Answer: If the bug in question is long rather than round or oval like a beetle, my guess is it's the California Timema. These are generally pests of native west coast trees, but I suppose they might eat the leaves of a tomato plant. Males often hitchike on the backs of the females, giving the insect pair a leaf-like appearance. There is no registered control for the pest so your best defense is to pick them off the plant. Thank goodness they're not eating the fruit!
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