Carbon dioxide output and mating in adult cabbage looper moths exposed to discrete light régimes

J. Insect Physiof.,

1975, Vol. 21, pp. 1233 to 1236.

Pergamon

Press.

P&&d

in Great Britain.

CARBON DIOXIDE OUTPUT AND MATING IN ADULT CABBAGE LOOPER MOTHS EXPOSED TO DISCRETE LIGHT Rl?GIMES NORMAN C. LEPPLA and WILLIAM K. TURNER

Insect .4ttractants, Behavior, and Basic Biology Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Gainesville, Fla. 32604, U.S.A. (Receiwed

29 November

1974)

Abstract-Carbon dioxide discharge and the number of spermatophores transferred were recorded from populations of adult cabbage loopers, Trichoplusia ni, maintained under various wavelengths and intensities of light. Nocturnal CO, output was enhanced by retaining 1 per cent of the diurnal intensity of near-u.v. and blue lights during the scotophase. However, addition of < 10 per cent of the diurnal intensities of u.v., blue, and white lights suppressed COB production. Exposure to gold light resulted in the lowest 24 hr CO, accumulations, and red was intermediate. Similarly, maximum levels of mating occurred when cabbage loopers were exposed to nocturnal intensities of 1 per cent of the diurnal u.v., blue, or white lights, even though higher intensities were inhibitory. Considering all nocturnal intensities ranging from 0 to 100 per cent of diurnal levels, U.V. and red yielded the highest mating frequencies, blue and gold were intermediate, and white was lowest. Thus, relatively unique action spectra resulted from each regime.

INTRODUCTION

pink bollworm, and motor responsiveness (electromyogram) similar to the attraction at high intensity. WEISS (1946) and STERMER (1959) were among the We discovered previously that an essentially first to report behaviourally determined spectral complete visible light spectrum (390-770 nm), responses to visible light for a variety of phylosupplemented with near-u.v. (300-390 nm) and of genetically unrelated insects; however, they did not relatively high intensity during the photophase and consider variations in intensity. HOLLINGSWORTH low intensity (cu. 1 per cent diurnal) during the (1961) summarized existing knowledge concerning scotophase, must be provided for optimum fecundity the sensitivity of insects to wavelength and discussed of adult cabbage loopers. In an effort to explain experiments involving attraction of adult pink these observations, we determined the influences of bollworms, Pectinophoru gossypiella (Saund.), a five discrete wavelengths of radiation on reprostrictly nocturnal insect, to both colour and intensity ductive behaviour, and investigated the effects of of light. He discovered that this species was most varying the intensities of these wavelengths during responsive to 486 to 546 run, with secondary the scotophase. This was accomplished by using a near 365 nm, and not appreciably attraction carbon dioxide monitoring device to determine influenced by wavelengths shorter than 300 nm or spectral sensitivity as it affects the metabolic rates longer than 600 nm. He also found a ‘shift in and behaviour patterns of confined populations of response characteristics’ in which the pink bollworm this species. moth was more attracted to 365 nm than to 515 nm, when intensities were greater than forty times the MATEXIALS AND METHODS base level. GLICK and HOLLINGSWORTH (1954), A Plexiglas box containing 100 cabbage looper HOLLINOSWORTHand HARTSTACK(1972), and many moths obtained from a colony at the Insect Attractothers also investigated the potential for using a ants, Behavior, and Basic Biology Research Laboravariety of lamps to attract insects and found the tory was positioned inside a bioclimatic chamber cabbage looper, Trichoplusiu ni (Hiibn.), and related constructed with white, reflective internal surfaces. nocturnal species to be most attracted to a mixture Incident light was measured at the location of the In of near-u.v. and 578 nm visible radiation. insects, O-61 m beneath the source. Nocturnal addition, MACFARLANEand EATON (1973), studying levels of 0, 1, 10, or 100 per cent of the diurnal light the effects of monochromatic light stimuli on intensities were obtained with a cam-operated cabbage looper moths by electrophysiological shutter, that provided gradual phase transitions to techniques, documented sensory spectral sensitivity simulate natural conditions. Thus, 2.75 hr were (electroretinogram) comparable to the attraction at required to pass from diurnal (100 per cent light) to low intensity reported by HOLLINC~WORTHfor the 1233

