go to previous section of this publication

In the cage trials the oral and residual effects of the following agents were tested:

1. neem oil (0.075% = 0.l% AZA (azadiractin) (Inst. f. Phytopathologie, Giessen/FRG))
2. neem oil (0.22% -: 0.2% AZA (IITA, Benin))
3. Beauveria bassiana (oil-formulated suspension (Mycotech, USA)) 4. dieldrin (Shell-Agro).

Neem oil (0.l%) and B. bassiana were applied in the field trials. Spraying was conducted between 06.00 and 10.00 h (windspeed < 2 m/ sec, temperature = 25°C) with a Micro-Ulva-spinning disc sprayer (dieldrin: ULV, other agents LV application) (see Table 1).

Table 1. Application parameters.

NB = number of batteries/sprayer; sp = spores; (*) = a constant flow of the suspension could only be achieved when widening the nozzle diameter and shaking the sprayer continuously during application; AZA = azadiractin.

In the Schouwia thebaica field 20 suitable 2 m quadrats with at least 15% vegetation cover were selected (minimum buffer zone between the plots = 15 m). After treatment (four replicates per insecticide, randomized cage order) the cages (steel frame, galvanized iron netting, 2 x 2 x 2 m size; cage design see Krall & Nasseh, 1990) were dug into the ground 20-30 cm deep. All arthropods in the cages were removed. Subsequently, each cage was stocked with 30 P. angulata tschadensis. Over a period of 16 days the following parameters were recorded:

1. mortality (M) (twice daily at 07.00 and 18.00 h.)
2. relative activity (RA) (i.e. percentage of beetles captured in one pitfall trap per cage; the traps were covered with a lid during the day and opened for one hour starting at 18.30 h).

At the end of the trial all remaining beetles were collected to assess potential losses by cannibalism or escape.

The calculations of mortality and activity correspond to the sum (S) of dead (D) or alive (A) test beetles collected until the end of the trial. The cumulative mortality on day i is calculated as:

(Di = number of dead animals collected up to day i).

The effects of the agents were calculated according to Schneider-Orelli (Krall & Nasseh, 1990). The relative activity on day i is calculated as:

(Gi= number of animals collected on day i).

Prior to statistical treatment all data were arc-sine transformed. In particular the following statistical calculations were performed:

1. mortality at the end of the trial (day 16): single classification ANOVA and Newman-Keuls-multiple comparison among means
2. RA of all days: cross correlation; days 3-15: Friedman-ANOVA and Wilcoxon-Wilcox-multiple comparison among means.

In each Schouwia thebaica field 4 permanent 1 m² plots were randomly established to survey potential mortalities of non-target organisms. To study effects on the activity abundance AA (= 'Aktivitätsdichte' sensu Heydemann (1953), 'availability' sensu Southwood (1978)) of ground-dwelling arthropods, four pitfall traps were placed in each test plot (conservation fluid: 5% formol) for a period of 15 days (3 days pre- and 11 days post-spray interval).

Mortality (M) was recorded daily between 07.30 and 08.30 h, 17.30 and 18.30 h in the permanent plots, and pitfall traps were emptied daily between 17.30 and 18.30 h.

At present only effects on the abundant tenebrionid species, Pimelia angulata tschadensis, P. subquadrata chudeaui, Trachyderma hispida, Blaps bifurcata mirei, and Prionotheca coronata coronata, can be given.

All data were transformed as : A_T = 10 x (In AA + 1) [A_T = AA transformed]. The mean catches of days 2 and 1 (pre-spray) were compared to the catches of days 2-4, 6-7 and 9-11 (post-spray) (Kruskal-Wallis). The effect of the agents is calculated as

D_T = mean difference between pre- and post-spray catches in the treated plot
D_C = mean difference between pre- and post-spray catches in the control plot

For the calculation of standard error see Everts et al. (1985).

To study the contact effects of B. bassiana on several tenebrionid beetles field tests and bioassays were conducted:

1. LV-application in an arena: 1 ml spore suspension/m² (as specified in Table 1) applied with a Micro-Ulva
2. topical application in the laboratory: approximately 1 µl suspension applied dorsally between thorax and abdomen by micro caps.

The test animals were analysed by the BBA Darmstadt-Germany for infection by B. bassiana.

go to next section of this publication