Corresponding authors: Benjamin Price (
Academic editor: Anne Thessen
There are approximately one hundred thousand aquatic insect species currently known to science and this figure is likely a significant underestimation. The ecology of aquatic insect groups has been studied due to their role as bioindicators of water quality and in the case of
We describe the NightLife: a cheap, robust, portable, LED based light source which targets insect trichromatic vision, is capable of autonomous operation and is powered by a single AA battery. Field trials show that the NightLife is capable of collecting sufficient samples of 12 insect orders, including all aquatic orders commonly collected by traditional light trapping and compares favourably with actinic fluorescent tubes and white LEDs. Future development in LED technology will likely result in LEDs replacing traditional light sources for collecting insects more widely.
The authors are not aware of any conflicts of interest. BWP is a subject editor of the BDJ.
Inland waters cover less than 1% of our planet's surface, yet provide habitat to approximately one hundred thousand aquatic insect species, i.e. those with at least one aquatic lifestage (
The majority of aquatic insect diversity is comprised of true flies (
Aquatic insects are surveyed using a variety of methods including light trapping (e.g.
Mercury vapour (MV) bulbs work by passing an arc of electric current through ionised mercury vapour; as a result these bulbs require a relatively high current to maintain the arc and thus are limited to use with either mains power or a petrol / diesel powered generator. Remote areas therefore cannot be sampled without significant effort. In addition MV bulbs are excessively bright for attracting aquatic insects, and tend to draw large numbers of night flying lepidoptera and other non-target species. MV bulbs are also delicate, easily damaged in transport and liable to break if exposed to rain during operation due to thermal fracture of the glass, and their high operating temperature is a waste of power.
Actinic fluorescent tubes also use mercury, but their method of operation requires a smaller current draw. While an improvement over MV bulbs, the current draw of fluorescent tubes does still require sizeable batteries if they are to be used in remote locations. For example a single 4W flourescent tube requires a 6v 12Ah battery weighing up to 2kg for an approximate 12hr run time. Fluorescent tubes are also delicate and liable to damage under field conditions.
Both MV bulbs and actinic fluorescent tubes contain mercury, which if released in the field can be hazardous for the environment.
An ideal aquatic insect light trap would have these properties:
Be able to run from small, standard, [potentially] rechargeable batteries. Use low power light sources, at frequencies targeted for insect vision. Be robust enough for field use without special packing or travel arrangements. Be capable of autonomous operation.
Light Emitting Diodes (LEDs) are semiconductor devices that are used in a wide range of scientific, home and commercial lighting solutions due to the following properties:
low power / high-efficiency (compared to incandescent / fluorescent) narrow spectral emissions (i.e. specific colours) long-life low-operating temperature durable (enclosed in a solid epoxy case rather than hollow glass) small size and weight
These same properties also lend themselves to the use of LEDs in insect collection.
Most insects studied have three types of photoreceptors: UV (λmax ∼ 350 nm), blue (λmax ∼ 440 nm) and green (λmax ∼530 nm) (
Many aquatic insects are nocturnal or crepuscular in the adult stage, and possess positive phototaxis: the attraction to light (
Green LEDs have been used in a number of traps for catching horticultural pests including the Auchenorrhynchan virus vector
The use of LED technology using light wavelengths suited for insect vision in insect traps has been studied previously by
However recent work by
In light of the previous work the aim of this study was therefore two-fold: (1) to build and field test a portable LED-based light-trap using LEDs targeting the UV, blue and green insect photoreceptors; and (2) to compare the targeted design against an actinic flourescent light (Philips Actinic BL TL 4W-10 UV-A G5) and a commercially available white
The NightLife traps are based on the
Design files for the Printed Circuit Board (PCB: Figs
Assembly of the device requires the following tools:
Soldering iron (and solder) Wire cutters ‘Helping hands’ or other PCB holder (optional, Fig.
