Low-Toxicity Baits Control Ants in Citrus Orchards and Grape Vineyards

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Title Low-toxicity baits control ants in citrus orchards and grape vineyards

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Journal California Agriculture, 58(4)

ISSN 0008-0845

Authors Tollerup, Kris E. Rust, Michael K. Dorschner, Keith W. et al.

Publication Date 2004

Peer reviewed

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RESEARCH ARTICLE 

Low-toxicity baits control ants in citrus orchards and grape vineyards

Kris E. Tollerup Michael K. Rust Keith W. Dorschner Phil A. Phillips John H. Klotz 

Effective ant control is critical for controlling honeydew-secreting homopteran agricultural pests such as whitefly and mealybug. Low-toxicity ant baits may more effectively control ants than the broad-spectrum insecticides currently used in California vineyards and citrus orchards. This study focused on developing effective ant baits for use in bait stations to control field ant and Argentine ant, which aggressively tend homopteran Field ants tend a vine mealybug colony, which is infesting the current season’s girdling pests. In the Coachella Valley, field ant wound. is associated with the vine mealybug, a destructive nonnative pest. We conducted preference experiments Citrus is often attacked by honeydew- ficus [Signoret]) is a recent arrival into Cal- ifornia, first reported on table grapes in for various commercially available producing homopterans such as soft scale (Coccus hesperidium L.), citrus the Coachella Valley (Riverside County) ant baits and a bait formulated with mealybug (Planococcus citri Risso) and in 1994. Since its arrival, the vine mealy- anchovy plus imidacloprid. Field ant wooly whitefly (Aleurothrixus floccossus bug has been reported on raisin and preferred the anchovy baits above all [Maskell]). Moreno et al. (1987) showed table grapes in the San Joaquin Valley others tested, and in field trials the that the natural enemies of these pests and on wine grapes in Santa Barbara, anchovy bait with 0.005% imidaclo- provided more effective control when San Luis Obispo, Sonoma and Napa prid significantly reduced foraging ac- the Argentine ant (Linepithema humile counties, for a total of about 30,000 acres tivity. Argentine ant is the primary ant [Mayr]) was absent. Itioka and Inoue statewide. Although little research has been conducted on the interaction be- pest in vineyards and citrus orchards (1996) demonstrated that ladybird beetles (Coccinellidae) and green lacewings tween ants and the natural enemies of of California’s nondesert growing (Chrysopidae) reduced a population of these mealybugs on grape, ant suppres- regions. We tested the efficacy of sev- the mealybug (Pseudococcus citriculus sion is thought to play a critical role in eral chemical bait treatments, all of Green) on Satsuma orange by 94% when their control. which significantly lowered Argentine the ant (Lasius niger L.) was controlled. In the Coachella Valley, the field ant ant populations. In California, three mealybug species — (Formica perpilosa [Wheeler]) is the pre- grape mealybug (Pseudococcus maritimus dominant ant species associated with [Ehrhorn]), longtailed mealybug (Pseu- vine mealybug. The acrobat ant (Cre- dococcus longispinus [Targioni-Tozzetti]) matogaster sp.) is also present but to a iological control programs aimed and obscure mealybug (Pseudococcus lesser extent. Two fire ants, the southern Bat suppressing honeydew-secreting viberni Maskell) — commonly attack fire ant (Solenopsis xyloni [Wheeler]) and pests on citrus and grape must include table, raisin and wine grape varieties. the thief ant (Solenopsis molesta [Say]), ant control in order to optimize the effec- Predators such as lady beetles (Cryp- are also found; however, their interac- tiveness of natural enemies. Honeydew tolaemus sp.) and lacewings attack each tion with vine mealybug is not fully un- provides a stable food source for several of these species, and up to five species derstood. The native gray ant (Formica species of ants (Beattie 1985). To protect of parasitoids are known to attack the aerata [Francoeur]) is similar to the field this food source, ants will disturb or kill grape and longtailed mealybugs. In ad- ant and is the primary ant associated predators and parasitoids (Gullan 1997). dition, the vine mealybug (Planococcus with vine mealybug in the San Joaquin

