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

276

100
90
.~80
~ 70
~ 60
- 50
c:
~ 40
G:i 30
a..
20
10
o

. .

C.S. CHARBONNEAU ET Al.

m Vectobac-G (5.1 ppm)
E:I Plant Washings

o 25 50 100
Percent surface area covered by macrophytes

Fig. 5. Efficacy of Vectobac-G4> to Chironomus riparius related to
water surface area covered by macrophytes (Vallisneria sp.). Test I
was conducted with sediment and Vectobac-G, and test 2 without
sediment with plant washings from the different surface area cover-
ages used in test I (N = 3, 10 larvae per replicate, 5.1 ppm
Vectobac-G).

or in the mats and is therefore unavailable to the larvae liv-
ing below them.
Our findings demonstrate that second- and third-instar
larvae of C. r;par;us were more susceptible to Yectobac-G
than fourth-instar larvae. These findings are consistent with
those of previous studies for both mosquitoes [25,29,31) and
other chironomid species [17,19]. Waldbauer [63] reported
approximate digestibility declines with age, as does the effi-
ciency of conversion of ingested food to body substance. Be-
cause the activity of the Bt; crystal is dependent on the action

100
90

!2 80
m 70
1:
~ 60
C 50
~ 40
CD
a.. 30
20
10
o

~ Control
II Yectobac.G (1 pprn)

Dilution Pond
Water Source

Fig. 6. Water source related to toxicity of Vectobac-G@ (1 ppm) to
Chironomus riparius with sediment (N = 3, 10 larvae per replicate).
G tests indicate no significant relationship between monality and the
source of water.

o Control
iii Vectobac-G (0.5 ppm)

100
90
80
-~ 70
m
1: 60
0
~ 50
C
CD 40
~
CD 30
a..
20
10
0

o 0.025
NFCRC Culture Food (mg)

Fig. 7. Additional food source related to toxicity of Vectobac-G@
(0.5 ppm) to Chironomus riparius (N = 3, 10 larvae per replicate).
G tests indicate no significant relationship between monality and the
addition of food to the test chambers. NFCRC = National Fisheries
Contaminant Research Center.

of proteolytic enzymes within the gut (64) and its digestibil-
ity declines with age, the older instars of chironomids may
be less susceptible to the crystal toxin.
Water from the wetland, higher in organic matter, did not
change the efficacy of Yectobac-G to chironomid larvae. This
result is inconsistent with findings of other studies in which
efficacy of Bt; was reduced in pond water [65], polluted wa-
ter [66], and water containing suspended organic material
(29) in contrast with clear dilution waters.
The NFCRC food tests determined that an additional

100
90
80
.~ 70
~
(; 60
::E
50

12 Control
II Vectobac-G (O.1 ppm)

,c
~ 40
G:i
a.. 30
20
10
o

0.3 0.9 1.3 1.6 2.7

Percent Organic Maller

Fig. 8. Organic matter related to toxicity of Vectobac-G@ to Chi- .
ronomus riparius. Five different percentages of organic matter in the
sediment were tested (N = 3, 10 larvae per replicate). G test indicates
no significant relationship between mortality and the amount of or-
ganic matter in the sediment.