The transistors are the most thermally sensitive components and require care when soldering. The risk of damage can be minimised by ensuring the solder joint is made quickly, or by clamping the legs of the component (on the opposite side to the solder) with pliers to act as a heatsink. The other electronic components are thermally stable enough to survive relatively prolonged soldering. Fig.
2 5mm UV LEDs [LED1; LED4]
1 5mm Green LED [LED3]
1 5mm Blue LED [LED2]
1 Photoresistor [R1]
1 Potentiometer [R2]
1 1KΩ resistor [R4]
1 10KΩ resistor [R3]
1 100KΩ resistor [R5]
1 22pF ceramic capacitor [C1]
1 470uH inductor [L1]
2 2N2222 NPN transistor [Q2; Q3]
1 2N2907 PNP transistor [Q1]
2 AA battery clips
These parts are best purchased in bulk (i.e. enough for 10 NightLife units) resulting in a total cost per unit of approximately £10 / €13 / $16 (currency conversion as at October 2014).
The spectral output of the 4W actinic fluorescent tube, the NightLife and the white LEDs were compared in laboratory settings using an Ocean Optics HR2000+ spectrometer and Ocean Optics SpectraSuite v1.6 (Ocean Optics Inc). Values were normalized for comparison between light sources by measuring from a standard distance and dividing by the integration time.
Battery life was tested using by placing a NightLife device into a sealed carboard box while powered by a single fully charged Eneloop rechargable 2000mAh AA battery. The output of the light was measured using a photoresistor in a potential divider with a fixed resistor. The voltage across the photoresitor was recorded to a microSD card using an
The NightLife was trialed over a three night period in November 2014 on the Gudu and Mahai rivers of the Royal Natal National Park, South Africa (S: 28.6828; E: 28.9296). The Gudu river begins in the "Gudu Bush" an isolated patch of northern Afrotemperate forest (
Five sites were selected between the rest camp and the source of the Gudu river with the traps set during the day, and sensitivity set to maximum to turn the trap on as early in the evening as possible. The following day traps were recovered and either sorted to morphospecies (
Each trap consisted of either (A) two NightLife devices (eg. Fig.
Due to limited materials and trapping nights on site the field trials focussed on testing the efficacy of the NightLife (6 traps, total of 12 trap nights) with limited comparison to the bike light (1 trap, total of 2 trap nights) and actinic tube (1 trap, total of 1 trap night). As a result comparisons are limited to qualitative (presence / absence) of particular orders and very basic comparisons of the
While the devices worked as expected in the field trials the exposed circuit of the NightLife PCB is vulnerable to oxidative damage when exposed to prolonged humidity or rainfall. In addition there is a risk of debris causing short circuits when the traps are in situ. The construction of enclosures that are both transparent and watertight is both complex and would dramatically increase the cost per unit. As a solution casting the NightLife board (apart from the battery clips) in clear polyester resin was trialled.
A mould was created by painting several layers of Latex over a block of Lego bricks of a suitable size. This mould was then peeled off of the Lego and filled with a well stirred mixture of polyester resin and a ‘catalyst’ (methyl ethyl ketone peroxide) to introduce free radicals to set the resin. The NightLife PCB is then suspended in the resin, to a level where all connections are immersed, but the battery clips remain accessible. Polyester resin is very clear when set, but takes a relatively long time (up to seven days in this case) to fully cure in a latex mould. To ascertain if the resin influenced the spectral output the enclosed version was compared to the exposed version used in the field trials as described previously.
Circuit board designs and the raw morphospecies collection data are available on the NHM Data Portal:
Analyses are available via GitHub:
A typical discharge curve is shown in Fig.
The output of NightLife is weaker than the actinic and white LED bulbs overall. The Nightlife output peaks at three distinct points: 397nm (long wave UV), 449nm (blue) and 512nm (green) (Fig.
