荒草地和荔枝园生境短期入侵的红火蚁与黑头酸臭蚁种间的干扰竞争

【背景】红火蚁入侵后对新发生地区生物多样性的影响及与土著物种的关系是入侵生物学研究的重点之一,解释红火蚁与类似生态位的土著蚂蚁的关系对全面了解该蚁入侵的生态学效应具有重要意义。【方法】通过野外模拟设置蚁巢,观察、记录距离红火蚁和黑头酸臭蚁蚁巢30 cm处诱集到的黑头酸臭蚁工蚁在红火蚁入侵前、入侵中及移除后的数量变化,研究短期入侵红火蚁实验种群与荒草地和荔枝园黑头酸臭蚁间的干扰竞争。【结果】红火蚁实验种群短期入侵对荒草地生境黑头酸臭蚁的干扰较明显,而对荔枝园生境黑头酸臭蚁的干扰较小;红火蚁未入侵荒草地生境黑头酸臭蚁受干扰最明显,移除红火蚁20 min后,处理诱饵上召集的黑头酸臭蚁数量才与入侵前差异不显著;红火蚁未入侵荔枝园生境黑头酸臭蚁受干扰最小,移除红火蚁仅5 min后,处理诱饵上黑头酸臭蚁数量就恢复到入侵前,甚至超过入侵前数量。【结论与意义】红火蚁入侵对黑头酸臭蚁的觅食行为存在较大的干扰抑制作用,其影响程度与生境的复杂性有着密切关系。研究结果可为了解红火蚁入侵的生态学效应提供证据。     

红火蚁入侵和未入侵生境中蚂蚁的觅食强度

采用诱饵诱集法,对华南地区3种典型的红火蚁入侵和未入侵生境中蚂蚁对4种诱饵（蜂蜜、花生油、火腿肠和黄粉虫幼虫）的搜寻时间、召集时间及召集数量进行研究,并分析了红火蚁入侵对蚂蚁觅食强度的影响.结果表明：草坪红火蚁入侵区,蚂蚁对黄粉虫幼虫和花生油的搜寻时间极显著或显著短于对照区（红火蚁非入侵区）;荒草地红火蚁入侵区,蚂蚁对4种诱饵的搜寻时间与对照区的差异均不显著,在花生油上的召集时间显著长于对照区;荔枝园红火蚁入侵区,蚂蚁对4种诱饵的搜寻时间及召集时间与对照区均无显著差异.诱饵设置30 min时,草坪红火蚁入侵区,花生油、黄粉虫幼虫、火腿肠上的红火蚁工蚁数量均显著多于本地蚂蚁工蚁数量;荒草地红火蚁入侵区,花生油上的红火蚁工蚁数量明显多于本地蚂蚁工蚁数量,其余诱饵上红火蚁工蚁数量与本地蚂蚁工蚁数量的差异不显著;荔枝园红火蚁入侵区,4种诱饵上红火蚁工蚁数量与本地蚂蚁工蚁数量的差异均不显著.     

