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Phototactic Response of Two Spotted Cricket (Gryllus bimaculatus De Geer) to Electric Bulb Light Colours and Types

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Phototactic Response of Two Spotted Cricket (Gryllus bimaculatus De Geer) to Electric Bulb Light Colours and Types

Abstract

This study examined the phototactic response of two spotted cricket (G. bimaculatus) to incandescent and LED bulb light of different colours. Light traps fitted with 25 Watts incandescent bulbs and 3 Watts Light Emitting Diode (LED) of different colours (red, yellow, green, blue and white) were used. Also included was a control trap. The traps were operated from 1800hr to 2400hr. G. bimaculatus collected were counted and the data subjected to variance analysis. Student Newman Keul’s test was used to separate significantly different means at 5% level of probability. Relationship between light intensity and insect density was assessed by correlation and linear regression analysis. Results indicated that LED had higher mean intensity despite lower wattage and that, Blue colour had the highest mean intensity (736.80 Lux) among the LEDs and white (1094.20 Lux) among the incandescent bulbs. Statistical analysis showed that differences in attractiveness among LED bulb colours were due to random variation (p = 0.17); however was significant (p < 0.001) among incandescent bulbs. Of the total G. bimaculatus collected attracted, 93.7% was by LED bulbs with blue LED bulb alone attracting 57.1%. Light intensity was positively and significantly correlated with density of G. bimaculatus attracted for both LED (r = 0.92, R2 = 84.4%) and incandescent (r = 0.96, R2 = 92.5%) bulbs. Higher attraction of G. bimaculatus to blue coloured LED bulbs could be attributed to preference and/or high light intensity. Blue LED bulbs of higher intensity can thus be used to manipulate G. bimaculatus for man’s benefit.
66
© 2020 Conscientia Beam. All Rights Reserved.
PHOTOTACTIC RESPONSE OF TWO SPOTTED CRICKET (
Gryllus bimaculatus De
Geer
) TO ELECTRIC BULB LIGHT COLOURS AND TYPES
Chukwu A. Timothy1
Okrikata
Emmanuel2+
1,2Department of Biological Sciences, Faculty of Pure and Applied Sciences,
Federal University Wukari, Taraba State, Nigeria.
(+ Corresponding author)
ABSTRACT
Article History
Received: 11 November 2019
Revised: 19 December 2019
Accepted: 22 January 2020
Published: 26 February 2020
Keywords
Bulb light
G. bimaculatus
Incandescent bulb
LED bulb
Light colour
Light intensity
Phototactic
Preference.
This study examined the phototactic response of two spotted cricket (G. bimaculatus) to
incandescent and LED bulb light of different colours. Light traps fitted with 25 Watts
incandescent bulbs and 3 Watts Light Emitting Diode (LED) of different colours (red,
yellow, green, blue and white) were used. Also included was a control trap. The traps
were operated from 1800hr to 2400hr. G. bimaculatus collected were counted and the
data subjected to variance analysis. Student Newman Keul’s test was used to separate
significantly different means at 5% level of probability. Relationship between light
intensity and insect density was assessed by correlation and linear regression analysis.
Results indicated that LED had higher mean intensity despite lower wattage and that,
Blue colour had the highest mean intensity (736.80 Lux) among the LEDs and white
(1094.20 Lux) among the incandescent bulbs. Statistical analysis showed that
differences in attractiveness among LED bulb colours were due to random variation (p
= 0.17); however was significant (p < 0.001) among incandescent bulbs. Of the total G.
bimaculatus collected attracted, 93.7% was by LED bulbs with blue LED bulb alone
attracting 57.1%. Light intensity was positively and significantly correlated with
density of G. bimaculatus attracted for both LED (r = 0.92, R2 = 84.4%) and
incandescent (r = 0.96, R2 = 92.5%) bulbs. Higher attraction of G. bimaculatus to blue
coloured LED bulbs could be attributed to preference and/or high light intensity. Blue
LED bulbs of higher intensity can thus be used to manipulate G. bimaculatus for man’s
benefit.
Contribution/Originality: The study is one of few that investigated the phototactic response of G. bimaculatus
to electric light type and colours. This information is necessary in manipulating the insect’s directional movement
behaviour for the benefit of man.
1. INTRODUCTION
The phototactic response of some insects explains why they are often seen hovering around lit artificial light
sources especially at night (Barghini & de Medeiros, 2010) thereby facilitating foraging, navigation and mate
selection (Adeoye et al., 2014) while also leading to the invasion of harmful species to inhabited areas (Barghini & de
Medeiros, 2010).
