The plant-feeding mite family Tenuipalpidae comprises ca. 35 genera and 900+ species (Mesa et al. 2009; Beard et al. 2012). Brevipalpus and Tenuipalpus are recognized as the genera that harbour species causing most economic damage, to a great variety of crops. This special issue of Experimental and Applied Acarology focuses on Raoiella, a genus of Tenuipalpidae that has gained economical importance in recent years and now poses new challenges to pest control. This genus should be included in the list of economically important Tenuipalpidae, especially because of the damage it inflicts on coconut palms, being a source of nutrition and income for people inhabiting the tropical world.

Most prominent among the species in this genus is the red palm mite, Raoiella indica Hirst. It is also known as coconut mite, coconut red mite, red date palm mite, leaflet false spider mite, frond crimson mite, or scarlet mite. Whereas important as a pest of coconuts, date palms and other palm species, it is also a pest of bananas in different parts of the world. Before it arrived in the New World, the mite was found in India, Philippines, Mauritius, Reunion, Malaysia, Israel and Egypt. The first report from the New World came from the Caribbean Islands: Martinique and St. Lucia in 2004, Dominica in 2005, and in 2006 Trinidad and Tobago, Guadeloupe, and Saint Martin (Kane and Ochoa 2005; Etienne and Flechtmann 2006). Damage by red palm mites was observed widespread on these islands and on various host plants, e.g. on lower leaves of coconut palm (Arecaceae) in St. Lucia (Kane and Ochoa 2006), on leaves of banana (Musaceae) in Dominica (N. Commodore, personal observation, 2005; FAO 2005) and on other plants within the Musaceae, ginger (Zingiberaceae) and bird of paradise plants (Strelitziaceae) (Etienne and Flechtmann 2006). Raoiella indica is not only found on the Carribean Islands, it has also started to spread on the mainland—for instance, it has now been reported from Florida, USA (FDACS 2007), Venezuela (Vásquez et al. 2008), Colombia (Carrillo et al. 2011) and Brazil (Navia et al. 2011, Rodrigues and Antony 2011).

Initially, the extensive damage to coconut palms on the islands was thought to be due to ‘lethal yellowing’ (LY), a highly prevalent disease of palms in various countries of the Caribbean Basin. This confusion arose because LY infection, like red palm mite feeding, results in extensive chlorosis and yellowing of the lower leaves. However, in a very early stage, LY disease differs in that it causes coconuts of all stages to drop from the tree, it distorts the emerging inflorescences and it causes the male flowers to become dark brown. Yet another difference is that LY disease is never associated with red palm mites, which by their red colour are easily recognized on the abaxial surfaces of older foliage and which leave scaly patches of exuviae behind. Once red palm mites were recognized as the cause of the damage to the coconut palms on the islands, it became clear that they can reduce coconut production by more than 50 % in the Caribbean Basin (CARDI 2010).

In the wake of the invasion of R. indica into the New World the need arose to bring together existing information on taxonomy (Sayed 1942), biology (Moutia 1958; Zaher et al. 1969; Jeppson et al. 1975; Gerson et al. 1983; Nagesha-Chandra and Channabassanna 1984; Sakar and Somchodhury 1989), and control (Moutia 1958; Saradamma 1973; Puttaswamy and Rangaswamy 1976; Daniel 1981; Somchoudhry and Sarkar 1987; Sakar and Somchodhury 1988; Jalaluddin and Mohanasundaram 1990; Nadarajan et al. 1990; Jayaraj et al. 1991). Although there are comprehensive compilations published on the world-wide web (a.o. FAO 2005; CARDI 2010) and in journals (Sayed 1942; Elwan 2000; Gupta 2001; Mendonca et al. 2005; PROSEA 2006; Rodrigues et al. 2007a, b; Vásquez et al. 2008; Carrillo et al. 2011), these tend to focus on the distribution, importance and current status of R. indica.

The need for a fuller coverage of also other topics—such as host plant range, taxonomy, phylogeny, morphology, species recognition by means of molecular techniques, dispersion and sampling techniques, population dynamics, classical biological control, natural enemies and chemical control—provided the impetus for this special issue of Experimental and Applied Acarology on Raoiella. Twenty-eight Raoiella experts took part in this attempt to assemble the existing knowledge and to pinpoint the gaps in knowledge. We hope it will also stimulate interest in the lesser known genera of the Tenuipalpidae, provide a basis for more rational control strategies, and help to identify the areas where more research is needed.