As orchid mites are very small, infestation is often only noticeable at an advanced stage. Initially, the older leaves turn a dull green, with sunken spots visible on the underside and silvery patches on the upper side. Later, infested leaves turn bronze to yellow-orange, and the infested areas become scarred. The leaves often dry out from the edges and eventually fall off. Since no webs can be found on the underside of the leaves, they are also referred to as false spider mites. All orchid species are susceptible to infestation with Brevipalpus. However, the mites mainly occur on Phalaenopsis, Doritaenopsis, Paphiopedilum and Masdevallia.
Due to their extremely small size, the spread of the mites can only be detected by the increasing whitish undersides of the leaves. The discarded cells fill with air and therefore shimmer whitish. With increasing age, the leaves dry out and the air-filled cells can no longer absorb moisture. The cells turn orange, reddish to greyish or brown. Eventually, the leaves gradually dry out and fall off.
They are closely related to soft-skinned mites, which are almost colourless and can also be found in very sheltered, hidden places under bracts or in the heart of the leaf.

Biology

Brevipalpus, commonly known as "false spider mites", "non-spider mites" or "orchid mites", are green to reddish in colour and often infest orchids. They are between 0.25 and 0.3 mm in size. As with all arachnids, their body is divided into two parts: a large body and a small head. Half of the eight legs typical of arachnids are oriented forwards and half backwards.

The three most common types found on orchids are:
the scarlet tea mite (Brevipalpus californicus Banks),
the red greenhouse spider mite (Brevipalpus obovatus Donn.)
and the orchid spider mite (Tenuipalpus pacificus Baker).

Brevipalpis reproduce sexually by laying eggs. Females usually lay their eggs on the underside of leaves or on shoots. Development proceeds through the stages of egg, larva, nymph and adult. Throughout their development, the animals feed on plant sap. Mites such as Brevipalpis pseudoaurantii (a common species) reproduce rapidly, especially in warm, dry conditions, and can also reproduce parthenogenetically (virgin birth), which promotes their population explosion.
Reproduction cycle:
Egg laying: Females typically lay 20–50 eggs individually or in small groups on leaves, often in webs.
Hatching of the larva: Six-legged larvae hatch from the eggs and immediately begin to suck plant sap.
Development (nymph): After several moults, the larvae develop into eight-legged nymphs, which also suck sap.
Adult: After further moults, the adult mites emerge and are now able to reproduce.

Special features:
Parthenogenesis: Females can reproduce without fertilisation by males, which enables rapid spread, especially when no males are present.
Growth promotion: Under favourable conditions (heat, dryness), mites such as Brevipalpis can develop many generations per year very quickly.

Spider mites must be controlled with acaricides. Insecticides are ineffective. The plants must be sprayed several times at short intervals with different active ingredients, as resistance develops very quickly. Checks must be carried out regularly, and only when the new leaves show no symptoms for a longer period of time, even when viewed with a magnifying glass, can the treatment be considered successful.

As the chemical options for controlling arachnids and mites are becoming increasingly limited, the use of biological antagonists must be considered. Brevipalpus can develop a high degree of dynamism and spread rapidly, particularly in Phalaenopsis. However, Brevipalpis reacts sensitively as soon as antagonists are introduced. The safest and most sustainable control method is the use of predatory mites. Brevipalpus sp. can be effectively controlled with the predatory mite Amblyseius swirskii. To begin with, a "medium dosage" of 50 animals/m² should be sufficient, with repetition every 14 days considered optimal. If the stock is symptom-free, a "low dosage" applied every 4 weeks may be sufficient to keep the stock clean. If visible symptoms reappear despite prevention, a "high dosage" of 100 animals/m² should be applied immediately. According to the experience of many gardeners, the use of the predatory mite Amblyseius swirskii is significantly more effective than chemical treatments.

Whatever was contained in these products, which were marketed at the end of the 19th century to combat spider mites and insects, we can be glad that they are no longer in use today. At a time when neither gloves nor masks were used, it is safe to assume that it was not only insects and arachnids that suffered when they came into contact with these products.