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Building capacity for testing genetic vector control measure against the tiger mosquito Aedes Albopictus

Final Report Summary - BLOCKTIGER (Building capacity for testing genetic vector control measure against the tiger mosquito Aedes Albopictus)

Executive Summary:


Aedes albopictus, commonly known as the Asian tiger mosquito, is currently the most invasive mosquito in the world and is classified as one of the 100 most dangerous invasive species. It is of medical importance due to its aggressive daytime human-biting behavior and ability to vector many viruses. Its colonization of vast region of the Asia, Europe and the American continents has not been without consequence as this mosquito species is a vector numerous human diseases including Dengue, Yellow fever, West Nile Fever and Chikungunya. This alarming situation contrasts with a substantial lack of scientific knowledge and cost effective control measures. Clearly this represents a serious obstacle to stop the spread of this mosquito species to new areas of the world but also for implementing surveillance and control measures in already infested regions. The threat posed by mosquitoes in Europe is increasing due to the inadequacy and cost of existing control measures. In Europe, Ae. albopictus was identified in 15 states in 2007 and is spreading in 12 more countries; most coastal areas are infested, up to about 700m altitude.

This project objective is to build up the capability of Area-Wide Control (AWC) against the tiger mosquito Ae. albopictus mosquitoes utilizing Integrated Vector Management (IVM), primarily in a European context.

Successful AWC programs often utilize a genetic component (such as sterile insect technique) including those targeting agricultural pests.

This project forges a unique combination of knowledge and expertise in the field of vector molecular biology, mosquitoes genetics, implementation of control measures and mosquito mass rearing technology provided.

The structure of the project, in terms of research activities, tasks distribution and management has been planned with the priority of facilitating the interactions of human resources, between the incoming visiting scientist and the host institution and the network of collaborating EU laboratories. This exchange of staff and transfer of knowledge has bridged to the scientific and cultural differences existing between US and European laboratory working in the field of genetic vector control.

The research activities were articulated in three work packages. They constitute a logical progression from exploiting the existing state of the art, to transfer SIT technology to Ae. albopictus and finally translating information and technology into an action plan to target this mosquito species in Italy.

Significant progress has been made in establishing mass production methods. Due to lack of cost/benefit data, no progress was made determining effectiveness of genetic control.

Work package 1: Adapt mosquito mass-rearing technology to Ae. albopictus and evaluate the suitability of the confined release facility at UNIPG

Task 1: Test and adapt mass-rearing technology for AE albipictus

Mass-rearing technology for mosquitoes was initially developed in 1900s. Most of the logistics were created for short-term projects without the view and the provision for expansion to larger projects. Major effort have been undertaken at International Atomic Energy Agency (IAEA) with the objective to review and improve protocols and equipment to optimize mass rearing of anopheline mosquitoes for large release programs. The objective of this work package was to exploit this unique experience for developing to AE. albopictus.

Assess diet suitability: a substantial research was undertaken in order to assess diet suitability for Ae. albopictus. After developing a diet for An. arabiensis that takes into account the importance of dietary fatty acids. The use of this diet for Ae. albopictus has been completed and has been published as a result presenting our proposal. The diet was promoted in several mosquito mass-rearing projects in Crevalcore, Italy and Khartoum, Sudan for Ae. albopictus and Ae. arabiensis respectively. Damien et al. diet has now been tested by another group contacted to pursue commercial development by discussing this possibility with the insect diet producer BioServ.

Develop equipment for larval culture

The system that I was instrumental in developing has been reproduced for use at CAA (Crevalcore) where it was tested the device with Ae. albopictus. With a footprint of less than 1 m2, a capacity of 1.2 million larvae has been accomplished by high density of larval trays – 50 per rack.

Female elimination: we planned to use a method that has been used successfully to remove female pupae from mosquito population to be released– size selection. Due to the limited time during which the Perugia insectaries have been available and the pending proper permits for working with transgenic mosquitoes, no advances were made on this effort.

