Reprinted from Proc. Fla. State Hort. Soc. 112:73-77. 1999.

A PEER REVIEWED PAPER ASSESSMENT OF MONITORING TECHNIQUES FOR (L.) (COLEOPTERA: )

H. N. NIGG that only young citrus trees could be seriously damaged by this University of Florida, IFAS . However, we now know that older trees are damaged and Citrus Research and Education Center decline as a result of larval feeding on the tree roots (Griffith, 700 Experiment Station Road 1975). Lake Alfred, FL 33850-2299 The female D. abbreviatus produces an average of 5,000 eggs over her lifetime with 50-150 eggs oviposited per mass (Wolcott, S. E. SIMPSON 1933; 1936; Simpson et al., 1996). Because of its reproductive and Florida Department of Agriculture and Consumer Services destructive potential, it is essential that adult in citrus Division of Plant Industry groves be detected early when the adult population is low. Various 3027 Lake Alfred Road methods have been evaluated as a surveillance tool for D. abbre- Winter Haven, FL 33881 viatus populations; none appeared to be effective (Beavers et al., 1979b; 1982; Schroeder and Jones, 1983; 1984; Jones and L. E. R AMOS AND N. CUYLER Schroeder, 1984; Schroeder and Beavers, 1985). Currently, modi- University of Florida, IFAS fied Tedders pecan weevil traps (Tedders and Wood, 1994) are Citrus Research and Education Center used for trapping D. abbreviatus adults in all seasons by some re- 700 Experiment Station Road searchers and citrus growers (Stansly et al., 1997; J. L. Knapp, Lake Alfred, FL 33850-2299 Univ. of Florida, pers. comm.). The modifications to the Tedders pecan weevil trap (Tedders trap) consist primarily of a reduction in height from 4 to 2 feet and enlargement of the hole in the cone top Additional index words. Diaprepes, trap assessment, monitoring. of the trap so that the larger D. abbreviatus can pass through the opening. The reduction in height is to more easily place the trap un- Abstract. When field-collected Diaprepes abbreviatus L. were der a citrus tree. The hole enlargement has never been assessed to given a choice of trap, tree or neither under young citrus trees, see if D. abbreviatus could pass back through the hole and thus es- 27% overall chose a modified Tedders pecan weevil trap. Un- der mature citrus trees 56% chose the modified Tedders trap. cape the trap. The percentage choosing the tree was about equal; 32% in ma- D. abbreviatus feigns death when disturbed and falls so that it ture trees and 35% in young trees. The umbrella capture meth- may be collected on a ground cloth or into an umbrella (Jones, od had an overall efficiency of 65%, an average daily efficiency 1915). Both of these are common collection methods for some in- of 66 ± 28%, and a weevil detection efficiency of 75%. Our data sects (Borror et al., 1981). The umbrella technique offered a prom- indicate that the threshold and efficiency of the Tedders trap ising method for efficiently collecting D.abbreviatus adults. It is should be assessed further before recommending its use for more rapid and less labor intensive than spreading a ground cloth D. abbreviatus research and monitoring. The umbrella tech- under the tree, but the umbrella technique takes more time than nique may provide the D. abbreviatus population base for cal- placing and monitoring a trap. The umbrella technique has never culating the threshold and efficiency of the Tedders trap. This been assessed for the percent of any population, including D. is the first comparative assessment of the efficiency of the Tedders trap and the umbrella collection technique for Di- abbreviatus, that it could collect. aprepes abbreviatus L. or for any insect. The purposes of these experiments were to assess the escape of D. abbreviatus from the Tedders trap top, to evaluate the capture Diaprepes abbreviatus L. is a generalist host feeder whose of adult D. abbreviatus with the modified Tedders pecan weevil most economically important host in Florida appears to be Citrus trap, and to evaluate the efficiency of the umbrella collection tech- spp. (Beavers et al., 1979a; Simpson et al., 1996). Since its intro- nique for D. abbreviatus adults. duction in 1964, D. abbreviatus has been documented in at least 20 counties in Florida, where it currently infests approximately Materials and Methods 164,000 acres of agricultural land (Anonymous, 1997; J. L. Knapp, Escape experiment. The collection cone top for the modified Univ. of Florida, pers. comm.). This area contains approximately Tedders pecan weevil trap is the same top used for the pecan wee- 30,000 acres of D. abbreviatus infested commercial citrus. Male and female adult weevils feed on young leaves of citrus. Eggs are vil trap. The small hole for the pecan weevil in this cone screen was enlarged to 8-9 mm in diameter so the larger D. abbreviatus could glued in a mass between two leaves and when they hatch, the lar- enter the trap. Weevils were placed under 12 boll weevil trap tops vae drop to the ground, feed on the roots and adults emerge from the soil 6 mo to 2 yr later (Griffith, 1975). It was initially thought on a flat surface at 4 PM. At 8 AM these were checked to see if weevils had entered the top. Because the largest weevils were able to pass through the cone, various sized, individual male and female Florida Agricultural Experiment Station Journal Series No. R-07068. We thank adult weevils were placed inside the trap above the cone and left James Simpson II and Chris Troesch of Simpson Fruit Co., Mt. Dora, Florida, for from 4 PM to 8 AM. Fifty replications of each sex were tested for their cooperation and assistance. Funds for this project were made available from escape. the Citrus Production Research Marketing Order by the Division of Marketing and Development, Florida Department of Agriculture and Consumer Services. We Tedders trap experiment. Four red modified Tedders pecan thank the Florida Citrus Growers for support of this program. weevil traps, (Stansly et al., 1997) were placed 18 inches away

