Ant Suppression Research Articles

Scavenging in two mountain ecosystems: Distinctive contribution of ants in grassland and non-ant invertebrates in forest.

Scavenging is a key process for the cycling of nutrients in ecosystems, yet it is still neglected in the ecological literature. Apart from the importance of specific groups of animals in scavenging, there have been few ecological studies that compare them. Furthermore, the ecological studies on scavenging have mainly focused on vertebrates despite the crucial importance of invertebrates in this process. Here, we performed a large-scale ant suppression and vertebrate exclusion experiment to quantify the relative contribution of ants, non-ant invertebrates and vertebrates in scavenging nitrogen-rich (insect carcasses) and carbon-rich (seeds) baits in two contrasting mountainous habitats in Brazil (grasslands and forests). Overall, bait removal was 23.2% higher in forests than in grasslands. Ants were the primary scavengers in grasslands, responsible for more than 57% of dead insect larvae and seed removal, while, in forests, non-ant invertebrates dominated, removing nearly 65% of all baits. Vertebrates had a minor role in scavenging dead insect larvae and seeds in both habitats, with <4% of removals. Furthermore, our results show that animal-based baits were more consumed in forests than seeds, and both resources were equally consumed in grasslands. Therefore, we demonstrate the superiority of invertebrates in this process, with a particular emphasis on the irreplaceable role of ants, especially in this grassland ecosystem. As such, we further advance our knowledge of a key ecosystem process, showing the relative importance of three major groups in scavenging and the differences in ecosystems functioning between two contrasting tropical habitats.

Functional compensation in a savanna scavenger community.

Functional redundancy, the potential for the functional role of one species to be fulfilled by another, is a key determinant of ecosystem viability. Scavenging transfers huge amount of energy through ecosystems and is, therefore, crucial for ecosystem viability and healthy ecosystem functioning. Despite this, relatively few studies have examined functional redundancy in scavenger communities. Moreover, the results of these studies are mixed and confined to a very limited range of habitat types and taxonomic groups. This study attempts to address this knowledge gap by conducting a field experiment in an undisturbed natural environment assessing functional roles and redundancy in vertebrate and invertebrate scavenging communities in a South African savanna. We used a large-scale field experiment to suppress ants in four 1 ha plots in a South African savanna and paired each with a control plot. We distributed three types of small food bait: carbohydrate, protein and seed, across the plots and excluded vertebrates from half the baits using cages. Using this combination of ant suppression and vertebrate exclusion, allowed us explore the contribution of non-ant invertebrates, ants and vertebrates in scavenging and also to determine whether either ants or vertebrates were able to compensate for the loss of one another. In this study, we found the invertebrate community carried out a larger proportion of overall scavenging services than vertebrates. Moreover, although scavenging was reduced when either invertebrates or vertebrates were absent, the presence of invertebrates better mitigated the functional loss of vertebrates than did the presence of vertebrates against the functional loss of invertebrates. There is a commonly held assumption that the functional role of vertebrate scavengers exceeds that of invertebrate scavengers; our results suggest that this is not true for small scavenging resources. Our study highlights the importance of invertebrates for securing healthy ecosystem functioning both now and into the future. We also build upon many previous studies which show that ants can have particularly large effects on ecosystem functioning. Importantly, our study suggests that scavenging in some ecosystems may be partly resilient to changes in the scavenging community, due to the potential for functional compensation by vertebrates and ants.

Evaluation of seed-dispersal services by ants at a temperate pasture: Results of direct observations in an ant suppression experiment.

