Techniques for studying the execution of foreign queens by temporal subcastes in fire ants (Solenopsis invicta)

Using monogynous and polygynous colonies of the fire ant, Solenopsis invicta Buren, we developed methodology to determine which behavioural subcaste of workers was responsible for executing unfamiliar queens that were introduced to them. Separation of subcastes and introduction of queens to each of these separately was partly effective, but more accurate results were obtained by removing workers that were in the act of executing queens, marking them individually, and returning them to the colony. Their subsequent behaviour was then recorded to determine whether they behaved like nurses, reserves, or foragers. The results showed that foragers are dominant in execution behaviour and that all morphological subcastes (minors, medias, and majors) are involved. This methodology may be applied to other social insect species.

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Résumé A l'aide de colonies monogynes de S. invicta Buren, nous avons testé la sensibilité de deux méthodes: Premièrement, nous avons isolé les trois sous-castes temporelles des ouvrières (nurses, réserves et fourrageuses) auxquelles nous avons introduit des reines étrangères. Nous avons trouvé que les fourrageuses étaient le groupe le plus agressif, exécutant un pourcentage élevé des reines qui leur étaient présentées. Le degré de physogastrie de la reine étrangère, sa colonie d'origine et la présence de couvain n'avaient pas d'effet visible sur sa destinée. La sensibilité de cette méthode était limitée par la difficulté d'une séparation complète des souscastes temporelles.Deuxièmement, nous avons capturé des ouvrières exécutant activement des reines étrangères, après marquage nous les avons remises dans leur colonie pour observations ultérieures. Nous avons remarqué que leur localisation dans le nid et leur comportement correspondaient aux séquences trouvées pour les fourrageuses bien plus qu'à celles des ouvrières réserves ou nurses. Cette méthode est plus sensible. Des mesures de la largeur de la capsule céphalique de ces ouvrières ont montré qu'aucune des sous-caste morphologiques (mineurs, moyennes et majeurs) étaient dominantes dans le comportement d'exécution. Nos résultats indiquent que la sensibilité des ouvrières à certaines phéromones de la reine et odeur de la colonie augmente avec leur âge.

     

SIMPLE GENETIC BASIS FOR IMPORTANT SOCIAL TRAITS IN THE FIRE ANT SOLENOPSIS INVICTA

Variation in queen phenotype and reproductive role in the fire ant Solenopsis invicta has been shown to have a simple genetic basis in a single introduced population in the United States. The evidence consists of an association between this variation and queen genotype at Pgm-3, a phosphoglucomutase-encoding gene. In the present study, we surveyed Pgm-3 allele and genotype frequencies in diverse populations from the native and introduced ranges of this ant to learn whether this simple genetic basis for reproductive traits is a general feature of the species or a genetic anomaly in introduced ants stemming from a recent bottleneck or the invasion of novel habitats. No egg-laying queens living in polygyne (multiple-queen) nests possessed the homozygous genotype Pgm-3^a/a in any of the study populations, yet nonreproductive females from such nests (workers as well as queens that had not yet initiated oogenesis) possessed this genotype at moderate frequencies. Remarkably, Pgm-3^a/a was the most common genotype among all classes of females, including egg-laying queens, in monogyne (single-queen) nests from all populations studied. Genotype proportions at Pgm-3 in polygyne populations typically departed strongly from the proportions expected under Hardy-Weinberg equilibrium, whereas those in monogyne populations did not. These patterns establish that a single mendelian gene influences queen reproductive role in S. invicta and that this gene uniformly is under strong directional selection in the polygyne social form only. Moreover, the perfect association of Pgm-3 genotype and reproductive role in all populations, combined with the known function of phosphoglucomutase in insect metabolism, suggest that this gene may directly influence queen phenotypes rather than merely serving as a marker for a linked gene that causes the effects.     

