Objectives: The purpose of this research is to better understand the relationship between the insecta class and bats and their many adaptations due to natural selection.
Rationale: In a recent study, Lee A. Miller and AnneMarie Surlykke have found that most insects are changing the way they sound in order to stay clear of the bats trying to hunt them and vise versa. Bats have been changing the ways they hunt and shifting their signals out of their prey’s hearing range due to their two major disadvantages: attenuation and forewarning. This study ties into coevolution because it’s dealing with two organisms modifying over time to become better suited for the environment and survival.
Hypothesis: If insects over time modify their survival instincts then the pressure for bats to modify their tactics and mechanisms will increase.
METHODS
Avoidance Behaviors:
Sensitivity to bat echolocation has been present in insects before preadaptation. Both crepuscular and nocturnal insects are on bat’s prey list. However, each type of insect has unique ways of protecting themselves.
For example, crickets in stationary flight completely stay away from ultrasound frequencies of bats while bush crickets dive when they hear huge batlike frequencies. Bush crickets use this mechanism due to their inability to tell where the sound is coming from so out of instinct they dive for cover.
Praying mantid’s tympanum organ has sensory cells attached so these insects in particular are very sensitive to batlike ultrasounds. Flying mantids can hear frequencies from 10m away and either turn, dive or take flight away from the frequencies.
Hedyloidea and Green lacewings have ears on their wings that are used as bat detectors. Since Hedyloidea and Green lacewings are tone deaf, natural selection has pressured them to modify their hearing.
Moth types: Noctuoidea, Pyraloidea, Geometroidea, Sphingoidea, and Drepanoidea have developed their eyes specifically for bat signals. Moths that are far from the source just fly away but when close to the source go into looping flight and power dives to throw off the predator. Size and sensitivity play a big role in survival. Big moths reflect more echo which means smaller moths are an easier prey.
Arctiid and noctuid moths behave very similarly. Arctiid moths produce a thick clicking sound from their tympanic organ when they hear batlike sounds. The clicking sound is generated from a high repetition of pulses per second which also spikes the muscle rates in the tympanic organ. These two factors can cause behavioral changes in arctiid and noctuid moths.
METHODS
Startle, Interference, and Warning:
Insects have used various methods of avoiding attacks by bats such as the startling method. For example, torpid butterflies produce ultrasonic clicks from a special membrane of their wing membranes when they open their wings. This click startles the bats and interferes with their biosonar system, signaling bats of undesirable prey. Insects get a chance to escape from bats using the clicks to alarm them, however, bats may learn to habituate to the sounds of clicks therefore insects must use this startle mechanism sparingly.
Miller tests the idea using bats that are trained to catch mealworms with the clicks from Phragmatobia Fuliginosa (Ruby Tiger Moth). The bats reacted using their harmonic structure of terminal signals which did not phase the success in capturing prey suggesting that the clicks do not interfere with the sonar system of bats. In psychophysical experiments with bats however, the clicks did interfere with the bats attacking and would miss its target when tested using false echoes or phantom objects.
Another method insects have used are to warn bats of unappealing prey. The Arctiidae family of moths are not appealing to bats and use their clicks to warn them of pernicious prey. Studies in labs show that bats quickly learned and recognized a toxic insect’s click apart and adapted to the clicks when given a reward. The startle, interference, and warning methods all offer various advantages to the arctiid moths in survival.
Bats have developed a variety of methods in order to attack prey without them noticing.High frequency emissions in response to insect defenses increases the ability to find small insects and the resolution of finding prey. Another method bats may use is emitting low frequencies – making them much less noticeable to moths, increases their range, and lowers their biosonar resolution. This method is not as effective because this only makes large insects noticeable to bats – shorter echolocation signals are less obvious to prey. So far studies have shown that this is an adaptation for bats.
Conclusion
In conclusion, the insecta class and bats have been evolving to improve their hunting and survival skills against each other for years. Insects have become increasingly harder to find because of their developed modifications of hearing – like the Praying Mantid’s tympanum organ now has attached sensory cells, the previous tone deaf Hedyloidea and Green lacewings now have ears as bat detectors on their wings. Various moth species such as the Noctuoidea, Pyraloidea, Geometroidea, Sphingoidea, and Drepanoidea have developed their eyes specifically for bat signals or a special “click” to interfere, warn, or startle bats. The moth species Arctiid and Noctuid moths use clicking to protect themselves from bats. In response to this development, bats have tried to keep up with this process of natural selection by using various methods of attack on insects such as emitting high or low frequency emissions. The best frequency which neural/behavioral responses have the lowest threshold lies between 20-60 kHz with thresholds between about 30-70 dB SPL. Overall It is hard to determine if these adaptations are in response to insects changing their protection strategies or environmental restrictions due to the large variety of responses.