Rearing adult mosquitoes: we intended to modify a cage currently under development at the International Atomic Energy Agency (IAEA) for this purpose. The main modifications anticipated are the method of egg collection. These modifications were made by our collaborator at the IAEA (F. Balestrino, pers. comm.) and can be considered completed.

Optimize sexual sterilization: we had planned to sterilize males by irradiation using either Co-60 or Cs-137 to determine the dose response. This work has now been published independently.

Task 2: Assess the suitability of the confined release facilities for Ae. albopictus

We planned to utilize the indoor release facility to assess the behavior of male insects under conditions that simulate natural environments. This fellowship planned to utilize an in- and outdoor facility, only the former of which has been completed. We have determined that for the albopictus we have tested, neither mating, oviposition nor longevity limit experiments.

Environmental tuning of the confined release facility

The environmental profile of the location where the UNIPG mosquito confined release facility was monitored during the spring-summer season. This objective was accomplished by ramping lighting and temperature (but not humidity) in the large environmental chambers in a way that successfully simulates summer conditions. There was no activity on two tasks in the work package: “Assessment of containment integrity” nor “Assess mosquito life history parameters.”

Work Package 2: Technology Assessment and validation

Task 1 Assess feasibility and cost effectiveness:

All activities consisted of literature surveys and were conducted on this subject during year 1.

Task 2. Implement quality control

An SOP for larval culture was created and tested and performs well for consistent and predictable routine culture of Ae. albopictus.

Work Package 3: An IVM Concept Including SIT for Italy

Task 1. Collecting information regarding the current infestation and control of Ae. albopictus.

Since the first detection of Ae. albopictus in Italy, it has become locally abundant in urban areas and widespread. Its role as a vector of chikungunya in Emilia-Romagna, Italy is unequivocal, however its actual and potential role in transmission of dengue is questionable. Therefore, the most likely future viral disease threat due to albopictus remains chikungunya. Most of Italy provides suitable habitat so all areas might require treatment if elimination were needed.

Few estimates have been made of the costs of control options. The conventional methods that are typically used are public education (to promote draining of larval containers, use of repellents, screening, insecticides (both larvicides and focal adulticiding), centrally organized larval container drainage/destruction and intensive use of e.g. ovitraps. From an ecological standpoint, it seems likely that the auto-dissemination approach will be more effective since in areas where there are many sites that compete for oviposition. This technology still has not been demonstrated to be useful on large scales. The auto-dissemination studies conducted in Peru have been mimicked in Rome on a reasonable scale and increased larval mortality has been demonstrated. Whether this translates into reduced adult abundance was not determined but it is a promising outcome. Reductions in larval density are claimed to result in higher larval survival (which does not appear to have occurred in this case) and larger, more fecund females. Regardless, due to the need for intensive application, it will be useful only in urban areas. We have described the mating activity of Aedes albopictus and larval bionomics of the related mosquito Ae aegypti. Three papers have been submitted and two accepted. We have also initiated experiments that explicitly test genetic control model assumptions that have been widely used.

Task 2. Determining costs of the status quo vs. a national elimination campaign: Due to the 2007 chikungunya epidemic, Emilia-Romagna has the best-articulated control program. It is composed entirely of conventional control methods and intends only to accomplish suppression.

Task 3. Addressing regulatory safety issues

No activity was performed on this objective.

Task 4: Devising a plan for permanent elimination of Ae. albopictus from Italy.

No activity was performed on this objective

Suitable methods and equipment now exist for an area-wide genetic control program against Aedes albopictus. Many of these advances were anticipated by this proposal but accomplished in collaborating laboratories. In the absence of clear cost-benefit data however, addition of this technology to a national control effort cannot be determined. Significant contributions to the understanding of Aedes biology are represented by three publications that have been submitted and which are listed in the specific section.

The project unleashed the full potential of the collective expertise towards the objectives of the proposal and has been instrumental in building collaborative links that will extend beyond the duration of the project.