Localization mechanisms of small plant-dwelling insects

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Movement is the basis of animal ecology, and understanding the causes and consequences of animal movement is a major goal of ecological research. Movement decisions involve an integrated process of sensory input and behavioral output. While environmental cues are important cues, social cues also likely influence movement decisions. For terrestrial insects, social cues in the form of substrate or plant-borne vibrations are extremely important. Here we investigate how vibratory communication or cues influence the movement behavior of two different terrestrial insect species: thornbug treehoppers (Umbonia crassicornis) and periodical cicadas (genus Magicicada). Thornbug males home in on a receptive female by use of duetting, during which a walking male and a stationary female signal in alternation. By describing the search paths of males we were able to identify key components of female responses, as changed by the plant, which influence male searching behavior. In periodical cicadas, millions of nymphs leave their borrows within a few days of each other to start their above ground life as adults. At present soil temperature is the only cue that has been investigated to explain emergence synchrony, but we collected data from the field for two broods (brood I and II) and emergence synchrony was best predicted be soil temperature plus the presence of social cues.

Negative feedback from maternal signals reduces false alarms by collectively signalling offspring

Within animal groups, individuals can learn of a predator's approach by attending to the behaviour of others. This use of social information increases an individual's perceptual range, but can also lead to the propagation of false alarms. Error copying is especially likely in species that signal collectively, because the coordination required for collective displays relies heavily on social information. Recent evidence suggests that collective behaviour in animals is, in part, regulated by negative feedback. Negative feedback may reduce false alarms by collectively signalling animals, but this possibility has not yet been tested. We tested the hypothesis that negative feedback increases the accuracy of collective signalling by reducing the production of false alarms. In the treehopper Umbonia crassicornis , clustered offspring produce collective signals during predator attacks, advertising the predator's location to the defending mother. Mothers signal after evicting the predator, and we show that this maternal communication reduces false alarms by offspring. We suggest that maternal signals elevate offspring signalling thresholds. This is, to our knowledge, the first study to show that negative feedback can reduce false alarms by collectively behaving groups.

Modeling the Rapid Transmission of Information Within a Social Group of Insects: Emergent Patterns in the Antipredator Signals

The study of group behavior in animals emerging from social interactions among individuals using agent based models has gained momentum in recent years. Although most of the individuals in a group of the treehopper Umbonia crassicornis do not have information about where the predator is, the signaling behavior of the group yields an emergent pattern that provides the defending adult with information about predator presence and location. Offspring signal synchronously to warn a defending parent of a predator attack. We develop a computational model of rapid signaler-receiver interactions in this group-living insect. We test the emergence of informative global patterns by providing interacting juvenile nymphs with limited locally available information with this agent based model. Known parameters such as size of the aggregation and spatial distribution are estimated from experimental recordings. Further, the model investigates the behavioral rules underlying group signaling patterns that reveal the predator’s location. We also show how variation in these behavioral rules can bring about variation in group signals, demonstrating the potential for natural selection to shape these rules.

OFFSPRING-PARENT COMMUNICATION IN A SUBSOCIAL TREEHOPPER (HEMIPTERA: MEMBRACIDAE: UMBONIA CRASSICORNIS)

Parental care of post-hatching offspring is widespread in insects, but the role of communication in parent-offspring interactions remains largely unknown. I have found that, in the subsocial treehopper Umbonia crassicornis , aggregated nymphal offspring produce substrate-borne, vibrational signals in synchronized bursts that elicit the mother's antipredator behavior. In this study I describe the signals used by nymphs and explore their role in mother-offspring interactions and within-brood communication. Nymphs were stimulated to signal in the laboratory in response to light contact, simulating the approach of a predator. Signals of nymphs at the site of disturbance triggered a rapid wave of signaling by many individuals within the aggregation. This coordinated signaling was associated with the mother's defensive behavior. Signaling was limited to the vibrational channel: when transmission of vibrations was blocked between signaling nymphs and the mother, the mothers' response was abolished. Nymphs signaled not only in response to contact, but also in response to playback of signals from their siblings. Nymphs in otherwise undisturbed aggregations signaled only in response to signals coordinated into synchronized, group displays, and not to signals in random temporal patterns. However, nymphal signaling thresholds were lowered after a recent experience of simulated predation. After a period in which nymphs were stimulated to signal (by light contact simulating a predator's approach), playback of one individual signal could trigger a coordinated burst within the aggregation. It remains unknown if coordination among siblings to produce synchronized, group signals is completely cooperative, or if siblings compete for the mother's proximity. But it is clear that a complex system of communication among siblings, and between siblings and their parent, is an important feature of maternal care in these subsocial insects.