In an attempt to identify ecologically friendly methods for controlling mosquito populations, researchers conducted ﬁeld experiments in India where aquatic nymphs of the dragonﬂy Brachytron pretense were used against the larvae of mosquitoes. For the experiment, the researchers selected ten 300-liter (L) outdoor, open, concrete water tanks, which were natural breeding places for mosquitoes. Each tank was manually sieved to ensure that it was free of any nonmosquito larvae, nymphs, or ﬁsh. Only larvae of mosquitoes were allowed to remain in the tanks. The larval density in each tank was assessed using a 250-milliliter (ml) dipper. For each tank, 30 dips were taken and the mean larval density per dip was calculated. Ten freshly collected nymphs of Brachytron pretense were introduced into each of ﬁve randomly selected tanks. No nymphs were released into the remaining ﬁve tanks, which served as controls. After 15 days, larval densities in all the tanks were assessed again and all the introduced nymphs were removed. After another 15 days, the larval densities in all the tanks were assessed a third time.
In the nymph-treated tanks, the density of larval mosquitoes dropped signiﬁcantly from 7.34 to 0.83 larvae per dip 15 days after the Brachytron pretense nymphs were introduced. Further, the larval density increased signiﬁcantly to 6.83 larvae per dip 15 days after the nymphs were removed. Over the same time period, the control tanks did not show a signiﬁcant difference in larval density, with density measurements of 7.12, 6.83, and 6.79 larvae per dip. The researchers concluded that Brachytron pretense can be used effectively as a strong, ecologically friendly control of mosquitoes and mosquito-borne diseases.
(a) Identify the research objective.
(b) What type of experimental design is this?
(c) What is the response variable? Is it quantitative or qualitative? If quantitative, is it discrete or continuous?
(d) What is the factor the researchers controlled and set to predetermined levels? What are the treatments?
(e) Can you think of other factors that may affect larvae of mosquitoes? How are they controlled or dealt with?
(f ) What is the population for which this study applies? What is the sample?
(g) List the descriptive statistics.
(h) How did the researchers control this experiment?
(i) Draw a diagram similar to Figure 7 or 8 to illustrate the design.
( j) State the conclusion made in the study.