Proc. Fla. State Hort. Soc. 112: 1999. 73 from the trunk of 4 adjacent 8 ft high 6H-yr-old ‘Valencia’ orange (Citrus sinensis (L) Osbeck) ‘young’ trees planted east to west in Candler sand in a 0.5 acre block at the Citrus Research and Educa- tion Center in Lake Alfred, Florida. This was approximately mid- way between the dripline and the tree trunk. Traps were placed at each of the cardinal coordinates. Tree 1 had the modified pecan weevil trap placed west of the trunk, Tree 2 had the north trap, Tree 3 had the east trap and Tree 4 had the south trap (Fig. 1). Adult Diaprepes abbreviatus captured with the umbrella tech- nique in the same grove were used for the release experiment. A pair of weevils (1 male, 1 female) was released at a predetermined position in relation to both the tree and the trap (Fig. 1). The sub- sequent behavior of the was observed over 30 min. The 3 release positions were: center, between the trap and the tree 9 inch- es away from both; 45°, an equal distance between the trap and the tree so that both targets were at 45° from the starting position and the weevils were 12 inches from each target; and across, 18 inches away from the trap so that the trap was between the weevil and the tree forming a straight line (Fig. 1). All release and trap positions were assayed each day between the hours of 8:00 AM and 12:00 Noon. The starting date for the experiment was 11 Mar and the last Figure 1. Trap and release positions. X = trap. Release positions in the upper replicate was conducted on 27 June. Weather conditions were not- left. ed as being sunny, overcast, partly cloudy or cloudy. No bioassays were conducted under rainfall. Incident solar energy was measured using a dp Solar Meter Model 776 (Dodge Products, Houston, Tex- entire canopy had been covered. A second observer watched the as) and recorded in Btuh/ft 2. Temperature and relative humidity tree being sampled for flying weevils. A third person watched the were measured using a sling sychrometer (Bacharach Instruments, sampled tree for weevils which dropped outside the umbrella. A Pittsburgh, Pennsylvania). fourth individual watched the next tree for either flying or drop- Once released, weevils were observed for target preference ping weevils because this was the next tree to be sampled. Beating and response time. Information was recorded by target and sex: the entire volume of foliage of one young tree took approximately tree, trap, away from the tree over a 36 inches distance or within 36 one minute. When the tree had been sampled and the weevils re- inches of the tree but without going to either tree or trap (No-tar- moved from the ground cloth and umbrella, three observers vigor- get). Since in the across position the weevils started 36 inches ously beat the sampled tree and then inspected the foliage, away from the tree trunk, 9 inches were added to the assay radius branches and ground cloths for weevils. The ground cloths were to consider the weevil out of the experiment. When a weevil went then moved to the tree beyond the next tree in the row (with ground to the trap, the time was taken when it touched the bottom of the cloths) and the next