Archival copy: for current recommendations see http://edis.ifas.ufl.edu or your local extension office. Circular 1065 September 1993 Citrus Root Weevils1 Stephen H. Futch and Clayton W. McCoy, Jr.2 Currently, there are eight described species of the tree canopy during the heat of the day. The most root weevils which are known to infest citrus in apparent visual plant damage is a marginal notching Florida. Of these species, five can cause damage of of the leaf on young, tender shoots. Adult feeding economic importance to both nurserymen and always begins at the leaf margin; the amount of leaf commercial growers. These species are: the southern consumption differing between species and food blue-green citrus root weevil, Pachnaeus litus; the requirements of the adult. More than one weevil may blue-green citrus weevil, Pachnaeus opalus; Fuller rose feed on a leaf. According to laboratory studies by beetle, Asynonychus godmani; the little leaf notcher, Syvertsen and McCoy (9) severe leaf injury can Artipus floridanus; and the sugarcane rootstalk borer decrease water use efficiency up to 20% and decrease weevil, Diaprepes abbreviatus. Other less important photosynthesis. However, injury from notching of the species include Tanymecus lacaena, Epicarerus leaf causes no subsequent economic effect on yields fermidolosus and Parapantomorus fluctuosus. These from mature trees. Once the leaf has matured, and other species can be found in other parts of the feeding is reduced or expanded to include alternate world and are a major production problem in the host plants. Caribbean region and South America. EGG-LAYING BEHAVIOR Growers might first notice the damage done by the adult weevil feeding on the leaves of citrus plants Except for the Fuller rose beetle, female root and become alarmed from the visual damage to the weevils generally lay their eggs between two leaves. foliage. However, the unseen damage done by the The female produces an adhesive substance that is larvae in the soil, which feed on the plant root system secreted at the time of egg laying that holds the can have a greater destructive effect on the vitality leaves together (10,14). Eggs are generally laid on and future productivity of the overall tree. new leaf flush. About 83% of the time Fuller rose beetles prefer to lay their eggs beneath the calyx of ADULT FEEDING BEHAVIOR the fruit and the remainder of the time in cracks formed by the leaves or on the bark of the tree (4). Adult weevils can feed on a wide range of host The eggs of each species are laid in masses and will plants including citrus. They feed at night, early differ in number, size, shape and color as shown in morning or late afternoon and generally hide within Table 1. 1. This document is Circular 1065, a series from the Department of Entomology and Nematology, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: January 1993. Revised: September 1993. 2. Stephen H. Futch, entomologist, Multi-County Citrus Agent, CREC-Lake Alfred; Clayton W. McCoy, Jr., Professor and Entomologist, CREC-Lake Alfred, Florida, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida. Trade names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Christine Taylor Stephens, Dean Archival copy: for current recommendations see http://edis.ifas.ufl.edu or your local extension office. Citrus Root Weevils Page 2 Table 1. Estimated Number of Eggs and Total Eggs Per Lifetime of the 5 Major Root Weevil Species. Type of Weevil Number of Eggs Approximate Number of Egg Size in mm Egg Color per Mass Eggs per Lifetime Pachnaeus spp. Southern blue-green weevil 50-75 4000 Blue-green weevil Asynonychus godmani 70 - 100 3000 Flatten Pale Fuller Rose beetle 0.035 long translucent 0.01 wide yellow Artipus floridanus 12 - 130 800 - 1000 0.03 long White to yellow Little Leaf Notcher 0.01 wide Diaprepes abbreviatus 30 - 264 5000 0.05 long White when Sugar Rootstock Borer weevil 0.016 diam. laid, brownish before hatching LARVAL BEHAVIOR infested with both Diaprepes and Phytophthora (foot rot). The length of time for larval feeding on the root After 10-20 days at 80-86°F, egg masses hatch into system varies depending on the species and soil neonate larvae. They fall to the soil surface and conditions. See Table 3 for the estimated time of immediately begin moving their way into the soil larval development. This long protracted period of where they begin feeding on the fibrous