As we’ve just seen, perhaps the easiest way to determine if a eukaryotic organism is a protist is to first determine if it’s an animal, a plant, a or fungus. If the organism isn’t any of those, then it’s a protist. Unlike the other kingdoms, which are grouped together based on shared characteristics, protists are grouped together out of convenience.

At the beginning of this chapter, we talked about the potential to use micro-algae, a type of protist, as a sustainable energy source. However, as we’ve learned, not all protists are benign.

Researchers at the Agricultural Research Service (ARS) have assembled and maintained collections that allow them to explore the diversity, evolution, and distribution of parasites and pathogens. This collection was established in 1892 and is among the largest parasite collections in the world. It holds more than 20 million catalogued specimens representing nematodes, tapeworms, flukes, protists, and some parasitic arthropods, such as fleas, ticks, and lice. Such archives provide a foundation to identify shifting geographic and host ranges for parasites and diseases that may emerge with accelerated global climate change.

Figure 1. Paratype specimen of S. invicta collected from Brazil.

At the Center for Medical, Agricultural and Veterinary Entomology (CMAVE), in Gainesville, Fla., researchers are using a collection of microsporidia to act as soldiers of biological warfare at the tiniest level against red imported fire ants. CMAVE entomologist David Oi is using species of spore-producing insect pathogens, such as Kneallhazia solenopsae, to bring about declines in red imported fire ant (Solenopsis invicta) populations. In Argentina, these infectious soldiers are associated with localized declines of 53 percent to 100 percent in fire ant populations, according to Oi.

In addition, Oi and CMAVE colleagues Sanford Porter and Steven Valles were able to get K. solenopsae to infect phorid flies without harming them. This is important because phorid flies may serve as vectors to infect red imported fire ants with the microsporidia—perhaps facilitating the spread of infection to other colonies.