UC Agriculture & Natural Resources California Agriculture Title Liquid baits control Argentine ants sustainably in coastal vineyards Permalink https://escholarship.org/uc/item/64z229kw Journal California Agriculture, 62(4) ISSN 0008-0845 Authors Cooper, Monica L Daane, Kent M Nelson, Erik H et al. Publication Date 2008-10-01 Peer reviewed eScholarship.org Powered by the California Digital Library University of California REVIEW ARTICLE ▼ Liquid baits control Argentine ants sustainably in coastal vineyards by Monica L. Cooper, Kent M. Daane, Erik H. Nelson, Lucia G. Varela, Mark C. Battany, Wild Alex Neil D. Tsutsui and Michael K. Rust Liquid ant baits are an alterna- tive to broad-spectrum insecticide sprays conventionally used to con- trol Argentine ants. We review the development of liquid ant baits, which capitalize on the ants’ sugar- feeding requirements and social structure to deliver small doses of toxicant throughout the colony. The ant bait program described here, developed for commercial vine- yards, also has the potential to fa- cilitate the use of biological controls for mealybug and scale pests. The implementation of an Argentine ant bait program will enable grape growers to target other pests more selectively with insecticides, further contributing to their sustainable An Argentine ant tends an adult mealybug. A drop of honeydew, the sugar-rich viticulture practices. mealybug excretion, can be seen in the ant’s mouthparts. he Argentine ant is an invasive pest grape mealybug (Pseudococcus maritimus out the colony. We also discuss future that has spread throughout Cali- [Ehrhorn]), obscure mealybug (P. viburni avenues of study to further control forniaT since it was fi rst reported from [Signoret]) (Daane et al. 2007; Phillips Argentine ant populations. Ontario, Calif., in 1905. Though popu- and Sherk 1991) and vine mealybug Argentine ant biology larly recognized as a household pest (Planococcus fi cus [Signoret]), a particu- (Vega and Rust 2001), the Argentine ant larly severe pest that recently invaded In agricultural systems, Argentine (Linepithema humile [Mayr]) also causes California (Daane, Bentley, et al. 2006). ants are most commonly found in areas severe problems in natural systems by Mealybug feeding may partially defoli- with disturbed habitats and some soil displacing native ants and other insect ate vines, and crop damage results when moisture. Their nests are composed of species, and even some vertebrate and mealybugs infest bunches and excrete reproductive females (queens), sterile plant populations (Holway et al. 2002). honeydew, which promotes the growth females (workers), winged reproductive In addition, in agricultural systems the of sooty molds and bunch rots (Godfrey males and immature ants (eggs, larvae Argentine ant is associated with out- et al. 2002). Mealybugs also indirectly and pupae). Outside the species’ native breaks of phloem-feeding insects such damage vines by vectoring leafroll vi- range, the social structure and biology as mealybugs, scale and aphids, which ruses (Golino et al. 1999) (see page 156). of the Argentine ant have increased the ants protect from natural enemies; To reduce vineyard damage from its pest status. In its introduced range, in exchange, the ants collect the sugar- mealybugs and promote their biologi- Argentine ant nests are unicolonial, form- rich food source (honeydew) excreted cal control (see page 167), the Argentine ing massive “supercolonies” character- by the phloem-feeders (Buckley and ant must be suppressed. We review the ized by the absence of aggression among Gullan 1991). development of liquid ant baits, which workers across large geographic areas In California vineyards, the capitalize on the ants’ sugar-feeding (Tsutsui et al. 2000). The main European Argentine ant has been implicated in requirements and social structure to supercolony has been reported to extend outbreaks of three mealybugs species: deliver small doses of toxicant through- up to 3,700 miles (6,000 kilometers), en- http://CaliforniaAgriculture.ucop.edu • OctOBER–DEcEMBER 2008 177 sprays targeted at ants may disrupt represents no mealybugs; “1” represents Alex Wild Alex integrated pest management (IPM) 1 to 10 mealybugs and/or honeydew; programs by suppressing populations “2” represents more than 10 mealybugs, of beneficial insects. While these sprays sooty mold and/or honeydew; and “3” may also kill foraging ants, unlike baits represents heavily infested, unmarket- they have little effect on ants in nests able clusters. and so allow for an eventual resurgence Because most insecticides are not of the population (Klotz et al. 2002; Rust highly soluble in water, one of the major et al. 1996). challenges facing the study group was to find suitable toxicants that can be