212 CALIFORNIA AGRICULTURE, VOLUME 58, NUMBER 4 http://CaliforniaAgriculture.ucop.edu • OCTOBER-DECEMBER 2004 213 slow acting so as not to impede recruitment and food sharing (Rust et al. 2000). Bait delivered in stations minimizes environmental exposure to the toxicant, but developing an effective and economically feasible bait station also presents a challenge. The biology of the ant and its foraging behavior must be understood when considering the volume of bait that a station should contain and the number of stations needed per acre. For example, population densities of Argentine ant can be quite large. Markin (1967) conducted experiments in a citrus orchard in San A choice-test arena (without lid) is used to determine the bait preferences of field ants. Diego County and estimated that between 50,000 and 600,000 Argentine Valley and San Luis Obispo County. improved the efficacy of chlorpyrifos ants could ascend an individual citrus The Argentine ant, as well as being a to approximately 8 weeks by using a tree in a single day. Also, Argentine ants primary ant pest in citrus orchards of hand-held, compressed-air sprayer and do not act aggressively toward nearby the coastal growing regions, is also the concentrating the application to the nests. Instead, they form a cooperative primary ant pest associated with vine trunk and trunk-soil interface. Klotz et network of colonies throughout an area mealybug in the wine vineyards of So- al. (2003) improved on this approach that represent one giant “supercolony.” noma and Napa counties. and designed a spray rig mounted on The biology and foraging behavior of an all-terrain vehicle, which delivered field ants are in sharp contrast to that of Limitations of ant control methods the insecticide to a 2-foot-wide strip of the Argentine ant; field ants do not form Current strategies to control ants in soil beneath the grapevines where field large colonies and are territorial. We are orchards generally include the applica- ant nests. This method provided control in the initial stages of bait development tion of residual insecticides, such as of field ant for approximately 9 weeks. and have made progress in finding pre- chlorpyrifos. Chlorpyrifos applied to ferred feeding stimulants and toxicants Development of baits and stations the trunk and ground beneath a citrus for field ant and Argentine ant. tree provides a repellent barrier and Toxic baits may offer a more effective Field ant baits and efficacy kills foraging workers that come into method for controlling ants in orchards contact with the insecticide. However, and vineyards. The recruitment and Bait tests. Under field conditions, only limited control can be achieved be- food-sharing behavior of ants can be we tested five commercially available cause the queen or queens and the vast exploited in order to spread a toxicant baits to control field ant: 1.0% hydra- majority of workers in the nest are not through the colony. Ant baits generally methylnon (Maxforce, Maxforce Insect affected. The effectiveness of chlorpyri- contain three components — a matrix Control Systems, Oakland, Calif.), fos is also limited by high temperature, or carrier, feeding stimulant and toxi- 1.0% hydramethylnon (Maxforce, fine irrigation and ground cover (Rust et al. cant. Each of these components plays a granular), 0.5% pyriproxyfen (Esteem, 2000). When using this method, citrus critical role in the bait’s attractiveness, Valent U.S.A., Walnut Creek, Calif.), trees must be skirt-pruned in order to which makes developing an effective 5.0% orthorboric acid (Niban, Rockford, prevent the ants from using alternative ant bait challenging. For example, the Tenn.) and 0.5% pyriproxyfen (Combat, routes into the canopy. Trunk banding particle size of the carrier affects the Combat Insect Control, Pleasanton, Ca- with an insecticide-impregnated paper rate of collection (Hooper-Bui and Rust lif.). In addition, we tested a granular or a sticky material is an effective meth- 2000); typically, larger ants prefer a large bait formulated with anchovy and od to prevent ants from foraging in the particle size. The optimal percentages 20–30 mesh corn grit developed in the canopy. However, trunk banding is la- of carbohydrate, protein and fat in the laboratory of Dr. Michael Rust. The bor intensive and has not been adopted feeding stimulant may vary according anchovy bait was tested with 0.005% by the majority of growers. to the species of ant or the nutritional and 0.05% imidacloprid. Chlorpyrifos is also the primary requirements of a colony. Also, the toxi- These active ingredients generally method to control ants in vineyards, cant must not deter feeding and must be have lower acute toxicity (LD50) than with similar limitations. Modifica- tions to application techniques, which Low-toxicity ant baits are more effective than broad- concentrate the spray to where the spectrum insecticides because a bait is shared among ants are located, have improved its effectiveness. Phillips and Sherk (1991) nest mates and the queens.

