The Boll Weevil May Be Spreading C

The boll weevil may be spreading C. A. Beasley T. J. Henneberry

Numbers increasing in lower deserts

The boll weevil was first found in the United States in about 1892. Infestations reported in Arizona in the 1960s are thought to have come from a boll weevil population in northern Mexico. Localized but damaging levels of the boll weevil, Anthonomus grandis Boheman, occurred in cultivated cotton in 1965 and 1966, as did growing numbers of pink bollworm, Pectinophora gossypiella (Saunders). Mandatory plowdown of cotton stalks after harvest and planting dates to ensure a host-free period eliminated economically important boll weevil infestations. Mi- nor infestations were detected from 1966 mu) to 1977; however, plowdown and planting a date regulations were relaxed in Arizona 0 in 1978. The next documented boll weevil b infestation was on August 31, 1978, in a 0 ti western Maricopa County (Arizona) field Q _I of stub cotton (perennial cotton from pre- a vious year's plants) near Gila Bend. Ari- P a zona infestations have spread since then, u and boll weevil adults and infested bolls Although boll weevil adults and larvae feed mainly in the unopened flowers, or squares, were found in southern California cotton of the cotton plant, they also attack developing bolls. Infested bolls may remain on the fields in 1982. plant but fail to open and fluff normally (left). Boll weevil populations are now estab- lished in California and, since numbers days at 59°F. Feeding and egg-laying oc- are increasing each year in the lower de- cur on cotton squares and bolls. Females serts, the potential for this insect to in- may lay more than 200 eggs, puncturing vade the San Joaquin Valley is also in- the fruiting form with their mouthparts, creasing. Average trap catches in the depositing a single egg in the puncture Bard-Winterhaven area and the remain- cavity, and then sealing it with excre- der of Imperial County between planting ment. time and November 27 in 1982, 1983, and Under Arizona and California field 1984, were 64, 4,175, and 8,330, respec- conditions, immature bolls that set during tively. Similar increases in numbers of the first fruiting cycle are also susceptible trapped boll weevil and in-field infesta- to infestation, even though squares are tions have occurred in the Parker Valley plentiful. In contrast, boll weevils in the and the Yuma areas in Arizona, and in the Southeast seldom infest bolls until late in Palo Verde Valley, California. the growing season. It is obvious from the The boll weevil in the southeastern short life cycle that many generations US. Cotton Belt has caused millions of may occur within the growing season, al- r dollars in annual losses. The potential for though previously reported research indi- u permanent establishment of the insect as cates that the high reproductive potential a pest in western cotton production sys- of the insect is not realized under the arid tems is unknown. The need for informa- high temperatures of Arizona and south- tion on the boll weevil under desert southern California. When squares are available, adult boll west growing conditions has prompted In the desert, some adult boll weevils weevils chew into them with their snouts, preliminary studies on the activity and overwinter outside bolls and cotton-plant consuming pollen, stamens, and pistils, occurrence of the insect in California. field trash, but most overwinter in cells leaving behind bright yellow frass. Eggs created by pupating larvae within imma- are laid in punctures similar to feeding Biology ture bolls left in the field. Some of the punctures and are sealed with frass. The boll weevil develops from egg to overwintering population reproduces adult in as little as 17 days at 86°F to 88 throughout the year, and females may lay

CALIFORNIA AGRICULTURE, JULY-AUGUST 1985 23 Monitoring and control Adult boll weevil activity early and late in the cotton-growing season can be Y detected with traps baited with Grand- lure, the synthetic boll weevil aggregation pheromone. In the southeastern Cotton