tree was sampled in the same manner. Trees in trap with at least 4 of its legs (to confirm commitment on part of five rows were used for this assessment over 19 sampling days. the weevil to climb up) and again when it reached the top of the Captured weevils were removed from the field on each sampling trap. If the weevil remained within 36 inches of the tree trunk but day. Three hundred ninety-two samplings were made for this as- did not climb up either the tree or trap in 30 min, a no-target was sessment. The total number of weevils collected per tree was divid- recorded. In each of the 10 days of the experiment, 2 weevils were ed into the number collected in the umbrella times 100 to provide released for each release position for each of the 4 trap positions or efficiency data for further calculations. The assumption for this ex- 24 weevils per day. The same experiment was conducted in ‘ma- periment is that we collected all of the weevils in a tree. None flew ture’ trees 10 to 12 feet in height. Differences in response were sta- away or escaped in some other manner. Based on our direct obser- tistically analyzed by the GLM procedure (SAS Institute Inc., vations this assumption is true. 1996). Umbrella technique experiment. The umbrella assessment ex- periment was conducted in a 5 acre red navel orange grove (Citrus Results sinensis (L) Osbeck) planted in 1994 in Astatula sand, 5-12% slope (Furman et al., 1975) at Mt. Dora, Florida. Trees 3-3.5 ft tall were Escape experiment. In the trap top escape tests, the enlarge- irrigated by a microsprinkler system and were in excellent horticul- ment of the cone screen allowed large females to pass into the boll tural condition. weevil trap cone top and no weevil passed back through the hole. Four queen-sized bed sheets (two per tree), 89 ´ 100 cm and No weevil placed in the cone top and left for 16 hr (4 PM-8 AM) light tan in color were used as ground cloths. Tan was chosen as passed back through the hole in the screen. most closely matching the color of sand. These were placed under Tedders trap experiment. Over the experimental days of the re- two adjoining trees, two sheets per tree. These enclosed the trunk lease experiments, the temperature ranged from 64-95°F; relative and about 40 cm beyond the dripline. One of the trees was then humidity 60%-90% and solar radiation from 220-250 btuh/ft2. sampled using the umbrella method (Jones, 1915; Borror et al., There appeared to be no effect of weather on choice of target by D. 1981). Straight-handled golf umbrellas, 4 ft in diameter, were abbreviatus (data not shown). There were no statistical differences placed under the tree to cover the distance from trunk to dripline, in the mean time a weevil took to reach and commit to a target in and one person beat the foliage of the tree over the umbrella from either experiment: trap (45°, 318 sec), tree (center, 305 sec), tree the top down with a 0.5 inch ´ 4 ft oak dowel rod. The umbrella (across tree, 45°, 304 sec), trap (across, 207 sec), trap (center, 206 was moved and another portion of the foliage was beaten until the sec). There were no statistical differences in target choice by sex or

