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Cage trials 91.3% of the original stock of P. angulata tschadensis were recollected. The 8.7% beetles undetected must be attributed to cannibalism. One out of four replications in the control group was proved significantly to be an outlier (Outlier text of Dixon as described by Snedecor & Cochran (1980) ) and was treated as missing (statistical analysis for unbalanced design).

All test agents had an adverse effect (Table 2 and Figs 1 & 2), but only dieldrin (P < 0.001) and neem 0.l% (P < 0.05) caused significantly increased mortalities. Surprisingly, neem 0.l% finally caused higher mortalities than neem 0.2%, which is probably due to the different additives used in both formulations. No infection could be detected in the B. bassiana-treated beetles.

Table 2. Mean mortality at the end of the trial.

Control different from dieldrin & neem (0.1 %) (P < 0.05; ANOVA & Newman-Keuls multiple comparison among means); other differences not significant.

Figure 1. Cumulative mortality (M) of Pimelia angulata tschadensis; neem (0.1 %) and neem (0.2%).

Figure 2. Cumulative mortality (M) of Pimelia angulata tschadensis; dieldrin and Beauveria bassiana.

The activity of the beetles is cyclical (Fig. 3). Data from days 1 and 2 are slightly biased due to a prolonged sampling period (day l: 90 min; day 2: 110 min). The periodicity of the data, although biologically important, is irrelevant for assessing the effects of the agents. This becomes evident when comparing the pattern of the activity of cage-tested tenbrionids in all replications (Table 3) and that of field-tested tenebrionids in all plots, respectively (see small-scale field trials, below). Differences in the effects of the agents are indicated by level of activity (Table 4) as compared to that of the control. Neem-treated beetles exhibit insecticide-caused hyperactivity whereas the dieldrin- and B. bassiana-treated groups exhibit hypeactivity.

Figure 3. Mean relative activity (RA) of Pimelia angulata tschadensis.

Table 3. Correlation matrix (Pearson's r) of the mean relative activity (RA) (all days).

Correlation coefficient significant at: ** P < 0.01; *** P < 0.001.

Table 4. Mean relative activity (RA) of P. angulata tschadensis on days 3-15 (retransformed data).

Control different from Neem (0.1%), Neem (0.2%) & Beauveria different from Dieldrin; Neem (0.2 %) different from Beauveria (P < 0.05; Friedman-ANOVA & Wilcoxon-Wilcox multiple comparison among means with days 3-15 as replicates); other differences not significant.

The field trials did not indicate any adverse effects of neem oil (0.1%) and Beauveria bassiana on tenebrionid beetles. No dead animals, neither tenebrionids nor other arthropods, could be found on the permanent plots.

There was no difference in the activity of tenebrionid beetles (species group listed in small-scale field trials, above) between pre- and postspray periods (Table 5). As with the RA of the beetles in the cage trials, the activity of the tenebrionids in the field tests is phased sequentially (Fig. 4; maximum on days -3, 1, 5, 8/9). This phenomenon can be shown clearly by a correlation matrix. A period of 5 days between the peaks is evident (Fig. 5 & Table 6).

Table 5. Effect of the agents on the activity abundance (AA) in the field trials.

Mean AA (number tenebrionids/trap) on days -2 & -1 (P), 2 to 4 (A(1)), 6 to 8 (A(2)) and 9 to 11 (A(3)); all differences not significant. (Kruskal-Wallis-ANOVA); E = effect, SE = standard error.

Figure 4. Mean activity abundance (AA) of tenebrionids (number of beetles/trap).

Figure 5. Correlation of the AA of tenebrionids in treated and untreated plots (LAG - 0, 1, 2, . . ., 7 means, that the AA in plot a on day x is correlated with the AA in plot b on day x + 0, 1, 2, . . ., 7; for negative LAGs the same applies: x - 0, 1, 2, . . ., 7); correlation coefficient > 0.6 or < -0.6 are significant at P < 0.05.

Table 6. Correlation matrix (Pearson's r) of activity abundance (AA) (all days).

Correlation coefficient significant at: ** P < 0.01; *** P < 0.001.

The synchronous pattern of activity of the beetles is evident not only within the cage or the field trials, but also between these as illustrated in Fig. 6 and Table 7 (simultaneous testing period). Only during days 11-13 are the curves not synchronous (probably due to increased silting of the pitfall traps in the Schouwia thebaica fields).

Figure 6. Mean AA in the field trials (total catch/day & plot) and mean RA in the cage trials (all replicated and treatments pooled) on simultaneous days.

Table 7. Matrix (Pearson's r) between relative activity (RA) (cage trials) and activity abundance (AA) (field trials) on simultaneous days.

Correlation coefficient significant at: * P < 0.05; ** P < 0.01; *** P < 0.001.

The activity abundance of the tenebrionids in the control area (field tests) is higher on most days than in the treated plots (Table 8, Fig. 4).

Table 8. Mean activity abundance (AA) of tenebrionid beetles (retransformed data).

Control different from Neem (0.1 %) & B. bassiana (P < 0.05; Friedman-ANOVA & Wilcoxon & Wilcox multiple comparison among means, days 1-15 as replications); other differences not significant.

Both in the laboratory (constant 35°C test temperature) and in in situ topical application tests, Pimelia angulata tschadensis showed no B. bassiana infection (analysis by BBA, Darmstadt). Only in Trachyderma hispida could sporulation be detected (the beetles had died 4 to 8 days after treatment without showing any specific symptoms; also, under increased post-treatment humidity conditions the fungus did not break out within an 8-week observation period; only when beetles were kept in wet chambers did mycelia and spores develop).

It is remarkable that the oil-formulated spore suspension remained virulent for more than 10 days even under extremely arid conditions.

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