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。     

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。     

华南地区典型生境中红火蚁觅食行为及工蚁召集规律

观察研究了华南地区几种典型生境中红火蚁对不同类型食物的觅食行为和工蚁召集动态规律。研究结果表明红火蚁觅食行为存在搜寻、召集及搬运等主要过程。不同生境中红火蚁对食物的搜寻时间存在一定差异,荔枝园中搜寻时间明显长于其它生境;荔枝园、荒地、路边生境中红火蚁对蜂蜜的搜寻时间明显长于其它几种食物;同一生境中红火蚁对不同重量的同种食物搜寻时间无明显变化。发现食物后召集的工蚁数量随着时间延长呈现不断增加的趋势,对于较大的食物一般30min左右召集的工蚁数量达到最大,之后趋于稳定并逐渐减少,而对于可以直接搬动的食物发现后15min左右群体召集数量达到最大并很快将其搬走。召集工蚁数量与发现后时间的关系符合二次非线性方程,建立了火腿肠、花生油和蜂蜜等食物上红火蚁工蚁召集数量与发现时间的关系模型,分别为Na=4183.91e^-0.0327T-4231.48e^-0.0346T,Na=3253.78e^-0.0233T-3314.59e^-0.0271T,Na=117.97e^-0.0131T-163.93e^-0.0808T。对于不同食物红火蚁发现后召集的最大工蚁数量间有明显差异,其中花生油上最大,平均为176．3头,火腿肠上次之,为90．4头,蜂蜜上最少,为68．0头。对于不同重量的同种食物,工蚁的召集动态规律较为一致,发现食物后25-30min左右工蚁的召集数量均达到最大值,之后缓慢减少,发现食物后时间长度和食物上工蚁数量也符合房室模型函数Na=c1×exp（-c2T）-c3×exp（-c4T）。同种食物不同重量之间同一时间召集的工蚁数量存在较大差异,呈随食物重量增大而增大趋势。不同生境中对相同质量同种食物工蚁召集数量动态总体变化规律相近,但在发现食物后工蚁数量增长的速度和最大召集工蚁的数量存在明显差异,以路边工蚁数量增长最快、工蚁总数最多,苗圃次之,荔枝园、荒地中工蚁增长速度均较低。红火蚁对不同食物种类切割、搬运耗时存在很大差异,搬运完0．5g的火腿肠需要26．23h,而黄粉虫幼虫（重量约为0．1g）仅为15．6min。不同生境中红火蚁对相同重量同一种食物的搬运耗时也不同,荔枝园要长于其它生境。     

两种蚂蚁在橡胶树上的空间分布类型及其竞争

为了探讨黑褐举腹蚁与橡副珠蜡蚧共生优势种黑头酸臭蚁的分布及其竞争关系,本研究采用目光搜寻法调查了橡胶林内黑褐举腹蚁和黑头酸臭蚁的空间分布型及黑褐举腹蚁对黑头酸臭蚁种群数量的影响,并分析了2种蚂蚁在室内人为干扰下的竞争关系。结果表明:2种蚂蚁在橡胶树上均呈聚集分布,并且在有黑褐举腹蚁及其蚁巢区黑头酸臭蚁的种群数量显著低于无黑褐举腹蚁区,可见黑褐举腹蚁对黑头酸臭蚁种群有一定的控制作用;室内1头黑褐举腹蚁与不同密度下黑头酸臭蚁攻击的各处理组合中,无死亡黑褐举腹蚁出现,2种蚂蚁配比在1∶9以下时,黑头酸臭蚁常遭到黑褐举腹蚁的迅猛攻击且死亡率均超过50%;2种蚂蚁配比在1∶9以上时,黑褐举腹蚁攻击行为由主动攻击变为被动防御,此时黑头酸臭蚁死亡率降至26.67%~9.78%;由此可知,1头黑褐举腹蚁最多可与9头黑头酸臭蚁对抗。     