Ants disperse seeds of many plant species adapted to myrmecochory. While advantages of this ant-plant mutualism for myrmecochorous plants (myrmecochores) have been previously studied in temperate region mostly in forests, our study system was a pasture. Moreover, we used a unique combination of observing the effect of ant-activity suppression on ant dispersal and comparison of the contribution of ant and unassisted dispersal to the distance from mother plant. We established plots without and with ant-activity suppression (enclosures). We offered diaspores of a myrmecochorous (Knautia arvensis), and a non-myrmecochorous (Plantago lanceolata) species in a choice test and followed ants carrying diaspores during days and nights (focus of previous studies was on diurnal dispersal). We measured frequency and distances of ant dispersal and compared them with unassisted dispersal recorded using sticky trap method. The dispersal frequency was lower in enclosures (3.16 times). Ants strongly preferred diaspores of the myrmecochore to non-myrmecochore with 586 and 42 dispersal events, respectively (out of 6400 diaspores of each species offered). Ant dispersal resulted in more even and on average longer distances (maximum almost tenfold longer, 994 cm) in comparison to unassisted dispersal. Ant dispersal altered the distribution of distances of the myrmecochore from roughly symmetric for unassisted dispersal to positively skewed. Ants dispersed heavier diaspores farther. Ants dropped the majority of diaspores during the dispersal (which reduces clustering of seeds), while several (11%) were carried into anthills. Anthills are disturbed microsites presumably favorable for germination in competitive habitats. Ants provided non-negligible dispersal services to myrmecochorous K. arvensis but also, to a lesser extent, of non-myrmecochorous P. lanceolata.

Testosterone effects on autonomic function in women with androgen excess polycystic ovary syndrome

Women with androgen excess-polycystic ovarian syndrome (AE-PCOS) present with increased blood pressure (BP) and impaired cardiovascular autonomic control. We tested the hypothesis that androgens play an obesity-independent role in impaired baroreflex (BR) sensitivity and renin-angiotensin system (RAS) control of BP in women with AE-PCOS. We measured the sympathetic baroreflex (sBR) and cardiovagal baroreflex (cvBR) with the modified Oxford procedure, and integrated baroreflex (iBR) and the RAS response to lower body negative pressure (LBNP) in obese, insulin resistant (IR) women with AE-PCOS (n=9; age=23±4 y; BMI=36.3±6.4 kg/m2) and obese, IR controls (CTL) (n=7; age=29±7 y; BMI=34.9±6.8 kg/m2). Studies were conducted at baseline (BSL), after 4 days of reproductive hormone suppression with a gonadotropin-releasing hormone antagonist (ANT, 250 μg/day), and after 4 days of ANT+testosterone (ANT+T, 5 mg/day). At BSL, AE-PCOS and CTL had similar systolic BP (137±14 vs.133±14 mmHg, respectively) and diastolic BP (76±8 vs.63±12 mmHg, respectively). Resting MSNA burst incidence was lower (10.3±3.1 vs. 14.3±4.4 bursts-1×100 hb, P=0.04), but total MSNA activity was greater in AE-PCOS compared to CTL (249±112 vs. 156±44 bursts/min, respectively, P=0.04). Hormone intervention did not impact resting MSNA or BP in either group. In the AE-PCOS group, sBR gain increased during modified Oxford with ANT suppression of T, but sBR gain was restored to BSL when T was reintroduced (-0.48±0.15, -0.63±0.19, and -0.50±0.15 bursts -1 ·100 hb·mmHg -1 for BSL, ANT and ANT+T, respectively, P=0.01). Hormone interventions did not impact sBR gain in CTL (-0.48±0.06, -0.47±0.10, and -0.46±0.09 bursts -1 ·100 hb·mmHg -1 for BSL, ANT and ANT+T, respectively). iBR gain for AE-PCOS and CTL was similar at BSL (1.4±0.9 vs. 1.0±1.3 FVR unit/mmHg, respectively). In AE-PCOS, T suppression increased iBR gain, which was restored to BSL with ANT+T (4.3±6.5 vs.1.5±0.8 FVR unit/mmHg for ANT and ANT+T respectively, P&lt;0.04), with no effect in CTL (1.9 ± 3.0 vs. 0.7±0.9 FVR unit/mmHg for ANT and ANT+T, respectively). cvBR gain was unaffected by group or treatment. Serum aldosterone was greater in AE-PCOS vs CTL (136.5±60.2 vs. 75.7±41.4 pg/ml, respectively, P&lt;0.04), but unaffected by hormone intervention. Serum angiotensin converting enzyme (S [ACE] ) in AE-PCOS was greater compared to CTL at BSL (101.9±93.4 vs. 38.2 ±14.7 pg/ml, respectively, P&lt;0.04). In AE-PCOS, S [ACE] was reduced by ANT (77.7 ±76.5 and 40.6±10.6 μg/L for ANT vs. ANT+T, respectively, P&lt;0.04), but hormone intervention did not impact CTL (43.4±27.3 and 40.6±1 μg/L for ANT vs. ANT+T, respectively, P&lt;0.04). These data suggest the milieu of AE-PCOS increases susceptibility to T driven autonomic perturbations as T elevation had differential effects in AE-PCOS vs. CTL. Our data indicate a powerful relationship among elevated androgens, autonomic function, and the kidney.NIH HL135089/P20GM 121334 National Institutes of Health, NHLBI HL135089 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Indirect control of decomposition by an invertebrate predator