214 CALIFORNIA AGRICULTURE, VOLUME 58, NUMBER 4 http://CaliforniaAgriculture.ucop.edu • OCTOBER-DECEMBER 2004 215 Fig. 2. On each sample date, population densities before Fig. 1. Mean percentage bait removed (± SEM) by field ant in choice-test arenas and after a single insecticide treatment were monitored by placed at the base of ant-infested grapevines (n = 10). Ants were allowed to for- allowing field ant to forage on about 20 grams of anchovy age freely for 24 hours. On May 24, pyriproxyfen (Combat) replaced pyriproxy- bait (nontoxic blank) placed at the base of four grapevines fen (Esteem) in each of the choice-test arenas. per plot and calculating the amount removed after 24 hours.

commonly used broad-spectrum or- placed at the base of vines near ant control. The experimental design was a ganophosphate insecticides. However, nests, separated from one another by completely randomized block, with four what makes these “low-toxicity” baits at least 80 feet within a vine row and treatments replicated five times. Plots is their dose. The anchovy bait formu- 24 feet between vine rows to ensure equaled about 0.04 acres and each con- lated with imidacloprid is unique; the that only one colony fed from each. sisted of 16 vines. In each plot, each of authors are not aware of any such ant Nests were exposed to baits only once the 16 vines was treated with either con- baits on the market. during the experiment. Ants were al- centration of imidadoprid in 20 grams The bait preference test was a com- lowed to forage freely in the arenas of anchovy or 1 gram of Maxforce in a pletely randomized design conducted for 24 hours. The arenas were then col- 90 ml. plastic vial placed and left at the in a 20-acre block of ‘Superior Seedless’ lected, and the average percentage of base of the vine. grapes. A visual inspection of the vine- each bait removed was calculated. The Pre- and post-treatment foraging ac- yard indicated that it was heavily infested percentage of a test bait removed from a tivity of field ant were monitored using with field ants. Approximately 6 grams of single arena was calculated as the num- 20 grams of blank anchovy bait (no toxi- each bait was placed in a 25-milliliter (ml.) ber of grams of a single bait removed di- cant) in 90 ml. plastic vials placed at the plastic vial and then randomly assigned vided by the total number of grams of all base of the four central vines within each to a position in a choice-test arena. The baits removed. Data were arcsine square- plot. After 24 hours, the vials were col- arenas were constructed from aluminum root transformed and analyzed using lected and returned to the laboratory, and pans (12 inches in diameter by 2 inches analysis of variance and least significant the average amount of bait removed was deep) with four equidistantly spaced difference to separate means within SAS. calculated. Monitoring was conducted holes located on the side of the pan flush On each of the test dates, the an- 2 days before treatment, and 10, 18, 93 with the bottom. Glass tubing (3/8 inch chovy baits were removed from the test and 122 days after treatment (DAT). inside diameter and about 4 inches long) arenas in significantly greater amounts At 10 DAT, foraging activity of field was inserted into each hole, so that ants than all other baits (fig. 1). The average ant significantly decreased in plots entering the arena would emerge from the percentage removed of the two baits treated with Maxforce and anchovy plus glass tubing at the center. Twelve small with anchovy plus imidacloprid varied 0.05% imidacloprid, but the foraging weigh boats (1-inch-by-1-inch-by-0.5-inch slightly between test dates, but the dif- activity returned to the pre-treatment plastic dishes used to weigh powder and ferences were not consistent across test level by 18 DAT (fig. 2). Maxforce signif- liquid compounds) were glued to the dates. This indicates that imidacloprid at icantly reduced foraging activity below floor of the pan equidistantly spaced the concentrations tested did not deter that of the control at 93 and 122 DAT. At from one another along the inside pe- collection by the ants. During this experi- 122 DAT, both anchovy baits reduced rimeter. The weigh boats were modified ment, field ant was observed foraging the foraging activity similarly, however so that the vials could be laid flat within on Maxforce but at a very low rate. only the lower rate of imidacloprid them and locked in place. In the field, Efficacy trial. We wanted to measure (0.005%) reduced the foraging activity each arena was covered with a piece of the short- and long-term impact of the significantly lower than the control. plywood to protect it from direct sun- most effective treatments for control- Foraging activity. The process by light and disturbance. ling field ant populations, as indicated which ants share food may explain Ten choice-test arenas were placed by later foraging activity. In the efficacy these results. Larval stages, especially in the vineyard for each of six trials, trial, we tested both concentrations of the later instars, are the only members which were conducted on different imidacloprid (0.005% and 0.05%) in of a colony that can feed on solid foods. dates. During each trial, arenas were anchovy, Maxforce and a nontreated Foragers bring solid food into the nest

