Herbivory-induced extrafloral nectar increases native and invasive ant worker survival

Ascertaining the costs and benefits of mutualistic interactions is important for predicting their stability and effect on community dynamics. Despite widespread designation of the interaction between ants and extrafloral nectaries (EFNs) as a mutualism and over 100 years of studies on ant benefits to plants, the benefits to ants have never been experimentally quantified. The success of invasive ants is thought to be linked to the availability of carbohydrate-rich resources, though reports of invasive ant visits to EFNs are mixed. In two laboratory experiments, we compared worker survival of one native (Iridomyrmex chasei) and two invasive ant species (Linepithema humile and Pheidole megacephala) exposed to herbivorized or non-herbivorized EFN-bearing plants (Acacia saligna) or positive and negative controls. We found that non-herbivorized plants did not produce any measurable extrafloral nectar, and ants with access to non-herbivorized plants had the same survival as ants with access to an artificial plant and water (unfed ants). Ants given herbivorized plants had 7–11 times greater worker survival relative to unfed ants, but there were no differences in survival between native and invasive ants exposed to herbivorized plants. Our results reveal that ants cannot induce A. saligna extrafloral nectar production, but workers of both native and invasive ant species can benefit from extrafloral nectar as much as they benefit from sucrose.     

Interspecific competition between Solenopsis invicta and two native ant species, Pheidole fervens and Monomorium chinense

This study was designed to understand the effects of the interspecific competition between red imported fire ant, Solenopsis invicta Buren and two native ant species, Pheidole fervens Smith and Monomorium chinense Santschi, by conducting colony interference and individual confrontation tests under laboratory conditions. The colony interference test showed that both native ant species, owing to their numerical advantage, killed the Solenopsis invicta virus-1 (SINV-1)-infected or healthy queens of S. invicta. Significantly less time was required for M. chinense to kill all SINV-1-infected S. invicta compared with the time required to kill the healthy S. invicta. Compared with healthy S. invicta, SINV-1-infected S. invicta spent a longer time eliminating the P. fervens colonies. In confrontation tests, M. chinense killed a significantly higher number of infected S. invicta minors than they did healthy minors, but the number of S. invicta majors (either infected or healthy) killed was substantially less. This study found that the viral infection weakened the competitive ability of S. invicta and made them prone to be eliminated by M. chinense but not by P. fervens.     

Phorid fly parasitoids of invasive fire ants indirectly improve the competitive ability of a native ant

Abstract.  1. The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), is an invasive species of south-eastern U.S.A. Since its introduction from South America approximately 70 years ago, this pest has devastated natural biodiversity.
2. Due to such ecological costs, Pseudacteon phorid fly parasitoids (Diptera: Phoridae) from South America are being introduced into the U.S.A. as a potential biological control agent. Here, the indirect effects of these specialised parasitoids on an interspecific native ant competitor, Forelius mccooki (Hymenoptera: Formicidae), are evaluated.
3. Over the course of a 50-day laboratory experiment, the results show that the native ant improved aspects of exploitative, but not interference, competition when S. invicta -attacking flies were present compared with when they were absent.
4.  Forelius mccooki colonies from the phorid treatment had approximately twice as many foragers at food baits relative to controls; however, there was no significant difference in interference aspects of competition or native ant colony growth between the two treatments.
5. These results suggest that the S. invicta -specialised parasitoids help shift the competitive balance more in favour of F. mccooki than if these flies were not present; however, this competitive advantage does not translate into increased colony growth after 50 days. These laboratory findings are interpreted with regard to the more complex interactions in the field.     

Mechanisms of interspecific competition among an invasive and two native fire ants