Preferences to different light bulb colours and types have been studied in a number of insects (Pawson & Bader,
2014; Wakefield et al., 2016; Nirmal et al., 2017; Wakefield et al., 2017; Chukwu et al., 2019) with some findings
showing that some electric bulb colours or types might pose a threat to the biodiversity of surrounding ecosystems
due to their high attractiveness to a wide range of insect species (Eisenbeis & Erick, 2010).
International Journal of Sustainable Agricultural Research
2020 Vol. 7, No. 2, pp. 66-72.
ISSN(e): 2312-6477
ISSN(p): 2313-0393
DOI: 10.18488/journal.70.2020.72.66.72
© 2020 Conscientia Beam. All Rights Reserved.
International Journal of Sustainable Agricultural Research, 2020, 7(2): 66-72
67
© 2020 Conscientia Beam. All Rights Reserved.
The two-spotted cricket (G. bimaculatus) has been considered a nuisance in some part of the world where they
periodically invade residential areas causing irritations especially by their chirpings. In some other places, the insect
have been reported as pest of crops such as tobacco, corn, sunflower, cotton and, some fruits and vegetables (Ogbalu
& Renner, 2015; Oso & Borisade, 2017).
On the other hand, the two-spotted cricket have been reported to be a better, more affordable and accessible
source of animal protein which can be used in balancing the essential protein needs in humans and livestock
including poultry, thereby reducing the risk of having individuals with such protein deficiency caused diseases or
death and hence improving the health and productivity of both humans and livestock (Miech, 2018). Additionally,
cricket farming is presently a trending agricultural practice in countries such as Thailand and Cambodia (Miech,
2018).
G. bimaculatus is also an important research specimen. For example, Seth & Cassandra (2016) reported that the
insect has long been used as a model for behaviour, neurobiology, physiology and insect developmental genetics as
well. Specifically, the two-spotted cricket have become models of speciation research and have been the subjects of
prominent research programmes in speciation over the years (Gray et al., 2016).
The rigors of controlling the insect in areas where they are pests and the means of harvesting it for food,
agriculture, research, trade, among others have been shown to be costly, stressful and discouraging. Therefore, the
objective of this study is to determine the preference of G. bimaculatus to LED and incandescent light colours for the
purpose of recommending easier and cost effective means of manipulating the insect for the benefit of man.
2. MATERIALS AND METHODS
2.1. Study Site
The study was carried out in May, 2019 in the Research farm of Federal University Wukari, Taraba State,
Nigeria. Wukari Local Government Area has an area of 4,308 square kilometres, lying in latitude of 7.89N and
longitude 9.77E. It is a guinea savannah zone which has an average elevation of 189m, an annual average
temperature of 26.8C and an annual precipitation of 1,205mm (Okrikata & Yusuf, 2016).
2.2. Insect Trap Design
Light traps were fabricated using transparent white plastic sheetings (served as the screen), wooden
frames/poles, 5 differently coloured (ECOMIN-QP05014/3W; AC220-240V/50-60Hz) light emitting diode (LED)
bulbs (yellow, red, blue, green and white); same for incandescent bulbs (JUNGSRAM 25W; G45, 220V, E27,
1000h).
The bulbs were powered by Tiger-generator (TG950). The light intensity of each bulb was measured in a dark
room using a digital Lux meter (Serial no.: 20111100416). White plastic sheeting was attached to two wooden
frames at both sides to form a screen for the trap. A bulb was placed on top of each trap to reflect on the screen at a
height of 1m above ground level. Each trap was placed at a 3m distance apart from each other to prevent masking
effect by adjacent light colours Figure 1.
A 10 litre capacity bowl which was ¾ filled with water containing 2% liquid soap (which served as a wetting
agent) was placed below each trap and used as the collection vessel. A total of six traps were made for each bulb
type, of which five had the different coloured bulbs (LED and Incandescent) mentioned above hunged on the screen.
A trap without bulb served as the control. Species attracted to the respective light colours and control, fell into the
bowl on hitting the screen and were trapped. Traps were not set when there are signs of rainfall and collections
were discarded any night it rained.
International Journal of Sustainable Agricultural Research, 2020, 7(2): 66-72
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© 2020 Conscientia Beam. All Rights Reserved.
2.3. Insect Collection and Identification
The trap was set from 1800 hours to 2400 hours and the two-spotted crickets trapped by the different bulbs
and colours were collected into different well-labelled sample bottles containing 70% ethanol for preservation and
subsequent counting.
