Seasonal Mounding, Colony Development, and Control of Nuptial Queens of the Ant Lasius neoniger

Seasonal Mounding, Colony Development, and Control of Nuptial Queens of the Ant Lasius neoniger

Reid M. Maier and Daniel A. Potter, Department of Entomology, S-225 Agriculture Science Bldg. N., University of Kentucky, Lexington 40546-0091

Corresponding author: Daniel A. Potter. dapotter@uky.edu

Abstract

The ant Lasius neoniger can be a significant pest when its mounds occur on golf course putting greens. We monitored seasonal mound building, colony development, and emergence of nuptial queens in central Kentucky, and evaluated feasibility of preventing new nests by intercepting newly-emerged queens with a pyrethroid insecticide. Mounding on sand-based tees started in late February or March and peaked in May or June. Winged pupae and adults were first found in nests in late June; winged adults were present until mid-September. Eggs and larvae were present in established nests throughout the growing season, but not in winter. Workers and root aphids, from which ants obtain honeydew, were present year-round. Sunken sand-filled cups, which captured young queens crawling on the turf, revealed pulses of nuptial emergence from mid-August to mid-September. One-day- and 1-week-old deltamethrin residues gave 94% and 75% control, respectively, of newly-emerged queens, but residual control markedly declined thereafter. Preventing new nests by targeting nuptial queens with a short-residual insecticide likely would require several applications but might have value in an overall management plan. Superintendents seeking to directly reduce mounding with surface insecticides or baits should start scouting in March and treat soon after mounds appear.

Introduction

Lasius neoniger, sometimes called the turfgrass ant, can be a significant pest when its mounds occur on golf course putting greens and tees (4,5,6). This cosmopolitan species is common in open grassy habitats of temperate North America (8). Nests consist of shallow interconnected chambers; each of the multiple nest entrances is surrounded by a mound of excavated soil particles. Mounds reduce smoothness and uniformity of playing surfaces, smother the grass, and dull mower blades (Fig. 1). Mounds on sand-based greens tend to be concentrated around the perimeter and connected to main nests located in natural soil of adjacent roughs (5).

Fig. 1. L. neoniger mounds smother turfgrass, dull mower blades, and reduce smoothness and uniformity of putting greens.

Most knowledge of L. neoniger seasonal biology comes from early studies (1,7) and reviews (2,8). Colonies have one reproductive queen. Workers forage for protein-rich foods, including eggs and larvae of other insect pests, and tend subterranean root aphids for honeydew (1,5,8). Successive broods are produced over an unknown number of years until a colony produces alates (winged reproductive adults).

Hölldobler and Wilson (2) describe the nuptial flights as follows: "L. neoniger emerges in immense swarms in the late afternoon in the second half of August or the beginning of September. The flights almost always occur within 24 h of moderate or heavy rainfall on warm, humid days with little wind. For an hour or so the air seems filled with winged ants, rising from the ground like snowfall in reverse." Some reports suggest that fertilization occurs within the nest (7), whereas others note mating in flight (9). New queens shed their wings, burrow into the soil, and begin laying eggs the following spring (8).

Seasonal patterns of mound building, colony development, and emergence of L. neoniger queens have not previously been studied in turfgrass. Understanding those factors is important because management recommendations usually emphasize early treatment, soon after the mounds appear (4,6). We monitored mound abundance, colony development, and nuptial emergence in central Kentucky, and evaluated a preventive management approach wherein newly emerged queens are intercepted with a short-residual insecticide.

Seasonal Mound Abundance and Colony Development

We counted L. neoniger mounds, indicative of active nest entrances, monthly from February to November in 2003 and 2004 on sand-based creeping bentgrass, Agrostis stolonifera, tees at Arlington Golf Course, Richmond, KY, and Champion Trace Golf Course, Nicholasville, KY. Ten tees were monitored at each course. String was used to subdivide each tee into 1-m wide alleys for ease of counting, then the whole tee was walked and all mounds were counted. The same tees were sampled on each date. No insecticides were applied during the study. Average counts (mounds per 100 m²) were plotted to show seasonal patterns. Ant identity was confirmed by mandibular characters (8).

