Ootai, several years ago we were also plagued by those little orange beetles. They attacked the leaves of pumpkins, water melons, cucumbers and courgettes which I subsequently learned all belonged to the same plant family... the gourd family. The larvae of these beetles also attack plant roots and nailed our crops of runner beans - the seedlings died before they reached a few inches long.
At the time I went to a seed shop with one of these beetles in a bottle and the guy gave me this tin can of some kind of pesticide that he said would kill the beetles. He told me to wear a mask and long trousers when spraying it.
Considering that a Thai had advised me to wear protective clothing, it must have been some pretty serious shit and I later decided not to use it. I just changed our veggie garden crop away from the gourd family.
I've also given up trying European crops, which all seemed to succumb to one bug or another, and now only grow the local vegetables. It was a shame to stop trying the English runner beans, but the Thai long bean is a close second for me.
This is our modest veggie garden now... surrounded by chicken wire to stop the dogs digging up the seedlings. We keep chickens and periodically I dig in rotted down chicken manure, although you have to let it rot down a long time as it's too strong when fresh. I surrounded the raised beds with used building blocks (dumped around our area) to try and stop the soil washing away in the wet season... not that we had one this year.
The crops are mainly morning glory, pak choi, some cabbagey kind of thing (ka na?), coriander and various other herbs and stuff. I've been trying to introduce crop rotation and leaving beds fallow but this seems to be a foreign concept, at least to our gardener. We will get one great crop of long beans, then he'll plant a second batch of bean seeds immediately after, along the same bed, and the seedlings don't grow past a few inches high. I keep working on this...
As for spraying these days... the gardener makes this purple liquid concoction from a combination of shrimp paste, some kind of Thai vitamin drink and lao khao. He reckons it works, but I think it smells so awful that the bugs just go away for a few days until the stench wears off. It's a worse smell than pla ra.
I'm forever finding these bottles of concoctions around the garden... there's another yellow coloured one that he makes from gone-off milk. it's no problem as it's all made from natural stuff... my main concern is that after a few Ya Dong's one night I get the bottles mixed up and end up taking a swig of rotted shrimp paste, sour milk and lao khao!