The mechanisms of interspecific competition among an invasive and two native Solenopsis fire ant forms were investigated in a series of laboratory experiments. In separate trials each with a different food resource, the native S. geminata × xyloni retrieved the greatest amount of a protein- and lipid-rich artificial food resource and a high protein natural food resource, and the native S. geminata retrieved the greatest amount of a high carbohydrate food resource. In trials investigating aspects of interference competition at the colony level, the invasive S. invicta proved to be initially more aggressive than S. geminata , but less aggressive than S. geminata × xyloni . Solenopsis invicta eventually controlled more of the foraging arenas against both native forms when colonies were equivalent by worker biomass, but not when colonies were equivalent by worker number. When paired with S. invicta , S. geminata suffered a significantly greater proportional reduction in both workers and entire colonies when colonies were initially standardized by worker biomass, but not when colonies were standardized by worker number. When paired with S. invicta , a significantly greater proportional reduction of workers occurred in S. geminata × xyloni , regardless of how colonies were standardized. In pairwise trials at the individual level, majors always exhibited significantly less mortality than minors, regardless of the Solenopsis form. The majors of both native forms suffered significantly less mortality than those of S. invicta . Superiority in colony-level interference ability appears to be an important mechanism allowing S. invicta to displace native Solenopsis forms. The ability of S. invicta to reach high population densities, because of intrinsic biological characteristics or an escape from natural enemies, plays an important contributory role. Similar mechanisms may underlie the success of other invasive ant species.     

Does Mutualism Drive the Invasion of Two Alien Species? The Case of Solenopsis invicta and Phenacoccus solenopsis

Although mutualism between ants and honeydew-producing hemipterans has been extensively recognized in ecosystem biology, however few attempts to test the hypothesis that mutualism between two alien species leads to the facilitation of the invasion process. To address this problem, we focus on the conditional mutualism between S. invicta and P. solenopsis by field investigations and indoor experiments. In the laboratory, ant colony growth increased significantly when ants had access to P. solenopsis and animal-based food. Honeydew produced by P. solenopsis also improved the survival of ant workers. In the field, colony density of P. solenopsis was significantly greater on plots with ants than on plots without ants. The number of mealybug mummies on plants without fire ants was almost three times that of plants with fire ants, indicating a strong effect of fire ants on mealybug survival. In addition, the presence of S. invicta successfully contributed to the spread of P. solenopsis. The quantity of honeydew consumption by S. invicta was significantly greater than that of a presumptive native ant, Tapinoma melanocephalum. When compared with the case without ant tending, mealybugs tended by ants matured earlier and their lifespan and reproduction increased. T. melanocephalum workers arrived at honeydew more quickly than S. invicta workers, while the number of foraging S. invicta workers on plants steadily increased, eventually exceeding that number of T. melanocephalum foragers. Overall, these results suggest that the conditional mutualism between S. invicta and P. solenopsis facilitates population growth and fitness of both species. S. invicta tends to acquire much more honeydew and drive away native ants, promoting their predominance. These results suggest that the higher foraging tempo of S. invicta may provide more effective protection of P. solenopsis than native ants. Thus mutualism between these two alien species may facilitate the invasion success of both species.     

红火蚁入侵对广东多种生境中蚂蚁类群的影响

采用陷阱法和诱饵诱集法研究了深圳红火蚁发生区和未发生区蚂蚁的类群多样性和相似性.结果表明:草坪和荒草地红火蚁发生区域的蚂蚁物种数明显减少,且草坪中蚂蚁种类减少的程度(6种)大于荒草地 (3种).红火蚁入侵后荔枝园、荒草地和草坪的蚂蚁优势种发生了明显改变,红火蚁替代了原来的优势蚂蚁种类,在数量上占据了主导地位,在荒草地和草坪这种优势种的改变更为明显.对蚂蚁类群指数的分析表明:红火蚁入侵荒草地和草坪后蚂蚁类群的多样性、均匀度降低,优势度明显增大;而荔枝园中蚂蚁类群多样性指数、均匀度指数均增大,优势度指数降低.荔枝园、荒草地和草坪的红火蚁发生区和未发生区蚂蚁类群相似性系数不同,分别为0.6316、0.5882和0.2941.     

Guards and thieves: antagonistic interactions between two ant species coexisting on the same ant-plant

Abstract.  1. The simultaneous occupation of a rare understorey ant-acacia Acacia mayana by its guarding ant Pseudomyrmex ferrugineus , and an apparent opportunist parasite of the mutualism, the generalist ant Camponotus planatus is described. The two ant species occur together in 30.7% of the 26 mature A. mayana plants [23.5% of all trees ( n  = 34)] surveyed, but C. planatus is absent from saplings below 1 m in height ( n  = 8).
2. While P. ferrugineus shows behaviour compatible with effective host-tree defence, C. planatus does not attack phytophagous insects and appears ineffective as an ant-guard. Camponotus planatus does, however, occupy swollen thorns (pseudogalls) on the host tree, and harvests nectar from extrafloral leaf nectaries. It is proposed that C. planatus is a parasite of the Acacia–Pseudomyrmex mutualism.
3. Camponotus planatus does not harvest the second trophic reward produced by the tree for its Pseudomyrmex ant-guards, protein-rich food (Beltian) bodies. Camponotus planatus lack the specialised larval adaptations needed to use Beltian bodies as brood food, suggesting that this resource is potentially more resistant to exploitation by generalists than extrafloral nectar.
4. In competition for access to nectaries, C. planatus effectively displaced P. ferrugineus in 99.8% of encounters. These results suggest not only that C. planatus is a parasite of this mutualism, but also that it is able to effectively counteract the aggression shown to other insects by the resident ant-guards.     

