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Effect~ of Bli on invertebrales 273 Table 3. Bemhic invertebrales (no.lsample) collected in core samples (N = 10) during enclosure test 2, before and 48 h after an application of Vectobac-G'" al .he RAR (5.6 kg/ha) and 5 x RAR (28.1 kg/hal, Lillie Bass Pond, Minnesota Valley National Wildlife Refuge Mean" (and so) number of invertebrates per sample Pretreatmem b POSI-lTeatmem' Com ro) RARd 5 x RAR ConlTol RAR 5 x RAR 0.7 (0.9) 2.2 (3.8) 1.5 (2.3) 1.4 (2.5) 2.8 (5.2) 1.2 (2.1) 14.3 (18.8) 11.3 (20.0) 10.4 (15.4) 6.7 (10.9) 5.2 (7.5) 10.7(12.0) 46.1 (30.2) 57.3 (25.8) 51.4 (38.2) 29.9 (18.9) 31.8 (26.3) 21.2 (15.6) 3.0 (6.0) 100.0 (0.0) 100.0 (0.0) Invertebrate group Amphipoda Oligochaeta Chironomidae Aedes spp. (070 mortality)' "Means are not significantly differem (P > 0.05) from each other when subject to ANOVA. bApril23, 1990. "April 26, 1990. dRAR = recommended application rate. "Verification test 2 conducted to confirm pesticide application. Results shown as percentages of mortality after 48 h. ronomids in Refuge sediment compared to control sediment (Table 7). Mitigation tests. Efficacy of Vectobac-G at 6 ppm is de- pendent on temperature (Fig. 3). At 270C, mortality was sig- nificantly higher than at II or 190C, but mortality was similar at II and 190C. Results for water depth test I indicated that toxicity was lower in the deeper water treatments (Fig. 4). Because two different chambers were used for water depth test I (250-ml beakers and I,OOO-ml graduated cylinders), we were unable to determine whether depth affected mortality or if differ- ences were due to the test chambers (there was more glass sur- face area to which the Bli crystals could adhere in the cylinder). A modified test chamber was designed to contain both depths for water depth test 2. Again, the mortality of larvae from the shallow depths was significantly greater (Fig. 4). The effect of Vectobac-G was inversely related to water depth. At the RAR in depth test 3, the efficacy of Vectobac-G Table 4. Benthic invertebrates (no.lsample) collected (N = 10) during enclosure test 3. following application of Vectobac-G8. Little Bass Pond, Minnesota Valley National Wildlife Refuge. May 9, 1990 Mean (and SD) number of invertebrates per sample Invertebrate group Control RAR" 5 X RARb Amphipoda 0.5 (1.0) A < 0.4 (1.3) A 0.8 (0.9) A Oligochaeta 14.3 (10.1) B 13.4 (15.9) BC 7.7 (8.0) C Chironomidae 16.3 (I5.2) D 17.7 (12.2) D 19.4 (17.4) D Aedes spp. (070 mortality)d 0.0 (0.0) 97.0 (6.0) 100.0 (0.0) "Recommended application rate: 5.6 kg/ha. bFive times the recommended application rate: 28.1 kg/ha. <Means in a row followed by the same letter are not significantly dif- ferem (P> 0.05) from each other when subject to ANOVA. dVerification test 3 conducted to confirm pesticide application. Re- sults shown as percentages of mortality after 48 h. to lield-collected chironomid (Micropsectra {Tony tarsus] and Endochironomus spp.) larvae was not affected by water depth (Fig. 4). However, at 5 x RAR the efficacy of Vectobac-G to field-collected chironomid larvae was decreased by the water depth. These three tests, conducted under different conditions, indicated/hat efficacy of the pesticide to chiron- omids is lower in deeper water. Various percentages of macrophyte surface area coverage were tested in macrophyte test I to determine if coverage in- fluenced the efficacy of Vectobac-G. Toxicity of Vectobac- Gat 5.1 ppm on C. riparius was dependent on the amount of surface area covered by macrophytes (Fig. 5). In macro- phyte test 2, washings from the macrophytes used in mac- rophyte test I were used to determine if Bli crystals were clinging to plant material. The mortality caused by Vectobac-G residue on the plant material (from macrophyte test I) de- pended on the amount of surface area covered by macro- phytes (Fig. 5). The effect of Vectobac-G on C. riparius larvae was inde- Table 5. Benthic invertebrates (no.lsample) collected (N = 10) following applications of Vectobac-G~, enclosure test 4, Minnow Pond. Minnesota Valley National Wildlife Refuge, May 21. 1990 Mean" and (m) number of invertebrates per sample Invertebrate group Control RARb 5 X RAR< Gammarus spp. 76.2 (35.9) 95.0 (68.0) 73.6 (25.2) Oligochaeta 132.0 (41.6) 125.6 (37.2) 121.3 (48.1) Chironomidae 134.4 (93.0) 120.3 (65.5) 120.5 (122.2) Culisela spp. (070 mortality)d 0.0 (0.0) 97.0 (6.0) 100.0 (0.0) "Means are not significantly different (P> O.OS) from each other when subject to ANOVA. bRecommended application rate: 5.6 kg/ha. <Five times the recommended application rate: 28.1 kg/ha. dVerification test 4 conducted to confirm pesticide application. Re- sults shown as percentages of mortality after 48 h.