NORMAN C. LEPPLAANDWILLIAMK. TURNER

1234

the lowest selected nocturnal level (0 per cent); and it took 1.75 hr to return. Temperatures ranged from 29 + 1 to 25 f 1°C and r.h. from 52 to 70% for the diurnal and nocturnal periods; transitions were gradual as with the light. General Electric or Luxor lamps of each colour were used to provide wavelengths in the near-u.v. (GE-F1 5T8aBLB # ), blue (GE-F1 5T8.B), white (Lux (Vita-lite)-l5-wBRC), gold (GE-Fl5T8.G0), and red (GE-FlST8.R) (Fig. 1). Illumination from 0.5‘ii0.4 f

?z v 0.3 -

3 t 0.2 zz I z - O.l-

Relationships between intensities of colours, and among colours were determined by comparing the extent of diurnal and nocturnal suppression of activity, monitoring the acuteness of the lights-off and lights-on responses, and establishing the thresholds of response to percentages of diurnal light remaining during the scotophase (designated sp percentages). Thus, 20 treatments were applied, consisting of the 4 intensities of nocturnal light for each of 5 colours (an erroneous < 1 per cent light leak was discovered after tests with dark, white, and gold; however, it produced only a slight increase in reported nocturnal activity at 0 per cent light levels). Each treatment was replicated four times, and analysis of variance was used to determine differences in the average level of CO, output or number of mated females. Duncan’s multiple range test was applied to groups having significant differences (P = 0.05). RESULTS

350

400

450 500 550 WAVELENGTH (NM)

600

650

700

Fig. 1. Approximate spectral energy distribution for lamps used to study the responsivenessof cabbage looper moths. each light source was equalized to a diurnal energy level of approximately 37 pW/cma using data from the manufacturer (substantiated with a Gamma Scientific Model 721 Linear Photometer) and adding appropriate neutral density filtering (fibreglass screens) to reduce outputs of the high intensity lamps to this standard. Depending on colour, one to four 15 W lamps were used. Cabbage loopers used in this study had been colonized continuously for more than 3 years according to standard procedures using a modified pinto bean diet (ANTONIOet al., 1975). Pupae were held for emergence in an incubator maintained at 27 f 2°C and 65 + 5% r.h., with a 12 hr photophase (white light on at 0800 hr). For a test, populations of 50 moths 1 to 2 days after emergence of each sex were transferred to a 0.012 ms Plexiglas box; the vigour of the insects was insured by providing a source of 5% sucrose solution. The box of entrained moths was placed in the bioclimatic chamber and connected to a carbon dioxide monitoring device (TURNER and CHARITY, 1971). Then, after a 24 hr recovery period, the hourly rate of CO, output of the confined population was recorded. Since peak mating occurred on the third night post-emergence, CO, expired from moths 2 to 3 days after emergence provided a suitable index to overall activity. After this test period, the females 4 days after emergence were dissected and transferred spermatophores served as a measure of mating success.

Average rates of COr discharge per hr from populations of 50 male and 50 female cabbage looper moths held under the tested wavelengths and intensities of light were graphed with hourly volume recorded at the beginning of each interval (Fig. 2).

$

I

Fig. 2. Response of cabbage looper moths to various wavelengths and intensities of light. (a) The experimental photoperiods superimposed on the pattern remaining after light was withheld. (b-f) CO, output from insects tested under the indicated light regimes (COB values = mean areas under the curves on strip chart records in ina x 10, 1 in8 = 3.0 cm3 CO,).

Carbon dioxide output and mating in adult cabbage looper moths

1235

Table 1. Effect of color and intensity of light on the CO* output and mating of cabbage looper moths * Volume (cc) of CO2 and number of matings

X diurnal light during scotophase

uv XkSE

Blue:

White?

