Do birch-feeding caterpillars make the right feeding choices?

Area of Science:

• Ecology
• Entomology
• Plant-insect interactions

Background:

• Leaf quality significantly impacts herbivore performance and feeding behavior.
• Understanding caterpillar feeding preferences in relation to leaf characteristics is crucial for ecological studies.
• Few studies integrate leaf quality, caterpillar performance, and feeding preferences.

Purpose of the Study:

• To investigate the relationship between leaf quality and caterpillar performance for specialist and generalist species.
• To determine if caterpillar feeding preferences align with leaf characteristics that promote optimal growth and survival.
• To compare feeding preferences and performance of *Achlya flavicornis* (specialist) and *Spilosoma luteum* (generalist) on different *Betula pendula* leaf types.

Main Methods:

• Larval performance (development, pupal size, survival) was assessed on *Betula pendula* leaves that were artificially damaged, mined, or undamaged, and on leaves of varying ages.
• Feeding preferences of *A. flavicornis* and *S. luteum* were recorded.
• Performance metrics were compared against observed feeding preferences.

Main Results:

• Feeding preferences did not consistently correlate with leaf types yielding superior caterpillar performance (e.g., faster development, larger pupae, higher survival).
• *A. flavicornis* preferred medium to older leaves, but medium leaves resulted in smaller pupae. Young leaves led to slower development and lower survival.
• *S. luteum* did not discriminate between damaged and undamaged leaves, though damaged leaves reduced pupal size and adult emergence.

Conclusions:

• Caterpillar feeding preferences may not always optimize performance, suggesting complex ecological factors influence choice.
• Generalist caterpillars like *S. luteum* may exhibit less selective feeding on-tree due to broader dietary experience.
• For specialist leaftiers like *A. flavicornis*, leaf selection for shelter (tying) may initially drive feeding preferences, overriding direct nutritional considerations.