AbstractUnderstanding the factors that control decomposition is critical for predicting how the carbon cycle will alter with global change. Until recently, the accepted paradigm was that climate primarily drives decomposition rates, and interactions among decomposers only control variation at finer scales. Although it is now understood that biotic agents can play an important role, we know less about the importance of species interactions with a lack of field experiments at a large scale. Predation is a key ecological interaction that could influence decomposition by directly or indirectly regulating the abundances of decomposer organisms, but a comprehensive understanding of the cascading effects that predation can have on decomposition, particularly at large scales, is missing.Here we report on an experiment where we suppressed the abundance of ants, which are major predators of termites, at a hectare scale in a natural African savanna and examined how this affected the decomposition of three common substrates (wood, grass and dung).Our study revealed that ants exert considerable top‐down control on decomposition via their predation of termites: decomposition of wood, grass and dung increased by 98%, 74% and 84% with ant suppression, respectively. Suppression of ants increased termite activity and consequently resulted in increased termite‐mediated decomposition. Remarkably, for all substrates, the suppression of ants nearly doubled decomposition by termites. Additionally, for grass and dung substrates, the dominant agent of decomposition switched from microbes to termites with ant suppression.Our study highlights the critical importance of considering species interactions in decomposition studies, particularly given declines in predatory species in the Anthropocene.Read the freePlain Language Summaryfor this article on the Journal blog.

A whole‐ecosystem method for experimentally suppressing ants on a small scale

Abstract Ant suppression experiments have emerged as a powerful method for assessing the role of ants in ecosystems. However, traditional methods have been limited to canopy ants, and not assessed the role of ants on and below ground. Recent advances have enabled whole‐ecosystem ant suppression in large plots, but large‐scale experiments are not always feasible. Here, we develop a small‐scale, whole‐ecosystem suppression method. We compare techniques for monitoring suppression experiments, and assess whether habitat complexity in oil palm influences our method's effectiveness. We conducted ant suppression experiments in oil palm agroforestry in Sumatra, Indonesia. We used targeted poison baits, a physical barrier and canopy isolation to suppress ants in 4 m radius arenas around single palms. We sequentially tested three suppression methods that increased in intensity over 18 months. We sampled ant abundance before and after suppression by fogging, using pitfall traps and extracting soil monoliths. We also monitored ants throughout the experiment by baiting. We tested the soil for residual poison and monitored other invertebrates (Araneae, Coleoptera, Orthoptera and Chilopoda) to test for cross‐contamination. Plots were established under four oil palm management treatments that varied in their habitat complexity: reduced, intermediate and high understorey complexity treatments in mature plantation, and a recently replanted plantation. Post‐treatment ant abundance was 92% lower in suppression than control plots. Only the most intensive suppression method, which ran for the final 9 months, worked. Baiting rarely reflected the other monitoring methods. The treatment negatively affected Orthoptera, but not other taxa. There was no residual poison in the soil. Coleoptera abundance increased in suppression plots post‐treatment, potentially due to reduced competition with ants. Our findings were consistent across management treatments. We developed a whole‐ecosystem method for suppressing ants on a small scale in oil palm plantations. Our method represents a significant advance; previous reductions in ant abundance have not exceeded 38%. We provide the first example of ants being experimentally suppressed belowground. Baiting alone is not adequate for assessing suppression effectiveness, and testing a range of taxa for confounding impacts is important. Our study can act as a blueprint for developing suppression methods for other taxa, which offer unique insights into community ecology.

