Proc. Fla. State Hort. Soc. 107:90-92. 1994. SUPPRESSION OF PACHNAEUS LITUS AND DIAPREPES ABBREVIATUS (COLEOPTERA: CURCULIONIDAE) ADULT EMERGENCE WITH STEINERNEMA CARPOCAPSAE (RHABDITIDA: STEINERNEMATIDAE) SOIL DRENCHES IN FIELD EVALUATIONS R. C. Bullock mopathogens conducted with caged D. abbreviatus larvae, na University of Florida, IFAS tive 5. carpocapsae was found to dominate infected hosts. S. Agricultural Research and Education Center carpocapsae was present at 16-36% of citrus sites surveyed and 2199 South Rock Road, Fort Pierce, FL 34945-3138 accounted for 38-68% mortality of all caged larvae during the wet summer months (Beaver et al., 1983). Laboratory and R. W. Miller greenhouse studies confirmed pathogenicity of S. carpocapsae Biosys, Inc. to P. litus and D. abbreviatus larvae (Montes, et al., 1981; Ro 1057 East Meadow Circle man and Figueroa, 1985; Schroeder, 1987; Figueroa and Ro Palo Alto, CA 94303 man, 1990). In an initial trial, Schroeder (1990) documented 55% overall reduction of D. abbreviatus adult emergence for5 Abstract Soil drenches of the entomopathogenic nematode, months following a soil drench of 5 x 106 5. carpocapsae per Steinernema carpocapsae (Weiser), were tested for suppres tree. Downing et al. (1991) recorded a 45% reduction of D. sion of subterranean stages of the citrus root weevil, Pachnae- abbreviatus and a 32% reduction of P. opalus with the same us litus (Germar), and the West Indian sugarcane rootstalk rates of S. carpocapsae. borer, Diaprepes abbreviatus (L), in spring and fall trials in Fort Pierce, FL citrus groves. Water suspensions of S. carpoc Our trials were conducted to determine the field efficacy apsae (5 x 106) were applied to soil at the base of citrus trees. of S. carpocapsae soil drenches for suppression of D. abbreviatus One day before and one day after treatments, soil was moist and P. litus in Indian River area citrus groves. ened to saturation. Conical hardware cloth ground traps (0.66 m2) were deployed next to tree trunks to monitor adult weevil Material and Methods emergence weekly from nematode-treated (n=100) trees. Over all weevil reductions during a post-treatment period of 5 to 7 Irrigated grove trials were conducted in a block of navel months ranged from 59-83% for P. litus and D. abbreviatus, re orange trees, planted 3.7 m apart on a row, on single beds spectively. Significant monthly and cumulative reductions in spaced 7.6 m apart in Winder loamy sand (fine-loamy, sili adult emergence were recorded in spring and fall trials from ceous, hyperthermic Typic Glossaqualfs) during March 1984. soil under nematode-treated trees. The 11 rows comprising this young block, as well as an adjoin ing 10-year-old block, were naturally infested with both D. ab The citrus root weevil, Pachnaeus litus (Germar), an im breviatus and P. litus. portant pest of citrus, is indigenous to the Caribbean and is In March, 1989, alternate rows were designated for the tri now established in most Florida citrus-growing regions from al and were hand hoed to provide a 2-m band of bare soil for central to southern Florida (Woodruff, 1981), and occurs in nematode drenches and ground trap placement. Intervening parts of Central America. The West Indian sugarcane root- rows were designated as buffers between treatments. Soil in stalk borer, Diaprepes abbreviatus (L.), another serious pest of treatment blocks were moistened to saturation 1 day before citrus, sugarcane, and other crops in the Caribbean, was in and 1 day after treatment. Treatments were applied by deliv troduced into Florida on ornamentals in 1964 (Woodruff, ering, in a pre-determined timed interval, a measured quan 1964), and is now established in at least 19 citrus-producing tity of suspension containing 5 x 106 nematodes (Biovector) counties. Both weevil species have similar life cycles, with lar to a 0.3 m2 area surrounding the base of each tree. Check val stages feeding on primary and secondary roots (Norman trees received water only. The grove received 2.5 cm mi- et al., 1974), leading to tree decline and reduced citrus yields crosprinkler irrigation 5 days after treatment and was irrigat (Schroeder and Beavers, 1977; Ortiz et al, 1981). Larvae feed ed weekly thereafter. on roots for 9 or more months, pupate, and then become ten- Conical hardware cloth ground traps (0.66 m2 at base, 60 eral adults below-ground. Adult weevils emerge from the soil cm tall) with 0.95 liter clear plastic cups, attached by 15 cm from March through November. Adults aggregate, mate, and long braided elastics, were placed next to the tree trunks to feed on citrus foliage. Females will oviposit between 2 citrus