Survival of insects in the wheel bays of a Boeing 747B aircraft on flights between tropical and temperate airports

Bulletin of the World Health Organization, 65 (5): 659-662 (1987) © World Health Organization 1987 Survival of insects in the wheel bays of a Boeing 747B aircraft on flights between tropical and temperate airports R. C. RUSSELL 1 Mosquitos (Culex quinquefasciatus), houseflies (Musca domestica), andflour beetles (Tribolium confusum) located in cages within the wheel bays of a Boeing 747B aircraft, survived travel on the following normal commercial routes: Sydney-Melbourne; Mel- bourne-Singapore; Singapore-Bangkok; Bangkok-Singapore; andSingapore-Melbourne. Survival of all three species was high, averaging 84% for mosquitos and higherforflies (93%) and beetles (>99 %). Although external temperatures were -42 OC to -54 0Cfor aircraft cruising at 10 700-11 900 m, minimum temperatures within the wheel bays ranged from +8 OCto +25 OC There is considerable concern among quarantine authorities about the international movement of insects that have medical, veterinary, or agricultural importance. Primarily because of its speed and frequency, international air transport provides the greatest potential for introducing many insect vectors or pests to countries. In the Pacific region, a major concern is that vectors of malaria could be introduced and become established in areas where anopheline mosquitos do not at present occur. There is also concern that Aedes vector species found in some islands could be trans- ported to and become established in similar islands where they do not exist at present. Also, during the last decade, the spread of arboviruses has reinforced quarantine concerns and highlighted the importance of maintaining efficient preventive measures to minimize the chances of disease outbreaks. Many countries have established rigorous quaran- tine precautions to prevent the introduction by aircraft of certain insects to areas where they are not in- digenous, and disinsection of passenger cabins and cargo holds is often carried out. However, concern has been expressed that aircraft wheel bays may also provide a haven for insects and that these could then be transported in a part of the aircraft often not included in routine disinsection procedures. During the Second World War, Cameron (1) noted I Senior Lecturer in Medical Entomology, School of Public Health and Tropical Medicine, University of Sydney, NSW 2006, Australia. that "... the retractable undercarriage offers a haven for winged insects, a haven which is automatically emptied before the plane lands and which must therefore be disinfected by mechanical devices while the machine is in flight." Such concern was re- inforced by a report from Kenya that Anopheles gambiae mosquitos in cages placed inside the wing of a flying boat survived a flight from Kisumu to Mombasa (2). Also, instances have been reported of moth-egg masses and of emerging larvae that sur- vived on the external surfaces of aircraft as well as of beetles that survived international flights on the external fuselage of an aircraft (3). It has been assumed that the high speed of modern commercial passenger aircraft and their much greater cruising altitudes preclude this prospect today. No evidence has appeared that insects can survive within the wheel bays of modern passenger aircraft, which fly at altitudes often above 10 500 m, where external temperatures are less than -40 'C. It is of interest to determine whether the conditions within the non-pressurized wheel bays are detrimental to most insects or whether some species might survive. A series of trials was therefore organized to in- vestigate this, and the results are reported here. MATERIALS AND METHODS The trials were conducted on a Boeing 747B aircraft that operated between Sydney and Bangkok 4827 -659- R. C. RUSSELL via Melbourne and Singapore, on 7 August 1986, and between Bangkok and Sydney via Singapore and Melbourne, on 9-10 August 1986. Three species of insects were selected for the trial -the domestic mosquito (Culex quinque- fasciatus), the house fly (Musca domestica), and the flour beetle (Tribolium confusum). The following numbers of insects were confined in plastic cups (185 ml) covered with plastic mesh ends: 10 mos- quitos per cup, 5 flies per cup, and 10 beetles per cup. In general, six cups (two of each insect type) were attached with adhesive tape to the internal walls of both the port and starboard inner wheel bays. A maximum-minimum thermometer was also attached to the wall adjacent to the insects to record extremes of temperature within the wheel bay. The flight engineer recorded external temperatures at the airports on departure and on arrival and also the external temperature at cruising altitude at intervals throughout the flight. Insect survival was scored immediately on arrival following travel between Sydney and Melbourne, Melbourne and Singapore, Sydney and Singapore, Singapore and Bangkok, Bangkok and Singapore, and Bangkok and Melbourne. The maximum and minimum temperatures inside the wheel bay were also recorded at this time. As a control for the insects "protected" within the plastic cups from the turbulence, inter alia, within the wheel bays, four cylindrical cages of wire mesh (17 cm x 5 cm), each containing 10 mosquitos and five flies, were also attached within the wheel bays on the Singapore-Bangkok route. General survival controls (in plastic cups) for the three test species of insects were placed in insulated containers in the aircraft cabin during each flight. The mosquitos and flies were maintained