Functional roles of ants in a temperate grassland.

Ants in temperate grasslands are consumers and ecosystem engineers, influencing biodiversity and potentially grassland productivity. However, the effects of ant exclusion or suppression on resource removal and the biological community in temperate grasslands have yet to be fully explored. We conducted ant-suppression experiments and evaluated the effects of ants on ground-dwelling arthropod communities in the field by using pitfall and bait traps. In the laboratory, we evaluated the effects of ants on the ant-attended aphid Aphis rumicis, which is a honeydew resource for ants, and the slug (Deroceras laeve), an aphid predator. Aboveground arthropod communities were not affected by the ant-suppression treatment. However, slugs (D. laeve and Ambigolimax valentianus) visited bait resources more frequently in the ant-suppression treatment area. In the ant-absence condition in the laboratory experiment, there were fewer aphids on the plants compared to the ant-presence condition owing to predation by D. laeve. Our results suggest that ant abundance in temperate grasslands influences the predation activity of slugs toward honeydew sources such as aphids.

No evidence of top‐down effects by ants on litter decomposition in a temperate grassland

AbstractAnts play multiple roles in ecosystems, but their ability to affect decomposition processes in temperate grasslands is relatively unknown. We investigated whether the suppression of ant populations influenced litter decomposition in grasslands via predation of some decomposers (e.g., mites and springtails) and/or microbial activity and composition. We performed two successful ant suppression treatments (seven weeks, 37% suppression, year 1, 10 weeks, 70% suppression, year 2) over the course of a 59‐week experiment. We then assayed the effects of ant suppression using coarse‐ and fine‐mesh litterbags and evaluated litter chemistry, microbial and arthropod communities, and microbial enzyme activity. Ant suppression efforts reduced ant abundance and altered ant, arthropod decomposer, and non‐ant predator community composition. However, ant suppression did not affect decomposer arthropod abundance, litter mass loss, microbial composition, or enzyme activity in litterbags. Litterbag mesh size did not alter microbial composition, perhaps due to a failure to exclude decomposers, as mites and springtails were more or equally abundant in fine‐mesh bags. Nevertheless, mesh size did change litter chemistry, suggesting that mesh size‐mediated microenvironments affect decomposition environment regardless of invertebrate exclusion. Coarse‐mesh litterbags had higher concentrations of microbial sugars, lignin, and N and lower concentrations of litter C and crystalline cellulose than fine‐mesh litterbags. Litterbag mesh size may alter decomposition processes irrespective of invertebrate abundance. We found no evidence that ant predation was an important driver of decomposer populations or decomposition in these systems, and we suspect redundancy at the top of the detrital food web dilutes the role of ants.

Ants provide biological control on tropical organic farms influenced by local and landscape factors

Multiple predator species can provide effective biological control of pest insects if predators have complementary effects. This could be the case of predatory ants in species-rich assemblages, such as in the tropics. However, predator assemblages are structured by variation in local and landscape factors. Different spatial scales can affect species interaction and consequently the biological control provided. We investigated ant suppression of pest insects in organic vegetable crops, and the role of local and landscape factors on biological control. We used a sentinel prey assay to determine the effectiveness of ant biological control on 18 organic farms in the Brazilian Federal District. Ants and other predatory groups were sampled on farms to determine natural enemy assemblage composition. Ants were the group that most contributed to the predation rates, and the other predator groups complemented the predation rates exerted by ants. The predation of sentinel prey increased 3.07-fold when ants were present. These results varied with the farming management practices employed. The species richness and occurrence were positively related to the predation rates, indicating that ant species-rich assemblage may be more relevant than single species in providing biological control. The predation exerted by ants and other predators were benefited by the abundance of predators in the landscape. Tree cover and cropped area in the landscape reduced ant predation but increased the predation exerted by other predators, because most ant species we sampled usually occur in open habitats. In conclusion, species-rich assemblages play a central role in providing biological control, and biological control provided by ants and other predators depends on local habitat management and landscape composition and therefore is a scale dependent process.

