> Dr Kevin Powell’s Phylloxera Fast Facts
- Adult grape phylloxera are strictly females and reproduce without male fertilisation. Hence it only takes one bug to start a new infestation.
- On average, adult phylloxera have a reproductive period of one to two months, during which time they lay three to six eggs per day. Egg laying of more virulent strains is considerably higher. Five to nine overlapping generations can occur during a single growing season.
- During the development of a grape phylloxera insect, it moults four times with a sequential increase in size with each instar.
- In the past, grape phylloxera have often been referred to as aphids, or aphid-like insects. However, phylloxera and aphids differ in a number of feeding and digestion characteristics, and the terminology “aphid-like” has resulted in a number of false assumptions regarding the biology of grape phylloxera.
- The length of a phylloxera’s piercing mouthpart (stylet) indicates that they feed on the thin-walled, unspecialised, filler cells (parenchyma) within the grapevine root system. This is a high protein, low sugar and low pH (4.0-5.0) food source. Aphids on the other hand feed on the phloem sap which is sugar rich, low in protein and of neutral pH (6.5-7.0).
- Because of the aphid’s high sugar diet, they excrete sugar-rich honeydew as waste. Phylloxera have weak anal muscles and due to their different diet, do not produce honeydew.
- Grape phylloxera have a sensory pore located at the tip of each of their antenna. Because phylloxera feed exclusively on Vitis species, it is suspected that this high level sensory system is likely to be important to help it locate a new host plant.
- Adult grape phylloxera are approximately 0.8 – 0.9mm long by 0.5mm wide – the length being marginally thicker than the width of a credit card. Eggs are one third of the length of adults, at 0.25-0.30mm long by 0.1-0.15mm wide. No wonder they are hard to spot!
- Phylloxera spend much of their life below the soil surface, sometimes as deep as 1.5 metres. In spring and summer they migrate above ground and crawl around on the soil surface, vine trunks, leaves, shoots and on grape bunches.