Runner bean muncher

Runner bean muncher

Observation - Runner bean muncher. Description: Some small bug is devouring my bean leaves from the bottom up. Is this the culprit? I can't see any caterpillars although the way the leaves are being chomped, the damage looks like caterpillar attack. In the end there is no leaf left. Last year my entire

Some small bug is devouring my bean leaves from the bottom up. Is this the culprit? I can't see any caterpillars although the way the leaves are being chomped, the damage looks like caterpillar attack. In the end there is no leaf left. Last year my entire bean crop was completely vaporised by these invisible pests, can anyone identify the cause and suggest a remedy? Thanks!