September 2010


Ladybug Nanophysiological Response to Flashing Light

Insects are awesome. I will tolerate no dissent on this point.

Honeybees have a sense of numbers; a common ant species has adapted to both urban and natural environments multiple times; micro- and nanoscale architecture on termite wings helps them fly in rain despite being weak fliers. Scientists clearly know a great deal about insects, yet knowledge of their physiology at the nanoscale tends to be limited (note the exception just mentioned).

This isn't just a "basic science" issue (although to quote Seinfeld from an entirely different context, "not that there's anything wrong with that"). There's undoubtedly much knowledge to be gained relating to agriculture, insect control, and other important scientific fields that are awaiting discovery, yet can only be addressed through nanoscale experimentation on insects.

Igor Sokolov (Clarkson University, United States) and coworkers' atomic force microscopy experiments have investigated ladybug adaptation to repetitive flashing light. They have additionally shown that ladybugs are blind to emerald light, despite being sensitive to light of similar wavelengths (colors).

Why use atomic force microscopy?

Atomic force microscopy is commonly used to image surface features and motions within the subnano- to microscale range. It's finding many uses in biotechnology and cell biology, e.g. towards sequencing individual RNA molecules, quantitating enzyme conformational changes upon substrate binding, and quantitatively relating changes in cell shape to changes in cell metabolism.

Extending this methodology to insects is typically far more challenging. This is because insect movement can easily exceed the range that is conventionally measurable via atomic force microscopy.

Nevertheless, ladybugs are small insects, and sensitive equipment is needed to record their small movements. Atomic force microscopy is well-suited to this task.

Ladybug reaction to a flashing UV light.

In this research, the scientists kept their atomic force microscope tip in place, and measured ladybug physical movement in response to optical stimuli (low-intensity light, i.e. lower than that at midday). The ladybugs were gently restrained to prevent lateral movement (e.g. left to right) and hinder vertical movement, and a microphone was used to distinguish actual beetle movement from background noise.

The scientists first found that the beetles reacted to flashing (1 to 2 flashes per second) UV light (375 nanometer wavelength). They're known to be sensitive to this wavelength, possibly as an anti-predation response (but this latter point is speculation).

In one experiment, the beetle was relatively still when the flashing light was off. After 10 seconds of darkness, the flashing light was turned on for 30 seconds.

The beetle initially moved up, then settled down halfway. At this time, the flashing light was turned off.

Over the course of a little over 10 seconds, the beetle rose back up to almost twice the initial maximum height. The beetle subsequently settled back down to baseline after a little over 10 more seconds.

What does this mean? The beetle reacted to the flashing UV light by rising up, then settling down somewhat; subsequently, the beetle apparently went into an even more heightened alert mode after the flashing light was turned off, before settling down again.

Does this mean that a flashing UV light alerted the beetle to possible predation, and after the threat went away, the beetle tried to move to a safer location? Such a hypothesis is interesting, but remains speculative without further research.

Ladybug adaptation to flashing UV light.

The scientists investigated ladybug adaptation to the flashing UV light by performed the experiments repetitively. They found that the beetles adapt to the light within a minute or two, i.e. do not move.

Four or five minute breaks between the flashing UV light are needed for the beetles to react as they had initially. In other words, the beetles "learn" to stop responding to the light after one minute, but "forget" to stop responding after 4 or 5 minutes.

This establishes the limits of beetle adaptation to repetitive flashing UV light stimuli. The scientists next analyzed their response to a broader color range of flashing light.

Ladybugs are blind to emerald light.

The scientists tested ladybug response to light from 700 nanometers to 375 nanometers. They found that the beetles reacted to flashing light of 550 nanometer wavelength (green), and 375 to 400 nanometers (near-UV), but not 500 nanometers (emerald).

Why? As previously mentioned, the beetles are known to be sensitive to UV light.

Furthermore, they are known to use the position of the sun (its most intense color is in the yellow-green color range) to stabilize themselves mid-flight. However, apparent beetle blindness to emerald light is unknown, and awaits an explanation.

Overall evaluation.

Atomic force microscopy is exceptionally well-suited for quantitating and understanding certain aspects of insect behavior. The experiments of Sokolov and coworkers have probed the extent of ladybug adaptability to repetitive visual stimuli.

They have further uncovered an unexpected blindness to emerald light. Future entomological research should figure out the biochemical and possible evolutionary basis of this discovery.

NOTE: The scientists' research was funded by Clarkson University. for more information:
Guz, N. V., Dokukin, M. E., & Sokolov, I. (2010). Atomic Force Microscopy Study of Nano-Physiological Response of Ladybird Beetles to Photostimuli PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0012834