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The Phytoseiidae are a family of which feed on thrips and other mite species. They are often used as a biological control agent for managing mite pests. Because of their usefulness as biological control agents, interest in Phytoseiidae has steadily increased over the past century. Public awareness of the biological control potential of invertebrates has been growing, though mainly in the US and Europe. In 1950, there were 34 known species. Today, there are 2,731 documented species organized in 90 genera and three subfamilies.
The larvae of these mites range from translucent white to tan in colour. They are tiny and oval in shape and size, have six legs, and are wingless. Nymphs look similar to larvae, with the exception of being slightly larger and having eight legs.
Adult phytoseiids are less than 0.5 mm in size, pear-shaped, wingless, and have eight legs. They are translucent white, but turn a pale tan, orange/red, or green after feeding.
Developmental rate is species-specific, ranging from less than a week to four weeks, with temperature and diet affecting the rate.
The body of Phytoseiidae is divided into two parts: the gnathosoma (anterior) and idiosoma (posterior). The gnathosoma includes chelicerae, sensorial palps, and a stylophore. Males have an added feature- a spermatodactyl to transfer spermatophore to females.
Scientists have proposed classifications of the Phytoseiidae based on their food sources. In the most current version, developed in 2013, phytoseiids are grouped into four types.
Phytoseiid species that act as biological control agents are influenced by the availability of their prey. Phytoseiids can postpone or delay egg production during periods when prey are scarce. This allows them to have a longer lifespan and likely serves as an adaptation to environments where prey availability is variable. In addition to being able to delay reproduction, phytoseiids are also capable of rapid reproduction when prey is readily available. They reproduce more when prey availability is high, which increases their effectiveness as biological control agents. When prey availability increases, females lay more eggs, and more healthy offspring are produced during reproductive periods. In addition, when prey availability increases, the Phytoseiidae kill more prey during reproductive cycles, and the ratio of prey killed to eggs laid increases.
Although Wolbachia bacteria do not benefit their hosts in any way, they are maintained in the population because infected mothers pass them to their offspring through the ovum. Over time, bacterial presence in a population can lead to complete reproductive isolation of that population from uninfected populations. Wolbachia causes speciation through reproductive isolation. Some hosts evolve with a dependency on Wolbachia for reproductive functions, so that individuals without Wolbachia infections have lower reproductive fitness.
Wolbachia influences the gender determination of its hosts, making females more common than males. In populations affected by Wolbachia, females commonly compete for the right to mate with males. This is one of the ways in which Wolbachia infections can lead to speciation, because females evolve traits that allow them to better compete for males. In extreme cases, the feminizing effect of Wolbachia can cause the host species to lose the chromosome responsible for female gender. Wolbachia infections are capable of causing the extinction of hosts by making females much more common than males.
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