Aphids are a relatively new problem in horticulture. Typical aphids are foxglove aphid (Aulacorthum solani), cotton aphid (Aphis gossypii) and the potato aphid (Macrosiphum euphorbiae). Due to their ability to reproduce rapidly they can quickly develop resistance against harmful chemical crop protection products.
The potato aphid and the foxglove aphid are particularly common in cut flower and vegetable cultivation. Because they secrete honeydew, causing sticky fruits and leaves, they can cause a great deal of damage.
In natural cultivation circumstances the life cycle is seasonal, but in covered cultivation, it is simplified. Reproduction is asexual. Specific males do not occur and all individuals are capable of reproducing. The development of aphids is characterised by four nymphal stages followed by the adult stage. The exuvia, or moulted skins, which are part of the development of the young aphids, betray their presence. Because the development time is short, a population can develop explosively, and this means that resistance to pest control substances can also be developed. If the population density becomes very high, winged aphids will also develop, enabling the insects to fly to other plants to establish a new colony. The development time varies depending on the type of aphid, the host plant and the climatic conditions, but in general is very short (a little more than a week at 20°C.)
- Aphids are characterised by the honeydew they secrete. This affects the photosynthesis process in the plant.
- When the aphid mouthpart penetrates the plant it can transmit viruses and toxic substances.
- The aphid can withdraw nutrients from the plant using its mouthpart. This inhibits the development of the plant and leads to deformed leaves.