Secretion profiles of venom alkaloids in Solenopsis geminata (Hymenoptera: Formicidae) in Taiwan

Biological Activities and Ecological Significance of Fire Ant Venom Alkaloids

Venoms produced by arthropods act as chemical weapons to paralyze prey or deter competitors. The utilization of venom is an essential feature in the biology and ecology of venomous arthropods. Solenopsis fire ants (Hymenoptera: Formicidae) are medically important venomous ants. They have acquired different patterns of venom use to maximize their competitive advantages rendered by the venom when facing different challenges. The major components of fire ant venom are piperidine alkaloids, which have strong insecticidal and antibiotic activities. The alkaloids protect fire ants from pathogens over the course of their lives and can be used to defend them from predators and competitors. They are also utilized by some of the fire ants' natural enemies, such as phorid flies to locate host ants. Collectively, these ants' diverse alkaloid compositions and functions have ecological significance for their survival, successful invasion, and rapid range expansion. The venom alkaloids with powerful biological activities may have played an important role in shaping the assembly of communities in both native and introduced ranges.

Sensitization of Guinea Pig Skin to Imported Fire Ant Alkaloids and Establishment of an Inflammatory Model

Imported fire ants (IFAs), Solenopsis invicta, release their venom through multiple stings that induce inflammation, allergies, shock, and even death. Although IFA venom protein sensitization and related subcutaneous immunotherapy have been studied, few studies have examined the potential toxicity or pathogenicity of alkaloids, the main substances in IFA venom. Here, IFA alkaloids were identified and analyzed by gas chromatography-mass spectrometry; we further determined an appropriate extraction method and its effectiveness for extracting high-purity alkaloids through comparative analysis and guinea pig skin sensitivity tests. The alkaloids released from the IFA abdomen included those present in the head and thorax, and the alkaloids in the abdomen accounted for the highest proportion of the total extract. The abdominal extirpation method yielded alkaloids with a purity above 97%, and the skin irritation response score and histopathological diagnosis suggest that intradermal injection of the extracted alkaloids produced symptoms effectively simulating those of IFA stings. The successful establishment of an inflammatory model in guinea pigs stung by IFAs provides a basis for further research on the mechanism of inflammatory diseases caused by IFAs.

Novel alkaloids from the fire ant, Solenopsis geminata

South American fire ants, Solenopsis richteri and Solenopsis invicta, were accidently introduced into the southern USA in the 1900s and 1930s, respectively. The rapid spread and high population densities of S. invicta, and its potent sting, resulted in broad economic impacts and a variety of research efforts. In the 1970s, their venom alkaloids were identified as a complex blend of trans-2-methyl-6-alkyl- and alkenyl-piperidines. Solenopsis geminata is a worldwide tramp species but a native of the southern coastal regions of the USA. It was found to only produce cis- and trans-2-methyl-6-undecyl-piperidines. These alkaloids were considered the Solenopsis ancestral alkaloid profile since they were identified from female sexuals (potential queens) of all Solenopsis species in South and North America. The dramatic modification of alkaloids in Solenopsis invicta was attributed to their response to evolutionary pressure and the lack of change in S. geminata alkaloids due to no response to evolutionary pressure. Here we report the unexpected discovery of 6-undecyl-pyridine, 2-methyl-6-undecyl-pyridine and 2-methyl-6-(1)-undecenyl-pyridine as components of S. geminata worker venom, suggesting that S. geminata like its South American relatives have responded to evolutionary pressures. Our results will stimulate future research on S. geminata populations throughout the tropical/subtropical world.

