Definition of the problem

The Asian Tiger Mosquito has been present in our country for over 15 years, during which time it has earned notoriety among millions of Italians and foreign tourists for its aggressiveness and the irritation caused by its bites. It is evident that the results achieved thus far through collective efforts to combat this mosquito are insufficient to guarantee a good quality of life in infested areas.

Alongside these considerations, there are others of a biological nature which make the species in question a suitable target for the application of SIT technology (Sterile Insect Technique):

  • it is an accidentally imported exotic species and hence there exist no ecological reasons to preclude its possible eradication;
  • most likely an exiguous number of insects were imported and it may thus be reasonably assumed that the genetic base of Italian populations is rather narrow;
  • its spread is linked to urban areas, with pockets of infestation involving a by now indeterminate number of cities and towns, the active dispersal capabilities of the species are limited to a few hundred metres while passive transport via motor vehicles that move from one area to another appears inevitable;
  • the species lends itself well to breeding in artificial structures.

On an international scale renewed attention is being focused on the SIT strategy, applied both as a defence against agricultural pests and in the sphere of public health. This revival of interest is tied in part to the success achieved by several SIT programs applied on a vast scale: against the screw-worm fly (Cochliomyia hominivorax) in Central America, the tsetse fly (Glossina spp.) in Africa and the fruit fly (Ceratitis capitata) in the southern United States, just to name the most important examples; it is also tied in part to new knowledge in the fields of genetics, breeding and quality control technology and territorial analysis by Geographic Information Systems.

Progress of the SIT project targeting Aedes albopictus

Research in this area began in 1999 and is presently being carried on by a workgroup composed as follows:

  • Centro Agricoltura Ambiente “Giorgio Nicoli”
  • Department of Agroenvironmental Science and Technologies, University of Bologna
  • Department of Genetics and Molecular Biology, La Sapienza University of Rome
  • ENEA (National Agency for New Technology, Energy and the Environment) Casaccia Research Centre, Biotech-Agro Section
  • Servizio Fisica Sanitaria Arcispedale S.Anna Ferrara

Over the years all aspects relevant for SIT strategy optimisation have been addressed. From a technological perspective the current state of the art may be summed up as follows:

  • Development of a pilot mass rearing facility: at the CAA in Crevalcore a mass rearing pilot unit has been set up which can potentially produce 100,000 males per week when operating at full capacity. The facility comprises three climate-controlled chambers (with complete control of temperature, relative humidity and photoperiod), where the adult rearing cages and larva rearing trays are kept, and a fully equipped entomological laboratory.
  • Blood meal: the system adopted involves the use of thermostat-controlled device capable of maintaining the blood at a temperature of 37 ± 1 °C. The blood is obtained from a nearby slaughter facility and adequately treated so as to render it suitable for this specific purpose. Breeding thus takes place without the use of host animals.
  • Collection and counting of eggs: the caged females are induced to lay eggs on rough paper, which makes it easy to collect and store them in the ideal conditions for embryo development. Eggs are counted directly on the substrate by means of an automatic digital system. This makes it possible to introduce the desired number of eggs into each tray.
  • Larva rearing: use is made of trays containing 3 litres of water and 4,000 first instar larvae. The standard diet presently used is a mixture of cat biscuits, brewer’s yeast and fish food, administered in programmed doses.
  • Sexing: it is necessary to separate the sexes so that only males will be released in the field. Separation is performed at the pupal stage by exploiting the difference in size between males and females. Using micrometric mesh metal screens it is possible to obtain a yield of 17-18% males with an impurity rate of 1 % females (these females will be sterilized by irradiation but are nonetheless able to bite, so their number must be kept to a minimum).
  • Sterilisation: males are sterilized by gamma irradiation of the pupae in water. Two gamma ray sources have been utilized to date: the Calliope plant at the ENEA Casaccia research centre, which uses 60Co as the source, and the irradiator at the Health Physics Department of S.Anna Hospital in Ferrara, which uses 137Cs as the source. Based on the results of dosimetric trials, it has been possible to establish the minimum dose required to induce close to 100% sterility in males. The current reference dose is 40 Gy.
  • Sterile male competitiveness: a crucial element of the strategy is the degree of competitiveness of sterile males versus wild males during mating. In nature, the males of this species form numerous mating swarms which are made up of few individuals and gather in shady areas to attract virgin females. The females are monogamous. Trials are conducted in cages and green houses to determine how the rearing conditions and irradiation affect male performance.
  • Experimental field releases of males: sterile males are released into the environment as pupae from fixed release sites set up in urban areas. Field trials have been conducted in order to assess the method’s efficacy in different localities: Desenzano sul Garda (2003), Rimini (2004), S.Monica di Misano (2005), Boschi di Baricella (2008-2010), Budrio di Correggio (2008) and Caselle di Albinea (2009).

The results show that the released sterile males are capable of mating with wild virgin females and induce sterility. However, at present the levels of sterility are too low to bring about a progressive suppression of the population and efforts are ongoing in order to improve males performances.

Current topics of investigation

The studies currently underway focus on the following aspects:

  • assessment of the health conditions of the strains reared and routine preventive measures;
  • techniques for maintaining the quality of reared males;
  • irradiation tests on pupae of different ages and adults;
  • tunnel studies to assess the levels of competitiveness of males submitted to different rearing and irradiation conditions;
  • field studies investigating the dispersal and longevity of sterile reared males versus fertile males.

 

Entities that have provided funding for the project

Italian Ministry for University and Research (2001-2002), Brescia Local Health Care Enterprise (1999-2000), Municipalities of Desenzano del Garda (1999-2003) and Rimini (2004), Hera Rimini Srl (2004-2005), ENIA Reggio Emilia (2008-2009), Region of Emilia-Romagna (2005-2013).

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logo C.A.A.
Centro Agricoltura Ambiente S.r.l.
3351, Argini Nord st.
40014 Crevalcore (BO)
Email: caa@caa.it
P.E.C: caa.srl@pec.it
Tel: +39 051 6802211
Fax: +39 051 981908