红火蚁与两种本地蚂蚁间的干扰竞争

为了探讨重大入侵生物红火蚁Solenopsis invicta Buren与本地蚂蚁的竞争机制以及红火蚁成功入侵的机理, 本研究以红火蚁和2种本地蚂蚁黑头酸臭蚁Tapinoma melanocephalum (Fabricius)及亮红大头蚁Pheidole fervida Smith为材料, 室内测定了红火蚁分别与黑头酸臭蚁、亮红大头蚁之间在个体水平和种群水平上的攻击性和攻击强度。一对一攻击试验结果表明：红火蚁和黑头酸臭蚁之间攻击级别多集中在Ⅲ级, 即竞争优势明显的红火蚁对黑头酸臭蚁缺乏激烈的攻击, 只是在相互攻击时多摆出威胁姿势; 红火蚁与亮红大头蚁之间攻击性较强, 尤其是红火蚁中型和小型工蚁与亮红大头蚁兵蚁之间的攻击性（3.35和3.30）显著强于红火蚁大型工蚁与亮红大头蚁兵蚁的攻击性（2.70）。群体攻击试验结果表明：与黑头酸臭蚁群体攻击的红火蚁各处理组合中, 无死亡红火蚁出现, 而黑头酸臭蚁死亡率为31.80%; 而与亮红大头蚁群体攻击中, 红火蚁死亡率为0.20%~12.00%, 而亮红大头蚁平均死亡率为49.91%。可见, 红火蚁的群体攻击能力强于黑头酸臭蚁和亮红大头蚁, 其中红火蚁与亮红大头蚁间的相互攻击程度激烈, 死亡率较高, 而与黑头酸臭蚁间的攻击程度较弱, 可能由于黑头酸臭蚁化学防御对本身起到一定的保护作用, 这为进一步加强红火蚁发生区本地蚂蚁优势种--黑头酸臭蚁的保护利用提供理论基础。     

Parasitoid–host relationships when host size varies: the case of Pseudacteon flies and Solenopsis fire ants

Abstract. 1. Phorid flies in the genus Pseudacteon are parasitoids of ants. Variation in host size preferences of four South American and two North American Pseudacteon species on monogyne and polygyne forms of their host Solenopsis species [ S. invicta Buren and S. geminata (F.), respectively] was documented.
2. Monogyne Solenopsis workers were, on average, significantly larger than polygyne workers, and the average size monogyne worker attacked was significantly larger than the average size polygyne worker attacked in four of the six Pseudacteon species.
3. Three South American Pseudacteon species attacked larger than average size workers, whereas one attacked smaller than average size workers, in both monogyne and polygyne forms. Both North American Pseudacteon species attacked larger than average size polygyne workers and smaller than average size monogyne workers.
4. Three Pseudacteon species were reared from eggs to adults in infected ants in the laboratory. The size of the emergent phorid fly was related positively to the size of the host worker ant, with females emerging from larger hosts. Similar patterns were documented for both monogyne and polygyne forms.
5. The mean size of worker host from which phorids emerged did not differ significantly between the monogyne and polygyne forms in the subsample of phorids reared to adults.
6. The observed patterns elucidate factors that may cause variation in Pseudacteon sex ratios, and have implications for biological control efforts of pest Solenopsis species.     