monitor weevil emergence from nematode-treated (n-100) leaves. Eclosion occurs about 7 days later, the neonate larvae and water-treated (n=100) trees. To seal traps to the ground, dropping to the ground and burrowing into soil in search of the circular base of each trap was banked with soil to a depth roots to feed on. Each generation takes about one year (Wol- of 1 to 4 cm. Weevils were removed from the trap cups and tal cott, 1936). lied on a weekly basis. Entomopathogenic nematodes are now routinely used as Cone traps from the spring trial were left in place for a inundative releases to control or suppress a number of soil- second trial initiated during August 1989. On the day before borne insect pests (Gaugler and Kaya, 1990; Georgis and and following treatment, soil was moistened by 0.5 and 3.4 cm Hague, 1991). In an initial survey for Florida citrus soil ento- rainfall, respectively. On the day of treatment, 7.6 liter water was applied before and following treatment applications, di rected through the cone trap to the soil beneath. For the third trial, untreated buffer rows from the 1989 Florida Agricultural Experiment Station Journal Series No. N-00962. trials were used in the spring of 1990 (Table 1, 1990A). Three 90 Proc. Fla. State Hort. Soc. 107: 1994. Table 1. Monthly capture of adult Diaprepes abbreviates. Mean ± SEM adult weevils caught in 10 traps Percent Spring 1989 Apr May Jun Aug Sep Oct Apr-Aug reduction Bio Vector 0.7±0.4 4.1±1.3 0.410.2 0.0 O.liO.l 5.311.4 66 Untreated 1.5±0.7 10.0±3.6 2.811.2 0.810.4 0.310.2 15.415.5 Spring 1990A Apr-Oct BioVector 1.911.0 1.0±0.3b 1.410.5b 0.310.2 0.0 0.211.0 0.211.0 4.811.7b 57 Untreated 2.6±1.3 3.5±0.8a 3.911.0a 0.510.2 0.210.1 O.liO.l 0.0 11.012.0a Summer 1989 Aug Sep Oct Nov Aug-Nov BioVector 0.2±0.1 0.0 O.liO.l 0.0 0.311.4a 82 Untreated 1.4±1.3 O.liO.l 0.210.1 0.0 1.611.4a Mean separation within columns by paired T-test, 5% level. days before treatment, soil in treatment rows was watered for and after treatment application. Treatments (n=90) were ap 8 hours with microsprinklers. One additional hr of irrigation plied with a sprinkling can in 3.8 liters of water. was applied 1 day before treatments. Just before and then im Weevil emergence data from the 3 irrigated trials were mediately following treatment applications, 7.6 liter water was grouped by month and subjected to paired T-tests. Analysis of applied directly through the cone traps to the soil beneath. variance, with subsequent Duncan's Multiple Range Test Treatments were applied with sprinkling cans to a 0.66 m2 cir (1955), was performed on weevil emergence data in the non- cular area of soil around each tree. irrigated trial (Table 2, 1990B). Two rates of 5. carpocapsae (2 x 106 and 5 x 106:) were used in a fourth trial, conducted in a non-irrigated grove of dou Results ble-bedded 3-yr-old 'Ruby Red' grapefruit/Swingle citrumelo trees infested with P. litus. Beds contained 2 rows of 34 trees. Mean emergence trap captures of Diaprepes and P. litus Treatments were replicated 3 times using half beds (each with adults from April through August from trees treated in the two 17-tree rows) as plots. End trees in each plot remained spring of 1989 are presented in Tables 1 and 2, respectively. untreated and served as buffers. Diaprepes mortality varied considerably within treatments, re Trees were prepared for treatment by raking debris from sulting in no significant differences in survival even though the soil beneath the tree and pruning the canopy to permit the cumulative reduction for Biovector was 66%. However, setting of the ground traps against the tree trunk. Soil was wet the 75% reduction in P. litus emergence in the Biovector ted (0.66 m2) with 3.8 liter water from a sprinkling can before treatment is significant at P=0.05. Table 2. Monthly capture of adult Pachnaeus litus. Mean 1 SEM adult weevil caught in 10 traps Percent Spring 1989 Apr May Jun Aug Sep Oct Apr-Aug reduction BioVector O.liO.l 0.410.2 O.liO.l 0.0 0.110.2 0.810.4b 75 Untreated 1.2+0.8 1.110.3 0.310.1 O.liO.l 0.510.4 3.2iO.9a Spring 1990A BioVector 0.410.2b 0.510.2b 0.210.2b 0.0 0.0 0.4i0.2b 0.110.1b 1.610.4b 82 Untreated 4.511.0a 2.110.8a 1.110.7b 0.0 0.210.1 0.810.5b 0.310.2b 9.0il.6a Summer 1989 Aug Sep Oct Nov Aug-Nov BioVector O.liO.l 0.210.2 O.liO.l 0.310.2 0.710.3a 59 Untreated 0.310.1 0.510.3 0.710.3 0.210.2 1.710.4a Spring 1990B Apr May Jun Aug Sep Apr-Sep BioVector 5' 1.010.4b 0.410.2 O.liO.l 0.0 0.0 0.610.4 1.610.4b 59 BioVector 2 0.610.2b 0.710.4 0.0 0.0 0.0 0.0 1.2iO.4b 70 Untreated 2.8iO.8a 0.910.3 0.210.1 O.liO.l 0.0 3.911.0a Mean separation within columns by paired T-test, 5% level.