Melon aphid (cotton aphid), Aphis gossypii

Melon aphids are common all over the world, except the northern regions. Since melon aphids often overwinter in greenhouses and can be brought into the field with a transplant in the spring, it can cause harm almost everywhere.

 Life cycle and description

The life cycle is radically different in the conditions of the northern and southern climate. In the north, female nymphs hatch from eggs with the arrival of spring heat, on the main host plants. They are able to feed, grow and reproduce without mating (viviparous) on this plant throughout the summer, as well as give birth to the winged form of females, which disperse to the next host plants and create new pest colonies.

Winged individuals usually choose new plants for food and can give offspring from wingless and winged individuals of females. With a high population density of the pest, damage to the host plant or a decrease in temperature, the formation of flying individuals increases with the arrival of autumn. By the end of the season, individuals appear, male and female ovipositors. After mating, the females lay yellow eggs. Overwintering of aphids occurs precisely at the egg stage. In a warm climate, generation can be parthenogenetically completed within 7 days.

In a warm climate, gender differences do not play a role. Females reproduce without mating with males as long as there are no factors preventing them from feeding and developing. Unlike many types of aphids, melon aphids do not experience discomfort even in extreme heat. Melon aphids are able to complete the cycle and multiply in just a week, so under the accompanying conditions, many generations are possible.

Egg: When first laid, the eggs are yellow, but after a short time they darken and turn into brilliant black.

Nymph: They have a wide variety of colours from yellow to gray and from brown to green, with a distinctive dark head, sternum, and rudiments of wings, as well as a dark green distal part of the abdomen. The body looks dull, because it is sprinkled with a waxy coating. The period of an immature nymph lasts on average about 7 days.

Adult: Females without wings have a length of 1-2 mm. The body is very diverse: the most common green colour is light and dark shades, but there are whitish, yellow and almost black forms.

The limbs of individuals are usually light, and the lower legs and the tips of the paws are dark. Small yellow shapes appear to be formed as a result of leaf folding and plant discomfort. The winged ones are 1.1-1.7 mm long. The head and sternum are dark, and the abdomen is green-yellow, not counting its ending, which is darker. The veins of the wings are brown. The oviparous female is dark green, the males are visually similar. The duration of the reproductive period of an adult is about fifteen days, and the post-reproductive period is 5 days. These data may vary significantly, as with most species, aphid cycles depend on temperature. It is reported that the most suitable temperature for generation ranges from 21 to 27 C. Viviparous females produce about 70-80 individuals of offspring at the rate of 3-5 individuals per day.

Host plants

Melon aphids have a huge number of host plants. It is believed that the hosts of these aphids can be about 700 representatives of flora around the world. Among pumpkins, they cause serious damage to watermelons, cucumbers and melons, as well as zucchini and pumpkin. These cultures formed the basis of the common name of melon aphids. Sometimes other vegetable crops are also affected: asparagus, beans, beets, carrots, celery, parsley, parsnips, peas, peppers, radishes, tomatoes, and aubergines. Some other important crops that are regularly injured are citrus fruits, cotton, and hibiscus. In the south, cotton is a significant host, which explains the second common name — cotton aphid.

Several studies have confirmed the existence of a host plant race; for example, aphids grown on cotton can be transferred to okro, but not to pumpkin. This inability to transmit to other hosts was subsequently determined for various other combinations.

The damage caused

The melon aphid feeds on the underside of the leaf, sucking the juices from the plant. The leaves become chlorotic and may suddenly die. Their nutrition also causes severe deformation and folding of the leaves, reducing the plant’s ability to photosynthesis. In addition, aphids produce sticky waste called pad, which serves as a medium for the development of a sooty fungus, as a result of which the quality and presentation of fruits suffer, and the ability of foliage to photosynthesis is even more difficult.

Melon aphid is a carrier of potyviruses among pumpkin, although it is only one of the many species involved in the spread of diseases. Cucumber mosaic virus, watermelon mosaic virus and zucchini yellow mosaic virus are transmitted despite the application of insecticides and oil sprays, probably because viruses can be transmitted within 15 seconds.

Natural enemies

Many beneficial insects, which are known to be effective biological agents in controlling other aphid species, also infect melon aphids: ladybirds (Coleoptera: Coccinellidae), flower flies (Diptera: Syrphidae) and braconid wasps (Hymenoptera: Braconidae). Ants are also closely related to melon aphids, but they feed on honeydew secreted by them and can even prevent the attack of other beneficial insects. Sometimes there is a lesion of melon aphids with mushrooms.

Control

Insecticides: If insecticides are used to suppress melon aphids, it is necessary to check that the foliage is fully treated. Leaf deformations caused by aphid nutrition serve as an excellent shelter for the pest, therefore systemic insecticides are recommended for use. Excessive and unnecessary use of insecticides should be avoided. At the beginning of the season, aphid lesions are usually spot-like, and with timely treatment of infected areas, you can protect yourself from significant damage at the end of the season. The use of insecticides against other, more dangerous pests is sometimes fraught with outbreaks of melon aphids. It is assumed that the cause of this phenomenon is the unintentional destruction of beneficial insects. However, the resistance of melon aphids to chlorinated hydrocarbons, organophosphates, and pyrethroid insecticides is widespread.

Cultural customs: A wide range of host plants for melon aphids complicates the successful implementation of crop rotation. In addition, crops grown in the wind from infected fields are especially susceptible, because aphids are weak fliers and, as a rule, the wind accompanies their dispersion. Infected crops should be destroyed immediately after harvest to prevent mass dispersal. If permanent farming contributes to the preservation of aphid populations, then a period without sowing is necessary. Reflective mulches also have an impact on aphid populations in open ground conditions. Light-coloured mulch (silver or white) reflects short-wave light, repelling flying aphids. Fewer aphids are planted on crops growing in fields with reflective mulch (compared to bare soil). In addition, when using reflective mulch, the frequency of viral diseases transmitted by aphids is lower, and the yield is higher.

Aphids are easily removed from plants if they are heavily sprayed with water, which reduces their numbers and reduces plant damage. While this is probably impractical in most vegetable growing environments due to the possibility of plant damage, sturdy vegetable plants in a home garden can benefit from water spraying.

The release of the Aphidius colemani (Hymenoptera: Braconidae) parasitoid into greenhouses can effectively reduce populations of melon aphids on a number of vegetable crops.