Bougainvilleas are ornamental plants mostly grown in warmer climates around the world, though they're also fairly hardy. This hardiness allows them to do well even in cooler climates. More vine-like and thorny than most would appreciate, they can grow to more than 35 feet in length. And though they're known to be resistant to a wide range of diseases as well as pests, there are some species of insect which still find the plant attractive.
Several species of aphid as well as the spider mite and a caterpillar tend to plague bougainvilleas. Additionally, the mealybug, which has a waxy outer appearance and a relatively hard outer shell that's pesticide-resistant, is a vigorous pest. Aphids are very small and pear-shaped while spider mites look like tiny, moving dots. They also leave webbing on the plant's leaves. The Bougainvillea Looper caterpillar is green or brown, about 1 inch long, feeds at night and can mimic branches.
Such pests can do significant damage to a bougainvillea. Most often, visible signs of spider mite problems include leaves dropping off the plant. That's because the mite sucks vital fluids from the leaf, eventually killing it. The Bougainvillea Looper caterpillar will eat the plant's leaves away. Aphids feed off of tender new leaves and leave a secretion that attracts ants while also promoting mold growth. Mealybugs create mold, too, though it's often black and sooty-looking.
It's always best to go with the most natural bougainvillea pest control method available. An effective organic solution is found in the use of ladybugs, which are predators of aphids and most of the other pests mentioned. You can also try something like Neem tree oil concentrate. It works as a mealybug and aphid (as well as mosquito) repellent. Just combine it with water and a bit of dishwashing liquid to create an effective spray.
If you're going to use chemical control pesticides, take care to follow application directions closely. This is not only for the safety of the plant but, more importantly, also for your own. Additionally, protective clothing and safety gear should always be worn when applying pesticides. Keep in mind that these pesticides might kill off natural predators that control insects like aphids and mealybugs, too. These include the praying mantis and helpful arachnids such as garden spiders.