Technical Bulletin 228 July 2001 a field guide to BBolloll WeevilWeevil IdentificationIdentification A Field Guide to Boll Weevil Identification Robert G. Jones Research Entomologist U.S. Department of Agriculture Animal and Plant Health Inspection Service Plant Protection and Quarantine Michael R. Williams Extension Entomologist Department of Entomology and Plant Pathology Mississippi State University For more information, contact Dr. Jones at (662) 320-7423 or [email protected], or con- tact Dr. Williams at (662) 325-2986 or [email protected]. Technical Bulletin 228 was published by the Office of Agricultural Communications, a unit of the Division of the Agriculture, Forestry, and Veterinary Medicine at Mississippi State University. A Field Guide to Boll Weevil Identification INTRODUCTION Identification of boll weevils in both The reduction in the boll weevil Introductioneradication and pest management programs population and the presence of large is critical. Control decisions based on iden- numbers of pheromone traps creates a new tification are major costs to the programs situation for even the most experienced and to cotton growers. Treatments resulting field people. Now, boll weevil scouts are from misidentified boll weevils are disrup- likely to find a variety of other snouted tive, unnecessary, and expensive. Failure to beetles – both in the traps and in the field treat when boll weevils are not correctly – that were not commonly seen before. identified could extend eradication pro- Additionally, differentiation in boll weevil gram operations into extra years. punctures and the small bollworm and Therefore, all identifications of weevils are budworm damage can become more critical. Second opinions should be encour- difficult and takes on new importance. aged. Specimens should be submitted to Boll weevil traps attract a large number specialists for verification. of other insects and spiders. While the The use of boll weevil traps and the boll pheromone is specific for the boll weevil, it weevil aggregation pheromone (Grandlure) is similar to that of related weevils. The has become a major component of all boll trap color alone attracts both boll weevils weevil control programs. Grandlure-baited and other insects. The placement of the traps are at least eight times more efficient traps next to flowering shrubs often results at detecting low-level populations of boll in an increase of different insect species weevils than hand sampling (Hardee and captured. Mitchell 1997). This publication is designed to help in Utilization of these traps makes it the identification of boll weevil adults. possible to control the boll weevil with less Since most people do not have reference insecticide and ultimately makes collections of insects to make identification eradication possible. Large geographical comparisons, color photographs are areas have traps placed around all cotton included. fields in Boll Weevil Eradication Programs. Mississippi Agricultural and Forestry Experiment Station 1 IDENTIFICATION Insects differ from other arthropods with Figures 1 through 9 are at the same magni- Identificationtheir bodies consisting of head, a three-seg- fication for comparison. mented thorax, and a segmented abdomen. THE BILLBUGS The presence of wings signifies an adult Figure 1 insect. The prothorax – the first thoracic The billbug (Figure 3) is probably the segment – holds the head and first pair of largest weevil found in traps. Its snout is Boll weevils are 1/8 to 1/3 legs. The mesothorax, or middle segment, short and stout. The antennae arise from inch long, and their color has the second pair of legs and the front the snout close to the eyes but not next to varies by age. As boll weevils mature, they pair of wings attached. The metathorax, or them. The elytra do not cover as much of become a dark red-brown last segment, has the third pair of legs and the sides of the abdomen and thorax and or mahogany. This figure second pair of wings. do not extend to cover the terminal shows a female boll weevil. Beetles’ front wings are leathery or abdominal segments. From the dorsal view, hardened covers. These wing covers, called this weevil is wide at the middle of the the elytra, meet in a straight line on the body and much narrower at both ends. abdomen. Structures used for beetle Billbugs often cover their bodies with a identification are the head, antennae, coating of mud. Size of the many species thoracic segments, legs, elytra, and varies from 1/5 to 3/4 inch in length. Color abdomen. The weevils of the Family varies by species including black individu- Curculionidae, including boll weevils, are als commonly found in