In 2003, ant mounds first appeared in February, and their numbers on both golf courses peaked in May (Fig. 2). At Arlington there was a steady decline from May through September and little mounding in autumn. Mounds were numerous throughout the summer at Champion Trace. Mounding activity started somewhat later (April) in 2004, peaking in May at Champion Trace, and in June at Arlington and steadily declining thereafter. The first instance of ambient air temperatures ≤ 0°C occurred 8 November 2003 and 1 December 2004.

Fig. 2. Seasonal abundance of L. neoniger mounds on sand-based, creeping bentgrass tees at two central Kentucky golf courses in 2003 and 2004. Data based on 10 tees per course.

A spade was used to locate and excavate five different established L. neoniger nests monthly from mid-March through late November 2004 to monitor presence or absence of various life stages. The site was a stand of Kentucky bluegrass, Poa pratensis, on Maury silt loam soil near Lexington.

Numerous workers and root aphids were found in nests excavated on 19 March, indicating those life stages had overwintered. Each nest presumably also contained a single reproductive queen (8) although generally she was not found. Brood (eggs, larvae, and exposed pupae destined to be workers) were absent in late autumn and winter, but those life stages were already present by mid-March. Winged reproductive adults (males and females) were first observed (in three of the five excavated nests) on 24 June; cocoons containing pupae destined to be new reproductives were found in the other two nests on that date. Winged males and queens were also found in all nests on 19 July, 20 August, and 18 September, but not thereafter.

Monitoring Emergence of Young New Queens

Malaise and black light traps have been used to monitor flight activity of other ant species (3) so we tested them for monitoring L. neoniger queens. One trap of each type was operated continuously on Sweetbriar Farm Golf Course, Danville, KY in 2003, Man O’ War Golf Learning Center, Lexington, KY in 2004, and at Spindletop in both years in areas with abundant L. neoniger mounds. Light traps (Gempler’s, Madison, WI) had a 15-watt, 45-cm fluorescent bulb at a 1.15-m height. Malaise traps (Townes style, Sante Traps, Lexington, KY), which passively intercept flying insects, had a bidirectional (1.8-×-1.8-m) mesh panel. Trap collections were preserved in 95% EtOH and examined for L. neoniger winged queens. Neither type of trap captured any queens in either year, although many other types of insects were captured.

About 3.5 cm of rain fell at Spindletop Research Farm on 11 August 2003. The next day, about noon, the mowing crew alerted us that numerous large ants were crawling on the creeping bentgrass putting greens. We arrived within 30 min and observed hundreds of L. neoniger queens crawling over and burrowing into greens, collars, and adjacent Kentucky bluegrass rough (Fig. 3). All observed crawling queens were wingless, and shed wings littered the surface. We saw no males or mating above ground, although winged queens were seen resting on the tips of grass blades with groups of workers beneath them. Neither we nor the mowing crew had previously seen any queens above ground.

Fig. 3. Lasius neoniger queens during nuptial emergence: (A) Alate emerging from soil; (B) crawling on creeping bengrass putting green after shedding wings; (C) burrowing into turf; (D) hole made by queen burrowing into green.

As the aforementioned light and Malaise traps had not detected the emergence event, that afternoon (12 August) we installed three types of pitfall-style traps along the collar of the aforementioned Spindletop green to monitor subsequent queen activity. Forty traps were 0.35-liter, 10-cm diameter plastic cups (Solo, Urbana, IL) filled to their tops with sand. Another 22 cups of the same type, along with eighteen, 50-ml, 2.75-cm diameter centrifuge tubes (Cole-Parmer, Vernon Hills, IL) were filled half-way with soapy water to compare their effectiveness versus the sand-filled cups. Traps were checked every 2 days until 10 October 2003, several weeks after captures had ceased. Those traps captured 21 total queens, all wingless, from 12 August to 15 September (Fig. 4). Eighteen captures were in sand-filled cups. Trap catches seemed to follow rainfall events.