214 CALIFORNIA AGRICULTURE, VOLUME 58, NUMBER 4 http://CaliforniaAgriculture.ucop.edu • OCTOBER-DECEMBER 2004 215 and place it on the mouthparts of the tion that can be filled with larva; the food is then chewed and an appropriate bait, such as digested. The larval stage uses much anchovy or Maxforce, and of the nutritional value for growth, placed near the entrance of but excess soluble proteins and amino each nest. acids can be stored (often in the salivary At this stage in our re- glands) and then later secreted to work- search, we do not fully un- ers as a liquid food (Abbot 1978). derstand how populations The decrease in foraging activity of other ant species — such observed at 10 DAT suggests that the as acrobat ant and the two workers that foraged and processed the species of fire ants — will Maxforce or anchovy plus 0.05% imida- respond in the absence of cloprid baits suffered significant mor- field ant. At no time during tality; the rebound occurred as a result the preference trial did we of the dead workers being replaced by observe acrobat ant foraging Ant bait stations submitted to the U.S. Environmental workers from within the nest. The more in the test arenas. However, Protection Agency for use in citrus orchards and grape delayed reduction in foraging activity the fire ants (S. molesta and vineyards were: (A) liquid, constructed from PVC pipe — design used in trials to control Argentine ant on citrus; observed at 93 DAT (Maxforce) and S. xyloni) foraged Combat, (B) granular (Kness Manufacturing Co., Albia, IA); (C) 122 DAT (Maxforce and anchovy plus and S. molesta also collected granular, B&G Perimeter Patrol System (B&G Equipment 0.005% imidacloprid) strongly suggests Niban. These baits may also Co., Plumsteadville, PA); (D) liquid, used to control that these baits affected significant mor- be candidates for registra- Argentine ant in citrus (Whitmire Micro-Gen, St. Louis, MO); and (E) liquid, (Km AntPro, Nokomis, FL). All except tality among the brood and reduced the tion in bait stations if the (A) are commercially available. colony size. population of any of these species were to increase to Developing bait stations pest status in the absence of field ant. Ant activity was estimated in each We are encouraged by these results. plot twice monthly using 50 ml. moni- Argentine ant baits and efficacy In subsequent experiments, we will toring tubes constructed according to vary both the percentage of imidaclo- In previous research, Rust et al. specifications described by Klotz et al. prid in the anchovy bait and the ap- (2000) designed the choice-test arena (2003). Tubes were filled with 25% su- plication rate to determine if we can described above in order to determine crose water, weighed and taped to the improve its efficacy. The advantage of food preferences of Argentine ant. They trunk of each of nine trees located in a formulating anchovy bait with imida- found that both 20% sucrose water and three-by-three configuration at the cen- cloprid is that imidacloprid is currently Maxforce granular (nontoxic blank) ter of each plot. Two additional control registered for use on grape as both a fo- were highly preferred and consistently tubes were hung in two of the central liar and systemic insecticide. We believe collected by Argentine ant year-round. trees to measure evaporation. To pre- that a bait such as this would quickly Rust et al. (2000) also determined the vent ants from foraging on the control be approved for use against field ant effective concentration range of several tubes, they were suspended from string as a broadcast bait, thereby eliminating toxicants in sucrose water for Argentine coated with Stickem Special (Seabright, the need for bait stations. The reduction ant. On the basis of their research, we Emeryville, Calif.). Ants were allowed in foraging activity in the plots treated chose a liquid bait (25% sucrose water to feed from the monitoring tubes for with Maxforce suggests that hydra- plus 0.0001% thiamethoxam) and Max- 24 hours. The monitoring and control methylnon is also an effective toxicant. force to test in citrus. tubes were then collected and reweighed Experiments conducted in the spring The baits were tested in a 40-acre to calculate weight loss. The evapora- and summer 2004 included various Valencia orange orchard. The liquid tive water loss from control tubes was rates of hydramethylnon formulated in bait, liquid-plus-solid baits and con- determined and used to calculate the net the anchovy bait. trols (nontreated) were randomly as- consumption from each monitoring tube, An advantage to the commercial ant signed to twelve 1.5-acre plots such which provided us with an estimate of baits is their availability once registra- that each treatment was replicated the activity of ants in each plot. During tion is complete. Our data indicates that four times. Each plot consisted of a the 24-hour monitoring period, the toxic Maxforce with 1.0% hydramethylnon is 9-by-12 block of trees. Plots were sepa- bait stations were temporarily sealed also a candidate for such registration, rated by seven rows of trees, which with plastic bags to prevent competition although we have not yet developed a served as a buffer. Baits were placed with the monitoring tubes. cost-effective bait station to deliver it. in stations at the base of every fourth Data was pooled across observation Densities of field ant can be high, with tree in a plot along the irrigation line, dates and analyzed using the Kruskal- approximately 50 nests per acre. Our providing an equivalent of 22 stations Wallis nonparametric procedure (Systat goal is to develop a disposable bait sta- per acre. version 9) to test for a treatment ef-