Alien and native tree species having extrafloral nectaries as favorite hunting area for arboreal endemic Philippine tiger beetles (Coleoptera: Cicindelidae) in human‐disturbed habitat in Lanao del Sur Province,Mindanao, Philippines

To document a relation between abundance of arboreal, predatory tiger beetles, their ant prey, and extrafloral nectaries attracting the ants, we gathered data from more than 10 species of native and introduced trees and large, tree‐like perennial plants in Lanao del Sur Province, Mindanao, Philippines. All specimens of tiger beetles (two Tricondyla and two Neocollyris species, all endemic to the country) were noted on five tree species characterized by presence of extrafloral nectaries, including three alien/invasive and two native ones. Invasive Spathodea campanulata and native Hibiscus tiliaceus were the most inhabited ones (respectively, 56% and 19% of beetles). Presence of tiger beetles on these trees most probably depends on high abundance of ants, which are typical prey for arboreal Cicindelidae, while occurrence of ants can result from presence of extrafloral nectaries on different parts of the plants. This suggests a new mutualistic insect–plant interaction between native and invasive species.     

Insect visitors to extrafloral nectaries of Byttneria aculeata (Sterculiaceae): relative importance and roles

Abstract. 1. Ants, parasitoids and flies are about equally frequent at foliar nectaries of Byttneria aculeata (Sterculiaceae) in lowland Costa Rica during the dry season, a pattern previously unreported but also observed at other plants in the area.
2. Species of Ectatomma, Crematogaster and Camponotus were the most frequent of twenty-four ant species on Byttneria, eight of which nested in the hollow stems. Ants spent most time at nectaries and little in patrolling.
3. Collections at nectaries yielded large numbers of species of parasitoid Hymenoptera with few individuals of each. Rearing studies of leaf-feeding herbivores yielded several species of parasitoids, including one species taken at a nectary and two others congeneric or closely related.
4. Flies appear to be nectar thieves, in the same sense as non-pollinating floral visitors, despite close association with Byttneria.
5. Ant-plants may be poor models for the larger number of species of less specialized plants with extrafloral nectaries. Plants which have only extrafloral nectaries may better suit the needs of parasitoids than ants, and plants such as Byttneria may benefit as much from parasitoids as from ants.     

Biogeographic effects of red fire ant invasion

The red imported fire ant, Solenopsis invicta , was accidentally introduced to North America over 60 years ago and has spread throughout the southeastern United States. We document the biogeographic consequences of this invasion. We censused ground-foraging ant communities on a 2000 km transect from Florida through New York that passed through invaded and intact biotas. Native ant species density peaks at mid-latitudes in the eastern United States, and the location of this peak corresponds to the range limit of S. invicta . In uninvaded sites, ant species co-occur less often than expected by chance. In the presence of S. invicta , community structure converges to a random pattern. Our results suggest that the effects of S. invicta on native ant communities are pervasive: not only does the presence of S. invicta reduce species density at local scales, it alters the co-occurrence patterns of surviving species at a biogeographic scale.     

Phylogeographic structure of the fire ant Solenopsis invicta in its native South American range: roles of natural barriers and habitat connectivity

We generated mitochondrial DNA (mtDNA) sequence data from 402 individuals of the fire ant Solenopsis invicta collected from 11 native populations and analyzed these data using a combination of demographic, phylogenetic, and phylogeographic methods to infer features of the evolutionary history of this species. Prior expectations regarding high levels of genetic structure and isolation by distance among populations were supported by the data, but we also discovered several unanticipated patterns. Our analyses revealed a major genetic break between S. invicta mtDNA haplotypes that coincides with the Mesopotamia wetlands region of South America, resulting in two higher level nested clade groupings. In addition, we identified contrasting patterns of genetic differentiation within these two major groups, which may reflect differences in connectivity of suitable habitat in different parts of the native range of S. invicta. Our study represents the first attempt to understand the phylogeographic history of S. invicta across its native range.     

The influence of extrafloral nectaries on parasitism of an insect herbivore

The extrafloral nectaries of many plants promote ant defense against insect herbivores. We examined the influence of extrafloral nectaries on the levels of parasitism of a generalist insect herbivore, the gypsy moth (Lymantria dispar L.). Larvae and pupae of the moth were collected from trees with and without extrafloral nectaries growing in the same forests in South Korea and reared to evaluate parasitism. More parasitism occurred on plants with extrafloral nectaries in seven of the nine season-long collections at the six sites and in four out of five collecting periods. Parasitism was higher on the four main genera of plants with extrafloral nectaries than on any of five main genera of plants without extrafloral nectaries. There was no difference in parasitoid richness; nine species occurred in each group, eight of which were the same. There was a positive and almost significant correlation between the abundance of plants with extrafloral nectaries and the parasitism of gypsy moth at the sites. Extrafloral nectaries may reduce herbivory by inducing more parasitism of the insect herbivores that attack plants bearing the glands.     