on sucrose solution when not involved in trials, while the beetles were not fed during the trial. RESULTS The proportion of insects that survived the various flights, together with the temperature control records, are presented in Table 1. In general, on all routes survival of the insects was very good and, even though the mortality of the controls increased mar- ginally towards the end of the study, there was little corresponding reduction in that of the test species. Insects on "double" flights (Sydney-Melbourne- Singapore and Bangkok-Singapore-Melbourne) also survived well compared with their single-flight, counterparts. There was no significant difference in the survival of insects in port or starboard wheel bays or in that of insects attached to the rear, front, or side walls of the wheel bays. The minimum external temperature during a flight was -54 'C at 11 890 m between Melbourne and Singapore and also, at the same height, between Singapore and Bangkok. External temperatures were Table 1. Survival of Culex quinquefasciatus, Musca domestica, and Tribolium confusum insects following confine- ment in Boeing 747B wheel bays during flights between Sydney, Melbourne, Singapore, and Bangkok, August 1986. Minimum temperature (OC) Mean survival (%)a External Internal Flight time Cruising Wheel Route (minutes) C. quinquefasciatus M. domestica T. confusum Departure altitude Arrival bay Sydney-Melbourne 80 97.5 100 100 +14 -52 +12 +15 Melbourne-Singapore 450 85.0 95 100 + 10 -54 + 27 + 8" Sydney-Singapore 530 82.5 90 100 +14 -54 + 27 + 8" Singapore-Bangkok 135 87.5 95 100 + 27 -54 + 26 + 20 Bangkok-Singapore 130 82.5 100 100 + 24 -47 + 28 + 25 Bangkok-Melbourne 560 67.5 80 97.5 +24 -49 + 5 + 8c 'Control mortality for C. quinquefasciatus or M. domestica never exceeded 20%, while that for T. confusum was always zero. bInfluenced by the ambient temperature at take-off, before the bays were closed, as well as by any "in-flight" conditions. ' Influenced by the ambient temperature upon landing at Melbourne as well as by any "in-flight" conditions. 660 INSECT SURVIVAL IN BOEING 747B AIRCRAFT WHEEL BAYS recorded hourly, and for the 6 hours at cruising altitude on the Melbourne-Singapore route, the minimum temperatures were as follows: -42 °C for 2 hours at 10 670 m, -48 °C for 2 hours at 11 280 m, and -54 °C for 2 hours at 11 890 m. The minimum temperature within the wheel bays did not fall below +8 °C and was as high as +25 °C (Table 1). The lowest minimum temperature, +8 °C on arrival in Singapore from Melbourne and in Mel- ourne from Singapore, correlated with the ambient temperature in Melbourne, indicating that the temperature in the wheel bays during flight may have been considerably higher. There was no difference in the minimum temperatures when the thermometer was placed on the inner or outer walls of the wheel bay. The maximum temperature in the wheel bays was not above that at the respective airport, and the greatest range was from +8 °C to +28 °C between Melbourne and Singapore and from +28 °C to +8 °C between Singapore and Melbourne. DISCUSSION Laird cited an early report of Bert in 1877 that beetles recovered (although inert and apparently life- less during the experiment) from 20 hours' exposure to pressures equivalent to those at approximately 15 250-18 300 m (4). Also, studies in aircraft indicate that Aedes notoscriptus mosquitos become sluggish below 8-10 °C at altitudes above approxi- mately 3000 m, while below 8 °C have no flight response (4). Laboratory studies confirmed that, at pressures equivalent to those at up to approximately 3000 m, mosquitos showed no observable reactions, but voluntary movements ceased at pressures approxi- mately equivalent to those above 9000 m; mosquitos kept at a pressure equivalent to that at approximately 12 000 m for 48 hours resumed normal activity as soon as they were restored to pressures below that at 3000 m. In temperature trials, the mosquitos could not be induced to fly below 8 °C, while those kept at -2 °C for 24 hours at normal pressure, and at pressures equivalent to those at approximately 3000 m and 9000 m, recovered normal behaviour within 10 minutes of return to favourable conditions; their survival was not affected thereafter (4). The results of the present study indicate that insects can survive in the wheel bays of aircraft on inter- national flights. Under the test conditions, the insects readily survived between tropical and temperate airports on flights of little more than 1 hour to at least 7 hours. The temperatures at Sydney and Melbourne were fairly typical for the time of year and were well below those at Singapore and Bangkok. However, temperatures before, during, and after flights were apparently not detrimental to the test insects. The take-off from Bangkok to Singapore occurred in heavy rain, and a considerable amount of water was sprayed into the wheel bays, but under these con- ditions the insects survived as well as they did under the dry conditions on other routes. It is perhaps questionable as to whether insects not "protected" by enclosure within the test cups or cages would remain in the wheel bays during aircraft taxiing or be driven from the wheel bays by air turbulence during take-off. Although the insects in wire cages survived as well as those in cups, indicating that they were not subject to detrimental buffeting, their "confinement" probably offered some relative degree of protection. Similarly, whether insects that survived in the wheel bays would be driven from the bays by air turbulence when the undercarriage was lowered, or would