Bacterial diversity and viral discovery in the invasive Argentine ant (Linepithema humile)

<p>Invasive species can lead to major economic and ecological issues. For this reason, biological controls are being developed in order to help with invasive species population management. Pathogenic bacteria and viruses offer good biological control opportunities as both micro-organisms have played a role in natural population declines. However, beneficial bacteria and viruses associated with the targeted invasive species may interfere with biological controls, by protecting their hosts from infections. Previous knowledge on both pathogenic and beneficial bacteria and viruses present in invasive species may then support the development of an active and efficient biological control. The Argentine ant, Linepithema humile, is a South American invasive ant species that has successfully spread over five continents. The ants were introduced to New Zealand after a complex invasion path, from Argentina their home range to Europe, then to Australia and finally to New Zealand. In their new environments, invasive Argentine ants affect species diversity and can cause agricultural losses. In the absence of any biological controls, the Argentine ant population is controlled by chemical sprays and poison baits. Management of these invasive ants in New Zealand is estimated to cost NZ$ 60 million a year. The Argentine ant population in New Zealand was reported to have unexpectedly declined. It was hypothesised that pathogens were the cause of this population collapse. In this study, bacteria and viruses present in the invasive ants were investigated using 454 sequencing and Illumina sequencing for future developments of possible biological controls for the Argentine ants, and a better understanding of the observed population decline in New Zealand. Bacterial diversity present in Argentine ants either declined or diminished along the invasion pathway. At the same time, the invasive ants maintained a core of nine bacteria genera, including Lactobacillus and Gluconobacter, two bacterial genera with members known for their beneficial associations with honey bees. The presence of these core bacteria may have participated in the success of Argentine ants in their new environments. In the laboratory, the use of ampicillin and gentamicin antibiotics on the ants increased bacterial diversity present in the ants. Furthermore, ampicillin, kanamycin and spectinomycin antibiotic treatments increased ant survival but did not affect the ant fitness or intra-species aggressiveness. Only spectinomycin treated ants presented a higher level of inter-species aggressiveness. Bacterial diversity may play an important role in the ant health and at length population dynamics. Finally, Argentine ants are the hosts of two viruses: the Deformed wing virus (DWV) involved in colony collapse disorder in honey bees, and Linepithema humile virus 1 (LHUV-1), a new virus related to DWV. Both viruses actively replicate within the ants, indicating a possible reservoir role of the ants. However, the effects of the viruses on the ants are not yet known. Further viral infection in the laboratory under different stress conditions and / or antibiotic treatment will give an insight in the role played by these viruses in the observed population collapse of Argentine ants in New Zealand. LHUV-1 may offer a possibility in the development of the first biological control for Argentine ants, depending on its specificity and its effects. This dissertation provides a first insight in the core bacteria as well as potential harmful viruses present in Argentine ants. These bacteria and viruses may play a role in the ant population dynamics. Invasive species may co-introduce harmful pathogens with them, and participate to the spread of local ones. The pathogens may affect both invasive ants and native species population dynamics.</p>

Bacterial diversity and viral discovery in the invasive Argentine ant (Linepithema humile)