<Emphasis Type="Italic">Catalpa bignonioides</Emphasis> alters extrafloral nectar production after herbivory and attracts ant bodyguards

Inducible anti-herbivore defenses are found within many plant taxa, but there are fewer examples of inducible indirect defenses that incorporate the third trophic level. This study links caterpillar foraging, herbivore-induced changes in extrafloral nectar production, and the attraction of ants to vulnerable leaves and plants. Catalpa bignonioides Walter (Bignoniaceae) uses extrafloral nectar to attract ant (Forelius pruinosus(Roger)) bodyguards in response to Ceratomia catalpae (Boisduval)(Lepidoptera: Sphingidae) herbivory. Ant density per leaf increased with the sugar content of extrafloral nectar excreted by sampled leaves, suggesting that increased nectar production could attract or retain beneficial arthropods. The masses of sucrose, fructose, glucose and all three sugars combined in the extrafloral nectar increased two- to three-fold on attacked leaves within 36 h of the experimental addition of caterpillars. Production rates for neighboring non-attacked leaves and non-attacked leaves on adjacent plants did not differ over the same time period. Ant attendance at caterpillar-attacked leaves increased two- to three-fold within 24 h of herbivory, relative to attendance at neighboring, undamaged leaves. These attacked leaves attracted the fewest ants prior to the onset of herbivory, suggesting the specialist caterpillar may avoid or be excluded from leaves with more bodyguards. The removal of leaf tissue with scissors did not alter ant attendance at damaged leaves. Mean ant attendance per leaf on attacked plants increased 6- to 10-fold after caterpillar introduction, relative to adjacent unattacked plants. The plant's biotic defense thus operates at two scales; the number of bodyguards (ant workers) on the plant increases after attack, and this increased workforce is biased towards attacked leaves within plants. Fewer caterpillars remained on plants that attracted greater numbers of ants, suggesting these bodyguards benefit the plant.     

No Defensive Role of Ants throughout a Broad Latitudinal and Elevational Range of a Cactus

Defensive mutualisms mediated by extrafloral nectaries are particularly variable; their net results may change with seasons, communities and environmental contexts. Particularly, an environmental factor that can promote changes in outcomes of ant‐plant interactions is elevation in mountainous regions. We tested whether (1) the interaction between the cactus Opuntia sulphurea and ant visitors of extrafloral nectaries is a defensive mutualism; and (2) ant‐plant interaction outcomes vary with elevation as a result of changes in herbivory rate and ant activity. To evaluate if the outcome of interactions was consistent at two extremes of the range distribution of O. sulphurea, we performed an ant‐exclusion experiment with plants at two growth conditions (natural or potted) in two sites with contrasting elevation (1235–1787 m asl) in a temperate region (Villavicencio Nature Reserve, Mendoza, Argentina), and in a tropical region (Huajchilla, La Paz, Bolivia). Although herbivory rate and ant visitation frequency increased with elevation, herbivore damage, plant reproductive success, and cladode growth rate were similar between plants excluded and non‐excluded from ants among sites, geographic regions and growth conditions. These results do not support the hypotheses that the interaction between O. sulphurea and ants is a defensive mutualism, and that elevation affects the net outcome of this ant‐plant interaction.     

Florivorous myrmecophilous caterpillars exploit an ant–plant mutualism and distract ants from extrafloral nectaries

Females of myrmecophilous butterflies tend to oviposit in plants visited by ant species that engage in stable associations with its larvae. In Banisteriopsis malifolia, caterpillars are attended by the same ants that feed on extrafloral nectaries. A conflict may arise when both the plant and caterpillars compete for ant attention, and ants are assumed to forage on the highest quality resource. By attending caterpillars, ants can be indirectly detrimental to plant fitness because florivorous larvae feed intensively until pupation. In this study, we specifically investigated (i) whether the occurrence of facultative myrmecophilous Synargis calyce (Riodinidae) caterpillars in B. malifolia was based on ant species (Camponotus blandus or Ectatomma tuberculatum) and abundance; (ii) the monopolization of ants by the butterfly larvae and (iii) the florivory rates incurred by the caterpillars on inflorescences. The abundance of S. calyce was six‐fold greater in plants with C. blandus, compared to E. tuberculatum treatments. Caterpillars monopolized up to 50% of C. blandus on the plants, indicating that the resources offered by S. calyce were more attractive to ants than extrafloral nectaries. Florivory by riodinids incurred losses of almost 60% of flower buds. Myrmecophilous riodinids exploited an ant–plant mutualism by attracting aggressive ants that become larvae bodyguards. Thus, this ecological interaction is potentially detrimental to B. malifolia, since the ants, which can provide protection against herbivores, shift to provide defence for one of these herbivores.     