Drought and presence of ants can influence hemiptera in tropical leaf litter

AbstractClimate change is predicted to impact tropical rain forests, with droughts becoming more frequent and more severe in some regions. We currently have a poor understanding of how increased drought will change the functioning of tropical rain forest. In particular, tropical rain forest invertebrates, which are numerous and biologically important, may respond to drought in different ways across trophic levels. Ants are a diverse group that carry out important ecosystem processes, shaping ecosystem structure and function through predation and competition, which can influence multiple trophic levels. Hemiptera are a mega‐diverse order, abundant in tropical rain forests and are ecologically important. To understand the roles of ants in exerting predation and competition pressure on invertebrates in tropical rain forests during drought and a post‐drought period, we established a large‐scale ecosystem manipulation experiment in Maliau Basin Conservation Area in Malaysian Borneo, suppressing the activity of ants on four 0.25 ha plots over a two‐year period. We sampled hemipterans found in the leaf litter during a drought (July 2015) and a post‐drought period (September 2016) period. We found significant shifts in the assemblage of hemipterans sampled from the leaf litter following ant suppression. Specifically, for ant‐suppression plots, the species richness and abundance of herbivorous hemipterans increased only during the post‐drought period. For predatory hemipterans, abundance increased with ant‐suppression regardless of drought conditions, and we found marginal evidence for a species richness increase during the post‐drought period with little or no change in the drought period. These results illustrate how ants in tropical forests structure invertebrate communities and how these effects may vary with climatic variation.Abstract in Malay is available with online material.

Quantifying the effects of an invasive thief ant on the reproductive success of rare Hawaiian picture-winged flies

Threats to endangered insect species that act independently of those associated with habitat loss are often suspected, but are rarely confirmed or quantified. This may hinder the development of the most effective recovery strategies, which are increasingly needed for listed insects. Since 2006, 14 species of flies within the large, showy Hawaiian picture-winged Drosophila group have been added to the US threatened and endangered species list. Many of these species are thought to be limited by host plant rarity, but also by predation on immature stages by invasive ants. We tested the latter hypothesis with a field experiment involving Drosophila crucigera, a more common surrogate for sympatric endangered species, and the invasive ant Solenopsis papuana, on the island of Oʻahu. We established ant suppression and control plots across three forest sites. Within each plot we placed a host plant branch piece, into which lab-reared flies had oviposited, and subsequently tracked weekly emergence of adults. Numbers of flies that emerged were 2.4 times higher in ant-suppressed plots than in control plots; this 58% reduction in survival from egg to adult in the presence of ants was similar across all three sites. Among plots, numbers of emerged flies exhibited a pattern suggesting that the detrimental effect of ants is density dependent. These results confirm that S. papuana, and possibly other invasive ant species, can strongly impact the reproductive success of Hawaiian picture-winged Drosophila. They also point to several management actions, beyond habitat restoration, that may improve the recovery of these imperiled flies.

The red imported fire ant, Solenopsis invicta, modifies predation at the soil surface and in cotton foliage

AbstractRed imported fire ants, Solenopsis invicta, are generalist predators that can have major impacts on foliar arthropod communities in agricultural systems; however, their effects as predators at the soil surface have not been adequately characterized. We examined the contribution of fire ants to predation at the soil surface and in cotton foliage at two sites and over the course of two field seasons in Georgia, using egg masses of the beet armyworm, Spodoptera exigua. To assess interactions between fire ants and other arthropod species, we also measured the densities of edaphic predators and honeydew‐producing hemipterans at both sites. The sites occurred in different growing regions (Piedmont and Coastal Plain), and allowed us to characterize the importance of fire ants as predators under different climatic and soil conditions. Fire ant suppression decreased egg predation at both field sites, and predation by fire ants at the soil surface was equal to if not greater than that in cotton foliage. However, the impact of fire ants on predation varied between sites, likely due to differences in climate and the composition and activity of the extant arthropod communities. Our study also indicates that fire ant suppression is associated with decreases in the density of honeydew‐producing insects, and increasing abundance of whiteflies on the plants coincided with a decrease in egg predation at the soil surface. This finding suggests the mutualism between ants and whiteflies may lead to a shift in predation intensity from edaphic towards plant‐based food webs.