西双版纳入侵长足捷蚁与土著黄猄蚁的种间竞争

【目的】入侵物种能够通过竞争影响本地物种的种群,从而影响入侵地的生物多样性。长足光捷蚁Anoplolepis gracilipes是全球最具破坏力的入侵蚂蚁之一。本研究旨在明确西双版纳地区入侵长足捷蚁与土著优势种蚂蚁黄猄蚁Oecophylla smaragdina之间的竞争关系。【方法】通过野外调查和室内控制试验相结合的方法,观察和对比分析长足捷蚁和黄猄蚁的体型大小,雾凉季和雨季的巢穴外觅食活动规律,觅食能力(搜寻食物的时间、在觅食时间内召集的最大工蚁数),打斗行为(不同打斗组合的攻击强度和死亡率)以及对饥渴的耐受性(无食物和水分供应时平均存活时间和存活率随时间的变化)。【结果】长足捷蚁工蚁体长(3.66±0.06 mm)显著小于黄猄蚁工蚁(8.27±0.16 mm)。在雾凉季时,长足捷蚁具有比黄猄蚁更长的觅食活动时间;而在雨季时,两种蚂蚁均在下午温度较高时段觅食活动的个体数量减少。苹果、蜂蜜和火腿肠3种食物作为诱饵时,长足捷蚁具有更快搜寻食物的能力,4~8 min便能找寻到食物,而黄猄蚁需要8~21 min才能找寻到食物,此外在寻找到食物后,长足捷蚁也有更快召集同伴的能力。在人工控制试验中,1头长足捷蚁和1头黄猄蚁同时存在时主要以不攻击和低强度攻击为主,而当两种蚂蚁中的任意其中一种的个体数量增加到5头时,攻击强度会显著增加,两种蚂蚁均存在种间协作行为。在饥渴状态下,两种蚂蚁工蚁的平均存活时间差异不显著,但长足捷蚁最长存活120 h,黄猄蚁最长存活96 h。【结论】在西双版纳地区,长足捷蚁相较于土著黄猄蚁具有更强的觅食的能力,雾凉季觅食活动时间更长,暗示长足捷蚁可能具有较强的温度适应能力。有必要加强对这一入侵蚂蚁的研究,并密切关注其种群在该地区的发展。     

红火蚁及其他两种蚂蚁毒腺细菌鉴定与多样性分析(英文)

【目的】本研究旨在分析红火蚁Solenopsis invicta毒腺细菌群落多样性,并与热带火蚁Solenopsis geminata和聚纹双刺猛蚁Diacamma rugosum比较毒腺细菌群落差异。【方法】采用Illumine Hiseq 2500测序平台对红火蚁(工蚁、有翅蚁和蚁后)、热带火蚁(工蚁)及聚纹双刺猛蚁(工蚁)毒腺细菌群落16S rRNA基因V3-V4区测序,基于测序数据进行生物信息学分析。【结果】变形菌门(Proteobacteria)在红火蚁工蚁、有翅蚁和蚁后以及热带火蚁工蚁毒腺中占优势,而厚壁菌门(Firmicutes)在聚纹双刺猛蚁工蚁毒腺中占优势。与红火蚁工蚁和有翅蚁相比,柔壁菌门(Tenericutes)在红火蚁蚁后毒腺中更丰富。广州红火蚁蚁后毒腺中假单胞杆菌Pseudomonas相对丰度显著高于其在有翅蚁及工蚁中的。螺原体Spiroplasma相对丰度在热带火蚁毒腺中显著高于在聚纹双刺猛蚁工蚁毒腺中的。毒腺中细菌多样性分析发现,芽孢杆菌属Bacillus和乳酸杆菌属Lactobacillus在广西红火蚁工蚁中的相对丰度显著高于在广州红火蚁工蚁中的。然而,乳酸杆菌属细菌在聚纹双刺猛蚁工蚁毒腺中的相对丰度显著高于广西的热带火蚁工蚁毒腺中的。【结论】毒腺细菌组成和多样性在3种不同种类蚂蚁工蚁和红火蚁不同品级中存在差异。     

红火蚁与热带火蚁间的干扰竞争

【目的】为了探讨入侵火蚁在我国成功定殖及其之间的竞争机制。【方法】运用行为学方法研究红火蚁Solenopsis invicta(Buren)和热带火蚁Solenopsis geminata(Fabricius)在个体水平和群体水平上的攻击性、攻击手段及合作能力。【结果】一对一攻击试验中,红火蚁和热带火蚁之间攻击级别多集中在3级,两种入侵蚂蚁间以相互威胁为主;红火蚁大型工蚁与热带火蚁兵、工蚁间最为好斗,其攻击级别达到4级的比例最高,分别为33.04%、37.92%。热带火蚁兵蚁与各型红火蚁间攻击强度差异不显著;热带火蚁工蚁与红火蚁小型工蚁之间的攻击性最强,其攻击性(3.49)显著高于热带火蚁工蚁与红火蚁大、中型工蚁的攻击性(3.32和2.97)。在攻击手段上,3级打斗时各型红火蚁更倾向以物理攻击主动威胁热带火蚁,而热带火蚁兵、工蚁会采取多种方式主动攻击红火蚁,双方皆以躲避应对为主;4级打斗时两种火蚁主要以混合攻击为主动或应对手段。群体攻击试验显示,红火蚁群体间攻击强度和合作性会随着群体数量的增加而显著增加,热带火蚁合作性较差,其群体对抗红火蚁的优势仅仅是由于个体数量的增加。【结论】红火蚁比热带火蚁具有更强的竞争优势。研究结果为入侵蚂蚁间不对称竞争机制和长期群落替代的内在原因提供理论基础。     

