Sorry, Rachael, but I think you ought to use "sucking insects". The expression "sucking pests" is commonly found with the same sense, and although it's less literally accurate you may prefer it, since sucking pests include spider mites, which are not actually insects, strictly speaking.

The trouble is that aphids are not the only ones, and you need a term that covers them all as "chupadores" does. Actually cochinillas are sucking insects too, so "cochinillas e insectos chupadores" is really a tautology (should be "otros insectos chupadores").

As well as aphids and cochineals there are mealybugs and other scale insects, lace bugs, white flies and spider mites. The term sucking insects is actually very common:

"Sucking Pests
Sucking insect pests cause damage by removing sap from plant tissues."
http://www.caes.uga.edu/publications/pubDetail.cfm?pk_id=618...

"What's Bugging Your Garden? Sucking Insects
A number of insects, such as aphids, whiteflies, leafhoppers, spider mites, and others suck out plant juices, causing a spotty or yellow discoloration on the leaves and shoots."
http://www.grit.com/farm-and-garden/whats-bugging-your-garde...

You'll find lots of examples of these expressions in gardening sites.

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Note added at 21 mins (2014-01-28 11:06:35 GMT)
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"Scale insects", again, only covers one kind. It includes cochineal and mealybugs, but not aphids and other bugs and mites that are sap-suckers.

"Siphoning insects" is quite an uncommon term and is too broad, because it includes insects that suck nectar.