ECOLOGICAL RELEASE OF AN EXOTIC SPECIES UPON SUPPRESSION OF ITS INVASIVE PREDATOR

Ecological release allows a species to expand beyond its currently occupied niche upon removal of a limiting mechanism such as a predator or competitor. Unfortunately, these interactions between exotic and invasive organisms are relatively unknown. We examine how a small-scale, intensive Red Fire Ant (Solenopsis invicta) eradication program may influence the herpetological and formicid community on a 1.85 ha plot in northeast Texas. Red Fire Ant mounds were individually treated with a series of pesticides in 2005, with follow up treatments in 2006 and 2007. Populations of Red Fire Ants, other ant species, reptiles, and amphibians were monitored throughout the study. Other ant species showed signs of recovery after two years of Red Fire Ant suppression. Although reptile and amphibian diversity increased during the study, only populations of the Mediterranean Gecko (Hemidactylus turcicus) showed a dramatic response. The removal of Red Fire Ants provided this exotic Gecko with the opportunity to proliferate. The potential for these kinds of unexpected responses must be considered when removing introduced species from communities containing multiple exotic and potentially invasive organisms.

Saving a tropical ecosystem from a destructive ant-scale (Pheidole megacephala, Pulvinaria urbicola) mutualism with support from a diverse natural enemy assemblage

Ants can disrupt the natural biological control of serious hemipteran pests by interfering with natural enemies, resulting in a change in ecosystem functioning. We focus here on interference by a highly invasive ant Pheidole megacephala on the regulation of a tree destroying hemipteran scale insect Pulvinaria urbicola on Cousine Island in the Seychelles archipelago, a tropical island ecosystem. We show how a diverse natural enemy assemblage contributes substantially to the collapse of the ant-scale mutualism following managed ant suppression. Natural enemy abundance and species richness increased significantly after ant suppression, with varying responses among the different functional guilds. Primary parasitoids coexisted with tending ants before ant suppression, but could not regulate the enormously high scale densities alone. After ant suppression, a significant increase in predators caused a collapse of the scale population. Guilds external to the mutualism were also affected, with primary parasitoids of various non-hemipteran taxa also increasing, which contributed significantly to the recovery of the community to its pre-invasion composition. Our results highlight the far-reaching and pervasive effects of the hemipteran-tending invasive ant within the natural enemy assemblage. In turn, we also illustrate the potential to restore the tropical ecosystem by encouraging an array of natural enemies through precision management of the ant.

Impact of the Red Imported Fire Ant (Hymenoptera: Formicidae) on Epigeic Arthropods of Cotton Agroecosystems

Abstract The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), has been studied extensively in its role in aboveground food webs of agroecosystems of the southern United States. There is also a limited body of evidence suggesting that S. invicta may significantly influence the soil fauna. This study examined the influence of fire ants on the arthropod communities at the soil surface of cotton, Gossypium hirsutum L., fields at two field sites operated by the University of Georgia in Athens and Tifton, GA (1 yr at each location). Fire ant abundance was suppressed in large plots with ant-specific hydramethylnon-based bait, and arthropods were collected from treatment and control plots by using pitfall traps during multiple week-long sample periods to measure the abundance of epigeic arthropods. Sampling was conducted from June through September 2006 in Athens and from July through September 2007 in Tifton. Although fire ant suppression decreased the abundance of erythraeid mites and nitidulid beetles at both sites, the majority of effects were site-specific. Other taxa positively associated with fire ants included oribatid mites and gnaphosid and linyphiid spiders. In contrast, the abundance of springtails, earwigs, endomychid beetles, and thrips increased with fire ant suppression. This study demonstrates that S. invicta can significantly influence both pest and beneficial epigeic arthropods and that although fire ants exert clear effects on specific taxa, their effects are not uniform within a given trophic group as members from the same guild were differentially impacted.