红火蚁入侵对玉米植株上节肢动物群落的影响

在农业生态系统中,入侵性红火蚁Solenopsis invicta Buren是一种贪婪的节肢动物捕食者,会不加区分地攻击害虫和有益昆虫。本文以玉米地作为研究生境,系统调查并探讨红火蚁入侵对玉米植株上节肢动物群落的影响。结果表明,红火蚁入侵使得玉米地内节肢动物的种类下降了64.7%,而减少的种类主要隶属于半翅目、鳞翅目和双翅目,并且这种负面影响主要体现在玉米生长后期。随着玉米植株上红火蚁数量的增加,相应的节肢动物群落物种丰富度、多样性和均匀度指数减少,生态优势度指数增加。进一步通过系统聚类分析表明,红火蚁发生区玉米植株上节肢动物类群结构在时间序列上波动较大,其入侵已显著影响了生境内节肢动物群落。     

Role of floral repellents in the regulation of flower visits of extrafloral nectary-visiting ants in an Indian crop plant

Abstract.  1. Field investigation of the association between sponge gourd, Luffa cylindrica plants and its ant visitors revealed that five of the six most frequent species: Camponotus compressus, C. paria, Pheidole sp., Pachycondyla tesserinoda and Tetramorium sp. mainly visited the extrafloral (EF) nectaries present on the leaves, bracts, bracteoles and calyx of the plant. Tapinoma melanocephalum was the only ant species observed at the floral as well as the EF nectaries.
2. A bioassay of ant behaviour revealed aversion to young and mature unisexual flowers of sponge gourd in the five predominantly EF nectary-visiting ant species, while floral preference was demonstrated in T. melanocephalum. A significant difference was not found in the number of insect pollinators visiting T. melanocephalum occupied and un-occupied flowers, suggesting the absence of deterrent effect of this tiny ant species on the pollinators.
3. Further behavioural assays showed preference for 2- and 4-day-old leaves and also 2-day-old buds, while the 4-day-old buds induced avoidance in all the species. Androecium and gynoecium had significantly higher repellent effects in comparison to the petals. Thus floral repellents, probably help to reduce nectar theft and prevent loss of pollen function.
4. This aversion was not demonstrated in the case of old flowers. A significantly greater number of insect pollinators visited young and mature flowers compared with old flowers, suggesting that selective exclusion of medium- and large-sized EF nectary-visiting ant species from the flowers, as a result of aversion to floral repellents, serves to avoid the threat of attack to insect pollinators of sponge gourd.     

两种火蚁与黑头酸臭蚁上颚形态及其超微结构观察

应用扫描电镜和光学显微镜观察了红火蚁Solenopsis invicta Buren、热带火蚁Solenopsis geminata Fabricius和黑头酸臭蚁Tapinoma melanocephalum Fabricius的上颚类型及形态特征。头宽和上颚长度测量结果表明:两种火蚁的头宽和上颚大小具有连续性特征,黑头酸臭蚁工蚁仅1个类型,3种蚂蚁中黑头酸臭蚁的上颚最小,其前端具4个锋利切齿叶,后部有一排小而钝的臼齿叶,上颚内缘较光滑。在形态上,红火蚁的大、中、小型工蚁与热带火蚁工蚁的上颚区别不大,表面纹理光滑,都具4个锋利小齿,上颚内缘也比较光滑;热带火蚁兵蚁上颚仅3个小齿且较钝,其上颚内缘凹面比两种火蚁工蚁的深且纹理粗糙,推测红火蚁工蚁不仅用于筑巢,还用于防御,而热带火蚁兵蚁的强壮上颚可能主要用于磨碎食物,而非保卫蚁巢。