7967

• UCREFRP Catalog Number: 7967
• Author: Charbonneau, C. S., R. D. Drobney and C. F. Rabeni
• Title: Effects Of
• USFW Year: 1994
• Copyright Material: YES

EffcCI' of lJli on invcrlcbralcs

wet weight or about 251110 surface area coverage, 1.0 g wet
weight or about 501170 surface area coverage, and 1.5 g wel
weight or 1001170 surface area coverage. A control was set up
with 1001170 surface area coverage of plant material to deter-
mine if Vallisneria sp. was toxic 10 C. riparius. The test was
conducted in I-L beakers with sediment, 800 m( dilution
water, and Vectobac-G applied at the surface area RAR of
the beaker.
After macrophyte test I was completed, plant material
from each test chamber was placed in a separate plastic bag
with 250 ml dilution water. The bags were placed in a water
bath at 20 j; I oC for 48 h. This procedure was termed plant
washing. The 200 ml of plant washings were isolated from
the plants using a sieve (425 I'm), and the washings were
tested with chironomid larvae for macrophyte test 2.
One test was conducted to determine if water, of a type
normally found in wetlands, changed the efficacy of
Vectobac-G to chironomid larvae that had been tested in well
water. Pond water (l.llLg/L chlorophyll-a [Chi-a)) was col-
lected from a control pond on the National Fisheries Con-
taminant Research Center (NFCRC) property and used as a
test water. The test was conducted at I ppm Vectobac-G with
sediment. A control with pond water was included in each
test to determine if it was toxic to C. riparius.
The influence of feeding on the efficacy of Vectobac-G
was evaluated. A test was run using Hartz@ Dog Kiss food
to culture midge larvae [54). The food was added to the test
chambers 1 d before application of Vectobac-G and every
24 h thereafter. The food test was conducted with control
sediment with 0.5 ppm Vectobac-G.
The influence of organic matter in the sediment on the ef-
ficacy of Vectobac-G was evaluated. LBP sediment was air
dried and half was burned in a muffle furnace at 5500C for
1 h to remove the organic matter [55]. This material was
mixed with the dried sediment to produce test sediments with
organic matter concentrations of 2.7, 1.6, 1.3,0.9, and 0.31170.
The test concentration was 0.01 ppm Vectobac-G in the wa-
ter. A control was included for each sediment type.
Fourth instar and a mixture of second and third instars

271

were tested to determine the toxicity of Vectobac-G on
midges at differenl ages. The instar test included a range of
concentrations: control, 0.0001, 0.0005,0.001, and 0.01 ppm
of Vectobac-G in water-only exposures. All larvae were pre-
served in formalin at the end of the tesl (54]. Larval head cap-
sules were subsequently measured 10 determine the instar of
the larvae used in the toxicity tests.
The Pro bit method was used to calculate EC50s. When
fewer than two concentrations were affected (i.e., dead) be-
tween 0 and 1001170 mortality, the Probit method could not
be used to determine an LC50 (56]. In the range tests in which
this was the case, interpolation was used to determine an ap-
proximate EC50, and a binomial test was used to determine
951170 confidence limits. Lack of movement was the criterion
for death. (The terms mortality and death are used inter-
changeably with the term effect throughout the text.)
The G test of independence was used to determine if the
controlled interacting variables in the tests were contribut-
ing to the observed effects. The G test of independence is
used to test whether two different properties (controlled en-
vironmental variable and the effect of Vectobac-G), each oc-
curring in two states, are dependent on each other [57).

RESULTS

Field tests
Enclosure tests. The three periodic applications of
Vectobac-G in enclosure test I did not result in a reduction
of benthic invertebrates compared to controls (Table 2), and
the power (0.71) was sufficiently high to conclude that no ef-
fect was present (Fig. I). Hyalella azteca densities increased
during the sampling period. There was a reduction of the oli-
gochaetes and chironomids (Table 2), but this effect was due
to population changes over time (p = 0.0004) rather than to
treatments of Vectobac-G (p = 0.9305). Verification tests IA
and I B, conducted for the second and third applications of
Vectobac-G, documented that the pesticide was an effective
mosquito larvicide (Table 2).
Results from the emergence traps (Fig. 2) indicate a re-

Table 2. Benthic invertebrates (mean no.lsample, sos in parentheses, N = 10) collected during enclosure test I, following applications of
Vectobac-G@l on May 10, May 25, and June 22, 1989, Little Bass Pond, Minnesota Valley National Wildlife Refuge

Mean (and so) number of invertebrates per sample

Hyatel/a azteca Oligochaeta Chironomidae
Control RARb Control RAR Control RAR
4.9 (3.9) 7.2 (2.7) 61.9 (43.0) 65.7 (79.7) 15.1(11.2) 19.3 (17.6)
7.0 (4.5) 7.1 (5.5) 90.1 (57.0) 87.6 (94.6) 15.8 (9.7) 11.4(8.1)
5.1 (2.9) 6.8 (6.0) 59.9 (33.5) 43.8 (42.9) 9.0 (5.5) 6.8 (3.3)
5.8 (4.6) 8.2 (9.6) 46.1 (27.3) 42.2 (31.9) 4.5 (3.1) 2.1 (2.6)
Verification test IA
15.7 (1 L5) 13.7 (13.8) 49.0 (33.0) 38.1 (25.1) 3.7(3.1) 2.4 (1.6)
Verification test I B
20.3 (9.7) 21.8 (22.6) 90.1 (57.0) 87.6 (94.6) 1.6 (1.6) 1.1 (1.2)

Date

May 1
May 8
May 12
May 22
May 25
May 31
Jun 22
Jun 28

Culiseta"
(11/0 mortality)

Control

RAR

0(0)
4 (9)

100 (0)
100 (0)

"Percentage of mortality after 48 h in verification testS I A and I B conducted to verify pesticide application.
bRecommended application rate.