Sample specimens were sent to the insect museum of Institute of Agricultural Research (IAR) in Ahmadu Bello
University, Zaria for confirmatory identification after conducting a preliminary morphological identification of the
insects using both the insect microscope and hand lens in the Department of Biological Sciences laboratory of
Federal University, Wukari.
2.4. Statistical Analysis
The count data were transformed using √x + 0.5 before variance analysis. Significantly different treatment
means were separated by Student Newman Keul’s test at 5% level of probability. Student’s t-test (two-tailed) was
used for comparing the attractiveness of LED and incandescent bulb colours to G. bimaculatus.
The relationship between intensity of light colours of each bulb type and density of G. bimaculatus attracted
were determined by correlation and linear regression analyses. All analyses were done using IBM SPSS Statistics
version 23.0 (SPSS Inc., Chicago, Illinois).
3. RESULTS
3.1. Light Intensities and Attractiveness of Bulb Light Colours to G. bimaculatus
The measured light intensities of the bulbs showed that Red, Yellow and White incandescent bulbs had higher
intensities than their corresponding LED bulbs while, Green and Blue LED bulbs had higher intensities than their
corresponding incandescent bulbs.
Overall, despite low wattage (3W) the LED bulbs had higher mean intensity (381.03 Lux) over the 25W
incandescent bulbs (338.63 Lux) Table 1.
Among the LEDs, Blue followed by white bulbs attracted the highest proportion of G. bimaculatus; 57.1% and
21.3%, respectively while the least was Red LED bulb with 1.3% attraction. Table 1 also indicates that the blue
LED bulb attracted the highest number of G. bimaculatus (4.07±1.67), and this was followed by white bulb
(2.61±0.64) and green bulb (2.11±0.49). The control trap attracted the least mean number of G. bimaculatus.
Variance analysis however showed that, the differences in G. bimaculatus attracted by LED bulbs were due to
random variation (p = 0.17) Table 1. Among the incandescent bulbs however, Table 1 shows a significant difference
(p < 0.001) in their attractiveness to G. bimaculatus. White colour attracted significantly the highest mean number
of G. bimaculatus while the other bulb colours were statistically at par with the control trap which attracted the
lowest mean number (0.71±0.00) alongside green and blue bulbs.
Table-1. Light intensities of LED and incandescent bulbs and their attractiveness to G. bimaculatus.
Bulb Colours
LED Bulb
Incandescent Bulb
Light intensity
(Lux)
Mean Number of
G. bimaculatus
Attracted
Light intensity
(Lux)
Mean Number of
G. bimaculatus
Attracted
Red
60.18±5.97e
0.86±0.15a
65.36±3.55d
0.86±0.15b
Yellow
243.20±16.47d
1.90±0.67a
334.00±3.36b
0.80±0.09b
Green
513.80±27.00b
2.11±0.49a
154.20±4.24c
0.71±0.00b
Blue
736.80±13.02a
4.07±1.67a
45.40±1.57de
0.71±0.00b
White
351.20±4.31c
2.61±0.64a
1094.20±38.51a
1.80±0.14a
Control
0.00±0.00f
0.71±0.00a
0.00±0.00e
0.71±0.00b
F-value
38.27
1.76
67.52
22.45
P-value
<0.001
0.17
<0.001
<0.001
Note: 1 - Means (±SE) followed by the same superscript letter(s) within a column are not significantly different using Student-Newman Keul’s (SNK) test (P
0.05).
International Journal of Sustainable Agricultural Research, 2020, 7(2): 66-72
69
© 2020 Conscientia Beam. All Rights Reserved.
Figure-1. Showing light traps setup [Trap 1: control, Trap 2: green, Trap 3: red, Trap 4: white, Trap 5: yellow and Trap 6: blue] spaced 3 m
apart in the field (Traps are numbered from left to right).
3.2. Relative Attractiveness of LED and Incandescent Bulb Light Colours to G. bimaculatus
Table 2 shows that, across the bulb colours and the pooled mean, LED bulbs consistently attracted more G.
bimaculatus than incandescent except, for red colour where both bulbs were at par (t-α = 0.00). Differences were
however due to random variation except for green colour [LED (2.11±0.49); (0.71±0.00)] (t-α = 0.04).
Table-2. Comparison between LED and incandescent bulb colours on the attraction of G. bimaculatus.