.x0 Belt, trap catches of more than 2.5 boll m 7 weevils per field per week during the ap- The "C" shape characterizes the boll pearance of the first one-third grown weevil larva, which forms a chamber of squares indicate a need for control action. frass as it feeds on seeds of a developing That threshold has been adjusted, both up cotton boll. Below, the boll weevil pupa and down, for some areas within the Cali- 1903 1904 inside the larval chamber. fornia eradication program. Boll weevil populations in Arizona and Fig. 1. Average boll weevil catches varied California, unlike those in most areas of greatly in traps placed to monitor move- the Southeast but similar to those in the ment of weevils west from infested fields subtropical areas of Texas, remain phys- in Arizona. iologically active throughout the year. California and Arizona state agencies, the federal government, the Universities of California and Arizona, and the Mexi- can government are cooperating in an ef- fort to eradicate or reduce population levels of the boll weevil to non-economic levels. The most important component of ex- isting control technology is creating a host-free period of two to three or more months through the establishment of eggs and start infestations whenever host planting dates and early crop termination material is available. and plowdown. Survey and detection sys- Trap number Adults emerge from bolls throughout tems with Grandlure-baited traps identify Fig. 2. Average trap catches were highest the winter when the average temperature areas of potential infestation. Boll wee- close to the Colorado River (trap I),de- is 55°F or higher, and they may emerge vils in these areas are treated with insec- creasing with distance from the river (#14). as late as the end of May. Emergence of ticides at the pinhead-square plant devel- weevils that develop in late-season bolls opment stage, followed by applications at 12 r (October and November) begins in late 08SERYATION five- to six-day intervals during the devel- TIMES December to early January, peaks in late opment of one or two boll weevil genera- January through February, and declines tions. Insecticides are also applied during SIO thereafter to late May. Burial of the in- the season when in-field infestations are AM NOON PM fested bolls reduces adult emergence. discovered or trap catches adjacent to Many of the boll weevils emerging fields indicate that treatments would be from December through mid-March die beneficial. (suicidal emergence), but a small percent- age may survive until early May. Moist Preliminary research conditions in bolls and plant trash en- During the fall and winter of 1982-83, hance survival. Weevils that emerge ear- the California Department of Food and ly in the spring do not have a source of Agriculture (CDFA) conducted extensive .-. - cotton for food needed for reproduction. trapping to detect and monitor boll wee- I! 3.00 Plants of Sphaeralcea spp. (the most vils in the Palo Verde Valley, California. X abundant is globe mallow) are commonly In the fall of 1983, we selected a 24-acre r 2 2.25 - found throughout the cotton-growing field reported to have had high trap areas in Arizona and California, however, catches during 1982-83 to study the occur- 0 1 and have been shown to be an alternative rence and development of infestations. .t 1.50 - source of food for adult boll weevils. Grandlure-baited traps placed in the field n Female weevils that survive until cot- on September 21 were checked every sev- m .-r ton squares are available feed and lay en days until December 7, 1983. Baits 0.96 - eggs on them. Most damaged squares be- were changed every 14 days. E gin to abscise on the second day after the Applications of ultra-low-volume ma- i feeding puncture occurs and about 65 per- lathion (triggered by the California eradi- d, a cent fall to the ground. Early in the grow- cation program) were made on October 11/22183- 12121183- 2/10/84- ing season, before full plant canopies 28, November 3, 10, 16, 22, and 29. Begin- 12/10/83 1/8/84 2/28/84 form in cotton fields, soil surface tem- ning on September 28, we collected 200 Observation periods peratures may reach 140°F; where these green bolls per day from the treated field temperatures are above 100°F for pro- to evaluate the effect of the treatments on Fig. 3. Weevil numbers on cage screens longed periods, boll weevil mortality is boll weevil infestations. The bolls were and mating activity were greater at mid- high in the shed squares. placed in ventilated plastic sweater boxes day than in morning and late afternoon.