Carriers and cutters: size-dependent caste polyethism in the tropical fire ant (Solenopsis geminata)

Body size is an important life-history trait in eusocial insects which plays a key role in colony fitness. The division of labour, represented by caste polyethism, correlates with divergent morphological traits. Size polymorphism has been noted in the tropical fire ant, Solenopsis geminata; however, little is known regarding the differences in the size distributions of workers performing foraging tasks. In the present study, task partitioning was observed in the foraging activities of S. geminata. Two subgroups among foraging workers of S. geminata were discovered using the Gaussian mixture model: a large worker group (head width ≥ 0.924 mm) and a small worker group (head width < 0.924 mm). The foraging worker population comprised two distinct groups - 25.64% were large workers and 74.36% were small workers. Larger workers delivered heavier seeds faster than smaller workers, but this difference became less apparent when lighter seeds were being carried. When large prey such as crickets was encountered during foraging, S. geminata partitioned their tasks into cutting and transportation. The large workers were observed to cut cricket prey into fragments with their longer mandibles, and the small workers then transported these fragments back to the nest. These results present evidence of task partitioning among tropical fire ants, with different tasks being performed by ants of different castes.

Application of Metabolomic Tools for Studying Low Molecular-Weight Fraction of Animal Venoms and Poisons

Both venoms and poisonous secretions are complex mixtures that assist in defense, predation, communication, and competition in the animal world. They consist of variable bioactive molecules, such as proteins, peptides, salts and also metabolites. Metabolomics opens up new perspectives for the study of venoms and poisons as it gives an opportunity to investigate their previously unexplored low molecular-weight components. The aim of this article is to summarize the available literature where metabolomic technologies were used for examining the composition of animal venoms and poisons. The paper discusses only the low molecular-weight components of venoms and poisons collected from snakes, spiders, scorpions, toads, frogs, and ants. An overview is given of the analytical strategies used in the analysis of the metabolic content of the samples. We paid special attention to the classes of compounds identified in various venoms and poisons and potential applications of the small molecules (especially bufadienolides) discovered. The issues that should be more effectively addressed in the studies of animal venoms and poisons include challenges related to sample collection and preparation, species-related chemical diversity of compounds building the metabolome and a need of an online database that would enhance identification of small molecule components of these secretions.

Honeybee venom proteome profile of queens and winter bees as determined by a mass spectrometric approach

Venoms of invertebrates contain an enormous diversity of proteins, peptides, and other classes of substances. Insect venoms are characterized by a large interspecific variation resulting in extended lists of venom compounds. The venom composition of several hymenopterans also shows different intraspecific variation. For instance, venom from different honeybee castes, more specifically queens and workers, shows quantitative and qualitative variation, while the environment, like seasonal changes, also proves to be an important factor. The present study aimed at an in-depth analysis of the intraspecific variation in the honeybee venom proteome. In summer workers, the recent list of venom proteins resulted from merging combinatorial peptide ligand library sample pretreatment and targeted tandem mass spectrometry realized with a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS/MS). Now, the same technique was used to determine the venom proteome of queens and winter bees, enabling us to compare it with that of summer bees. In total, 34 putative venom toxins were found, of which two were never described in honeybee venoms before. Venom from winter workers did not contain toxins that were not present in queens or summer workers, while winter worker venom lacked the allergen Api m 12, also known as vitellogenin. Venom from queen bees, on the other hand, was lacking six of the 34 venom toxins compared to worker bees, while it contained two new venom toxins, in particularly serine proteinase stubble and antithrombin-III. Although people are hardly stung by honeybees during winter or by queen bees, these newly identified toxins should be taken into account in the characterization of a putative allergic response against Apis mellifera stings.

The insecticidal activities of fire ant (Hymenoptera: Formicidae) venoms against Plutella xylostella (Lepidoptera: Plutellidae) larvae

Although fire ants frequently have negative impacts on agricultural systems and public health, they have additional beneficial insecticidal effects. To evaluate the potential effect of fire ant venoms on agricultural pests, the compositions of the venoms and their insecticidal activities against Plutella xylostella (L.) larvae were evaluated under laboratory conditions. The alkaloids found in Solenopsis geminata (F.) venom are primarily saturated C11, which occur in both cis and trans forms, whereas the venom of S. invicta Buren contains six principal alkaloids (from trans C1, to C17). Moreover, the proportions of unsaturated alkaloids in the venom of polygynous S. invicta were significantly higher than the corresponding proportions in the monogynous S. invicta, as shown by our previous studies. Fire ant venoms were topically applied to the dorsal thoracic region of fourth-instar larvae of P. xylostella. The results of the experiment showed that the larval symptoms induced by fire ant venom include contractile, flaccid paralysis, black coloration and death. P. xylostella larvae were most susceptible to S. geminata venom. The order of the susceptibilities of the larvae to the venoms was as follows: S. geminata > S. invicta (monogyne form) > S. invicta (polygyne form), as measured by the corresponding LT50 values at 24 h.

