A recent study of the effects of the presence of bees near crops revealed that these bees are providing a much bigger beneficial effect than just simple polination. The 'buzz' of their wings causes vibrations in the air around them, which in turn causes nearby caterpillars to either freeze (stop eating) for a while or drop off the plant altogether. These caterpillars can't tell the difference between the vibrations of a carniverous wasp (that would normally try to eat them) and a bee looking for pollen or nectar. So they don't take any risks! In fact, the presence of bees nearby feeding catterpillars resulted in a visible and clear reduction of leaf damage, and when measured, these results (for two crops) were significant and highly significant (statistic-speak). The only caveat was that where fruit were present, the catterpillars hid inside!
So what does this mean for us veggie-growers? On non-fruiting crops that are prone to catterpillar attack, such as cabbage, broccoli, rocket, and kale, interplanting a bee-friendly plant (borage or phaecalia, for example) may help a lot. Firstly, the crop is not so obvious to the butterflies who lay the eggs, and so there will be less caterpillars overall. Secondly, the bees visiting these flowers will greatly reduce the damage caused by any catterpillars that did manage to hatch. Thirdly, many bee-friendly plants also contribute positively to the soil, eg nitrogen-fixers, errosion and leaching-prevention, aeration, and micro-nutrient and -fungal development. And last, but definitely not least, bees will have more forage, and thus a greter chance of survival to do an even better job for us next year!