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Species richness.
Rarefaction curves of species richness were calculated for both trials (Figures 5-6). In the
winter experiment, species richness estimated at n = 495 did not differ between sites before
treatment (Figure 5, A), in spite of marked differences between site abundances (numbers
at the B. bassiana site were twice-fold those at the control site). In both post-spraying
sampling dates, species richness at the control site felt slightly out of the confidence
interval calculated around B. bassiana rarefaction curve, while λ-cyhalothrin rarefaction
curve felt out the lower confidence limit of B. bassiana rarefaction curve (Figure 5, B-C).
Spring results indicated that the control and λ-cyhalothrin species richness were similar and
higher than the B. bassiana species richness before treatment, at n = 402 (Figure 6). After
treatment, the confidence limits of B. bassiana and λ-cyhalothrin overlapped and included
the control species richness, therefore the treatments did not alter species richness in this
season.
Evenness.
In the winter experiment, evenness before treatment at the control site was higher than
evenness at both B. bassiana and λ-cyhalothrin sites but there was no significant difference
between these latter two sites. Twenty days after a single spraying of B. bassiana or λ-
cyhalothrin, estimates of Hurlbert’s PIE showed a different pattern: control and B. bassiana
sites showed no differences (α = 0.05), but evenness at λ-cyhalothrin site was significantly
lower (Figure 3, centre). The same result was obtained when evenness values were
calculated from samples taken 40 days after treatment (Figure 3, center).
Pre and post-spraying values for evenness in the spring experiment are shown in Figure 4
(centre). Samples taken before spraying indicated that evenness in untreated and treated
sites was similar. Thirty days after spraying, estimates of Hurlbert’s PIE showed slight,
although statistically significant, differences between control and B. bassiana sites and a
more marked decreased evenness at λ-cyhalothrin site (Figure 4, centre).
Dominance.
In the winter experiment, dominance was similar between treated sites, but it was lower at
the control site (Figure 3, right). Twenty days after spraying, dominance remained high at
the λ-cyhalothrin site (where the most dominant species accounted for more than 60% of
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