EFFECT OF MICROMITE® ON THE EGG PARASITOIDS CERATOGRAMMA ETIENNEI (HYMENOPTERA: TRICHOGRAMMATIDAE) AND QUADRASTICHUS HAITIENSIS (HYMENOPTERA: EULOPHIDAE)

Abstract

The Diaprepes root weevil, Diaprepes abbreviatus (L.), was first detected near Apopka, Florida in 1964 (Woodruff 1964). Since then, it has spread throughout the citrus growing areas of the state causing growers millions of dollars in losses each year. In south Florida, D. abbreviatus is also a problem in root crops and ornamental plants (Peina & Amalin 2000). One of the components of the pest management program for this weevil is the use of Micromite? (diflubenzuron), a chitinase inhibitor that sterilizes the egg by interrupting the formation and deposition of chitin in developing embryos. Early studies indicated that diflubenzuron significantly reduces the reproductive potential of D. abbreviatus when applied to citrus foliage (Schroeder et al. 1976; Lovestrand & Beavers 1980; Schroeder et al. 1980). Later, Schroeder (1996) reported that residues of diflubenzuron significantly affected the reproductive potential of D. abbreviatus for more than one month after application to citrus foliage. Micromite has been described as a foundation product for reducing citrus root weevil populations, in part due to its compatibility with root weevil natural enemies (Anonymous 1996). However, there are no reports on the effect of micromite on egg parasitoids that have been imported and established for biological control of D. abbreviatus (Hall et al. 2001; Peina et al. 2000; Pena et al. 2003). A study was initiated to evaluate the impact of Micromite on Ceratogramma etiennei Delvare and Quadrastichus haitiensis (Gahan), two egg parasitoids of Diaprepes root weevil. Green buttonwood (Conocarpus erectus L.) seedlings were grown from cuttings in 3.7-liter pots. Adult D. abbreviatus were collected from an insecticide-free ornamental orchard in Homestead, Florida. A Guadeloupe strain of C. etiennei was obtained from J. Etienne, Institut National de la Recherche Agronomique (INRA). The culture was maintained at the Tropical Research and Education Center (TREC) insectary, Homestead, Florida. Insect cultures were maintained at 26.5 ? 1.0?C, 12:12 L:D and approximately 78% RH, on eggs of D. abbreviatus laid on strips of wax paper using the methodology of Etiennei et. al (1990). Quadrastichus haitiensis originally from Puerto Rico was obtained from Ru Nguyen, Division of Plant Industry, Gainesville, Florida, and maintained as above. The effect of Micromite ingestion by the adult Diaprepes root weevil plus absorption of residues from leaves into eggs was evaluated in experiment 1. Three green buttonwood seedlings planted separately on 3.7-liter pots were sprayed with Micromite to run-off using the simulated field rate (0.485 g/l liter of water). Another three seedlings were sprayed with water as control checks. All the seedlings were enclosed separately in screen cages (240 cm x 120 cm x 120 cm). One hundred adults of D. abbreviatus were introduced inside each cage for oviposition. After 3 days, 20 egg masses on leaves still attached to branches were collected from each seedling, arranged as bouquets in flasks of water and placed in Plexiglass cages (30 cm x 30 cm x 30 cm) separately. Six cages, 3 treated and 3 untreated, were prepared for each parasitoid species. One hundred 2to 3-dold C. etiennei and Q. haitiensis adults were introduced into each Plexiglass cage. Bouquets were removed after 3 days and portions of the leaves with individual egg masses laid between two leaf surfaces (covered with two leaf layers intact) were placed in culture tubes (12 mm x 75 mm). After 7 d, egg masses were exposed by removing one leaf surface and parasitized eggs counted. Parasitized eggs were recognized by the characteristic golden egg chorion for C. etiennei and silver transparent egg chorion for Q. haitiensis (Penia et al. 2000). Effects of ingestion of micromite by adult D. abbreviatus alone were evaluated in a separate experiment. Ten adult D. abbreviatus females were exposed to Micromite -treated seedlings and to untreated foliage for 3 days as described above. The adults were allowed to oviposit on to double strips of wax paper inside Plexiglass cages (30 cm x 30 cm x 30 cm). After 2 d, paper strips containing 20 egg masses were collected from each cage and each egg mass was placed separately inside culture tubes (12 mm x 75 mm). One 2-d-old mated female wasp was introduced into each tube (20 tubes per treatment for each parasitoid species). After 7 d, eggs were examined as described above. In a third test, 10 untreated female weevils were allowed to oviposit on wax paper for 2 days. Wax papers containing approximately 20 egg