74 Proc. Fla. State Hort. Soc. 112: 1999. by compass point in trap position and these data were combined in Discussion Tables 1 and 2 to yield an overall n of 240 in each experiment. In young trees, more weevils went to the trap (40%) when the Where the trap is placed in relation to where the weevil emerg- trap was between the weevil release site and the tree compared to es from the soil is a factor in trap efficiency. In both young and old the tree (15%) (Table 1). More weevils chose the tree (46.2 and trees, nearly twice as many weevils were trapped when released 42.5%) compared to the trap (17.5 and 25.0%) when released in the beyond both the trap and the tree trunk than when released between center or in the 45° position, respectively. Overall, about 35% of the two. If we average the percent trap catches of the center and the weevils went to the tree, 27% to the trap, 33% wandered out of the 45° position where the weevil could choose between the tree trunk experiment and 5% were no-target over the 30 min observation pe- and trap in young trees, the tree trunk was preferred to the trap by riod. However, in mature trees 81.3% of the weevils chose the trap a two-fold advantage of 35% compared to 17%. In mature trees, when the trap was between the weevil and the tree (Table 2). In the these percentages were about equal. At present, it is not known center and 45° release positions the numbers choosing the trap and where weevils emerge under the tree. tree were about equal (Table 2). The overall percentage choosing Tedders traps are recommended to growers at 10 per acre the trap was 56%. placed in areas where D. abbreviatus has been seen or is suspected Umbrella technique experiment. Of the 392 trees sampled to to be present based on tree condition or observation of the feeding determine the efficiency of the umbrella collection method, there notches left in leaves by the adults. Overall in our experiments were 103 trees (26%) with weevils (Table 2). In 289 trees (74%) 27% of the weevils chose the trap in young trees and 56% in ma- no weevils were detected using the combination of ground cloths ture trees. If a weevil does enter the trap it has little chance of es- plus umbrella plus visual inspection. No weevils were observed to caping according to our data. fly or to drop to the ground from the tree next to the tree being sam- If we assume that one of the 10 traps in our grove caught one pled. In 61 positive trees (59%) all weevils (37 males: 34 females) D. abbreviatus, what can the grower assume? From our knowledge were caught in the umbrella. In 26 positive trees (25%) all weevils that the Tedders trap catches weevils emerging from the ground escaped the umbrella and were captured on the ground cloth (15 and the life cycle of the weevil is about one year, our grove had a males: 16 females). In 16 trees (16%) some weevils were caught in D. abbreviatus infestation that is at least one year old. From the the umbrella (12 males: 13 females) and some dropped to the 5000 eggs produced by one female only about 28 larvae make it to ground cloth outside the umbrella (10 males: 10 females). There the adult stage (Beavers and Selhime, 1975; Beavers, 1982). We do was no tendency of males or females to preferentially drop into the not know how a female distributes her eggs in a citrus grove, but if umbrella (1.05:1.0 ?:/) or onto the ground cloth (0.9:1.0 ?:/) (Table she laid her eggs in our grove and we subsequently caught one 2). There were 147 weevils captured, 96 in the umbrella for an adult weevil, there is not 1 free adult, but 27 free adults because she overall efficiency of 65%. The average daily efficiency of the um- produced 28 adults. About 14 of these will be female. These 14 fe- brella method was 66 ± 28% (mean ± SD, n = 19 days). The effi- males will each produce about 28 adults (14 will be females) or ciency of detecting a weevil with the umbrella method was 75%. about 196 total females. For example, the 147 total (male and fe- These efficiencies may be lower in larger trees due to greater dif- male) weevils we captured in the umbrella technique experiment ficulty in covering the area under the foliage with the umbrella and came from only 5.2 females (147 ¸ 28). Because of this reproduc- greater difficulty in beating all the foliage of larger trees. tive capacity, and low trap catch efficiency, any detection likely re- veals the presence of a significant infestation. Although an