应用诱饵诱集法和陷阱法收集的红火蚁工蚁数量间关系研究

准确获得红火蚁Solenopsis invicta Buren发生程度数据是做好防控工作的基础和前提,明确不同调查方法之间的定量关系可为建立该蚁发生程度度量的标准化体系提供依据。本研究比较了应用诱饵诱集法和陷阱法获得的红火蚁工蚁数量,并分析了二者的相关性,建立了模型。累计设置了840个诱饵,共诱集到183753头工蚁;设置840个陷阱,共收集工蚁93787头。一年中不同时期诱饵诱集法采集的工蚁数量以4月-6月最多,为285.8头/诱饵;陷阱法是7月-8月,为171.7头/陷阱。诱集法、陷阱法收集到的工蚁数量极显著相关,描述该关系的6个模型分别为Y=0.2693X+27.9010(1月-3月)、Y=0.2309X+22.6450(11月-12月)、Y=0.2818X+61.1160(4月-6月)、Y=0.6219X+28.1070(7月-8月)、Y=0.3067X+32.2510(9月-10月)、Y=0.3635X+32.2510(1月-12月)。本研究结果对建立红火蚁发生程度主要指标的转换体系具有参考意义。     

Exploitation and interference competition between the invasive Argentine ant,Linepithema humile,and native ant species

Interactions between the invasive Argentine ant, Linepithema humile, and native ant species were studied in a 450-ha biological reserve in northern California. Along the edges of the invasion, the presence of Argentine ants significantly reduced the foraging success of native ant species, and vice versa. Argentine ants were consistently better than native ants at exploiting food sources: Argentine ants found and recruited to bait more consistently and in higher numbers than native ant species, and they foraged for longer periods throughout the day. Native ants and Argentine ants frequently fought when they recruited to the same bait, and native ant species were displaced from bait during 60% of these encounters. In introduction experiments, Argentine ants interfered with the foraging of native ant species, and prevented the establishment of new colonies of native ant species by preying upon winged native ant queens. The Argentine ants' range within the preserve expanded by 12 ha between May 1993 and May 1994, and 13 between September 1993 and September 1994, with a corresponding reduction of the range of native ant species. Although some native ants persist locally at the edges of the invasion of Argentine ants, most eventually disappear from invaded areas. Both interference and exploitation competition appear to be important in the displacement of native ant species from areas invaded by Argentine ants.     

Imported crazy ant displaces imported fire ant, reduces and homogenizes grassland ant and arthropod assemblages

A recently introduced, ecologically dominant, exotic ant species, Nylanderia fulva, is invading the Southeastern United States and Texas. We evaluate how this invader impacts diversity and abundance of co-occurring ants and other arthropods in two grasslands. N. fulva rapidly attains densities up to 2 orders of magnitude greater than the combined abundance of all other ants. Overall ant biomass increases in invaded habitat, indicating that N. fulva exploits resources not fully utilized by the local ant assemblage. At high density, as N. fulva spreads, it eliminates the current ecologically dominant invasive ant, red imported fire ants (Solenopsis invicta). Compared to imported fire ant dominated habitat, N. fulva invasion zones have lower non-ant arthropod species richness and abundance with impacts differing by trophic category. Further, N. fulva reduces abundance and species richness of the remainder of the ant assemblage and does so in a non-random manner: impacting species with small sized workers much less than species with larger workers. In these and other ant assemblages with a large exotic component, the exotics tend to be small bodied species. As a result, N. fulva almost completely eliminates regionally distributed species, but leaves globally distributed species largely unaffected, thereby systematically favoring introduced over native diversity. S. invicta impacts wildlife and arthropod assemblage structure and is nearly ubiquitous in non-forested habitats of the Southeastern United States and Texas. Its displacement by N. fulva has critical implications for the natural systems of this region.     

