1981); two of those named as hosts of the former, and not of the latter, were castor bean, Ricinus communis L., and sicklepod, Cassia tora L., (Stegmaier 1981). Both occur in the Everglades agricultural area (EAA) of south Florida where the majority of Florida's celery is grown. These weeds, serving as hosts of L. sativae, could act as potential reservoirs for parasitoids which could possibly enhance the biological control of L. tifolii in celery. Dayflower, Commelina diffusa Burm., a weed common in the EAA, was reported as containing significantly more chalcidoid leafminer parasitoids than other weeds sampled (Genung 1981). The only leafminer known to attack dayflower, L. commelinae (Frost), may have parasitoids in common with L. trifolii. In February of 1984 a study was initiated at Everglades Research and Education Center (EREC), Belle Glade, to determine the leafminer species occurring on castor bean, sicklepod, and dayflower and the parasitoids attacking the leafminers on these host plants. The weeds were planted at EREC at two sites, each consisting of three plots per weed species. Plots were 3 m by 3 m and consisted of five rows. Castor bean and sicklepod were thinned to 10 plants per row and dayflower, a prostrate plant grown from transplants, was allowed to cover the entire plot. Sampling was conducted once per week for eight weeks from late May until the third week in July. Three leaves of castor bean and three trifoliates of sicklepod were excised from 10 randomly selected plants per plot. Dayflower was sampled by collecting all foliage from 10 randomly selected 18 cm x 18 cm areas within a plot. Foliage was taken to the laboratory where it was held on wire screen in closed 4-liter cardboard containers. Adult larval parasitoids and leafminer puparia were collected after the foliage had dried. Puparia were held in glass vials until all adult leafminers and larval-pupal parasitoids had emerged. Representative specimens of parasitoid species were identified by E. E. Grissell, A. S. Menke, and M. E. Schauff, Systematic Entomology Laboratory, USDA, Washington, D.C., R. A. Wharton, Department of Entomology, Texas A&M University, College Station, Texas, and C. M. Yoshimoto, Canadian Forestry Service, Department of Environment, Ottawa, Ontario, Canada. Adult leafminer identifications were made by the senior author. No leafminers or parasitoids were reared from sicklepod foliage. Only two active (= those containing living leafminer larvae) mines were found on this weed and neither larva survived to pupation. Four active mines were collected from dayflower and from these were reared an adult L. commelinae and a cynipid pupal parasitoid.