Rose-grain aphid

Description
This aphid has a spindle-shaped body with rather long siphunculi. It is green, with a noticeably lighter stripe along the back. The apterae are up to 3 mm (0.118 inch) in length, the oviparous females less than 2 mm (0.078 inch). The length of the antennae is about ¾ that of the whole body.

Damage
Like all aphids, M. dirhodum feeds on plant sap, which it obtains by puncturing phloem vessels. Its saliva does not contain any substances that are toxic to the plant, but the drain of nutrients and water can lead to yield losses if the aphid occurs in large numbers. Plants that are already under water stress may start to yellow and become stunted. Depending on the course of an infestation, both the number and size of the grains may be reduced; infestations during the period between tillering and the end of flowering are particularly harmful.

Apart from the direct damage it causes, M. dirhodum is also a vector of several plant viruses, most importantly barley yellow dwarf virus, but maize mosaic virus and potato viruses can also be damaging.

The honeydew it produces promotes growth of saprophytic fungi that are detrimental to plant health.