Crystal structure of Sol I 2: a major allergen from fire ant venom

Sol i 2 is a potent allergen from the venom of red imported fire ant, which contains allergens Sol i 1, Sol i 2, Sol i 3, and Sol i 4 that are known to be powerful triggers of anaphylaxis. Sol i 2 causes IgE antibody production in about one-third of individuals stung by fire ants. Baculovirus recombinant dimeric Sol i 2 was crystallized as a native and selenomethionyl-derivatized protein, and its structure has been determined by single-wavelength anomalous dispersion at 2.6 Å resolution. The overall fold of each subunit consists of five helices that enclose a central hydrophobic cavity. The structure is stabilized by three intramolecular disulfide bridges and one intermolecular disulfide bridge. The nearest structural homologue is the sequence-unrelated odorant binding protein and pheromone binding protein LUSH of the fruit fly Drosophila, which may suggest a similar biological function. To test this hypothesis, we measured the reversible binding of various pheromones, plant odorants, and other ligands to Sol i 2 by the changes in N-phenyl-1-naphthylamine fluorescence emission upon binding of ligands that compete with N-phenyl-1-naphthylamine. The highest binding affinity was observed for hydrophobic ligands such as aphid alarm pheromone (E)-β-farnesene, analogs of ant alarm pheromones, and plant volatiles decane, undecane, and β-caryophyllene. Conceivably, Sol i 2 may play a role in capturing and/or transporting small hydrophobic ligands such as pheromones, odors, fatty acids, or short-living hydrophobic primers. Molecular surface analysis, in combination with sequence alignment, can explain the serological cross-reactivity observed between some ant species.

ASSOCIAÇÃO ENTRE FORMIGAS (HYMENOPTERA:FORMICIDAE) E BACTÉRIAS PATOGÊNICAS EM CINCO HOSPITAIS DO MUNICÍPIO DE PELOTAS, RS

RESUMO O presente estudo teve por objetivo verificar a ocorrência de formigas em cinco hospitais do Município de Pelotas, analisar sua sazonalidade e identificar bactérias patogênicas a elas associadas. Para tal, foram utilizadas duas iscas, uma contendo mel, açúcar e minhoca da espécie Eisenia foetida, e outra contendo sardinha da marca Coqueiro®. Ambas foram fixadas próximas aos rodapés de 19 a 21 setores de cada hospital (99 setores no total), e retiradas após 24h. O trabalho foi realizado durante as quatro estações de 2008 e 2009, totalizando 792 pontos amostrais. Foram encontradas sete espécies de formigas, distribuídas em 13 setores dentre os 99 amostrados (13,1%). O verão foi a estação onde a maior porcentagem de amostras foi coletada, 57,6%, sendo o menor número no inverno, 9,1%. Foram coletadas assepticamente formigas de 28 pontos amostrais, sendo que 25 (89,3%) apresentaram a ocorrência de bactérias patogênicas. As Enterobactérias estiveram presentes em 17 amostras, seguidas por Staphylococcus epidermidis e Staphylococcus saprophyticus em 13 e 9 amostras, respectivamente. Além disso, formigas de 20 pontos amostrais apresentaram mais de uma espécie bacteriana, com um máximo de cinco. Concluiu-se que as formigas são importantes carreadoras de bactérias patogênicas nos hospitais do município, e devem ser controladas a fim de se evitar maior ocorrência de infecções nosocomiais. Deve ser dada atenção ao controle na área externa dos hospitais, onde ocorre a nidificação da maioria dos espécimes coletados.