Alternative air vehicles for sterile insect technique aerial release

The majority of current sterile insect technique (SIT) programmes release chilled adult sterile insects into the wild by means of small fixed-wing aircraft or occasionally helicopters. Besides being the fastest method of release, it has been demonstrated to provide uniform distribution over target areas and to help ensure sterile insect quality and survivability. It is, however, also the most expensive method of release, and on average, current aerial release contracts constitute about 40% of the annual operating budget of sterile fly emergence and release centres. This is mainly due to the fact that the aircraft used are highly over-specified relative to the requirements of small to medium SIT aerial release programmes. Furthermore, this stage of the SIT process has traditionally been neglected, while research and process optimization efforts have focused mainly on the mass rearing and sterilization of insects. This study addresses this gap by presenting an extensive survey of other forms of aerial transport, of which five alternative types of aerial vehicles are identified as having the potential to make significant cost savings compared with the current aircraft of SIT programmes. These different alternatives were further evaluated against the requirements of current SIT programmes and also compared in terms of cost. Of these, two fulfilled all requirements, but given that an unmanned aircraft could bring even more cost savings, we present two further proposals for unmanned vehicles, the first a custom-built fixed-wing unmanned aerial vehicle or long-range radio-controlled aircraft and the second an unmanned dirigible, which is easier to control remotely in view of its natural tendency to stay airborne. Both these alternative aircraft proposals present major cost savings in terms of pilot wages, maintenance and fuel consumption, with the largest cost saving made by eliminating the need for a pilot, as the take-off weight is the largest source of fuel consumption. Considering that current aerial release contracts represent a significant proportion of the operating budget of SIT programmes, the financial savings of implementing either of these options will have a significant impact on the financial attractiveness of the overall SIT process. Cheaper alternatives to currently used aircraft will also allow smaller SIT programmes to use aerial release methods, thereby widening applicability of aerial release methods.