feeder roots time in the soil includes an inactive pupal stage of of the plant. Feeding damage by older larvae may be two to four weeks. Following pupation in the soil, the seen on major lateral (Plate 4, Plate 5) or pioneer adult can emerge or remain in the soil for three to roots when a tree is removed from the soil. Preferred four weeks. Adult emergence from the soil frequently feeding sites by weevil larvae are listed in Table 2. occurs after a period of extensive rainfall. Larvae cause damage by channeling on the outer bark tissue into the cambium layer to the woody portion of In typical flatwood soils where groves have a the root, or by girdling a root thereby causing root shallow root system, larval damage appears to be death. In addition to the damage done to the root more pronounced. Since a greater percentage of the itself, channeling on the outer portion of the root root system is close to the soil surface, larval could conceivably allow for pathogen invasion. movement through the soil to the roots is much Considerable tree kill has been observed in groves easier. Table 2. Characteristic Citrus Root Feeding Behaviors by Root Weevils. Weevil Genera Root Part Diaprepes Asynonychus Pachnaeus Artipus Crown + - - - Major Lateral + + + - Tap (vertical) + + + - Pioneer + + + + Fibrous + + + + + Indicates feeding on root part by weevil genera - Indicates no known feeding on root part by weevil genera Archival copy: for current recommendations see http://edis.ifas.ufl.edu or your local extension office. Citrus Root Weevils Page 3 FULLER ROSE BEETLE Table 3. Approximate Larval Development Time in the Field. (Asynonychus godmani) Weevil Genera Time The Fuller rose beetle was first reported in Florida in 1916 and can be found on a wide range of Diaprepes 6 - 24 months plants in both coastal and central Florida and as far Asynonchus 9 - 12 months north as Gainesville and south to Homestead. Adults are brownish to grey in color and are about 0.33 Pachnaeus 9 - 12 months inches long. Since there are no males in this species Artipus 35 - 40 days females reproduce by the process called parthenogenesis which means the eggs develop without fertilization. Both adult Fuller rose beetle and little leaf notcher are flightless, limiting their BLUE-GREEN CITRUS ROOT WEEVIL movement from grove to grove. Adults will lay about 70 to 100 yellowish eggs per mass over a 4 month Southern blue-green citrus root weevil (Pachnaeus period. Eggs hatch in about 17 days. The larvae are litus) and the northern citrus root weevil (Pachnaeus white except for a yellowish head capsule (5). This opalus) are the most widespread weevil pests in species presents a problem for fresh fruit packers Florida (14). The southern blue-green citrus root because egg infested fruit is rejected in quarantine by weevil is commonly found in flatwoods plantings in Japan where the beetle is not found (4). south central and south Florida, the east coast as far north as Brevard County and on the west coast to Adult Fuller rose beetle can emerge anytime Sarasota County. The northern blue-green citrus root throughout the year but peak emergence is from May weevil is commonly found in north and north central through July, as shown in Figure 2. Since the adults Florida. The two species can be found in the same are flightless, they use the tree trunk, low hanging grove in some central Florida counties such as Polk, branches and/or grasses to migrate into the tree to Orange and Lake. Citrus root weevil is bright blue- feed on the leaves (13). green to aqua in color. The northern citrus root weevil is a pale grey-green in color but occasionally is LITTLE LEAF NOTCHER bright aqua (5). For the grower who would like to (Artipus floridanus) differentiate between the 2 species of citrus root weevil one must look at the pronotal notch on the Little leaf notcher was reported in Florida as leading edge of the wing covers illustrated in Figure early as 1876 and is found mainly along Florida’s east 1. The adult weevil with the notch is the southern coast from Volusia County to the Keys. This species citrus root weevil; the one with a smooth anterior can be found on a wide range of host species which portion of the wing cover is the blue-green citrus root include 150 species (15) including salt tolerant plants weevil. Both species are fairly large, 0.33 to 0.55 as well as other species such as teaweed, ragweed, inches in size.