Int J Biometeorol (1988) 32:65-69

meteorology

A laboratory technique for examining the flight activity of insects under controlled environment conditions

B. Grace and J.L. Shipp Agriculture Canada Research Station, P.O. Box 3000 Main, Lethbridge, Alberta, Canada T1J 4B1

Abstract. A technique was deve loped for s tudying the flight activity o f the b lack fly, S imul ium arcti-

cure, under control led env i ronmen t condit ions. Wind speed, light, t empe ra tu r e and humid i ty could be control led and m o n i t o r e d in the flight chambers . Accura te m e a s u r e m e n t and recording o f individual insect activity were achieved with a high-sensit ivity video recording and mon i to r ing system. The con t ro l l ed -env i ronment mon i to r ing sys tem is adap tab le for invest igat ions o f the envi- r o n m e n t a l behav iour and phys io logy o f var ious in- sect species.

Key words: Black Fly - Simul ium arct icum - Con- trolled env i ronmen t - Fl ight activity - Video mon i - tor ing

S. arct icum and thereby aid in the deve lopmen t o f a pest m a n a g e m e n t p r o g r a m for black flies.

However , exper iments with live insects under control led env i ronmen t condi t ions present special p roblems. A l though m a n y control led env i ronmen t systems are avai lable for p lan t studies, none were judged suitable for the p r o p o s e d invest igat ions of env i ronment -ac t iv i ty relat ionships o f insects such as black flies. F o r such studies, a sys tem mus t al- low for the accura te m e a s u r e m e n t and recording o f individual flight act ivi ty and for accura te con- trol and mon i to r ing o f light, t empera tu re , v a p o u r pressure and wind speed.

This pape r repor ts the deve lopmen t o f tech- niques tha t allow a quant i ta t ive assessment o f black-f ly flight act ivi ty under control led environ- men t condit ions.

Introduction

Weathe r is one o f the ma in factors tha t cause the popu la t i on levels o f b lack flies to f luctuate d r a m a t - ically (Davies 1952; Choe et al. 1984; McCread ie et al. 1986). The daily flight activity o f S imul ium

arct icum Mal loch in a pas tu re s i tuat ion in central Alber ta has recently been examined (Shipp et al. 1987) and related to var ia t ions in several wea ther pa ramete r s . I t was suggested tha t these var iables act s imul taneous ly to influence the energy and water balances o f the insect.

The identif icat ion o f the i m p o r t a n t weather pa- rameters affect ing the flight act ivi ty o f S. arct icum by Shipp et al. (1987) indicated the need for con- trolled l a b o r a t o r y studies to de te rmine the rela- t ionship between flight activity and each o f the wea ther var iables m o r e precisely. This i n fo rma t ion is required to cons t ruc t a mode l to predic t the opti- mal wea ther condi t ions for the flight act ivi ty o f

Offprint requests to: B. Grace

Materials and methods

The black fly species S. arcticum was used in all experiments. The flies were reared to the adult stage in the laboratory from field-collected larvae from the Crowsnest River (49 ~ 42' N, 114 ~ 30' W) near Burmis, Alberta, Canada. On emergence, adults were placed in opaque cardboard ice-cream cartons (473-ml containers) and maintained on sugar cubes at a temperature of 4.0 ~ 0.5 ~ C and 90% _+ 5% relative humidity. Adult flies used for testing were less than 10 days old.

Controlled environment flight chambers. Two types of flight chamber were constructed and tested. For studies of tempera- ture-humidity relationships, a simple flight box was con- structed. A more elaborate wind tunnel-flight chamber was re- quired to provide conditions of controlled light, humidity, wind speed and temperature.