Gold:

Red

FkSE

FTSE

@jE

Ti+SE _

Total CO2 0

36.5752.07 a

35.52g.98 a

44.85+1.89 a

34.1721.35

37.62L2.16

1

45.4850.69 b

44.82T3.99 b

45.09T2.52 a

35.91t2.37

46.38T2.91

10

45.783.47 b

36.24~2.43 a

44.85TO.78 a

36.759.77

40.86t3.18

100

39.33LO.96 a

27.099.53 c

33.815.65 b

34.5622.49

43.65~1.83

0

20.403.17 a

21.72g.41 a

27.63TO.99 a

20.91+0.84

25.20+1.29

1

27.1850.75 b

26.85T2.40 b

27.4551.47 a

22.175.95

30.3e2.55

10

27.693.03 b

20.73g.41 a

25.4151.11 a

23.19+1.83

25.71g.83

24.7220.90 b

13.6550.69 c

17.97g.23 b

20.135.47

27.99+0.99

Nocturnal CO2

100

Females Mated 0

42.5e3.50

41.7552.32 ab

39.25+0.25 a

41.00+1.87

39.00+2.oci

1

43.5OAO.50

47.00+0.71 a

45.00+1.23 b

36.50~3.23

42.00+0.00

10

42.00+1.00

29.00+2.16 bc

27.00~0.00 c

36.0052.71

42.25tO.48

100

41.5Ok2.50

26.5025.72 c

11.00+2.35 d

33.25L2.39

40.00+2.12

* Means followed by the same letter are not significantly different at the SO,/,level of confidence. Columns without letters contain means that are not significantly different. t Values for 0% diurnal intensity during the nocturnal period should be slightly lower than reported because of an erroneous < 1% light leak. The patterns of expiration were unimodal for all treatments, indicating a single peak period of 2 to 8 hr duration depending on the quality of light. Characteristic transitional responses occurred at lights-off (2000 hr) and lights-on (0630 hr). The duration of peak activity and magnitude of response to phase change were indicators of the spectral sensitivity of these insects. The pattern remaining from the initial 1 to 2 days of photoperiodic entrainment with white light, provided a means of comparing the influences due to coloured lights. During the 24 hr post-entrainment dark test (Fig. 2a), an average of 47 Z!I0.24 ems of CO, was released and 42-50 + 2.50 females mated. Compared with darkness during the scotophase, U.V. light entrained at all sp percentages; and increases in nocturnal intensity tended to enhance CO, output (Fig. 2b). These moths were also exceptionally sensitive to blue light, and the addition of 1 per cent during the scotophase again actually increased expiration (Fig. 2~). However, the transition from diurnal blue light to nocturnal levels of 10 per cent sp resulted in a proportionally lowered response. The extreme occurred with constant blue light (100 per cent sp), since an

essentially minimal level of metabolism was exhibited throughout the 24 hr period. White light was less inhibiting to this insect than blue; however, the pattern of CO* release was similar and both produced delayed responses to the change of phase at 1815 to 2000 hr (Fig. 2d). Significant reductions in COz output did not result from increases in the intensity of gold or red light during the scotophase, but moths were entrained by these wavelengths (Fig. 2e and f). Trends in mating under blue and white lights also revealed increases at 1 per cent and proportional reductions at 0, 10, and 100 per cent sp (Table 1). Near-u.v. and red, unlike the other colours, caused entrainment without producing a concomitant suppression of CO, discharge and mating. At nonmating frequencies were inhibitory intensities, lowest under gold light. Red light, like u.v., effected rates of total CO, discharge and spermatophore transfer that approximated levels recorded from controls exposed to total darkness, whereas suppression by blue and a lack of stimulation with gold yielded lower responses (Table 2). COa output under white light was equivalent to u.v., red, and dark, but mating was severely inhibited by this

NORMA C. LEPPLA ANDWILLIAMK. TURNER

1236

Table 2. Effects of combined light intensity and color rCgimes on CO* output and mating of cabbage looper moths * CO, discharged 24-hr Color

CO2 discharged nocturnal T?SE

iT?SE

FEfMles mated @SE

uv

167.16%2.67a

99.99+2.07a

169.50+_ 4.50 a

81M

143.67+90

81.99Ll.50b

144.25+ 3.99 b 122.oof 0.00 c

b

White

172.17+7.86P

98.76t3.84a

Gold

141.3623.45b

86.3722.37b

146.76z3.59 b

Red

156.75L9.30ab

108.12L4.35a

16&w+_ 3.00 a

Dark

190.17tO.96a

107.19+0.33a

I7o.m~o.00 a

Means followed by the same letter are not signilicantly different at the 5% level of confidence. *

colour. ‘Strong’ lights (400-550 nm) increasingly suppressed nocturnal activity to diurnal levels as percentages during the scotophase increased; ‘weak ones (550-700 nm) allowed levels of nocturnal activity to remain relatively high. DISCUSSION