216 CALIFORNIA AGRICULTURE, VOLUME 58, NUMBER 4 http://CaliforniaAgriculture.ucop.edu • OCTOBER-DECEMBER 2004 217 The Interregional Research Project Number 4 (IR-4) was organized to facili- K.E. Tollerup is Ph.D. Student, and M.K. tate pesticide registration in cases where Rust is Professor, Department of Entomolo- economic incentives for the companies gy, UC Riverside; K.W. Dorschner is Ento- are lacking. Such registrations have mology Coordinator, IR-4 Project, Rutgers been termed “minor use.” For minor University, N.J.; P.A. Phillips is Area IPM use, the costs of achieving registrations Advisor, UC Cooperative Extension, Ven- are normally more than the potential tura County; and J.H. Klotz is Cooperative economic benefit to the companies. Ant Extension Specialist, UC Riverside. The baits for use in vineyards and orchards authors thank Sun World, Tudor Ranches would be considered by most of the and Roger Essick for providing the experi- companies to be minor uses. mental sites. We also thank Les Greenberg In cooperation with University of for his assistance with data analysis and Hawaii and UC Riverside researchers, Ken Kido, Edna Diaz, James Lee and Fig. 3. Mean grams of sucrose water re- IR-4 has been working on ant baits in Patrick Dixon for their help with data col- moved from monitoring tubes. Data was pineapple fields, vineyards and or- lection. We gratefully thank the Citrus pooled across observation dates. Monitor- ing tubes were placed on citrus tree trunks chards. IR-4 negotiated with the EPA for Research Board, UC Statewide IPM Project and Argentine ants were allowed to feed concessions that will make it easier to and the UC Exotic Pest and Disease Re- for 24 hours. Means with the same letter are register ant baits. In lieu of a broadcast search Project for financial support. not significantly different. application, ant baits will have to be delivered in bait stations placed in the References pineapple field, orchard or vineyard, Abbot A. 1978. Nutrient dynamics of and the bait stations must prevent any ants. In: Brian MV (ed.). Production Ecology fect, and the Nemenyi procedure was potential contact of the pesticide with of Ants and Termites (Int Prog, no. 13). New York: Cambridge Univ Pr. p 242–3. used to test for differences among the the harvestable crop. The degree of Beattie AJ. 1985. The Evolutionary Ecol- treatments. During the pre-treatment protection provided by the bait stations ogy of Ant-Plant Mutualisms. London: Cam- observation period (May 14 through convinced EPA that certain expensive bridge Univ Pr. 182 p. July 1), consumption of sucrose water data requirements could be waived, Gullan PJ. 1997. Relationships with ants. In: Ben-Dov Y, Hodgson CJ (eds.). World Crop did not differ significantly among the making future registration of these in- Pests: Soft Scale Insects, Their Biology, Natu- experimental plots (P = 0.99925). Post- novative technologies much more likely. ral Enemies and Control. New York: Elsevier treatment consumption of sucrose wa- Sci. p 351–73. Effective