Aggressive interactions between the introduced Argentine ant, Linepithema humile and the native odorous house ant, Tapinoma sessile

The Argentine ant (Linepithema humile) is an invasive species that disrupts the balance of natural ecosystems by displacing indigenous ant species throughout its introduced range. The mechanisms by which Argentine ants effectively compete against native ant species have been previously addressed in field studies that centered on interference and exploitation competition at baits and mainly examined the colony-level performance of Argentine ants. Detailed behavioral observations explaining the basis for the strong competitive ability of L. humile are comparatively rare. To gain a better understanding of the mechanisms by which Argentine ants displace native ants we examined the aggressive interactions between the Argentine ants and the odorous house ant, Tapinoma sessile in four different aggression assays: (1) worker dyad interactions, (2) symmetrical group interactions, (3) intruder introductions into an established resident colony, and (4) a resource competition assay which focused on competition for food and nesting space. Our results demonstrate a clear disparity between worker-level and colony-level fighting ability of Argentine ants and provide behavioral evidence to explain the superior interference ability of Argentine ants in group assays. Argentine ants experienced mixed success in fighting against odorous house ants in dyad interactions, but gradually gained a numerical advantage in symmetrical group interactions by active cooperation among nestmates. Results of the resource competition assay indicate that Argentine ants recruit rapidly, numerically dominate food and nesting sites, and aggressively displace T. sessile from baits. Taken together, the results of these assays allow us to pinpoint the behavioral mechanisms responsible for the remarkable competitive ability of Argentine ants.     

Nest raiding by the invasive Argentine ant on colonies of the harvester ant, Pogonomyrmex subnitidus

Invasive ants often displace native ants, and published studies that focus on these interactions usually emphasize interspecific competition for food resources as a key mechanism responsible for the demise of native ants. Although less well documented, nest raiding by invasive ants may also contribute to the extirpation of native ants. In coastal southern California, for example, invasive Argentine ants (Linepithema humile) commonly raid colonies of the harvester ant, Pogonomyrmex subnitidus. On a seasonal basis the frequency and intensity of raids vary, but raids occur only when abiotic conditions are suitable for both species. In the short term these organized attacks cause harvester ants to cease foraging and to plug their nest entrances. In unstaged, one-on-one interactions between P. subnitidus and L. humile workers, Argentine ants behaved aggressively in over two thirds of all pair-wise interactions, despite the much larger size of P. subnitidus. The short-term introduction of experimental Argentine ant colonies outside of P. subnitidus nest entrances stimulated behaviors similar to those observed in raids: P. subnitidus decreased its foraging activity and increased the number of nest entrance workers (many of which labored to plug their nest entrances). Raids are not likely to be the result of competition for food. As expected, P. subnitidus foraged primarily on plant material (85% of food items obtained from returning foragers), but also collected some dead insects (7% of food items). In buffet-style choice tests in which we offered Argentine ants food items obtained from P. subnitidus, L. humile only showed interest in dead insects. In other feeding trials L. humile consistently moved harvester ant brood into their nests (where they were presumably consumed) but showed little interest in freshly dead workers. The raiding behavior described here obscures the distinction between interspecific competition and predation, and may well play an important role in the displacement of native ants, especially those that are ecologically dissimilar to L. humile with respect to diet. Received 15 July 2005; revised 19 October 2005; accepted 26 October 2005.     