Flight boxes. Cubical flight boxes (12 cm 3) (Fig. 1) were con- structed of 5 mm thick plexiglass to allow viewing of the insects. A 2 cm deep reservoir was located in the bottom of the chamber to hold saturated salt solutions. The solutions were used to produce relative humidities between 12% and 97% at 25~ (Wexler and Hasegawa 1954; Grace et al. 1985). A stage located 2 cm from the bottom of the chamber separated the reservoir from the flight chamber. The stage consisted of a 70-mesh nylon screen (27.6 mesh/era, no. HC3-243, Research Instrument Man-

R

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Fig. 1. Diagram of humidity-controlled flight box. O access opening for insertion of flies; R retainer rings; S screen; So saturated salt solution

ufacturing Co. Ltd.) attached to a removable retainer ring. A removable airtight lid on top of the chamber permitted easy access to the reservoir for the addition of the salt solutions. A small (1 cm diam.) opening in the lid provided access to the flight chamber for the insertion of black flies. Except for the few seconds required to insert the insects, the opening was sealed to ensure uniform humidity conditions within the chamber.

The salt solutions were allowed to stand for 48 h in the chambers prior to the insertion of flies to ensure equilibration of temperature and humidity within the flight chamber. Light intensity was measured with a LiCor photometric sensor (model LI-210SB), incident flux density with a LiCor pyranometer (model LI200S), and temperature with copper-constatan ther- mocouples. Signals from the sensors were recorded with a Campbell Scientific datalogger (model CR21). Thus, by varying the lighting regime and temperature within a controlled envi- ronment room (Conviron model CP240) and altering salt solu- tions the effects of atmospheric vapour pressure, temperature and light on flight activity were assessed.

Wind tunnel-flight chamber. To examine the combined interrela- tionships of wind, light, temperature and humidity on flight activity, a 1.5 m long wind tunnel (Fig. 2) was constructed. The internal dimensions of the tunnel were 20 x 25 cm. Air was drawn through the 25-cm-long flight chamber by a variable speed, AC-powered fan (Dayton Electric, model V67L). As with the flight boxes, the flight chamber of the wind tunnel was constructed of 5 mm thick plexiglass to allow light penetration and viewing of the insects. Stainless steel mesh (no. 10, 2 mm) was used on the intake and outlet surfaces of the flight chamber to allow air passage and prevent the flies from being drawn into the fan.

A pan measuring 4 x 25 x 100 cm and containing a sam-

rated salt solution was positioned in a 10 cm deep cavity below the wind tunnel floor. Air was drawn across the surface of the solution before being cycled back into the wind tunnel. Humidity of the air stream was therefore a function of the salt solution used and the air temperature. A DISA low velocity flow meter (model 54N50) and a Datametrics hot wire anemom- eter (model 100 VT) were used to calibrate the tunnel for wind speed. Temperature and humidity were measured with a tem- perature-humidity probe (Campbell Scientific, model 207) lo- cated in the air stream and recorded on a Campbell Scientific datalogger (Model CR21) located outside the wind tunnel. Con- trol of air temperature and light was possible by placing the tunnel in a controlled environment room (Conviron model CP240) and varying the lighting and temperature regimes.

Monitoring system. Flight activity of black flies was recorded with a video monitoring system. The monitoring system was composed of a high resolution (384 horizontal and 491 vertical picture elements), monochrome, CCD video camera (Sony model AVC-DI). The high sensitivity (minimum illumination: 3 lux) of the camera allowed the monitoring of flight activity for light levels ranging from near darkness to full daylight con- ditions. Power to the camera was supplied by a 12 volt, 1 amp Sony camera adaptor (model CMA-D1).

The signal from the video camera was monitored on a high resolution (1000 TV lines), 17 inch (43.2 cm), monochrome video monitor (Electrohome model EVM1719) and recorded on a videocassette recorder (Sony model SLHF900).

The recorder allowed high resolution recording on the Su- perBeta format. The bidirectional tape speed control allowed forward and rewind capabilities at twice normal speed, normal speed, one-fifth normal speed and still frame. Employing the slow speed and frame-by-frame capabilities of the recorder, ac- curate counts of black-fly flights were possible. An electronic tab-marker indexing system provided rapid access and recall capabilities.

Preliminary tests. As a test of humidity control, flies were anaes- thetized by exposure to carbon dioxide gas for 1-2min, weighed, and then released into the chambers of known vapour pressure (0.3, 1.5, 2.7, 3.0 kPa). Sample size varied from 5 to 15 flies and each vapour pressure (VP) was replicated five times. The flies were allowed to revive and kept in the chambers for 4 h. At that time they were again anaesthetized, removed from the experimental chambers and weighed to determine water loss.