Variable
Mean Count
for LED
Mean Count for
Incandescent
Mean
Difference
t-value
P-value
Red
0.86±0.15
0.86±0.15
0.00±0.21
0.00
1.00
Yellow
1.90±0.67
0.80±0.09
1.10±0.67
1.64
0.16
Green
2.11±0.49
0.71±0.00
1.40±0.49
2.84
0.04
Blue
4.07±1.67
0.71±0.00
3.36±1.67
2.01
0.10
White
2.61±0.64
1.80±0.14
0.81±0.66
1.23
0.27
Pooled Mean
2.31±0.71
0.97±0.06
1.33±0.71
1.89
0.12
3.3. Relationship between Attractiveness of G. bimaculatus by Bulb Light Colours and their Intensities
Light intensity was positively and significantly correlated with G. bimaculatus density in both LED (r = 0.92, R2
= 84.4%) and incandescent (r = 0.96, R2 = 92.5%) with p-values of 0.01 and 0.04, respectively Table 3.
Table-3. Correlation analysis and linear regression between G. bimaculatus count and bulb light intensity.
Variable
Correlation
Coefficient (r)
Regression
Equation
Coefficient of
Determination (R2)
Insect count x LED Intensity
0.92**
Y = 4.315 + 0.025x
0.844*
Insect count x Incandescent Intensity
0.96*
Y = 3.768 + 0.006x
0.925**
Note: * = significantly different (P 0.05).
** = significantly different (P 0.01).
*** = significantly different (P 0.001)
ns = not significantly different (P > 0.05).
4. DISCUSSION
Different insects have preferences for different light bulb colours and types which could be attributed to the
differences in wavelength/intensities of these respective colours (Nirmal et al., 2017; Chukwu et al., 2019; Okrikata
et al., 2020). Insect abundance including G. bimaculatus is known to be more in the tropics, but this abundance is not
adequately harnessed for man’s benefit. Blue colour has been reported by Cruz & Lindner (2011) as a region of
maximum stimulation for majority of insects. This was apparently noticed in the current study with respect to
LED. That white light was highly attractive to G. bimaculatus in the current study have been reported by Nirmal et
al. (2017) and Miech (2018) with Miech (2018) pointing out that white light is being used in insect traps to harvest
International Journal of Sustainable Agricultural Research, 2020, 7(2): 66-72
70
© 2020 Conscientia Beam. All Rights Reserved.
G. bimaculatus in Cambodia and Thailand. Cumulatively, blue coloured LED bulb proved to be most attractive in the
present study. This contrasts the finding of Chitra (2018) who found red coloured incandescent bulbs most
attractive to orthopterans predominated by G. bimaculatus. The high attractiveness of G. bimaculatus to blue
coloured LED is of interest as it can be harnessed for proper management of the species especially in the tropics
where the species is abundant. In areas where G. bimaculatus are nuisance, reducing the use of blue LEDs as outdoor
lights (as seen at night in some recreation centres) can effectively reduce the density of the attracted insect species
thus saving the cost of pesticide and potential danger of exposure to some of the toxic chemical pesticides which are
largely used for their management. Making insecticidal traps using blue coloured LED will be efficient in managing
the species in areas where they occur as pests thereby providing a better, cost effective and environmentally friendly
management strategy for the species. Additionally, the rigors of collecting G. bimaculatus for food, agriculture,
scientific research, conservation and even export can be drastically reduced with the knowledge that blue coloured
LED bulbs are effective attractants of the species. Hence, appropriate blue coloured LED insect traps can be used to
effectively and efficiently harvest the species. LED bulbs have been reported to be insect friendly (Eisenbeis &
Erick, 2010; Okrikata et al., 2020), eco-friendly and energy saving (Wakefield et al., 2017) and hardly emits
ultraviolet radiations. It has also been observed that different bulb types attract insects at varying levels (Nirmal et
al., 2017; Ebadi et al., 2018). Contrary to the findings of the current study, Barghini & de Medeiros (2012) and
Wakefield et al. (2017) in their studies opined that LEDs are less attractive to many insect species than their
incandescent, compact fluorescent and metallic halide counterparts as many insect species according to them, are
disproportionately attracted to UV lights. However, even though the difference between LED and incandescent
bulbs with respect to attractiveness to G. bimaculatus in the present study was due to random variation, that LED
was more attractive than incandescent as observed in the present study, buttresses the findings of Pawson & Bader
(2014) who showed that of Incandescent, Compact Fluorescent and LED bulbs; LED bulbs was most attractive to
insects. In addition, even though Wakefield et al. (2017) reported higher insect attractiveness to halogen bulbs
because of its emission of UV light in southern England, LED bulbs was reported by the authors to attract greater
insect diversity than incandescent bulbs. In a study conducted by Nirmal et al. (2017) and Chitra (2018) they
observed that irrespective of colours, incandescent bulbs were more attractive than compound fluorescent light with
respect to orthopteran species. That incandescent bulbs were more attractive to fluorescent light in their study and
LED to incandescent in the present study underscores the need to evaluate the responses of insects to different
electric light types. Even though the LED bulbs used in the current study were of lower wattages (3W) compared
to their incandescent counterparts (25W); overall, the LED bulbs had higher mean light intensity than the
incandescent bulbs. This might be responsible for higher attraction of the insect species to the LED bulbs than to
the incandescent bulbs, thus buttressing the report of Pawson & Bader (2014) and Chukwu et al. (2019) who opined
that higher light intensity for LED bulbs relative to incandescent resulted to higher attractiveness of the insects to
LEDs. Similarly, Wakefield et al. (2016) showed that higher attractiveness of insects to light sources was due to
relatively higher light intensity. These, agrees with the current study which showed rising attraction of G.
