Fortuitous Biological Suppression of the Boll WeeviP by the Red Imported Fire Ant2•3 WINFIELD L. STERLING' Department of Entomology, Texas Agricultural Experiment Station, Texas A&M University, College Station 77843 ABSTRACT Environ. EntomoJ. 7: 564-568 (1978) The efficacy of the red imported fire ant (Solenopsis invicta Buren) as a predator of larval stages of the boll weevil (Anthonomus grandis Boheman) was evaluated in 2 areas of Texas. In the Trinity River area the ants consumed up to 85% of the weevils with a weekly avg of 66%. Ants never consumed more than 37% of the weevils in the Brazos-Navasota River area and averaged 22% in Aug. The fire ant exhibits characteristics that may make it a valuable predator of cotton insect pests. It tends to disperse fairly uniformly across cotton fields at high densities and tends to increase in abundance as the growing season progresses. Downloaded from https://academic.oup.com/ee/article/7/4/564/2366799 by guest on 24 September 2021 Ants have been considered the most important predators Trinity River. An 8.3-ha area of cotton, which had been of the boll weevil, Anthonomus grandis Boheman. (Hinds cleared of timber in 1975 and cropped for the 1st time in 1907. Hunter 1917, Hunter and Hinds 1905, Mally 1902). 1977, served as the experimental plot. No chemical insec- Pierce et aI. (1912) and Hunter and Pierce (1912) listed 16 ticides were applied to the area during 1977. The study cot- species of Texas ants reported as predatory on the boll wee- ton field was located at one end of a 202-ha cotton field and vil. Solenopsis geminata (F.), S. molesta Say. andS. texana was buffered by 77 ha of cotton that were occasionally Emery were among the species cited (Pierce et aI. 1912). treated with chemical insecticides to control boll weevils, with S. geminata having a greater impact on weevil abun- cotton fleahoppers, Pseudatomoscelis seriatus (Reuter), dance during the summer than the combined effect of heat tarnish plant bugs. Lygus lineolaris (Palisot de Beauvois), and parasites (Hinds 1907). Since the early 19OO's, two cotton bollworms, Heliothis zea (Boddie), or tobacco bud- additional species of 50Jenopsis, (5. invicta Buren and S. worms, HeJiothis virescens (F.), by ground application richteri Forel), have accidentally invaded the southern equipment rather than by air in an attempt to prevent insec- U.S.A. (Buren ]972). Their efficacy in suppressing boll ticidal drift into the untreated test plot. The remaining] ]6.7 weevil abundance has been largely unknown. Arant et al. ha were treated by TDC with several insecticides by air as (1958) reported that a laboratory colony of imported fire needed for Heliothis spp. control. The boll weevil was ants (species not cited) killed and consumed 20 adult boll treated with azinphosmethyl at 281 gmlha; the cotton flea- weevils in 2 h. These same ant species devoured boll weevil hopper was treated with dimethoate at 224 gm/ha. larvae and other destructive insects in the field. This early A 2nd field, located at the confluence of the Navasota observational research was not followed by careful field and Brazos rivers south of Navasota, Tex., was also used to evaluation. evaluate fire ant predation. This plot is referred to hereafter At least one attempt was made to introduce an ant pre- as the USDA field because it was leased by USDA-ARS dator to the United States for boll weevil suppression. O. F. researchers during 1977. The field had been in grass hay Cook distributed 89 colonies of the kelep ant (Ectatomma production for several years prior to 1977. Previous to our tuberculatum Oliver) in Texas (Hunter and Hinds 1905); evaluations starting on Aug. 4, the field had been treated however, as predicted by Wheeler (1904), none survived. with methyl parathion at 280 gmlha and diflubenzuron at The efficacy of ants in suppressing boll weevil abundance 70 gmlha on June 14 and methyl parathion at 1120 gmlha, is variable. Ants destroyed as many as 84% of the weevils and diflubenzuron at 70 gmlha on July 4. in fallen squares at Overton, Tex. and such mortality aver- The Ellis untreated cotton was grown under dryland con- aged 20% in east, south, central, northeast, and southwest ditions, whereas the USDA field was irrigated once. Soils Texas and western Louisiana (Hinds 1907). Boll weevil on the Ellis farm were black clay, cracking soils while those mortality from ant predation at Rorence, S.C., never ex- in the USDA field were largely the same except for some ceeded 2% during 1925 and 1926 (Fenton and Dunnam sandy portions. 