A facultative mutualism between aphids and an invasive ant increases plant reproduction

1. The consequences to plants of ant–aphid mutualisms, particularly those involving invasive ants, are poorly studied. Ant–aphid mutualisms may increase or decrease plant fitness depending on the relative cost of herbivory by ant‐tended aphids versus the relative benefit of increased ant suppression of other (non‐aphid) herbivores.2. We conducted field and greenhouse experiments in which we manipulated the presence and absence of cotton aphids (Aphis gossypii) on cotton plants to test the hypothesis that a mutualism between cotton aphids and an invasive ant, the red imported fire ant (Solenopsis invicta), benefits cotton plants by increasing fire ant suppression of caterpillars. We also manipulated caterpillar abundance to test whether the benefit of the mutualism varied with caterpillar density.3. We found that more fire ants foraged on plants with cotton aphids than on plants without cotton aphids, which resulted in a significant reduction in caterpillar survival and caterpillar herbivory of leaves, flower buds, and bolls on plants with aphids. Consequently, cotton aphids indirectly increased cotton reproduction: plants with cotton aphids produced 16% more bolls, 25% more seeds, and 10% greater seedcotton mass than plants without aphids. The indirect benefit of cotton aphids, however, varied with caterpillar density: the number of bolls per plant at harvest was 32% greater on plants with aphids than on plants without aphids at high caterpillar density, versus just 3% greater at low caterpillar density.4. Our results highlight the potential benefit to plants that host ant–hemipteran mutualisms and provide the first experimental evidence that the consequences to plants of an ant–aphid mutualism vary at different densities of non‐aphid herbivores.

Testing Baits to Control Argentine Ants (Hymenoptera: Formicidae) in Vineyards

Liquid baits were evaluated for control of the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), and associated mealybug and soft scale pests in California vineyards. In 2003, liquid baits with small doses of imidacloprid, boric acid, or thiamethoxam dissolved in 25% sucrose water resulted in lower ant and mealybug densities and fruit damage, compared with an untreated control. Similar treatments in a soft scale-infested vineyard showed only a reduction of ant density and fruit infestation in only the boric acid and thiamethoxam treatments. In 2004, commercial and noncommercial formulations of liquid baits reduced ant densities in three separate trials, but they had inconsistent effects on mealybug densities and fruit infestation; granular protein bait had no effect. Using large plots and commercial application methodologies, liquid bait deployed in June resulted in lower ant density and fruit infestation, but it had no effect on mealybug density. Across all trials, liquid bait treatments resulted in lower ant density (12 of 14 trials) and fruit damage (11 of 14 sites), presenting the first report of liquid baits applied using commercial methodologies that resulted in a reduction of ants and their associated hemipteran crop damage. For commercialization of liquid baits, we showed that any of the tested insecticides can suppress Argentine ants when properly delivered in the crop system. For imidacloprid, bait dispensers must be protected from sunlight to reduce photodegradation. Results suggest that incomplete ant suppression can suppress mealybug densities. However, after ant populations are suppressed, there may be a longer period before hemipteran populations are effectively suppressed. Therefore, liquid baits should be considered part of a multiseason program rather than a direct, in-season control of hemipteran pest populations.

Testing Baits to Control Argentine Ants (Hymenoptera: Formicidae) in Vineyards

Liquid baits were evaluated for control of the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), and associated mealybug and soft scale pests in California vineyards. In 2003, liquid baits with small doses ofimidacloprid, boric acid, or thiamethoxam dissolved in 25% sucrose water resulted in lower ant and mealybug densities and fruit damage, compared with an untreated control. Similar treatments in a soft scale-infested vineyard showed only a reduction of ant density and fruit infestation in only the boric acid and thiamethoxam treatments. In 2004, commercial and noncommercial formulations of liquid baits reduced ant densities in three separate trials, but they had inconsistent effects on mealybug densities and fruit infestation; granular protein bait had no effect. Using large plots and commercial application methodologies, liquid bait deployed in June resulted in lower ant density and fruit infestation, but it had no effect on mealybug density. Across all trials, liquid bait treatments resulted in lower ant density (12 of 14 trials) and fruit damage (11 of 14 sites), presenting the first report of liquid baits applied using commercial methodologies that resulted in a reduction of ants and their associated hemipteran crop damage. For commercialization of liquid baits, we showed that any of the tested insecticides can suppress Argentine ants when properly delivered in the crop system. For imidacloprid, bait dispensers must be protected from sunlight to reduce photodegradation. Results suggest that incomplete ant suppression can suppress mealybug densities. However, after ant populations are suppressed, there may be a longer period before hemipteran populations are effectively suppressed. Therefore, liquid baits should be considered part of a multiseason program rather than a direct, in-season control of hemipteran pest populations.