The effect of vapour pressure on black-fly flight activity was selected for examination. Shippe t al. (1987) suggest that this parameter is one of the most important weather variables governing the flight activity of S. arcticum. Ten black flies were released into flight chambers containing different vapour pres- sures (0.3, 1.5, and 2,7 kPa). Temperature, light, and wind speed were constant during initial testing. The settings for tempera- ture (23 ~ C), light (1200 tux, 161 J m - 2s- 1) and calm conditions for wind were selected on the basis of Shipp et al. (1987) who suggested that these values would not limit the flight activity of S. areticum. Flight activity was recorded with the video moni- toring system for 5 min each hour for a total of 6 h.

Results and discussion

Flight boxes

Air temperatures within the flight boxes in the con- trolled environment room could be held constant ( _ 0.5 ~ C) and thus vapour pressures varied by no

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J J J J

\ 1 10 volt

Fig. 2. a Schematic diagram of a controlled environment system for monitoring flight activity A hinged door to allow insertion and extraction of tray, T; A S air stream; T removable tray containing saturated salt solution; S screen; FC plexiglass flight chamber; I access opening for insertion of flies; C video camera; R video recorder; M video monitor; F fan; CP camera power unit. b Working diagram of controlled environment system for monitoring flight activity (b)

b

more that 0.17 kPa during any one run. Figure 4 shows water loss from black flies after 4-h expo- sures in the boxes at vapour pressures ranging from 3.0-0.3 kPa (saturation to 12% relative hu- midity) at 23 ~ C. Water contents of the flies ranged from a gain of 5.9% (per fly basis) to a 62.8% loss. The variability of water content at each va- pour pressure treatment was high (SD -- 8.0-20.6, see Fig. 4) and was attributed to individual vari- ability within the group of insects and the possible effects of the CO2 treatment. W.O. Haufe (per- sonal communication) suggests that CO2 causes temporary spiracular dilation and hence decreased resistance to vapour loss. Although mean values of water content indicated an increasing water loss with decreasing air vapour pressures, some flies actually took up water under near saturation con- ditions. This is surprising as the water concentra- tion of insect haemolymph is equivalent to 99.5%-99.8% (Wharton and Richards 1978) and

hence the gradient for water movement is positive, indicating evaporation from the insect to the air except in saturated atmospheres. Therefore, water loss was expected on all tests of the system as true saturated conditions are difficult to obtain under laboratory conditions without external cooling of the chambers. Further tests are required to exam- ine the loss/gain of water at high humidities.

Flight activity varied with the vapour pressure of the air and with the time of exposure (Fig. 5). The greatest number of flights recorded in the 5-min sampling period occurred with the first sam- pling period in the driest atmosphere (284 flights, VP=0 .3 kPa). The number of flights recorded at this humidity, however, diminished rapidly with time, with no flights recorded after 90 min (Fig. 5). The initial activity may be the result of an avoid- ance response by the insect. Similarly, flight activi- ty in an atmosphere of 1.5 kPa was high initially but declined over time with few flights observed

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20

15 A

E ,9 ~ .r= to .

"1"

Top surface ---o

5-

~d Bottom surface I I 1 I I 1 2 3 4 5

Windspeed (m/s) Fig. 3. Profile of wind across the tunnel of the controlled envi- romaaent system for monitoring flight activity

80

O 60 ~ + M a x

m

$ 40

+ ~ M e a n

Min a.

o

- 1 0 = ! I 3 . 0 2 . 7 1.5 0.3

Vapour pressure (kPa) Fig. 4. Water loss as a percentage of initial weight vs vapour pressure. Exposure time 4 h (SD of the mean for 3.0=11.0, 2.7=11.2, 1.5=8.0, 0.3=20.6)

after 210 min. In the more humid atmosphere of 2.7 kPa, initial flight activity was less than in the drier environments with only 107 flights observed in the first 5-min observation period. Flight activi- ty at this humidity declined only slowly from the initial level and actually increased after 210 min. Unlike exposures at the lower humidities, flight activity at the higher humidity of 2.7 kPa never ceased during the 270 min of this experiment, indi- cating a less stressed enviromment for the insect.