Table 1. Diaprepes abbreviatus adult movement after release in young trees.*

Target

Release position N Tree Trap Over 36 inches No-target Center 80** 3.8 ± 1.2 a*** 1.8 ± 1.0 bcdef 2.2 ± 1.2 abcdef 0.2 ± 0.4 f (47.5%) (22.5%) (27.5%) (2.5%) 45° 80 3.4 ± 1.6 ab 1.4 ± 1.0 cdef 2.6 ± 1.4 abcd 0.6 ± 0.8 ef (42.5%) (17.5%) (32.5%) (7.5%) Across 80 1.1 ± 1.1 def 3.2 ± 1.5 abc 3.2 ± 1.9 abc 0.5 ± 1.0 ef (13.7%) (40.0%) (40.0%) (6.3%) Overall 240 8.3 ± 2.8 (1) 6.4 ± 2.4 (1) 8.0 ± 3.2 (1) 1.3 ± 1.7 (2) (34.6%) (26.7%) (33.3%) (5.4%)

*3 to 4 feet high trees with skirt radius of 32 to 38 inches. Means in any column or row followed by the same letter are not significantly different µ = 0.05. Overall means followed by the same number are not significantly different µ = 0.05. **n is by release position. ***Mean weevils per day ± S.D. Percentage captured for a given release position shown in parentheses. economic threshold for D. abbreviatus has not been established, periment may not accurately reflect capture of weevils in the field the damage potential of this pest is such that any detection warrants because of the 30 min observation period, because the adults used control measures. had previously emerged from the soil, and because larvae (and the The problem with the Tedders trap is that we do not know its subsequent adults) may not be equally distributed in a citrus grove. threshold (how many weevils must emerge before one is caught From a practical standpoint, these catch percentages appear with high probability) or the percentage of the weevils present that useful. However, if an infestation in a citrus grove had 1 weevil ev- it catches. The trap catch percentages determined in our release ex- ery 10 trees at 110 trees per acre, about 11 weevils would be avail-

Proc. Fla. State Hort. Soc. 112: 1999. 75 Table 2. Diaprepes abbreviatus adult movement after release in mature trees.*

Target

Release position N Tree Trap Over 78 inches No-target Center 80** 3.4 ± 1.8 a*** 3.7 ± 1.3 a 0.1 ± 0.3 b 0.8 ± 1.0 b (42.5%) (46.3%) (1.2%) (10.0%) 45° 80 3.9 ± 1.2 a 3.2 ± 1.2 a 0.2 ± 0.4 b 0.7 ± 0.8b (48.8%) (40.0%) (2.5%) (8.7%) Across 80 0.4 ± 0.5 b 6.5 ± 1.2 c 0.1 ± 0.3 b 1.0 ± 1.3 b (5.0%) (81.3%) (1.2%) (12.5%) Overall 240 7.7 ± 2.5 (2) 13.4 ± 1.9 (1) 0.4 ± 0.7 (3) 2.5 ± 2.3 (3) (32.1%) (55.8%) (1.7%) (10.4%)

*10 to 12 feet high trees with skirt radius of 72 to 80 inches. Means in any column or row followed by the same letter are not significantly different µ = 0.05. Overall means followed by the same number are not significantly different µ = 0.05. **n is by release position. ***Mean weevils per day ± S.D. Percentage captured for a given release position shown in parentheses.

Table 3. Ground cloth and umbrella capture of Diaprepes abbreviatus.

Capture position Males Females ?:/ Total Weevils Trees* Weevils/tree Umbrella only 37 34 1.1:1 71 61 1.2 Ground cloth only 15 16 .9:1 31 26 1.2 Both 45 16 2.8 a) umbrella 12 13 .9:1 b) ground cloth 10 10 1:1 Subtotal (both) 22 23 1:1 Total 74 73 1:1 147 103

