I have been one of the first to use imidacloprid/Confidor on orchids, about 15 years ago. It is efficient for a few weeks after application, providing there are no resistant bugs. It proved to be ineffective from nearly the beginning against thrips palmii ( the crap that eats the crown of the plants and makes nice marks, but usually is never seen outside).
A few notes :
- Against thrips, you need a drench, as the larvae are very damaging, usually around the roots, the new shoots ( ever seen strange orangish cast to very tiny new shoots), and the crowns ( leaf pleating can be a symptoms, especially if the emerging leaves look 'dirty').
- For all the remaining insects ( not the mites), drenches are usually very effective, Merit can be eventually used, with some precautions.
Imidacloprid can induce a burst in reproduction and growth of mites, especially brevipalpus. The treated mites are much more resistant as well to common miticides. I got the problem, and I have unfortunately not been alone. It requires then very harsh miticides ( bromopropylate + clofentezine) to get rid of the problem.
I prefer to use carbamate insecticides, namely aldicarb and carbofuran.
Though they are deadly and their LD50 is very low, they are not likely to be carcinogenic. I do not trust many of the growth regulators/metabolism disruptor insecticides regarding the risk of getting a cancer. To my mind, even many fungicides are way more dangerous than insecticides regarding mutagenicity/teratogenicity.
When I used imidacloprid, I got rid of the scales, got plenty of mites on the other side, and did not control the thrips palmi at all ( so I went back to Curater and Parathion...).
I must report that twice, as a tech advisor of two phalaenopsis nurseries, I got report of chlorosis or long term plant stunting when azoxystrobin was used shortly after an imidacloprid treatment. It is anecdotal though.