<p>Invasive species can lead to major economic and ecological issues. For this reason, biological controls are being developed in order to help with invasive species population management. Pathogenic bacteria and viruses offer good biological control opportunities as both micro-organisms have played a role in natural population declines. However, beneficial bacteria and viruses associated with the targeted invasive species may interfere with biological controls, by protecting their hosts from infections. Previous knowledge on both pathogenic and beneficial bacteria and viruses present in invasive species may then support the development of an active and efficient biological control. The Argentine ant, Linepithema humile, is a South American invasive ant species that has successfully spread over five continents. The ants were introduced to New Zealand after a complex invasion path, from Argentina their home range to Europe, then to Australia and finally to New Zealand. In their new environments, invasive Argentine ants affect species diversity and can cause agricultural losses. In the absence of any biological controls, the Argentine ant population is controlled by chemical sprays and poison baits. Management of these invasive ants in New Zealand is estimated to cost NZ$ 60 million a year. The Argentine ant population in New Zealand was reported to have unexpectedly declined. It was hypothesised that pathogens were the cause of this population collapse. In this study, bacteria and viruses present in the invasive ants were investigated using 454 sequencing and Illumina sequencing for future developments of possible biological controls for the Argentine ants, and a better understanding of the observed population decline in New Zealand. Bacterial diversity present in Argentine ants either declined or diminished along the invasion pathway. At the same time, the invasive ants maintained a core of nine bacteria genera, including Lactobacillus and Gluconobacter, two bacterial genera with members known for their beneficial associations with honey bees. The presence of these core bacteria may have participated in the success of Argentine ants in their new environments. In the laboratory, the use of ampicillin and gentamicin antibiotics on the ants increased bacterial diversity present in the ants. Furthermore, ampicillin, kanamycin and spectinomycin antibiotic treatments increased ant survival but did not affect the ant fitness or intra-species aggressiveness. Only spectinomycin treated ants presented a higher level of inter-species aggressiveness. Bacterial diversity may play an important role in the ant health and at length population dynamics. Finally, Argentine ants are the hosts of two viruses: the Deformed wing virus (DWV) involved in colony collapse disorder in honey bees, and Linepithema humile virus 1 (LHUV-1), a new virus related to DWV. Both viruses actively replicate within the ants, indicating a possible reservoir role of the ants. However, the effects of the viruses on the ants are not yet known. Further viral infection in the laboratory under different stress conditions and / or antibiotic treatment will give an insight in the role played by these viruses in the observed population collapse of Argentine ants in New Zealand. LHUV-1 may offer a possibility in the development of the first biological control for Argentine ants, depending on its specificity and its effects. This dissertation provides a first insight in the core bacteria as well as potential harmful viruses present in Argentine ants. These bacteria and viruses may play a role in the ant population dynamics. Invasive species may co-introduce harmful pathogens with them, and participate to the spread of local ones. The pathogens may affect both invasive ants and native species population dynamics.</p>

Temporal Variation in Toxic Bait, Carbohydrate and Protein Preference and Toxic Bait Efficacy in Argentine (Linepithema Humile) and Darwin’s Ants (Doleromyrma Darwiniana)

<p>By determining if there is any temporal variation in toxic bait, carbohydrate and protein preference in Argentine and Darwin’s ants, we can provide better control options because we can identify with more accuracy when ants will be foraging for one food type over another. Improving our understanding is also fundamental as we can improve future bait formulations, bait application and timing, and increase levels of bait uptake. I have two aims in this thesis. First, I investigated toxic bait, carbohydrate and protein preferences for Argentine ants (Linepithema humile) and Darwin's ant (Doleromyrma darwiniana). The second aim in my thesis was to examine the efficacy of toxic baits in laboratory colonies of Argentine ants. Food preferences varied between species and within species considerably throughout the year, although Darwin's ant consistently favoured foods higher in carbohydrates. Argentine ants showed a significant preference for protein over carbohydrates during December and January. Despite differences in carbohydrate and protein preferences the preference for individual toxic baits showed little temporal variation. The toxic bait efficacy experiment revealed that Xstinguish™ and Exterm-an-Ant® baits produced the highest mortality rate. Other commercially available toxic baits had little effect on workers or queens. The efficacy of the toxic baits was influenced by the starvation level of the ant colonies, and only the colonies that were starved for 48 hours experienced a 100% mortality rate. Due to these results, I recommend that bait application with Xstinguish™ and Exterm-an-Ant® in late winter-spring would be optimal as this time frame is when ants are likely to be starved, and when foraging activity is increasing, thus maximising the chances of bait uptake. A second round of baiting treatment with both baits (Xstinguish™ and Exterm-an-Ant®) in summer when Argentine ants have been shown to undergo a second wave of reproduction could also be beneficial.</p>

Temporal Variation in Toxic Bait, Carbohydrate and Protein Preference and Toxic Bait Efficacy in Argentine (Linepithema Humile) and Darwin’s Ants (Doleromyrma Darwiniana)