Wind tunnel-flight chamber

Light levels could be controlled to a maximum of 28000 lux, with a radiant flux density of 36000 J m-2s -1. Wind speed measured in the centre of the flight chamber in the wind tunnel could be controlled (+0.1 m/s) to a maximum of 4.2 m/s. It was noted that this wind speed was sufficient

300 ,,

~. 200

" j \ \ �9

100 J < I--

0 0 30 90 150 2t0 270

TIME OF EXPOSURE (min) Fig. 5. Total number of flights recorded during 5-min observa- tion periods versus time of exposure at atmospheric vapour pressures of 0.3 kPa (n), 1.5 kPa (+) , and 2.7 kPa (zx)

to halt black-fly flight activity at 26 ~ C and 90% relative humidity. Over the possible range of wind speeds, velocity was linearly related to the voltage supplied to the fan. A wind profile across the tun- nel at right angles to the velocity indicated that wind speed was uniform across most of the chamber and decreased only close to the sides of the tunnel (Fig. 3). Air temperature within the wind tunnel could be maintained _+ 0.5 ~ C with va- pour pressure variation of less than 0.1 kPa. At 25 ~ C, these variations in temperature and vapour pressure resulted in a less than 1% change in rela- tive humidity.

Although the techniques and the controlled en- vironment system presented here are being used to study black-fly flight activity, it is suggested that they are applicable to studies on the environmental physiology or behaviour of other insects. For ex- ample, grasshoppers, Camnula pelIucida (Scudder), placed in the flight chamber of the wind tunnel at 33 ~ C ceased activity when presented with condi- tions of a 4 m/s wind speed and a relative humidity of 12%. The individuals drew their hind legs up to their abdomen and assumed a 'crouching' pos- ture close to the surface, the majority orienting their bodies so that they were parallel to the air stream. In a review, Willmer (1982) states that ori- entation and postural control are important in in- sects such as Orthoptera with elongated bodies. He notes that insects can alter their radiative heat gain by exposing maximum or minimum surface area to the sun. It seems apparent that posture control can also be employed as an avoidance strategy to reduce desiccation.

The techniques reported here are being used to provide a quantitative assessment of black-fly

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flight activity under controlled environment condi- tions. These techniques allow more precise deter- mination of the relationship between flight activity and various weather variables. In particular, the evaluation of the black-fly's ability to cope with its hygrothermal environment is being examined. These techniques are also applicable to a wide range of insect behaviour and environmental phys- iology studies.

Acknowledgement. W.O. Haufe is acknowledged for his review of this manuscript.

References

Choe JC, Adler PH, Kim KC, Taylor RAJ (1984) Flight pat- terns of Simulium jenningsi (Diptera : Simuliidae) in central Pennsylvania, USA. J Med Entomol 21:474~476

Davies DM (1952) The population and activity of adult female

black flies in the vicinity of a stream in Algonquin Park, Ontario. Can J Zool 30:287-321

Grace B, Gillespie TJ, Puckett KJ (1985) Uptake of gaseous sulphur dioxide by the lichen Cladina rangiferina. Can J Bot 63: 79%805

McCreadie JW, Murray HC, Bennett GF (1986) The influence of weather on host seeking and blood feeding of Prosimu- lium mixtum and Simulium venustum/verecundum complex (Diptera: Simuliidae). J Med Entomol 23:289-297

Shipp JL, Grace BW, Schaalje GB (1987) Effects of nficrocli- mate on daily flight activity of Simulium arcticum Malloch (Diptera: Simuliidae). Int J Biometeorol 31:9-20

Wexler ML, Hasegawa S (1954) Relative humidity-temperature relationships of some saturated salt solutions in the temper- ature range 0 ~ to 50 ~ C. J Res Natl Bur Stand (US) 53:19-25

Wharton GW, Richards AG (1978) Water vapour exchange kinetics in insects and acarines. Annu Rev Entomol 23 : 309-328

Willmer PG (1982) Microclimate and the environmental physi- ology of insects. Adv Insect Physiol 16:1-57

Received June 29, 1987; accepted October 13, 1987