for- Developing liquid baits mulated into sugar water solutions. The Ant control in vineyards has been in- first vineyard trials were in 2000 and vestigated using granular protein baits 2001, and compared a no-bait control to for Formica species (Klotz et al. 2003; four liquid bait treatments: boric acid Argentine ants are aggressive and social. Above, Tollerup et al. 2004) and liquid sugar (0.5%), imidacloprid (0.0001%), fipronil three Argentine ants attack the native harvester baits for Argentine ants (Daane, Sime, (0.0001%) and thiamethoxam (0.0001%). ant (Pogonomyrmex subdentatus) en masse. et al. 2006; Daane et al. 2008; Nelson These initial trials showed little differ- and Daane 2007). The liquid bait trials ence between the no-bait control and compassing millions of nests and com- discussed here were conducted either the liquid bait treatments. prising billions of workers (Giraud et al. in Central Coast vineyards (San Luis However, valuable lessons were 2002). In the absence of aggression and Obispo, Santa Barbara and Monterey learned and applied to subsequent tri- territoriality, more resources can be di- counties) populated with obscure als, in which measurable differences rected to colony growth, the domination mealybug, or in North Coast vineyards were recorded among treatments of food and nesting resources, and the (Napa and Sonoma counties) populated (Daane, Sime, et al. 2006). First, bait sta- displacement of native ants in direct, ag- with grape mealybug. The initial liquid tions left in the field for longer than 3 gressive encounters (Holway et al. 1998). bait trials were conducted from 2000 to weeks, without the addition of preser- However, the ants’ biology can also 2002, based on methodologies devel- vative, fouled as the sugar fermented. be used against them. The Argentine oped for urban systems by Klotz et al. Second, unlike the urban systems ant diet is composed mainly of carbohy- (2002) and described in detail by Daane, tested, the vineyards had incredibly drates (sugars) in a liquid form, such as Sime, et al. (2006). large Argentine ant populations: up to honeydew (Rust et al. 2000). Therefore, In brief, the liquid baits were com- 1.2 ounces (35 grams) of sugar water while granular protein baits are not heav- posed of 25% sugar water laced with a per day were removed from monitor- ily foraged by Argentine ant workers, small dose of one of four different toxi- ing tubes, the equivalent of more than sugar water laced with insecticide is an cants, and were deployed in approxi- 100,000 ant visits! excellent method for delivering small but mately 250- to 500-milliliter containers In a later trial in 2002, researchers lethal amounts of toxicant to the colony placed on the ground or attached to refilled and cleaned the bait stations (Silverman and Roulston 2001). Liquid the vine trunk. Treatments were rep- every 2 weeks to reduce bait fermenta- baits exploit the social behavior of ants licated four to six times in large ex- tion, increased the distance between to distribute toxicant to colony members, perimental plots ranging from 0.25 to including larvae and queens (Silverman 0.5 acre (0.1 to 0.2 hectare) to account The ants’ biology can be and Roulston 2003). Argentine ants also for the movement of Argentine ants, used against them. use persistent trail pheromones to recruit which forage up to 150 feet from their colony members to food resources, result- nests (Ripa et al. 1999). ing in fidelity to bait-station locations Ant feeding activity was used to plots to keep the large ant population (Aron et al. 1989; Vega and Rust 2001). quantify ant densities and was based on from spilling over between treatment Because bait is exchanged among colony the amount of nontoxic sugar water ants plots, and increased the number of bait members via trophallaxis (i.e., ants feed- removed from 50-milliliter plastic tubes stations deployed from 35 per acre (85 ing other ants), baits have the potential (monitoring tubes). Sugar-water removal per hectare) to 65 to 250 per acre (160 to affect the nest population and provide rates are related to ant density because to 620 per hectare). The researchers season-long control (Forschler and Evans each milliliter removed represents ap- also used only one bait formulation 1994; Klotz et al. 2006). proximately 3,300 ant visits to the moni- (0.0001% thiamethoxam) and deployed Liquid baits reduce undesirable toring tube (Greenberg et al. 2006). bait stations earlier in the season to environmental impacts because they Mealybug densities were assessed take advantage of spring foraging require a relatively small amount of using 2.5-to-3-minute visual searches of activity. With these changes, research- insecticide, and the dispenser design randomly selected vines (timed counts),