Fire ant venom alkaloids: Their contribution to chemosystematics and biochemical evolution

Studies on the chemistry of the 2,6-dialkylpiperidines in the venom of various fire ant species have shown that these alkaloids have practical value as chemotaxonomic characters. In addition, the finding that variations exist in the distribution of the geometric isomers between species and castes has led to a hypothetical construct for the biochemical evolution of these compounds. These various results, obtained previously, are integrated here as a coherent whole.     

红火蚁与扶桑绵粉蚧互惠关系对松粉蚧抑虱跳小蜂和美棘蓟马的影响

蚂蚁与蜜源昆虫互作是物种间重要的关系之一,发挥着重要的生态功能。红火蚁Solenopsis invicta Buren是重要的入侵害虫,对生物多样性的影响已被熟知,但它与蜜源昆虫互作的生态学效应却不被充分理解。本研究评价了红火蚁与扶桑绵粉蚧Phenacoccus solenopsis Tinsley这两种入侵害虫之间的互作对寄生性天敌和粉蚧竞争性昆虫的影响。研究发现红火蚁的照看显著减少了寄主植物上粉蚧重要寄生蜂松粉蚧抑虱跳小蜂Aenasius bambawalei Hayat的种群数量,提高了寄主上粉蚧的存活率,有利于寄主上粉蚧种群的扩增和繁殖。同时红火蚁的存在也显著降低扶桑寄主上粉蚧竞争性昆虫美棘蓟马Echinothrips americanus Morgan成虫和幼虫的数量,抑制了美棘蓟马种群的竞争力,使得粉蚧可以占有更多的寄主植物,为粉蚧种群的繁殖提供了更好的条件。可见,红火蚁与扶桑绵粉蚧的互惠关系的生态效应可能是通过它们与多物种互作综合形成的结果。     

诱饵诱集时间与红火蚁工蚁诱集量的关系研究

为了明确诱饵诱集时间与红火蚁工蚁诱集量之间的关系,确定最佳的诱饵放置时间,本研究采用火腿肠诱饵诱集法,观察不同季节、不同时间段红火蚁诱集的个体数量,利用房室模型分析诱饵诱集时间与红火蚁工蚁诱集量之间的关系。结果表明,随着诱饵放置时间的增加,红火蚁工蚁的诱集数量会出现一个高峰,春季诱集高峰出现在诱饵放置后38-44 min,秋季出现在诱饵放置后24-29 min,并建立了不同季节、不同时间段红火蚁诱集量与时间的关系模型,分别为Y=12764.8807×e(-0.029102 X)"12820.4625×e(-0.030064 X)(春季上午)、Y=16166.6800×e(-0.023994 X)"16217.0808×e(-0.024866 X)(春季下午)、Y=12211.9095×e(-0.040576 X)"12275.2496×e(-0.041620 X)(秋季上午)、Y=12306.4111×e(-0.049724 X)"12383.6907×e(-0.051217 X)(秋季下午)。因此,在利用火腿肠诱饵监测红火蚁时,春季诱饵放置的最适时间约为40 min,秋季的最适时间约为30 min。     

红火蚁病原真菌AUGM47早期发育超微结构研究

在前期筛选已获得对红火蚁Solenopsis invicta Buren高效致病真菌罗伯茨绿僵菌Metarhizium robertsii AUGM47的基础上,为进一步明确病原真菌对寄主昆虫的侵染机制。本试验在室内条件下,以红火蚁工蚁为侵染对象,利用荧光显微镜和透射电镜观察了罗伯茨绿僵菌AUGM47侵染单元分生孢子在体表附着萌发、穿透和体内增殖的早期发育过程。结果表明,菌株AUGM47分生孢子在红火蚁体表可萌发并形成附着胞侵入,接种后12 h观察到萌发,在36 h内普遍出现穿透结构穿透体壁。接种后48 h为菌体在血腔内的增殖阶段。菌丝体在穿透表皮和体腔内增殖过程中伴随着机械压力和酶的活动。接种后96 h,观察到自噬现象,菌体通过自噬降解并回收细胞器,为从体内穿出的晚期发育过程提供物质基础。本研究对罗伯茨绿僵菌AUGM47分生孢子在红火蚁体外至体内的发育进程研究证实了菌株的高致病性,为红火蚁生防真菌菌种改良和后续开发利用奠定理论基础。     