*392 trees total, 103 positive for weevils. able for capture. If a modified Tedders pecan weevil trap were Beavers, J. B., J. M. Stanley, H. R. Agee and S. A. Lovestrand. 1979b. Diaprepes placed under every tree, 4-8 weevils might be trapped. Of the re- abbreviatus response to light traps in field and cage tests. Fla. Entomol. 62:136- 139. maining 3-7 weevils, one half could be female and one female has Borror, D. J., D. M. Delong and C. A. Triplehorn. 1981. An introduction to the the potential to lay 5000 eggs in 60-100 egg masses (Fennah, 1942; study of . 5th ed. Saunders College Publ., New York, NY. Simpson et al., 1996). So 2-4 females have the potential to infest Fennah, R. G. 1942. The citrus pest’s investigation in the Windward and Leeward all 110 trees in the acre. Islands, British West Indies 1937-1942. Agric. Advisory Dept., Imp. Coll. The four monitoring technique assessments in this study Tropical Agr., Trinidad, British West Indies. Furman, A. L., H. O. White, O. E. Cruz, W. E. Russell and B. P. Thomas. 1975. Soil showed that although no escapes were made by D. abbreviatus from survey of Lake County area, Florida. USDA Soil Conserv. Ser. & Univ. Fla. the Tedders trap top, the Tedders trap may be an ineffective trap for Exp. Sta., Gainesville, FL. grower or research use as currently recommended. The umbrella Griffith, R. J. 1975. The West Indian sugarcane rootstock borer weevil in Florida. technique had a 75% D. abbreviatus detection rate. The umbrella Proc. Fla. State Hort. Soc. 88:87-90. Jones, I. F. and W. J. Schroeder. 1984. Capture of Diaprepes abbreviatus (Co- technique also captured about 65% of the weevils present in imma- leoptera: Curculionidae) in frass extract-baited traps in citrus. J. Econ. Entomol. ture trees. This efficiency should allow the umbrella technique to 77:334-336. serve as a total D. abbreviatus population estimation technique for Jones, T. H. 1915. The sugarcane weevil rootborer (Diaprepes spengleri Linn.). In- further evaluation of the threshold and efficiency of the Tedders sular Expt. Sta. (Rio Piedras, PR) Bull. 14:1-9, 11. trap. This is the first assessment of the efficiency of the Tedders trap SAS Institute, Inc. 1996. Proc Genmod. SAS/STAT Software: Changes and En- hancements through Release 6.11. SAS Inst., Inc., Cary, NC. and the umbrella collection technique for D. abbreviatus or for any Schroeder, W. J. and J. B. Beavers. 1985. Semiochemicals and Diaprepes abbre- insect. viatus (Coleoptera: Curculionidae) behavior: Implications for survey. Fla. En- tomol. 68:399-402. Schroeder, W. J. and I. F. Jones. 1983. Capture of Diaprepes abbreviatus (Co- Literature Cited leoptera: Curculionidae) in traps: Effects of location in a citrus tree and wick materials. J. Econ. Entomol. 76:1312-1314. Anonymous. 1997. Diaprepes Task Force Minutes. July 17, 1997, Univ. of Fla., Schroeder, W. J. and I. F. Jones. 1984. A new trap for capturing Diaprepes abbre- Lake Alfred, FL. viatus (Coleoptera: Curculionidae). Fla. Entomol. 67:312-314. Beavers, J. B. 1982. Biology of Diaprepes abbreviatus (Coleoptera: Curculionidae) Simpson, S. E., H. N. Nigg, N. C. Coile and R. A. Adair. 1996. Diaprepes abbre- reared on an artificial diet. Fla. Entomol. 65:263-269. viatus (Coleoptera: Curculionidae): Host plant associations. Environ. Entomol. Beavers, J. B., T. P. McGovern and V. E. Adler. 1982. Diaprepes abbreviatus: Lab- 25:333-349. oratory and field behavioral and attractancy studies. Environ. Entomol. 11:436- Stansly, P. A., R. F. Mizell and C. W. McCoy. 1997. Monitoring Diaprepes abbre- 439. viatus with Tedders traps in Southwest Florida citrus. Proc. Fla. State Hort. Soc. Beavers, J. B. and A. G. Selhime. 1975. Development of Diaprepes abbreviatus on 110:22-26. potted citrus seedlings. Fla. Entomol. 58:271-273. Tedders, W. L. and B. W. Wood. 1994. A new technique for monitoring pecan wee- Beavers, J. B., R. E. Woodruff, S. A. Lovestrand and W. J. Schroeder. 1979a. Bib- vil emergence (Coleoptera: Curculionidae). J. Entomol. Sci. 29: 18-30. liography of the sugarcane rootstock borer weevil, Diaprepes abbreviatus. Bull. Wolcott, G. N. 1933. An economic entomology of the West Indies. Chapter IX. The Entomol. Soc. Amer. 25:25-29. root-boring beetles. Richard Clay, Bungay, England. Wolcott, G. N. 1936. The life history of “Diaprepes abbreviatus” L., at Rio Piedras, Puerto Rico. J. Agr. Univ. Puerto Rico 20:883-914.

76 Proc. Fla. State Hort. Soc. 112: 1999.