February 2013. A message to PestNet from Laurence Mound, CSIRO, thrips expert and PestNet Associate. It's an interesting story, Laurence explain as follows:
The attached images (courtesy of Jamie Street) are of cotton plants in southern Queensland, Australia, during January, 2013. Most readers seeing such a large number of thrips on a plant will assume that this indicates a host-plant relationship, and that the thrips is a pest of the plant. However, in this instance, as in many such situations with thrips, such a deduction is entirely incorrect. These thrips caused no damage to the tissues of the cotton plants, and there was no indication that the thrips were feeding, let alone breeding.
The species is the Australian Black Plague Thrips, Haplothrips froggatti, that breeds only in the flowers of certain grasses, particularly Buffel Grass, Cenchrus ciliaris, and populations in arid areas of Australia are sometimes vast. But as the grass dries in the summer heat, adult thrips disperse to find somewhere where a few can survive until the next flowering season.
This is essentially similar to the well-known Thunder Flies of Europe, Limothrips cerealium, that emerge from drying grasses and cereal crops and search for an overwintering site. In nature this is under the bark of trees, but adults of Limothrips can be found hiding in many less natural places including smoke detectors, the backs of framed pictures, blocks of polystyrene, even sealed within tampons and hypodermic needles straight from the manufacturers.
Assuming a host relationship from the presence of one, or even hundreds, of adult thrips is commonplace among entomologists. But such assumptions are often invalid, with many published “host records” of thrips species being no more than “finding places” of adults with little biological significance. This subject of thrips host associations is further discussed in the June 2013 issue of Florida Entomologist.
“With thanks to Lewis Wilson, Cotton Research Scientist, Narrabri, for drawing my attention to this situation. Laurence.email@example.com”