Physically stressed bees expect less reward in an active choice judgement bias test

Area of Science:

• Animal behavior
• Cognitive science
• Insect neurobiology

Background:

• Judgment bias tests are used to infer emotion-like states in animals.
• Previous studies on insect judgment biases are limited by alternative explanations like motivation and attention changes.
• A novel judgment bias test is needed to control for these confounding factors in insects.

Purpose of the Study:

• To develop and validate a novel judgment bias test for bumblebees.
• To investigate whether physical stress induces judgment biases in bumblebees.
• To determine if stress-induced judgment biases in bees are characterized by pessimism.

Main Methods:

• A novel judgment bias test was developed for bumblebees, requiring active choices between ambiguous stimuli.
• Bumblebees were trained to associate distinct colors with high or low rewards in separate chambers.
• Physically stressed and control bees were presented with ambiguous colors to assess their choices and response patterns.

Main Results:

• Physically stressed bumblebees were significantly less likely than control bees to enter the high-reward chamber when presented with ambiguous cues.
• Signal detection and drift diffusion models indicated that stressed bees were more prone to choose low-reward locations.
• Signal detection analysis revealed that stress reduced the estimated probability of high rewards in stressed bees.

Conclusions:

• This study provides strong evidence for the existence of judgment biases in bumblebees.
• Stress-induced behavior in bumblebees is explained by a reduced expectation of higher rewards, consistent with a pessimistic judgment bias.
• The findings suggest that cognitive biases and their modulation by stress are present in insects, extending beyond vertebrates.