Monitoring Red Imported Fire Ant (Hymenoptera: Formicidae) Foraging Behavior and Impact on Foliage-Dwelling Arthropods on Soybean Produced Under Three Ant Suppression Regimes

The red imported fire ant, Solenopsis invicta Buren, has been reported to contribute to the biological control of key arthropod pests in soybean, Glycine max (L.) Merrill, and other crops. Solenopsis invicta also has been implicated as a major disrupter of biological control and a direct crop pest associated with reduced yields. In 2000 and 2001, fire ant foraging, survival of sentinel lepidopteran eggs and pupae, seasonal abundance of common foliage-dwelling soybean arthropods, and crop yield were assessed under three different fire ant suppression treatments at two test sites in Tift Co., GA. The treatments included an untreated control, hydramethylnon ant bait, and hydramethylnon bait in combination with the broad spectrum insecticide chlorpyriphos. Fire ant foraging was reduced in the chemically-treated plots in comparison to the control, based on fire ant numbers on hot dog baits after a 1-h field exposure in the early morning. Survival of soybean looper, Pseudoplusia includens Walker, eggs in 2000 and corn earworm, Helicoverpa zea Boddie, eggs in 2001 was lower in the untreated plots after a 24-h field exposure, where S. invicta foraging rates were high. Soybean looper pupal survival was 34 and 88% lower on foliage and the ground, respectively, in the control compared to those with reduced fire ant foraging. The seasonal abundance of foliage-dwelling soybean arthropods was primarily unaffected by the fire ant suppressing treatments. However, in 2001, green cloverworms, Hypena scabra F., and spiders were significantly lower (38.6 and 40.5%, respectively) in the chlorpyriphos plus hydramethylnon bait treatment in comparison to the other treatments. Season-long suppression of fire ants had no effect on soybean yield. The results of this study suggest that S. invicta, at naturally-occurring levels, is an active predator on some common soybean lepidopteran pests.

Impact of Solenopsis invicta Buren Suppression on Arthropod Ground Predators and Pest Species in Soybean

The red imported fire ant, Solenopsis invicta Buren, reportedly contributes to the biological control of key soybean pests. However, S. invicta may negatively affect ground-dwelling natural enemies such as ground beetles and earwigs. Information on the interactions between natural enemies is important for anticipating the success of biological control in agroecosystems with multiple interacting entomophagous species. Ground arthropods were monitored in soybean using pitfall traps in the 2000 and 2001 growing seasons to determine their response to selected fire ant controls. Three treatments were examined: an untreated check, Amdro™ (hydramethylnon) bait (ant-specific), and Lorsban™ (chlorpyriphos) (broad spectrum) plus Amdro. Fire ant captures in pitfall traps were lower in the Amdro and in the Amdro plus Lorsban treatments compared to the untreated control. Reduced fire ant density plus chemical treatment impacted the abundance of certain ground predators. Spiders, primarily Lycosidae, were significantly more abundant in the untreated control plots on some sampling dates; whereas, the earwig Labidura riparia Pallas was more abundant in the Lorsban and Amdro plots, presumably due to the removal of fire ants and other natural enemies. Ground beetles (Carabidae) were not different between treatments on any sampling dates. This study supports the assumption that spiders are compatible with fire ants as natural enemies and that earwigs are not compatible with fire ants. Numbers of lesser cornstalk borer, Elasmopalpus lignosellus Zeller, were not affected by the suppression of fire ant predation or the chemical treatments in 2000, the only year when they were captured. Crickets (Gryllidae), mole crickets (Gryllotalpridae), click beetles (Elateridae), scarab beetles (Scarabaeidae), and false darkling beetles (Melandryidae) also were not different between the fire ant suppression treatments.