Fig. 4. Queen captures in pitfall-type traps at Spindletop Research Farm in 2003 (lower graph) in relation to rainfall. Bars represent total for the indicated date plus the 2 days preceding it.

Sand-filled cups, as described above, were used to monitor nuptial queen emergence in 2004. Ten traps were operated at each of four sites (Spindletop, Man O’ War, Arlington; also Plantation Links Golf Course, Nicholasville, KY). Traps were placed in the collars of several greens on each course (2–3 traps per green) and at the same Spindletop location as in 2003. Traps were checked every 2 days from 23 July to 26 September. Rain data were obtained from the University of Kentucky weather station (Spindletop or Lexington) nearest to each trapping site.

The earliest capture (one queen) was at Arlington on 16 August (Fig. 5). Queens were captured at all four locations on 23 August, following rains on 20-21 August (Lexingon, 2.1 cm; Spindletop, 0.4 cm). There had been no rain for 8 days before 20 August at either site. Another pulse of queens was captured at Spindletop on 28 August, following three successive days with rainfall (1.22 cm total, 24-26 August). There had been only 0.38 cm total rainfall at Spindletop from 13-23 August. Queens were also captured at the Man O’ War site on 25 August, coincident with 0.28, 1.22, and 0.81 cm rain on 24, 25, and 26 August, respectively. Queen emergence was not synchronous at all locations but did occur within a 3-week interval.

Fig. 5. Proportionate and total queen captures in sand-filled pitfall traps at four central Kentucky turfgrass sites in 2004 (lower graph) in relation to rainfall.

Residual Control of Young Queens Following Insecticide Treatment

An experiment initiated on 26 July 2004 at Spindletop examined feasibility of preventively controlling nuptial queens with a pyrethroid insecticide. Thirty-six plots (each 1 × 1 m, six replicates) were marked in Kentucky bluegrass mowed at 5.1 cm height. Each week a different set of plots was sprayed with deltamethrin (DeltaGard GC, 4.75% AI; Bayer, Montvale NJ) at label rate for ants (0.09 kg a.i./ha), without post-treatment irrigation. The hand-held CO₂ sprayer had a 0.91-m wide boom with two nozzles (Tee Jet 8004, Spraying Systems Co., Wheaton, IL) that delivered 374 liters/ha spray volume. Treatment dates were 26 July, and 2, 9, 18, and 23 August. The turf was mowed weekly with clippings left on the surface. Weekly rainfall following the first four treatment dates was 9.0, 4.8, 0.3, and 0.4 cm, respectively. No rain fell between the final application and challenge (see below).

One day after the last application (24 August), a PVC cylinder (15.2 cm diameter × 38.1 cm deep) was driven into each plot with 5.1 cm protruding above ground. About 500 winged new queens were collected 23 August by excavating L. neoniger nests in a different Kentucky bluegrass stand. Queens were held overnight in cartons with moist soil. Ten active queens were added to each PVC enclosure the following day. Window screen covers prevented escapes. Thus, queens were confined on turf having dry deltamethrin residues aged 1, 7, 14, 21, or 28 days, or on untreated plots, each replicated six times.

Enclosures with turf, soil, and queens were pried out of the ground after 24 h and taken to the lab. Queens were recovered by carefully examining the turf and soil. Viability of found queens was evaluated by placing them into 210 ml plastic cups filled with sand. Healthy queens quickly burrowed down whereas dead or moribund queens remained on the surface. Percentage mortality (dead plus moribund) was arcsine transformed; then two-way analysis of variance was used to test for treatment effects. Dunnett’s test (a = 0.05) was used to compare each residue age with the control. Finally, polynomial contrasts were used to test for a linear decrease in mortality with residue age (Statistix, Analytical Software, Tallahassee, FL).

