Thrips are tiny sucking insects with fringed wings of the order Thysanoptera. Thrips arose during the Permian long before flowering plants and fed originally on mosses. Some species still do while others are predatory. Most are now phytophagous, feeding on pollen and plant cells. Because of this they are mostly known as pests of food crops. Because of their small size and weak flight abilities they were not considered effective pollinators. This has changed greatly as more and more plants are found to be at least partially pollinated by thrips (Terry, 2003). Thrips found in Mesozoic amber not only have the pollen of gymnosperms attached to them, these fossil thrips have specialized attachments for carrying pollen like bees today (Peñalver, Labandeira, Barrón, Delclòs, Nel, Nel, Tafforeau, Soriano, 2012). Thrips no longer have these specialized pollen carriers but still pollinate modern cycads moving from male to female according to the amount of volatiles given off by the male plants (Terry, Walter, Moore, Roemer, Hull, 2007). Avocado growers setup honey bee hives in orchards and spray the trees to prevent thrips. There is no hard evidence that honey bees effectively pollinate avocados and experiments so far (Hoddle, Hofshi, Arpaia, 2010) have shown evidence of thrips pollination. Understanding how this works could save avocado growers much cost, labor and use of pesticide.
The Arctostaphylos genus of which local manzanita species belongs has its own relationship with thrips. Thrips have been found to pollinate A. Uva-ursi in Spain (García‐Fayos, Goldarazena, 2008) and they are studying thrips pollination of A. pungens at the University of Arizona. Ancient connections in the plant family Ericaceae between the California Floral Zone and Mediterranean Europe (Hileman, Vasey, Parker, 2010) seem to be mirrored in certain thrips lineages (Hoddle, Mound, Nakahara, 2004) although the species most associated with Arizona manzanita is Orothrips kelloggii. It’s sister species in Europe, Orothrips priesneri, was not found to pollinate A. Uva-ursi in Spain (García‐Fayos, Goldarazena, 2008).
Thrips have been found to be alternate pollinators in the complex web of associations that form around a plant community. It must be noted that nowhere in the literature but with the exception of cycads, do they contribute more than 20% to the pollination of any one plant. Given the massive fluctuation of the number of pollinators in any given season, any contribution can be an important one.