Thysanoptera Californica

Objectives and limitations

The objective here is to facilitate the identification of most of the thrips species that have been recorded from California, and thus to enable future studies on the biology of various members of this diverse fauna. Also included in the system are about 40 species that are likely to be introduced into this State, and that are thus of interest to quarantine services as well as agricultural and horticultural entomologists.

The studies presented here do not constitute a “taxonomic revision”; that would require extensive field work. The data here is based on microscope slides available in various museum collections. Unfortunately, many such specimens have been slide-mounted with inadequate techniques, and structural features used in current studies are not visible. Moreover, the available label data is often imprecise, with no indication of the host on which breeding occurs, or even if the species is associated with leaves or with flowers.

There are two major groups of biologists who work on thrips, the economic entomologists and the taxonomists. Members of both groups share a particular priority – they both kill thrips; one to control pests, the other to slide-mount specimens for microscope study. As a result, knowledge of how each species lives, behaves and maintains its populations, is remarkably scarce. Even the basic biological information in lists of “host plants” is often misleading, because records are commonly based on the collection of one or more adults with no evidence that the insect was breeding or even feeding on the plant recorded. The lack of knowledge about where a species lives results in great difficulty in acquiring information about useful and interesting biological aspects such as population structure, seasonality, geographic distribution, and sexual behaviour.

Illustrations of thrips

Most of the thrips species described from North America remain unillustrated, even though J. D. Hood at Cornell prepared many outstanding but unpublished line drawings (Hoebeke, 1994). High quality line drawings are expensive to produce, thus photomicrography is used increasingly. Many of the images presented here have been processed through the software, Automontage. However, this requires specimens that are fully cleared chemically, and slide-mounted to a very high standard - see Preparing Thrips for Study. In contrast, data-rich images can rarely be prepared from older slides in museum collections. The most informative detailed images presented here were produced using differential interference contrast (Nomarski) illumination on a Leica 2500. However, many of the images were taken using either phase-contrast or bright field microscopy, and some of these are reproduced here in monochrome to avoid color aberrations.