bimaculatus with increased light intensity. The effect of light intensity on the attraction of G. bimaculatus in this
study was also observed among the incandescent bulbs in which white incandescent bulb which had the highest
intensity resulted to higher attractiveness of the insect species. That LED bulbs are more efficient than
incandescent bulbs in relation to light intensity as reported by Wakefield et al. (2017) was obvious in the current
study where 3W LED bulbs produced higher light intensity than 25W incandescent bulbs. This apparently
indicates that higher wattages of the LED bulbs will produce even higher light intensity which may result to higher
attraction of G. bimaculatus.
International Journal of Sustainable Agricultural Research, 2020, 7(2): 66-72
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© 2020 Conscientia Beam. All Rights Reserved.
5. CONCLUSION
Aside being an important source of protein for humans and livestock, the two spotted cricket (G. bimaculatus) is
a key nocturnal Agricultural pest. This study has shown that G. bimaculatus are attracted to artificial light at night.
It has also shown that the species are attracted predominantly to blue LED bulbs and that lights of higher
intensities attract more of the species than lower intensity lights. It is therefore suggested that their attraction to
bulb types and colours is due to the influence of colour and/or light intensity. Hence appropriate use of bulb colour
and light intensity can be instrumental in manipulating the insect species for the benefit of man.
Funding: This study received no specific financial support.
Competing Interests: The authors declare that they have no competing interests.
Acknowledgement: This study is part of a Project leading to the award of a Degree in Biology
of Federal University, Wukari, Nigeria. Sincere thanks to Samaila Nuhu and Stephen Yakubu
for their support during the field work. The expertise of Mr. Ishaku Musa of the Insect Museum
of Institute of Agricultural Research (IAR) in Ahmadu Bello University, Zaria, Nigeria in
identifying the insect samples is well appreciated. Sincere gratitude also, to Mr. Adeniyi
Ogunmola of Mathematics and Statistics Department, Federal University, Wukari for running
the data analyses.
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Article History Keywords Attractiveness Hexapod orders Incandescent Light colours Light-emitting diode (LED) Light trap Phototactic. Dearth of information on response of hexapod orders to light sources and colours informed this study. The study was conducted in Federal University Wukari, Nigeria in the month of May, 2019 to evaluate the attractiveness of hexapod orders to Light-emitting Diode (LED) and Incandescent bulb light colours. Daily sampling using fabricated light traps with 5 different colours (white, yellow, red, green and blued) for each bulb type in 6 replicates was done. A trap with no lighting source was the control. Hexapods collected were sorted into their respective orders. Of the overall 13 insect orders collected, LED bulbs attracted 11 while incandescent, 10. Even though, certain hexapod orders exhibited higher affinity to specific colours, statistical analysis revealed that of the 11 orders from LED, differences in the mean number of insects attracted among the bulb colours was significant (p<0.05) only in Coleoptera and Lepidoptera while for incandescent bulb colours, the mean number of insects attracted was significant for Coleoptera, Lepidoptera, Hemiptera, Hymenoptera, Orthoptera, Mantodea, Odonata and Homoptera. Insect orders generally had higher affinity to white and blue colours. LED bulb colours significantly attracted higher number of insects than their corresponding incandescent colours, except for white on which incandescent was more attractive (p>0.05). Overall, attractiveness to hexapod orders increases with rinsing light intensity and LED bulbs were found to be more attractive to hexapods than do incandescent bulbs. Therefore, LED bulbs of higher light intensity with colours around the blue/white spectrum show potential for use in manipulating hexapods for man's benefit. Contribution/Originality: This study discovers that hexapod orders are largely highly responsive positively to blue and white electric light of higher intensity. It also shows that, the LED bulbs were generally more attractive to the hexapod orders than the incandescent. This knowledge can be harnessed in manipulating the hexapods for man's benefit.
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