Unadapted behaviour of native,dominant ant species during the colonization of an aggressive,invasive ant

Among the factors driving the invasive success of non-indigenous species, the “escape opportunity” or “enemy release” hypothesis argues that an invader’s success may result partly from less resistance from the new competitors found in its introduced range. In this study, we examined competitive interactions between the little fire ant Wasmannia auropunctata (Roger) and ant species of the genus Pheidole in places where both are native (French Guiana) and in places where only species of Pheidole are native (New Caledonia). The experimental introduction of W. auropunctata at food resources monopolized by the Pheidole species induced the recruitment of major workers only for the Guianian Pheidole species, which were very effective at killing Wasmannia competitors. In contrast, an overall decrease in the number of Pheidole workers and no recruitment of major workers were observed for the New Caledonian species, although the latter were the only ones able to kill the Wasmannia workers. These results emphasize the inappropriate response of native dominant New Caledonian species to W. auropunctata and, thus, the importance of enemy recognition and specification in the organization of ant communities. This factor could explain how invasive animal species, particularly ants, may be able to successfully invade species-rich communities.     

B-chromosomes in the myrmicine ant,Leptothorax spinosior

B-chromosomes of ants (Formicidae, Hymenoptera) were observed for the first time in the myrmicine ant Leptothorax spinosior using an improved squash technique. The B-chromosomes are minute heterochromatic metacentrics resembling isochromosomes. They were found almost entirely in male germ cells and exhibited intra- and inter-individual numerical variation, with numbers ranging between 1 and 12. B-chromosomes were rarely found in female germ cells or somatic cells (cerebral ganglion cells) of all castes, which suggests that the B-chromosomes are unstable in those cells. The number of heterochromatic bodies in interphase nuclei corresponds well to that of metaphase B-chromosomes. The analysis of heterochromatic bodies in female cells suggested that B-chromosomes are maintained in oocytes but almost totally eliminated from nurse cells.     

Foraging energetics of the ant,Paraponera clavata

The energy currencies used by foraging animals are expected to relate to the energy costs and benefits of resource collection. However, actual costs of foraging are rarely measured. We measured the ratio of energetic benefit relative to cost (B/C) during foraging for the giant tropical ant, Paraponera clavata. The B/C ratio was 3.9 for nectar-foragers and 67 for insect prey foragers. In contrast, the B/C ratio during foraging for seed harvester ants (Pogonomyrmex occidentalis) is over 1000, demonstrating that the B/C ratio can vary widely among ants. The B/C ratio was 300 times lower for nectar-foraging Paraponera than for the seed-harvesting Pogonomyrmex because of: (1) a 5-fold lower energetic benefit per trip, (2) a 10-fold greater cost due to longer foraging distances, and (3) a 6-fold greater energy cost per meter due to larger body size. For Paraponera daily colonial energy intake rates are similar to expeditures and may limit colony growth and reproduction. In contrast, for Pogonomyrmex energy intake rates are an order of magnitude higher than estimated costs, suggesting that Pogonomyrmex colonies are unlikely to be limited by short-term energy intake. We suggest that variation in individual B/C ratios may explain why the foraging behavior of Paraponera but not Pogonomyrmex appears sensitive to foraging costs.     

Chromosome polymorphism in the ant,Pheidole nodus

A survey of chromosome polymorphism was made in populations of Pheidole nodus (Hymenoptera, Formicidae). A total of 1,666 males were collected from 11 localities in Japn. Four polymorphic karyotypes were observed: (1) n = 17 with 4 metacentrics (abbreviated as 4M), (2) n = 18(3M), (3) n = 19(2M) and (4) n = 20(1M). These differences are due to the Robertsonian type rearrangement. The karyotype 18(3M) is found in all the populations examined, but the others are more or less localized in their distribution. The 17(4M) appears mainly in Shikoku and the northern Kyushu populations, 19(2M) along the Pacific coast of Honshu, Shikoku and Kyushu, and 20(1M) in the eastern part of Honshu and Shikoku. This distribution pattern indicates that 18(3M) is the oldest, 19(2M) and 20(1M) are derived from 18(3M) by centric fission, and 17(4M) by centric fusion. The most probable mechanism of karyotype evolution in this species is considered to be the centric fission.