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。     

扶桑绵粉蚧及其蜜露对红火蚁的召集作用

为了明确扶桑绵粉蚧Phenacoccus solenopsis Tinsley及其蜜露对红火蚁Solenopsis invicta Buren的召集作用,利用双向选择诱集装置测定了扶桑绵粉蚧雌成虫及其分泌蜜露对红火蚁工蚁的诱集数量动态。结果表明：（1）蜜露对红火蚁工蚁具有强烈的召集作用,不管扶桑绵粉蚧存在与否,均可在10~20 min出现觅食工蚁的数量高峰,之后随着蜜露量减少,觅食工蚁诱集数量也逐渐降低,明显高于对照;（2）仅有扶桑绵粉蚧雌成虫存在时,红火蚁觅食工蚁数量呈现逐渐增加的趋势,50 min才达到数量高峰,之后无明显下降趋势;（3）对比蜜露和雌成虫对红火蚁工蚁的诱集结果发现,蜜露对红火蚁工蚁的召集作用明显较强,10 min即可出现91.50头的觅食工蚁数量高峰,而雌成虫对红火蚁的诱集量较低,诱集高峰出现在42 min,诱集量仅为39.17头。因此,扶桑绵粉蚧及其蜜露均对红火蚁工蚁具有一定的召集作用,蜜露的召集作用明显较强,而雌成虫的召集作用较为稳定,未随着时间延长出现明显下降。     

Foraging behavior and recruitment of red imported fire ant Solenopsis invicta Buren in typical habitats of South China

The foraging behavior consisted of three steps: searching, recruitment and transportation. Searching time was different for different foods; searching time for honey was longer than that for any other food tested. It was also affected by habitats with the searching time of fire ants in a litchi orchard being significantly longer than that for other habitats (p<0.01). However, the weight of the food had no obvious effect on the searching time. The recruitment of fire ant workers during foraging was regular, and there was a strong relationship between the number of recruited workers and the transportation time. When the food was too heavy to transport immediately into the nest, the number of recruited workers was maximum at 30 min after the food was initially found. For smaller sized food sources maximum recruitment of workers was possible at a shorter time and the food was more rapidly transported back to the nest. For different foods, the dynamics of recruitment were similar although the number of recruits was different. The weight of the food and the habitats also deeply affected the time spent on transportation.     

Identification and action of juvenile hormone III from sexually mature alate females of the red imported fire ant,Solenopsis invicta

Analysis of extracts of hemolymph obtained from sexually mature alate females of Solenopsis invicta from monogyne colonies resulted in identification of juvenile hormone III (JH III). The average amount of JH III was 0.32±0.04 pmol/μmolof hemolymph. Topical application of 0.038 pmol of JH III was sufficient to stimulate alates to shed their wings in the presence of the queen. The time in which alates were induced to dealate decreased linearly with increasing concentrations of JH III from 0.038 to 3.8 pmol. However, higher JH III concentrations deviated from linearity and did not reach dealation times comparable with those that occur after mating flights. Thus, it appears that the mechanism of dealation that occurs when female alates are out of the influence of their queen is different from the one associated with mating flights. Application of 0.42 μmol of precocene II inhibited dealation of alates in queenless colonies. However, this inhibition was reversed after applying 38 pmol JH III to precocene-treated alates. The sizes of corpora allata (CA) from sexuals treated with JH III did not differ from those of controls. However, the sizes of CA were reduced in alates treated with precocene II. The results indicated that JH was important to dealation.