Residues aged ≤ 1 week caused significant mortality of queens placed on the turf (F = 11.9; df = 5, 25; P < 0.001); 1 day- and 1 week-old residues provided 93.5 and 70.6% mortality, respectively (Fig. 6). Effectiveness decreased linearly with residue age (polynomial contrasts; t = -5.75; df = 1; 20 P < 0.001). In the untreated cylinders 100% of the queens were recovered and survived. Extraction and assessment of all samples was completed in 1 day with 93% overall recovery rate (live and dead queens). All queens had wings at the start of the experiment, but 28% of the recovered queens had shed their wings. Most recovered queens were found just under the surface in the thatch.

Fig. 6. Mortality of alate L. neoniger queens following 48-h exposure to different aged residues of deltamethrin on Kentucky bluegrass turf. Asterisks (*) denote treatment means significantly higher than untreated control (Dunnett’s test, P < 0.05).

Discussion and Recommendations

Management recommendations for L. neoniger often suggest applying a surface insecticide early in the spring as soon as mounds appear, ostensibly because colonies persisting from the previous year are weakened from overwintering, and those founded by young queens are still small (4,6). In Kentucky, superintendents following that strategy should start scouting for ant mounds in early March. Applying surface insecticides (e.g., pyrethroids) soon after mound appearance often provides 4 to 6 weeks of mound suppression, whereas treatments made later in spring or summer may give only 2 to 3 weeks’ suppression (6). Spot-treating with insecticidal (e.g., hydramethylnon) bait also can be effective (4). Control measures should focus on the perimeter of greens, collar, and also adjacent rough where the main nests are located (5).

Winged reproductive ants were first found in nests during June. We believe that they remained there until the new queens emerged in August or September, as indicated by our pitfall traps. It is not known if virgin queens remain so long in the nest to allow their reproductive systems to mature, or for other reasons.

We observed no nuptial flights or above-ground mating at our study sites. In contrast, Wilson and Hunt (9) described swarms of L. neoniger queens flying obliquely upward and against the wind over non-irrigated fields. They tracked some flying queens for 45 m, and observed mating pairs flying at head level. Had such flights occurred at our sites, presumably some winged ants would have been captured in the Malaise or black light traps. Perhaps new queens from nests in irrigated turfgrass tend to mate underground, emerge, and locally disperse by crawling, whereas colonies in relatively less suitable sites are more prone to nuptial and dispersal flights.

Sand-filled cups were effective for monitoring localized emergence and dispersal of queens. Pulses of emergence seemed to somewhat follow heavy rains, as noted by Wilson (17). Emergence occurred from mid-August to mid-September in both years. Although newly emerged queens were seen crawling on and burrowing into sand-based greens, the fate of such queens is unknown. Nearly all queens in sand-filled cups were alive when found, so queens apparently can survive for the short term in a high-sand environment. Near-absence of nest chambers with brood within sand-based greens suggests that such greens may not be suitable for permanent nests (5).

Fresh (≤ 1 week old) deltamethrin residues killed new queens crawling over and burrowing into treated turf, but older residues were not effective. Intercepting new queens with short-residual insecticides therefore would require fairly precise timing. Emergence may occur over several weeks, so multiple applications might be required. Fast-acting surface insecticides may not control new queens that have already made burrows, nor would they be likely to reach queens within established colonies which may remain active for several years. Nevertheless, if a superintendent planned to treat for black cutworm, Agrotis ipsilon, in late summer, timing that application for when ant queens are emerging, and treating a boom width just outside the collar would eliminate some new founding queens. Such action may have value as part of an overall ant management plan.

Acknowledgments

We thank the cooperating golf course staffs for their assistance, D. Williams for access to Spindletop research greens, D. Held, C. Prater, C. Redmond, Y. Saeki, and L. Simpson for technical assistance, and C. Redmond, M. Rogers, and two anonymous reviewers for constructive criticism. Funding was provided by the United States Golf Association and O. J. Noer Research Foundation. Paper 05-08-006 of the KY Agricultural Experiment Station.

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