1929). Ant predation was highest in eastern and southern The standard experimental technique used in these exper- Texas and western Louisiana. iments was to stake 100 yellow, flared, weevil-infested squares on the ground in a large X pattern across the cotton Materials and Methods field. Engineering flags on wire posts were thrust through The predatory efficacy of the red imported fire ant was one of the square bracts and pegged to the soil near the base evaluated on the Ellis farm of the Texas Department of Cor- of a cotton plant. The immature weevil in the square was rections (TDC) located north of Huntsville, Tex., on the placed in the shade to eliminate heat and desiccation as im- portant mortality factors. A square was flagged every 4 m I An,honomus gmndis 8cheman (Coleoptera: Curculionidae). 1 SoleIWpsis invicra Buren (Hymenoptera: Formicidae). down the row and over 2 rows to complete each transect of , This research was supported iD part by the NatioDal Science Foundation and the En- vironmental PrOlection Agency. through a grant (NSF G8-34718) 10 the Uniy. of Calif. an X pattern. The same pattern was used in both the Ellis The findings. opinions and recommendations expressed herein arc those of the author and and the USDA fields. This technique minimized any effect not necessarily those of the Uniy. of Calif .• the NSF or the EPA. This work was con- dueled in cooperation with the Agricultural Research Service. USDA, and was p:u1ially of predator clumping. supported by Entomology Cooperatiye Agreement DO. 12-14-100-9752 (33). Ap- proved for publication as TA 14197 by Director. Texas Agricultural Experiment Station. Ragged squares were exposed to field mortality factor Received for publication Apr. 17. 1978 . for 3-7 days before being collected. Each of the squares • Associate Professor, Department of Entomology, Texas A&M Uniyersity. College Station 77843. was carefully examined for evidence of fire ant predation, 564 ©1978 Entomo]ogical Society of America 0046-225X/78/0007 -0564$00. 75/0 August 1978 STERLING: BOLL WEEVIL SUPPRESSION BY FIRE ANT 565 parasitization, weevil mortality due to other factors or adult sion was made to treat most fields with azinphosmethyl at weevil emergence. a rate of 281 gmlha. The untreated field had sufficient num- Fire ants were sampled by taking 30 cm of row sample bers of overwintered weevils to damage 15% of the 1st 1/3 units containing at least one plant per 20-25 paces, while grown squares (flower buds) produced. However, it was walking a large circle through the field. At least 25 of these noticed that essentially no square damage resulted after the samples were taken in each field on each sampling date. FI generation had emerged, indicating a high degree of Ants on the soil were counted on the 20 cm of row extend- mortality in the FI immatures. Therefore, we decided to ing 50 cm on each side of the plants. Upon approaching the assess the reasons for this developmental failure. Initially 30-cm sample unit, the foot was stamped firmly on the soil we examined a number of dried squares with boll weevil ca. 10 cm from the plant stalk before attempting to count egg punctures and with characteristic ant entry holes as re- the ants. This stamping action excited the ants and caused ported by Hinds (1907). To confirm our diagnosis of these them to emerge from their holes and crawl about rapidly on entry holes as being ant caused, we exposed several yellow, the soil surface where they could be counted. Large plants flared and weevil-infested squares to a laboratory colony of Downloaded from https://academic.oup.com/ee/article/7/4/564/2366799 by guest on 24 September 2021 were spread to allow light penetration and to disturb the soil red imported frre ants and predation was observed. The ants surface which assisted in exciting ants near the plant base rapidly distinguished weevil-infested squares from unin- where they frequently congregate. Using this method, fire fested ones, and within minutes workers chewed holes in ants may be found in cultivated fields where no ant mounds infested squares and removed the immature weevils through are present. As a year or more is required for the fire ant the holes. These fire ant holes can be distinguished from mounds to develop to noticeable size (Green 1962), it is of those made by Heliothis larvae or emerging adult weevils. little value to count only mature mounds in cultivated Heliothis larvae generally make a large excavation in the agroecosystems as an estimate of ant densities. square as they feed on the contents, thus leaving a large Boll weevils were sampled using a biased sample tech- hole and a nearly hollow square. Boll weevil adult exit nique. Our action level was set at finding one adult in the holes are characteristically circular and of sufficient size to field and an avg of 2 adultslStoryR trap on the week during allow adult emergence. Furthermore, when there was doubt which the 1st matchhead squares, i.e., flower buds, were that the emergence hole had been caused by an emerging formed.