leave of their own volition during or after taxiing, or remain and be available for "on-arrival" disinsection, also remain unresolved. The possibility that insects could escape from wheel bays after landing but before "on- arrival" disinsection has been recognized for some time, and disinsection of aircraft wheel bays as close as possible to the departure time has been recom- mended (5-8). Data on mosquitos collected from aircraft have been reviewed by Smith & Carter (9), who also detailed reports of diseases transmitted by the intro- duction and establishment of mosquitos in areas where they were previously not indigenous. Recent cases of "airport malaria" in Europe, caused by infected Anopheles mosquitos from Africa, have renewed interest in aircraft disinsection (10); although cabins and cargo holds are usually pre- eminent in discussions on disinsection, the results reported here point to the risk associated with wheel bays. Aerosol disinsection of wheel bays immediately prior to departure would assist in preventing transport of many insect types, depending on insecticide formulation. In contrast, aerosol disinsection im- mediately after arrival may have limited value. In this respect, use of residual insecticides to provide a toxic substrate deposit within wheel bays is problematic, primarily because of build-up of films of grease and oils on the surfaces of the bays. The results reported here indicate that disinsection of aircraft wheel bays should be considered. Aerosol disinsection at the last departure airport is recom- mended as the most appropriate technique, unless an "automatic disinsection device" can be incorporated into the bays. 661 662 R. C. RUSSELL ACKNOWLEDGEMENTS The trials were undertaken with the willing cooperation and assistance of Qantas flight and ground staff. The Qantas Facilitation Manager at Sydney, Mr R. Millward-Grey, provided logistical and technical assistance during the trial, and his contribution is gratefully acknowledged. RESUME SURVIE D'INSECTES TRANSPORTES DANS LES LOGEMENTS DE ROUES D'UN BOEING 747B ENTRE UNE REGION TROPICALE ET UNE RtGION TEMPIRtE Pour eviter le transport involontaire de moustiques et autres insectes, on soumet generalement les avions assurant des liaisons internationales a une desinsectisation preven- tive dans le cadre des procedures gen6rales de quarantaine, mais si la cabine et les soutes sont regulierement traitees, il en est rarement de meme pour les logements de roues. La presente etude visait a determiner si des insectes peuvent survivre dans ces compartiments sur un avion moderne de transport de passagers. Trois especes d'insectes ont ete choisies pour l'experience: un moustique (Culex quinque- fasciatus), la mouche domestique (Musca domestica), et une blatte (Tribolium confusum). Les insectes ont ete plac6s dans des cages fixees sur la surface interne des logements de roues d'un Boeing 747B et leur taux de survie a ete controle a la fin de chaque etape sur l'itineraire suivant: Sydney-Melbourne, Melbourne-Singapour, Singa- pour-Bangkok, Bangkok-Singapour et Singapour- Melbourne. Sur chaque 6tape, les trois especes ont tres bien survecu, de meme que les insectes qui ont effectu6 I'aller-retour. Le taux de survie des moustiques a e en moyenne de 84%, tandis que celui des mouches et des blattes a ete encore plus eleve (93% et > 99% respectivement). Bien que la temperature exterieure ait varie entre -42 °C et -54 °C, pour des durees de vol comprises entre un peu plus d'une heure et sept heures, A une altitude de croisiere de 10 700 m a 11 900 m, la temp6rature minimale a l'interieur des logements de roues est restee comprise entre +8 °C et +25 'C. Les conditions etaient donc propices a la survie des trois especes. L'etude montre que des insectes peuvent survivre dans les logements de roues d'un avion lors d'un vol international, si l'on admet que les conditions observees lors de cet essai sont repr6sentatives et que les insectes ne sont pas expulses par la turbulence de l'air au decollage. REFERENCES 1. CAMERON, T. W. M. The possible transfer of tropical disease due to war conditions. Canadian Medical Association journal, 49: 273-279 (1943). 2. GARNHAM, P. C. C. The efficacy of insecticidal sprays in aircraft. East African medical journal, 23: 272-277 (1946). 3. LAIRD, M. Insects collected from aircraft arriving in New Zealand from abroad. Zoological publications of the Victoria University College, Wellington, New Zealand, No. 11 (1951). 4. LAID, M. Reactions of mosquitoes to the aircraft environment. Transactions ofthe Royal Society ofNew Zealand, 77: 93-114 (1948). 5. LAIRD, M. The accidental carriage of insects on board aircraft. Journal ofthe Royal Aeronautical Society, 55: 735-743 (1951). 6. WHO Technical Report Series No. 206, 1961 (Aircraft disinsection: eleventh report of the Expert Committee on Insecticides). 7. International Health Regulations (1969) adopted by the Twenty-second World Health Assembly in 1969 and amended by the Twenty-sixth World health Assembly in 1973. Second annotated edition. Geneva, World Health Organization, 1974. 8. BAILEY, J. Guide to hygiene and sanitation in aviation, 2nd edition. Geneva, World Health Organization, 1977. 9. SMIrH, A. & CARTER, I. D. International trans- portation of mosquitoes of public health importance. In: Laird, M., ed. Commerce and the spread ofpests and disease vectors. New York, Praegar, 1984. 10. CURTIS, C. F. & WHITE, G. B. Plasmodium falci- parum transmission in England: entomological and epidemiological data relative to cases in 1983. Journal oftropical medicine and hygiene, 87: 101-114 (1984).