These results demonstrate the physiological effects of discrete portions of the visible spectrum and near-u.v. light on laboratory colonies of cabbage looper moths. With light intensities of 37 pW/cma or less, this species is most sensitive to wavelengths between 400 and 550 nm. SHOREY(1966) reported that light influences the periodicity of mating, and SHOREYand GA~TON(1970) found that short-range orientation is important to the performance of courtship sequences and related mating behaviour. We have shown that in response to light intensity within the 300 to 700 nm range, CO, output is proportonal to the expression of overt behaviour, and that low level nocturnal illumination is essential to peak activity. Wavelength-intensity relationships are also known to affect the circadian rhythms of responsiveness to chemical cues (SHOREY and GASTON, 1965; SOWER et al., 1970). Our findings are consistent with theirs, even though rather than studying actual behaviour patterns, we measured the resulting rates of expiration and mating. CO, output proved to be an accurate and convenient index to overall activity in these experimental populations. HOLLINGSWORTH(1961) emphasized that the influence of radiation is directly proportional to absorption, and that the effects are primarily chemical below 390 nm and visual from 390 to 770 nm. This distinction between near-u-v. and visible ranges, along with an indication of the complexities of associated physiological responses, IS evident in our results. If, as MACFARLANE and

(1973) suggest, perception of near-u.v. primarily affects motor responses, whereas visible light is important for sensitization and perhaps orientation; then differences in direction and magnitude of response to these two kinds of electroAccordingly, magnetic stimuli should occur. relatively high intensity U.V. introduced during the scotophase is stimulatory and visible light is inhibitory. In our tests, differences in total CO* and mating values resulted primarily from nocturnal inhibition by 10 and 100 per cent sp light levels, and it became apparent that particular combinations of wavelengths and intensities are required for the biological efficiency of cabbage looper moths. EATON

Acknowledgements-The authors express their appreciation to W. J. PONS, F. L. LEE, and D. M. BLACKWELL who accurately performed several of the routine operations essential to this study. L. L. SOWER contributed a particularly helpful review of the manuscript.

REFERENCES ANTONIOA. Q., hkL.wcmm J. R., LEPPLA N. C., and GREEN C. W. (1975) Culturing the lesser Peachtree borer. J. econ. Ent. In press. GLICK P. A. and HOLLINGSWORTHJ. P (1954) Response of the pink bollworm moth to certain ultraviolet and visible radiation. J. econ. Ent. 41, 81-86. HOLLINGSWORTHJ. P. (1961) Relation of wavelength to insect response. USDA, ARS (Ser.) 20-10, 9-25. HOLLINGSWORTH1. P. and HARTSTACKA. W. 119721 Effect of components on insect light trap perforkance: Trans. Am. agric. Engrs 15, 924-927. MACFARLANEJ. H. and EATON J. L. (1973) Comparison of electroretinogram and electromyogram responses to radiant energy stimulation in the moth, Trichoplusia ni. J. Insect Physiol. 19, 811-822. SHOREY H. H. (1966) The biology of Trichoplusiu ni (Lepidoptera: Noctuidaej-IV. Environmental co&o1 of mating. Am. ent.,Soc. Am. 59, 502-506. SHOREY H. H. and GASTONL. K. (1965) Sex pheromone of noctuid moths-VIII. Orientation to light by pheromone-stimulated males of TrichopZusia ni (Lepidoptera: Noctuidae). Ann. ent. Sot. Am. 58, 833-836. SHOREYH. H. and GASTONL. K. (1970) Sex pheromones of noctuid moths-XX. Short-range visual orientation by pheromone-stimulated males of Trichoplusia ni. Ann. ent. Sot. Am. 63, 829-832. SOWER L. L., SHOREY H. H., and GASTONL. K. (1970) Sex pheromones of noctuid moths-XXI. Light : dark cycle regulation and light inhibition of sex pheromone release by females of Trichoplusia ni. Ann. ent. Sot. Am. 63, 1090-1092. STERMER R. A. (1959) Spectral response of certain stored-product insects to electromagnetic radiation. J. econ. Ent. 52, 888-892. TURNER W. K. and CHARITY L. F. (1971) Determining response of insects to radiation by continuous monitoring of their carbon dioxide output. Ann. ent. Sot. Am. 64,419-424. WEISS H. B. (1946) Insects and the spectrum. r. New York ent. Sot. 54, 17-30.