ant control Hooper-Bui LM, Rust MK. 2000. Oral tox- ter, however, did differ among the plots icity of abamectin, boric acid, fipronil and (P < 0.0001). The plots treated with the The management of ants that tend hydramethylnon to groups of workers and liquid and liquid-plus-solid baits had homopteran pests is a key component queens of the Argentine ant, Linepithema less consumption of sugar water than of integrated pest management in vine- humile (Mayr). J Econ Entomol 93:858–64. Itioka T, Inoue T. 1996. The role of preda- the control, but did not significantly dif- yards and citrus orchards. Low-toxic- tors and attendant ants in the regulation fer from one another (fig. 3). ity ant baits are more effective than and persistence of a population of the citrus broad-spectrum insecticides because mealybug Pseudococcus citriculus in a Sat- Registration considerations suma orange orchard. Appl Entomol Zool 31: a bait is shared among nest mates 195–202. All pesticide formulations must be and the queen(s). Additionally, ant Klotz JH, Rust MK, Greenberg L, et al. registered on a crop before they can be baits are target-specific and when ap- 2003. Directed sprays and liquid baits to used legally to control a pest species, plied in stations, the risk to nontarget manage ants in vineyards and citrus groves. J Urban Agric Entomol 20:31–40. an essential consideration for taking organisms and risk of environmental Markin GP. 1967. Food distribution within control technologies from research and contamination is minimized. colonies of the Argentine ant, Iridomyrmex demonstration projects to production Although we focused our study on humilis (Mayr). Ph.D. thesis, UC Riverside. agriculture. To achieve registration, the developing baits to control ant pests in 139 p. Moreno DS, Haney PB, Luck RF. 1987. agricultural chemical companies that vineyards and citrus orchards, the meth- Chlorpyrifos and diazinon as barriers to handle the active ingredients must first ods we have developed to screen poten- Argentine ant (Hymenoptera: Formicidae) agree to their use; their pesticides can- tial baits for feeding preference and test foraging on citrus trees. J Econ Entomol 80: 208–14. not be used without consent. Finally, the their efficacy under field conditions are Phillips PA, Sherk CJ. 1991. To control U.S. Environmental Protection Agency applicable to other cropping systems. mealybugs, stop honeydew-seeking ants. Cal (EPA) must approve the registration, Our goal is to provide growers with Ag 45(2):26–8. which normally requires data to be cost-effective, easy-to-use bait delivery Rust MK, Reierson DA, Paine E, Blum LJ. 2000. Seasonal activity and bait pref- submitted. These data requirements can systems, and through collaboration with erences of the Argentine ant (Hymenop- be extensive, and agricultural chemical IR-4 to obtain registration of these prod- tera: Formicidae). J Agric Urban Entomol companies normally bear the expense. ucts for use in agriculture. 17(4):201–12.

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