It is necessary to describe the aphid reproductive process so that you can 'know thine enemy', and understanding how the population explosion occurs explains why control measures have to be very thorough.
This is what has happened. In early spring, with warmer temperatures, eggs that have over-wintered on host plants hatch into female greenfly - there are no males at this stage - the vast majority of which have wings.
Furthermore, as strange as we may find the reproductive process, the feeding procedure is also rather unusual. It consists of inserting a very slender tube into the plant cells, sucking out the liquid sap, absorbing the nutrients it needs, and 'spewing' or 'spitting' what is left back down the tube into the plant again.
This reproductive process, called parthenogenesis, is not at all uncommon in the insect world, and by a long, long way is nothing like as incredible or bizarre as some examples. It does, however, explain how a plague can appear almost overnight. The multiple birth continues through the summer months, encouraged by mild weather and suitable host plants like your roses.
With roses and ornamental plants, there is no problem, but with plants that are intended for food we have to be careful, and it is important to obey the makers' instructions to the letter. Most preparations indicate the safe period required to intervene between applying the systemic and human consumption - always make sure that the information is clearly stated on the bottle.
Nature tries to solve its overcrowding at home by equipping the next generation with the means to go away quickly and start colonies elsewhere. Of course, there are natural predators - birds, other insects, wasps, hover fly lavae, beetles like the ladybird, and so on - and, it is a good job the aphids don't all live otherwise the world would very soon be 6ft (2 metres) deep in greenfly! Shortening hours of daylight, lower temperatures and changes within the host plants themselves at the onset of autumn and winter triggers another hormone which leads, not to winged females, but to a generation of males, the only time that they occur. Mating follows, which results not in live young, but in eggs, deposited deep into crevices and cracks to over-winter, and in due course to emerge and begin the process all over again. The adult parents die during the cold of winter, unless they can make their way to an obliging greenhouse, conservatory or shelf indoors with suitable host plants.
This is what has happened. In early spring, with warmer temperatures, eggs that have over-wintered on host plants hatch into female greenfly - there are no males at this stage - the vast majority of which have wings.
Furthermore, as strange as we may find the reproductive process, the feeding procedure is also rather unusual. It consists of inserting a very slender tube into the plant cells, sucking out the liquid sap, absorbing the nutrients it needs, and 'spewing' or 'spitting' what is left back down the tube into the plant again.
This reproductive process, called parthenogenesis, is not at all uncommon in the insect world, and by a long, long way is nothing like as incredible or bizarre as some examples. It does, however, explain how a plague can appear almost overnight. The multiple birth continues through the summer months, encouraged by mild weather and suitable host plants like your roses.
With roses and ornamental plants, there is no problem, but with plants that are intended for food we have to be careful, and it is important to obey the makers' instructions to the letter. Most preparations indicate the safe period required to intervene between applying the systemic and human consumption - always make sure that the information is clearly stated on the bottle.
Nature tries to solve its overcrowding at home by equipping the next generation with the means to go away quickly and start colonies elsewhere. Of course, there are natural predators - birds, other insects, wasps, hover fly lavae, beetles like the ladybird, and so on - and, it is a good job the aphids don't all live otherwise the world would very soon be 6ft (2 metres) deep in greenfly! Shortening hours of daylight, lower temperatures and changes within the host plants themselves at the onset of autumn and winter triggers another hormone which leads, not to winged females, but to a generation of males, the only time that they occur. Mating follows, which results not in live young, but in eggs, deposited deep into crevices and cracks to over-winter, and in due course to emerge and begin the process all over again. The adult parents die during the cold of winter, unless they can make their way to an obliging greenhouse, conservatory or shelf indoors with suitable host plants.
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