24 CALIFORNIA AGRICULTURE, JULY-AUGUST 1985 for two weeks and then examined for boll weevil adults, pupae, and larvae. No boll weevils were caught in traps before September 30, but numbers in- creased (0.2 to 0.3 per trap per day) in mid- to late October. Weevil catches declined sharply (less than 0.05 per trap per day) after the second malathion applica- tion and did not increase thereafter. Ap- parently, the treatments reduced boll weevil trap catches, but numbers caught were low and no data from untreated fields are available for comparison. It is possible that the decline in trap catches was due to normal weevil movement out of the field as it dried after the last irriga- tion. No boll weevils were found in bolls collected from the field during September 28 to November 10. Emerged adults or lar- In one field test to monitor movement of vae in bolls were found on eight of the the boll weevil, the capture of adult wee- sampling dnys between November 11 and vils ranged as high as 80 per trap in I December 7, 1983, showing that an active Grandlure pheromone traps placed every in-field infestation had begun. half mile north and west from the Colora- We studied boll weevil movement west do River. Traps were checked daily. from the Parker Valley, Arizona, into the California desert by installing 14 Grand- intervals are referred to in figure 3 as sets Mating activity and occurrence of all lure-baited traps about a half mile apart 1, 2, and 3. weevils on cage walls were greater at with the first trap on the California side Immature cotton bolls (10 per cage) midday than in the morning or late after- approximately 50 yards from the Colora- were placed in each cage for weevil food noon (fig. 3). These results indicate that do River and the last trap north and west and egg-laying. The bolls were replaced midday insecticide applications would at the San Bernardino County line. Traps weekly during the studies. These bolls and probably be the most effective for weevil were installed November 1 to November all those provided for food in screen-ven- control. However, honey bees and other 11, 1983, and checked daily through tilated holding boxes were opened and ex- beneficial insects active during the day March 31, 1984. amined for boll weevil forms to deter- might be endangered. Boll weevil catches varied (fig. 1). The mine whether reproduction occurred most weevils were caught in traps closest during the study period of November 3, Discussion to the Colorado River and thus to infested 1983, to February 9, 1984. The future status of the boll weevil as cotton fields in Arizona (fig. 2). The high- Some feeding activity occurred on an economically important pest in Ari- est numbers were in early November, and bolls placed in outdoor screen cages zona and California cotton production sys- peaks also occurred in mid-December and throughout the winter, as indicated by the tems remains unclear. Crop sanitation early and late January. Catches de- numerous feeding punctures. Maximum and establishment of a host-free period creased in late February through March. numbers of feeding punctures were re- reduced boll weevil populations in Ari- Since relatively little is known about corded from weevils placed in the cages zona to noneconomic levels during the the biology of the boll weevil in the south- on November 22. However, we found no mid-1960s. When mandatory plowdown of western desert cotton-growing area, we infested bolls. This result is difficult to cotton plants and trash as well as restrict- began stddies to detect reproduction and explain, since we found some live weevil ed planting dates were observed, the boll activity cycles of late-season trapped progeny in the bolls placed for food in weevil was of minor importance. Arizona weevils. screen-ventilated holding boxes during has recently reinstated similar cotton Live weevils caught daily in traps the three collection periods showing that production regulations, and the same de- from November 3 to 21 were placed in reproduction did occur. gree of success in reducing boll weevil screen-ventilated holding boxes with 25 to Boll weevil activity was recorded in populations may occur. If these cultural 50 immature cotton bolls. On November the cages between 8:OO and 10:30 a.m., practices have a more limited effect, 22, all live weevils (532) were divided into noon and 1:30 p.m., and 3:30 and 5:OO p.m. however, greater emphasis on sanitation four samples. Each sample (133) was Numbers of weevils on the cage screens, practices and a longer host-free cotton pe- placed in a 3-square-foot screen cage over as well as mating pairs, were recorded riod may be the most important compo- soil covered with approximately 3 inches daily for each observation period for all nents of integrated pest management sys- of tamarisk needles. The procedure was cages until February 29, 1984. Activity of tems developed to keep populations below repeated for live boll weevils (250 per weevils declined to nil by about 18 days economic injury levels and prevent move- cage) trapped between November 23 and after they were placed in the cages; there- ment of the pest to California’s San Joa- December 20, except that the floors of the fore, we report data only for those 18-day quin Valley. cages were covered with cotton trash periods. We estimated activity by plotting C. A. (Bud) Beasley is Area Integrated Pest Manage- (stalks, leaves). Similarly, two cages over normalized activity values (numbers of ment S ecialist, Cooperative Extension, University of Calikkia, Imperial County, and T. J. Henneberry soil covered with tamarisk needles were single boll weevils or mating pairs per is Director. Western Cotton Research Laboratorv. seeded with live weevils collected be- date or observation time divided by the Agricultural Research Service, US. Department tween December 21, 1983, and February numbers of boll weevils placed in cages Agriculture, Phoenix, Arizona. This research was supported in part by the California Cotton Pest Con- 9, 1984 (350 per cage). These three time for observation). trol Board.

CALIFORNIA AGRICULTURE. JULY-AUGUST 1985 25