Blue passionflower

Tiny (0.3–0.5 mm) arachnids, hard to spot with the naked eye, feeding on the underside of leaves. Symptoms: fine, pale speckling (feeding punctures); over time the leaves turn grey, yellow and dry out. Under heavy infestation a fine webbing becomes visible. Warm, dry air favours their development — a common problem for houseplants in winter near radiators. Spider mites are not insects but mites of the family Tetranychidae — adults have 8 legs (larvae only 6). The most common in cultivation is the two-spotted spider mite (Tetranychus urticae): yellowish-green females carry two dark spots on the sides of the body, while overwintering females turn orange-red. In orchards the fruit tree red spider mite (Panonychus ulmi) is frequent, whose red eggs overwinter in clusters on the bark of the shoots. Feeding mechanism: the mites puncture the cells of the epidermis and mesophyll on the underside of the leaf and suck out their contents, and the emptied cells fill with air — hence the characteristic, silvery-grey, fine speckling visible from the upper side of the blade (resembling a mosaic discolouration). At high numbers the leaves turn brown, curl and drop prematurely, and the whole plant weakens and loses its growth. Dense webbing spun between the leaves and shoot tips appears only under an advanced attack and is a sign of the risk of the pest spreading to neighbouring plants. The development cycle is very fast in warmth and drought — at a temperature of 25–30°C a single generation can be completed in 1–2 weeks, hence the numerous generations per season and the rapid, exponential build-up of the population. Females lay spherical, transparent eggs on the underside of the leaves. Fertilised females overwinter (in bark crevices, leaf litter and plant debris) or — in the fruit tree red spider mite — the eggs on the bark. Early infestation is easy to miss; diagnosis is helped by shaking a leaf over a white sheet of paper (moving specks become visible) or examining the underside of the leaf with a magnifying glass.

Insects covered in a white, cottony, waxy coating, gathering in leaf axils, at the base of shoots and on the underside of leaf blades. They look like tufts of cotton wool. They suck sap, weaken the plant and excrete sticky honeydew, on which black sooty mould develops. A common pest of houseplants and succulents. Adult females are oval, soft-bodied insects about 2-5 mm long, with a pinkish or grey body hidden under wax, often bearing waxy filaments along the sides and at the tip of the abdomen. Males are tiny, winged and do not feed. In most species eggs are laid in white, cottony ovisacs (cocoons), from which mobile larvae (crawlers) hatch and spread across the plant, carrying the infestation to neighbouring specimens; some mealybugs (e.g. Pseudococcus longispinus), however, are ovoviviparous and give birth to live crawlers without a distinct ovisac. In the warm, dry conditions of homes and glasshouses mealybugs develop all year round, in several overlapping generations - which is why a single treatment is rarely enough. Feeding symptoms are stunted growth, yellowing, deformation and premature leaf drop, and under heavy infestation dieback of shoots; the black sooty mould on the honeydew further reduces photosynthesis and disfigures the plant. A separate form is the root mealybug (Rhizoecus), forming white, waxy clusters on the roots and inside the root ball - the plant weakens and wilts with no visible pest on the above-ground parts. Mealybugs are often attended by ants, which eat the honeydew and protect the colonies from natural enemies.