Chapter 45, Problem 1DAA

Testing Biological Control Biological control agents are used to battle red imported fire ants. Researchers have enlisted the help of Thelohania solenopsae, a natural enemy of the ants. This microsporidian (Section 23.4) is a parasite that infects ants and shrinks the ovaries of the colony's egg-producing female (the queen). As a result, a colony dwindles in numbers.

Are these biological controls useful against imported fire ants? To find out, USDA scientists treated infested areas with either traditional pesticides or pesticides plus biological controls (both flies and the parasite). The scientists left some plots untreated as controls. FIGURE 45.16 shows the results.

FIGURE 45.16 A comparison of two methods of controlling red imported fire ants. The graph shows the numbers of red imported fire ants over a 28-month period. Orange triangles represent untreated control plots. Green circles are plots treated with pesticides alone. Black squares are plots treated with pesticide and biological control agents (parasitoid flies and a microsporidian parasite).

How did population size in the control plots change during the first four months of the study?

Summary Introduction

To determine: The variation in population size in the given control plots during the first four months of the study.

Introduction: Biological control agents are the natural enemies like predation, parasitism, and other methods that are used to control the pests like weeds, insects, mites, nematodes, and so on in order to generate a pest-free- yields. The biological control agent such as Thelohania solenopsae is a natural enemy of the red imported fire ants. This microsporidian can decline the ant’s colony by infecting and shrinking the ovaries of the queen which are the female reproducing ants.

Explanation of Solution

The USDA scientists conducted a study by treating the infected area by using the traditional pesticides and pesticides with biological controls. They kept some plots as controls that are untreated. They observed that the red imported fire ants over a period of 28 months.

Refer Fig. 45.16, “A comparison of two methods of controlling red imported fire ants” in the textbook. The graphical representation shows the percentage of the number of ants versus the months of treatment. The orange triangle indicates the control plots that are untreated. The green circle indicates the plots that treated using pesticides alone and the black square indicates the plots that treated using pesticide with biological control agents (using both parasite and flies).

During the first four months of the treatment, the variation in the population size of the control plots of fire ants increased. Initially, the percentage of the number of ants was 100%. However, after first four months, it had increased to 140%. Hence, there was a variation of about 40%.