Aphids or aphids are one of the main pests that affect many horticultural crops grown under greenhouses, including ornamental products and vegetables. In general, aphids tend to select certain plants and certain varieties, preferring them over others. Which is the reason? The main reason can be attributed to the nutritional quality or the nutrient content in the plants.
A proliferation of aphids on old leaves may vary depending on the type of the plant. The growth rate is higher in the lower leaves compared to the upper ones.
For example, cultivars may vary in their susceptibility to aphids, such as the green peach aphid (Myzus persicae), basically due to the nutritional quality of certain cultivars. In fact, the nutritional quality or the content of nutrients in a plant, or in a cultivar, can be strongly correlated with its susceptibility, that is, with the concentration of amino acids in plant tissues and the attraction that these plants present to aphids. Insects require amino acids to grow, develop and reproduce. The aphids are fed into the sieve tubes of the phloem and therefore may tend to select the developing leaves of certain cultivars that contain higher concentrations of amino acids in the phloem.
Cultivars that improve the reproduction of aphids have higher risks
The number of aphids that colonize plants varies depending on the cultivar, and is related to nutritional quality or nutrient content. Also, studies suggest that aphids select the plants that are most favorable for their reproduction process. Some reports indicate that aphids select the plants that are most favorable for their reproduction process.
For example, reports indicate that Myzus persicae prefers to feed on certain cultivars that help it improve its reproduction process. Also, the time of their development cycle may end up differing, depending on the cultivar from which they are fed.
Therefore, there may be differences in the length of the life cycle and in the reproduction of Myzus persicae populations when these aphids feed on different cultivars. In fact, in some cultivars, the speed of reproduction is higher when aphids, including the Myzus persicae aphid, feed on the underside of the leaves, instead of feeding on the beam.
Any improvement in reproduction can directly affect the effectiveness of insecticides and biological control. For example, applications of more frequent insecticides may be required, due to the number of aphids that occur in a certain time; which could increase aphid populations that develop resistance to insecticides.
Furthermore, the reproductive potential of aphids in susceptible crops can result in natural enemies, ie biological control agents, such as parasitoids and predators, not being able to control populations effectively, compared to the control they can exercise over aphids that feed on less susceptible crops. This may be due to the difficulty of managing the number of aphids that occur in such a short time.
The aphids are redistributed as the plants grow, resulting in variations in the vertical distribution. In most cases, the growth points are the main regions in which they tend to accumulate to feed. For example, in certain cultivars of chrysanthemums, the populations of Myzus persicae migrate towards the upper parts of the plant as soon as the plants develop buds.
As the flower buds develop changes in the concentration of amino acids in the leaves, with which the foliage becomes more suitable for aphids; allowing the number of individuals to increase, compared to plants that do not bloom. When the plants bloom, the leaves that are above the flowering plants are the most suitable for aphids. This is how the distribution of the aphid populations changes, which move up the plants until they accumulate in the flowers and upper leaves. The movement towards the upper parts of the plants during the flowering season may be the explanation for suddenly observing large quantities of aphids feeding on the flowers.
The preference of aphids for the upper leaves can help control them
The preference of aphids for the upper leaves can influence their control, since they are more exposed to contact insecticides and natural enemies, even when the open flowers can protect them from exposure to contact insecticides and possibly even from insects. natural enemies. Aphids that colonize growth points may be easier to control than those that reside on mature leaves or on the underside of leaves, because they may be difficult to come in contact with insecticides at these sites.
When populations of aphids increase, some individuals develop wings to redistribute among nearby plants.
Also, when populations of aphids increase excessively, some individuals become more mobile; that is, they develop wings that allow them to be distributed again among nearby plants. These changes in the distribution of populations can influence both the effectiveness of insecticides and the ability of natural enemies to regulate aphid populations effectively.
When populations of aphids increase, some individuals develop wings to redistribute among nearby plants.
The mobility of aphids is linked to nutrition
Although aphids generally tend to gather at plant growth points, some species differ in the way they are distributed in plants. For example, populations of melon aphid (Aphis gossypii) tend to move upward, to accumulate in upper leaves. All aphids tend to move upwards as the plants grow, but the Myzus persicae aphid will disperse faster than other aphid species.
The movement of aphids may be related to the mobilization of essential amino acids in the tissues of the plant phloem, since the developing leaves and the terminal leaves have higher levels of amino acids than the older or senescent leaves. For this reason, some aphid species do not colonize those old or senescent leaves. This may be related to a decrease in nutritional quality or nutrient content. When the leaves age, or enter the period of senescence, they tend to support lesser populations of aphids. Likewise, aphids tend to be less visible and more difficult to detect in the oldest and lowest leaves at the time of monitoring.
The type of plants determines the region colonized by aphids
However, the colonization of aphids on older leaves varies depending on the type of crop. For example, it has been reported that the Myzus persicae aphid in potato plants (Solanum tuberosum) prefers the oldest leaves in the lower areas, which are the first to enter senescence. The rate of growth and the reproduction rate are higher in the leaves located in the lower areas of the plants, in comparison with the rates of reproduction and growth of leaf aphids in the upper areas, which is an associated factor with the composition of the sage of the phloem of the leaves in senescence, whose basic content of carbohydrates changes to a predominant content of amino acids.
Therefore, the reason that the green peach aphid prefers the lower leaves of the potato, instead of the upper leaves, may be due to the fact that the concentration of amino acids is related to their reproduction rate.
Aphids in general, tend to accumulate in the growth points of plants; however, the species of aphid and the architecture of the plants can affect its distribution.