Chaetosiphon fragaefolii-strawberry aphid: Microscopic exam, molecular diagnosis (PCR) and species identification (PCR and sequencing)
This insect is an aphid belonging to the Aphididae family, Homoptera order, characterized by a soft body with piercing mouthparts, which serve to feed on the nutrient-rich liquids of plants. Approximately the size of the head of a pin, in large quantities they can weaken plants significantly, damaging flowers and fruit. Chaetosiphon fragaefolii, commonly known as strawberry aphid, which belongs to the genus Chaetosiphon is the biggest pest for strawberries. Adults are 0.9 to 1.8 mm long, oval, pale green in color, and have long pale green-yellow siphons. There are adult winged forms, but not all adults have wings; those that do develop them do so in response to overcrowding, nutritional or environmental signals. On the plant, they can be found on the underside of the leaves, concentrated at the base of the petiole. Their distribution is worldwide; however, they are more frequent in the United States, Argentina and Chile.
These aphids cause direct damage by sucking the sap from the fruit and leaves, thus reducing the yield and quality of the fruit. In addition, they secrete a honeydew that makes the leaves sticky, and they contribute to the development of an opportunistic fungus (Tricholoma terreum) that blackens the plants (“grey knight”).
The life cycle of these aphids includes four molts before reaching maturity. In each molt they lose a whitish skin, which reveals their presence on the plant. They reproduce by parthenogenesis during the growing season. Viviparous females (those that do not lay eggs), although they are not fertilized, continuously produce new generations of females, more than 40 nymphs during their life cycle, with an estimated life span between 13 and 52 days. Females developed at a warmer temperature have significantly fewer winged young than those developed at a lower temperature and photoperiod. Feeding on young leaves has a positive effect on earlier reproduction than feeding on old leaves. Winged aphids appear from October to December, and they facilitate the spread to other plants and fields. In mid-spring and early autumn, the peaks of maximum population development take place, on the contrary, during the summer months the populations are generally very small due to the heat.
The strawberry aphid is an important vector of several plant viruses that affect strawberries. The main ones are “Strawberry mild yellow-edge virus” and “Strawberry crinkle virus”. Sometimes coinfections of both viruses can occur, producing a decrease in the development of plants (dwarfism), mottling, distortion of the leaf or mosaicism. The short life cycle of aphids, together with the short latent period of the virus, favor that the spread of the plague is not rapid; even so, these viruses cause significant economic losses for strawberry crops.
Under laboratory conditions, C. fragaefolii develops between 10 and 29.4ºC, being the optimum temperature 21.1ºC; at this temperature development is completed in 7 and a half days. The established photoperiod is 18 hours of light and 6 of darkness.
Diagnosis of the presence of this aphid requires microscopic examination, as it is an organism with such small dimensions. Currently, molecular PCR and sequencing methods are used to accurately determine the genus and species.
The treatment of this pest can be carried out in several ways, the most used and more effective being biological control. The most common natural predators of C. fragaefolii are: Aphidius colemani, Aphelinus abdominalis, Lysiphlebus testaceipes, Aphidius ervi, Aphidius matricariae, Ephedrus cerasicola and Praon volucre. Exposure to these predators should take place at the end of winter, and it is advisable to repeat the inoculations two to three times to achieve an efficient population. A less common alternative to control this pest is the use of pesticides, which must always be authorized in the Register of Phytosanitary Products of the Ministry of Agriculture, Fisheries and Food.
Tests carried out at IVAMI:
- Microscopic examination.
- Molecular diagnosis (PCR).
- Molecular identification of species (PCR and sequencing).