<p>By determining if there is any temporal variation in toxic bait, carbohydrate and protein preference in Argentine and Darwin’s ants, we can provide better control options because we can identify with more accuracy when ants will be foraging for one food type over another. Improving our understanding is also fundamental as we can improve future bait formulations, bait application and timing, and increase levels of bait uptake. I have two aims in this thesis. First, I investigated toxic bait, carbohydrate and protein preferences for Argentine ants (Linepithema humile) and Darwin's ant (Doleromyrma darwiniana). The second aim in my thesis was to examine the efficacy of toxic baits in laboratory colonies of Argentine ants. Food preferences varied between species and within species considerably throughout the year, although Darwin's ant consistently favoured foods higher in carbohydrates. Argentine ants showed a significant preference for protein over carbohydrates during December and January. Despite differences in carbohydrate and protein preferences the preference for individual toxic baits showed little temporal variation. The toxic bait efficacy experiment revealed that Xstinguish™ and Exterm-an-Ant® baits produced the highest mortality rate. Other commercially available toxic baits had little effect on workers or queens. The efficacy of the toxic baits was influenced by the starvation level of the ant colonies, and only the colonies that were starved for 48 hours experienced a 100% mortality rate. Due to these results, I recommend that bait application with Xstinguish™ and Exterm-an-Ant® in late winter-spring would be optimal as this time frame is when ants are likely to be starved, and when foraging activity is increasing, thus maximising the chances of bait uptake. A second round of baiting treatment with both baits (Xstinguish™ and Exterm-an-Ant®) in summer when Argentine ants have been shown to undergo a second wave of reproduction could also be beneficial.</p>

[IN1336] Argentine ant, Linepithema humile (Mayr) (Insecta: Hymenoptera: Formicidae)

The Argentine ant, Linepithema humile (Mayr), is an insect native to South America, but an invasive species in many parts of the world. It is globally distributed. Linepithema humile is considered a pest species, primarily due to its feeding habits of tending and protecting honeydew producing insects, such as scale insects, which are often damaging to crops and ornamental plants. This aggressive, populous ant species also has a negative effect on native ant species. Linepithema humile colonies have multiple queens, allowing colonies to grow and spread rapidly. Under certain conditions, the argentine ant may also become a household pest if it finds a way into homes. Linepithema humile has been designated as a tramp ant species, meaning that it has an incredible ability to spread and establish in new areas and is difficult to control. Linepithema humile, like other tramp species, can establish in new locations quickly due to the multi-queen nature of the colonies, their abitlity to forage and find resources, and the extensive network of interrelated colonies they are able to form. This document provides an in-depth synopsis of the insect's life history, biology, and management.

Update on the invasion status of the Argentine ant, Linepithema humile (Mayr, 1868), in Madrid, a large city in the interior of the Iberian Peninsula

New geolocated records of the invasive ant Linepithema humile (Mayr, 1868) are added to the previous references for the city of Madrid and its surroundings, and the possible causes of the occurrence and permanence of this species in urban areas are discussed. The data collection corresponds to a series of samplings carried out for the last three years in green areas of the city, bibliographic searches, citizen science platforms and personal communications. To date, eleven locations in the urban area of Madrid and four points outside the city have been registered. The city of Madrid is undergoing a colonisation by the Argentine ant, although it is not widespread yet, since observations over time and space are isolated and apparently unrelated. However, this species has a great capacity to disperse and establish new colonies, mainly human-mediated through the transport of goods, plants, gardening tools, etc. Considering the numerous colonizable urban green areas in the city that can provide the necessary conditions for its expansion, the Argentine ant should not be underestimated, and immediate action is strongly recommended.

Uso de Linepithema humile Mayr, 1868 (Hymenoptera: Formicidae) como agente biológico para la limpieza de osamenta de Philodryas chamissonis (Wiegmann, 1834) (Squamata: Colubridae)

Se documenta por primera vez el uso de la hormiga argentina, Linepithema humile Mayr, 1868 como agente limpiador de osamenta de culebra de cola larga, Philodryas chamissonis (Wiegmann, 1834). Tras la remoción de la piel, principales paquetes musculares y vísceras, la osamenta de la serpiente fue puesta en un dispositivo que contenía un cebo basado en sacarosa. La limpieza completa de las piezas se logró luego de tres meses a temperatura ambiente en el exterior.