Aphids are soft-bodied and often pear shaped insects that can be seen with the naked eye. The most notable physical characteristic that distinguished aphids from other pests are the exhaust like tubes called “cornicles’ that stick out of their back end. These cornicles can also be used to help identify which species of aphid is present. In the greenhouse, aphids are generally all female and capable of asexual reproduction. Female aphids give birth to daughter aphids that already have their own young developing inside them. When population densities become high, the aphids give birth to a winged generation that can then move to a new location and start a new colony.
Aphids moult many times before they become adults, leaving behind a white skin on the leaves, which is a dead giveaway that they are present. They also secrete honeydew and the presence of this sticky liquid or the sooty mould mentioned above is also a good indicator that aphids are present. Some aphid species can also cause damage to young leaves from feeding activity, causing them to look deformed as they grow. Foxglove aphids are one species known to cause noticeable leaf distortion.