Tropicoseius is a genus of hummingbird mite in the Kingdom Animalia, Phylum Arthropoda, Class Arachnida, Subclass Acari, Order Mesostigmata, Family Ascidae. This genus, along with the genus Rhinoseius and some species of the genus Proctolaelaps are known for their tendency of phoresy, the behavior of using hummingbirds as a means of “hitchhiking” from one flower to another (Dusbabek et al. 2007). These mites feed on nectar and pollen from the flowers they live on (Colwell 1995, Colwell & Naeem 1999, Lara & Ornelas 2002, Dusbabek et al. 2007, Lindquist & Moraza 2008, Velásques & Ornelas 2010, López-Orozco & Cañón-Franco 2013, Britto et al. 2015).
The genus has highly variable in morphology, but typically males and females are similar in size (Lindquist & Moraza 2008). Hummingbird mites tent to have a body length of approximately 400-600μm (Dusbabek et al. 2007). Adult males have peripheral modified setae (hair-like structures) on the back of the body and on back-facing surfaces of the legs. These structures are used for mate competition (Lindquist & Moraza 2008).
Species have been found in Southern Mexico (Velásques & Ornelas 2010, Lara & Ornelas 2002), Costa Rica (Lindquist & Moraza 2008, Colwell & Naeem 1999, Dusbabek et al. 2007), Colombia (López-Orozco & Cañón-Franco 2013), and Brazil (Britto et al. 2015), suggesting a Neotropical distribution.
Species of Tropicoseius are mainly found in tropical lowlands (Britto et al. 2015) and are most common at times when flowers are abundant, during high precipitation seasons (López-Orozco & Cañón-Franco 2013).
These mites are transported from flower to flower by riding in the nasal cavities of hummingbirds (hence the name Hummingbird Mite) (Dusbabek et al. 2007). A single hummingbird can transport 1-15 mite individuals (Colwell & Naeem 1994). This functional relationship of ”hitchhiking” on another organism is known as phoresy. In this case, plants act as a transitory habitat, while the organism on which the mites ride is the transporter, but is not a host for reproduction (López-Orozco & Cañón-Franco 2013). The mites are not parasitic and there is no known detectable effect impact on the hummingbirds as a result of the mites (Colwell & Naeem 1994).
Their diet consists of pollen and nectar from the flowers they live in (Velásques & Ornelas 2010, Lara & Ornelas 2002, Dusbabek et al. 2007, Lindquist & Moraza 2008, López-Orozco & Cañón-Franco 2013, Britto et al. 2015, Colwell & Naeem 1999, Colwell 1995). Mites of the Ascidae family feed on pollen during the nymphal (immature) stages and nectar during the adult stage (López-Orozco & Cañón-Franco 2013). Adult mites consume, on average, 40% of the nectar from host flowers (Colwell 1995). It is thought that this high nectar consumption causes the mites to impinge on the nectar supply for hummingbirds, thus causing the mite-hummingbird association to be negative for the birds (López-Orozco & Cañón-Franco 2013).
Colwell & Naeem (1999) Describe behavior of Tropicoseius as follows: Typically, each species of Tropicoseius occupies only one species of hummingbird-pollinated flower in a community. Species have been shown to prefer the nectar of that species over others. Most tropical hummingbird flowers last for only one day, so mites must find their way to another flower when one flower dies. To do this, they move on foot to a new different bract (modified leaf situated at the base of a flower or inflorescence that protects the flower and attracts pollinators even when flowers are not in bloom) on the same inflorescence and wait for the flower to bloom, or ride in the nasal cavities of hummingbirds to the next flower they feed from. More than one species of mite can be found on a single hummingbird beak at one time. Colwell (1973) found that mites will climb onto anything entering a flower that remotely resembles a hummingbird bill (for example, forceps, twigs, and artist’s brushes). When he used a stuffed hummingbird to simulate bill-insertion into a flower, many of the mites simply ran around the artificial bills with no direction toward the stuffed-bird’s nostrils. Thus, he speculates that the inhalation of the hummingbird’s breath allows the mites to easily enter the nasal cavities.
Lindquist and Moraza (2008) found that pollen from host flowers may stick to the body and leg setae (hair-like structures) of adult and deutonymphal (second stage in larval development) mites, thus causing the mites to contribute to self-pollination of host plants when they travel between flowers on the same inflorescence, though they may also contribute to cross-pollination when they exhibit phoresy and move from flower to flower within the same host species.
Courtship, mating, and oviposition occur on the inflorescences of hummingbird-pollinated flowers (Colwell & Naeem 1999). The general life cycle of hummingbird flower mites was described by Velazquez and Ornelas (2010) in their study of Tropicoseius chiriquensis. They describe that many individuals remain on the same inflorescence throughout their entire life cycle, which begins with a brief egg stage. Following this is a six-legged larva stage, an eight-legged protonymph (first larval stage in the development of most mites) and finally, the deutonymphal stage (second larval stage in the development of most mites) before adulthood (Velazquez and Ornelas 2010). The entire life cycle is approximately 2 weeks long (Velázquez and Ornelas 2010).
