Some research has shown that Line Transects are effective for Europe (Low butterfly diversity zone compared to Asia) and if this method is applied here (Asia) many butterflies(canopy preferring) will be overlooked and the accuracy of data will be questionable. So, I would like to know the effective methods for butterfly survey applicable here.
This is also a problem in North America, as some butterflies (e.g., Early Hairstreak, Erora laeta) rarely descend from the canopy. Butterfly watchers commonly use close-range binoculars and zoom photography to observe butterflies without disturbing them. Another method is to entice the insects to come closer to the ground by "sugaring", that is, baiting with fermenting fruit and stale beer, and this is commonly used in Mexico and Central America. Some butterflies (even in Europe, e.g., Purple Emperor, Apatura iris) that otherwise spend most of their time in the canopy are attracted to dung, especially carnivore dung, and to sites where they can sip mineral-rich water ("puddling" behavior). Some observers urinate at a location and then return to it later, after the butterflies have discovered the mineral-laden water. You may have to use a combination of these approaches, e.g., perform the usual ground transects, then do a spot-check in randomly chosen locations using the more time-consuming methods. Or simply admit that documentation may not be representative because of canopy-dwelling butterflies' behavior, and compare results from transects with other results from transects. The only way that I know of to get an accurate count of insects in the canopy is to drape an entire tree with insecticide, which is far too drastic a method, particularly as this requires killing every insect, not just the butterflies.
Thank you very much Andrew K. Rindsberg for your suggestions. Unfortunately, there are many canopy dwellers which are not attracted to sugars. It seems that we will have to go with opportunistic surveys, after all....
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