Flight mills have been used by researchers to explore the flight capacity of many insects. The effects of biotic factors such as sex, age, and mating status, or abiotic factors such as temperature or humidity have been tested in the laboratory with insects from a number of orders including Diptera, Lepidoptera, Hemiptera, and Coleoptera (Schumacher et al. 1997; Sarvary et al. 2008; Zhang et al. 2008; Taylor et al. 2010). Different designs of the physical flight mill apparatus have been created and used. Early flight mill systems were designed to assess flight of mosquitoes, including several Aedes species (Diptera: Culicidae), and some papers detailed the associated circuitry for recording data (Hocking 1953; Rowley et al. 1968). Several other flight mills were designed and tested by Clements (1955) and Atkins (1961), including mills for use with Mexican fruit fly (Diptera: Tephritidae) and boll weevil (Coleoptera: Curculionidae) (Chambers & Connell 1969; McKibben 1985). Weber et al. (1993) used polarized magnets to repel each other to create a frictionless pivot and suspended an axle with support arms to secure the insect. Current flight mills use similar designs, and data recording is conducted through the use of photogates or Hall effect sensors (Jones et al. 2010), data collection modules, and accompanying software (Bradley & Altizer 2005; Castro et al. 2014; Lee & Leskey 2015). The declining cost of electronics and access to open-source software has made it relatively easy to create individualized data recording modules and programs. We designed and created circuitry and a program to measure flight capacity of Halyomorpha halys Stål (Hemiptera: Pentatomidae), the brown marmorated stink bug, coupled with a photogate and an Arduino board, an open-source hardware platform.

Our original designs were based on work of Rowley et al. (1968). The current iteration of our flight mill uses 2 small magnets (1 for counterbalance) attached to prongs on the underside of the hub. These magnets spin with the hub, and circle over a Hall effect sensor used to record the number of rotations the insect flew by counting the instances of the magnets passing over the sensor. The data acquisition software DASYLab? Basic (Registration No. 1919405, National Instruments Corporation, Austin, Texas, 2014) and accompanying data collection module, USB-1024 (Measurement Computing Corporation, Norton, Massachusetts), were used to measure the number of rotations flown by the insect.

A new design was created to account for problems encountered with the model described above by using household circuitry, hardware, and complimentary software of Arduino to create a laser tripwire system. This design records every time the insect breaks the path of the laser, which then is recorded on an associated computer with the hardware of the Arduino circuit board and is cost efficient in comparison with much of the commercial software available for data acquisition. A single Arduino board and breadboard and associated circuitry can run up to 6 flight mills. Components for a recording from a single flight mill include two 100-Ohm ½-Watt resistors, a coil of wire, 1 LED bulb, a photoresistor (light-dependent resistor), and a 1.5 V laser pointer (with a power source) (Fig. 1). The laser tripwire is created by pointing a laser at a photoresistor, a resistor whose resistance is lowered with increasing light intensity, which in this arrangement is triggered by the photons emitted by a laser pointer. If the laser is broken, the Arduino board and computer register on which mill the break was detected, record the time of the break, and add an increment to a counter.

The Arduino program is able to detect the voltage running through the circuit. We can record exactly when the path of the laser has been broken because of the voltage change in the circuit due to the resistance change of the photoresistor. The change in voltage also influences a second circuit wired to an LED bulb. When the voltage breaks a certain threshold, the LED bulb is turned on, signaling the break in the laser's path and incrementing a counter variable. The process is timed and recorded to the nearest millisecond, allowing the user to determine average and instantaneous speeds.

The coding for the recording of the flight mills is in the Arduino coding language, which is an open-source software ( https://www.arduino.cc/en/Main/Software). Our code allowed us to record the number of rotations and the time when the laser was interrupted (Fig. 2). Although there are 2 metal arms, the code allows for the voltage threshold to be such that the thin metal does not influence readings and only records when the insect or a paper tab breaks the laser. In addition to the timing, humidity and temperature are recorded with a DHT22 sensor (Aosong Electronics Co., Ltd, Guangzhou, China). This sensor, connected to an Arduino board, accurately displays the humidity, temperature, and heat index. Additional open-source software called CoolTerm ( http://www.freeware.the-meiers.org/) allows all data to be printed in the Arduino serial monitor and saved as a text file.

With a maximum of 6 flight mills per Arduino board, the laser tripwire is a cost-efficient addition to the flight mill apparatus that is not hindered by magnetic fields, interference, complex wiring, or programming, and is simple and editable. An Arduino Uno can be purchased on the company's website for US$25 ( https://store.arduino.cc/product/GBX00066), and resistors, LED bulbs, photoresistors, a breadboard, and wiring should cost between US$20 and US$30.

Fig. 1.

The schematics for 4 laser trip wire systems on a single breadboard and a single Arduino board. Lasers have been excluded. Note how the Arduino board allows for the hybrid use of both analog and digital circuitry systems.

Fig. 2.

The coding used to record the number of rotations flown by the insect on the flight mill.