As in 2011 slugs and snails topped the list but this time they generated almost twice as many enquiries as cushion scale, the number two pest. The previous year both pests had almost a similar number of enquiries.
RHS principal scientist plant health Andrew Halstead said: "The dominant feature of 2012 was the weather and this had a big impact on garden pest problems. As we all know this was the second wettest year in the last hundred years.
"Pests that like damp conditions therefore did well. Last summer the demand for slug controls, especially nematodes used as a biological control, sometimes exceeded supplies."
Mosquitoes and biting midges were the other beneficiaries because of the plentiful supply of temporary pools and wet soil. These provided ideal breeding sites where the larvae could develop.
But below-average temperatures and wet weather may have also had some positive effects. These conditions can reduce the mating success and rate of development of pests, as well as restricting their mobility.
Some pests, such as horse chestnut leaf-mining moth, euonymus scale and viburnum beetle, were noticeably less troublesome last summer.
Other pests, particularly aphids and scale insects, are susceptible to fungal infections that can spread rapidly in wet conditions, and this may have resulted in reduced populations.
"It will be interesting to see what effect the wet winter has on pest populations in 2013," said Halstead. "Insects that overwinter underground or spend part of their life cycle there can drown when the soil becomes waterlogged. This affects not just pests but also some beneficial insects, such as ground-nesting solitary bees."