traps. Figure 2 called the snout beetles. Adult weevils THE BARIDINE WEEVILS have heads that extend into elongated This figure shows a male boll weevil. Variations in snouts with chewing mouthparts at the Baridine weevils (Figure 4) include 500 the snout are the simplest distal end. The antennae arise on the sides species in North America, all of which are means for distinguishing about 1/5 inch long. Several species have between the sexes. of the snout with the long basal segment fitting into a groove on the snout. This been found in traps. Body shape is similar long basal segment, with the attached to that of the billbugs: widest in the middle smaller segments, has an elbowed when viewed from top and side. The elytra appearance. The small segments increase in cover all segments of the abdomen but diameter near the end of the antenna, leave the sides exposed. The snout is longer which gives it a club-like appearance. than the billbug snout, and it is slender There have been numerous species of with a sharp bend close to the eyes. This weevils found in the boll weevil traps. shape gives the appearance of the snout Some representatives of common groups always being bent back under the body. Figure 3 are described in the following sections. The body is covered by plate-like scales. There are more scales on the sides and THE BOLL WEEVIL The billbug varies from 1/5 under surface of the weevil. These to 3/4 inch in length, probably the largest weevil The boll weevil specimens (Figures 1, 2) generally white scales give a two-tone found in traps. Color varies pictured are among the larger of the appearance to the weevil’s body, dark top by species including black species. Figure 1 is of a female, and Figure 2 and light bottom. Color varies by species individuals commonly found in traps. is of a male – both collected in Webster with some appearing blue, black, gray, and County, Mississippi. For more detailed tan, but the body shape and size are information on the boll weevil, see the generally consistent. “Boll Weevil Identification” section. 2 A Field Guide to Boll Weevil Identification Figure 4 Figure 5 Figure 6 Figure 7 Baridine weevils are about 1/5 The cowpea curculio is a shiny The nut or pecan weevil looks like a The plum curculio has a rough, inch long. Color varies by black weevil, about 1/4 inch long. boll weevil in shape, color, and multicolored appearance and is species with some appearing size, but its snout is thinner and about 1/4 inch long. blue, black, gray, and tan. longer in proportion to its 3/8-inch body length. THE COWPEA CURCULIO brown body is covered with white hairlike scales. The cowpea curculio (Figure 5), a shiny black weevil, has no scales or hairlike THE PLUM CURCULIO setae. It has prominent round punctures on The plum curculio (Figure 7) has a most of its body surface. The snout is slen- rough, multicolored appearance. The body der – about a third the length of the 1/4- is red-brown with black spots. There are inch-long body. The elytra cover the entire patches of white and gold hairlike scales. top and most of the sides of the abdomen, This weevil’s snout is stout and is a third as the mesothorax, and the metathorax. This long as the 1/4-inch body. It has ridges run- weevil does not fly. It is a pest of seedling ning the length of the elytra with four cotton where cowpeas are present or used prominent humps and a few lesser ones. in rotation with cotton. This weevil is often seen in traps during THE NUT OR PECAN WEEVIL The nut weevil (Figure 6), when viewed from a top rear position in a trap, looks like a boll weevil in shape, color, and size. However, its snout is very thin and long in proportion to its 3/8-inch body length. The snout can range from half as long as the body to equal to the length of the body. The main part of the head appears spheri- cal. The legs are long and slender with no spurs. As with the boll weevil, the nut wee- vil’s elytra have a pattern of parallel grooves that run the length of the insect and curve to join at the end. The red- Mississippi Agricultural and Forestry Experiment Station 3 the spring and is plentiful where wild plum to the boll weevil. On the distal end of the and other stone fruit trees occur. femur is a single-toothed spur, as opposed to the double-toothed spur found on the THE RICE WATER WEEVIL Figure 8 boll weevil. The enlarged top view of this The rice water weevil (Figure 8) is light species (Figure 10) shows a triangular struc- Rice water weevils are light tan tan with some darker spots on the ture called the scutellum, which is covered with some darker spots. prothorax and elytra. Its snout is short and by thickly clustered, white scales.