A total of 12 insect orders were collected by the NightLife, more than the white LED (9 orders) or the actinic trap (6 orders), however there was more opportunity to collect with the NightLife which likely skewed results (Table
The emission spectra of two NightLife devices, one enclosed in resin and one as standard were determined. The resin has little effect on the (human) visible part of the spectrum, but does absorb approximately 30% of the UV light (Fig.
Light traps are an efficient way of sampling the emergent adults of freshwater habitats, however current lighting options are limited by the power requirements of actinic and MV bulbs. The NightLife LED based lightsource is a step towards the goal of a cheap, truly portable light trap for the emergent adults of freshwater insect species with a current cost of £10 per unit when produced in small runs.
Haitz's law, as described by
The field trials show that the NightLife device is capable of attracting 12 orders of insects, including all of the aquatic insect orders typically collected by light trapping (Table
The white LED light attracted representatives of all the aquatic orders usually collected, although there were fewer specimens attracted to the trap (in agreement with
Through developing NightLife we have demonstrated the feasibility of using small, lightweight and inexpensive LED based light traps for studying the biodiversity of aquatic insects.
Studying the biodiversity of aquatic insects in remote areas, away from reliable sources of power, could be greatly aided by the use of the NightLife light source. Compared to other light sources the devices are small and robust, with similarly compact and reliable power sources (AA batteries). The low cost of the devices makes them a feasible alternative to more expensive solutions in developing countries, and could be used to greatly increase the number of sites sampled at once. The limiting factor on the number of sites sampled is no longer based on the cost and weight of the device, but on the number of sites which can be visited by the researcher(s) to setup and retrieve the traps.
We would like to thank Helen Barber-James and Ferdy De Moor (Albany Museum, Grahamstown) for information on actinic lights and discussions around the initial trap design. Akimitsu Sadoi assisted with information on his LED Joule Thief light and discussion on LEDs in general. The Natural History Museum provided collections enhancement funding to Daniel Whitmore and Ben Price which enabled field testing during the KwaZulu-Natal Expedition 2014. Ashley Kirk-Spriggs (National Museum, Bloemfontein) and Vaughn Swart (University of the Free State, Bloemfontein) are thanked for organising this expedition and Louise Allan is thanked for assistance collecting samples during the field trials. Steen Dupont is thanked for designing the NightLife holder. Nick Everdell and Dimitrios Airantzis (University College London) are thanked for measuring the spectral output of each device for comparitive purposes. Mike Strick kindly provided guidance on resin casting. Vince Smith and Laurence Livermore (Natural History Museum) provided comments on the draft manuscript. We would like to thank the reviewers for helpful suggestions that significantly improved the manuscript. Philippa Richardson (University College London) identified several improvements to the final manuscript.
Both authors devised the research. The devices were constructed by Baker, and Price conducted field trials. Both authors wrote the manuscript.
The authors are not aware of any conflicts of interest. BWP is a subject editor of the BDJ.
PCB design for Nightlife made using Fritzing. Copper traces complete the circuit between components. Traces run on the top surface (yellow) and bottom surface (orange) of the PCB. Text and figures in black are silk-screen printed onto the top surface.
Commercially fabricated PCB from the design in Fig.
Assembly of a NightLife board using 'helping hands' tool for supporting the PCB.
Completed NightLife board viewed from above. Total length = 50mm.
Two NightLife lights set up on a single pan trap and awaiting dusk before automatically turning on. Each device is protected by a clear rain shield.
White LED bike light in operation.
Typical light output (intensity) of a NightLife device during battery discharge.
Spectra of 4W actinic fluorescent tube, NightLife and white LED light.
Comparison of the maximum number of
Comparison of emission spectrum of NightLife with and without being enclosed in polyester resin.
Specimens collected using the NightLife LED light, the traps were usually dominated by
Specimens collected using the white LED light, note the low numbers of
Summary of insect orders collected using the three light sources, major aquatic groups are shown as bold. Only flying insects are reported, in addition the traps occasionally collected mites and spiders.
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