Markers for toxic grease formulations


Experiments are underway to find an adequate marking agent to use in
evaluating the delivery of acute toxicants to rats via grease formula-
tions. These markers are needed to gain information on the percentage
of rats that come in contact with toxic grease under field conditions.
Preliminary tests have been conducted in the laboratory with three
markers: rhodamine B, tetracycline, and calcuflour. Each was pre-
pared at a concentration of 10 percent in a multipurpose ultra-lube
grease. About 500 mg of each was applied to the mid-line abdominal
surface of each of three individually caged ricefield rats (R. r.
mindanensis). Rhodamine B was the better marker under these condi-
tions. Seven days after application it could still be readily seen on
the tail, feet, lips, and abdominal fur without the aid of fluorescent
light. Additional laboratory tests with closed rat colonies are
planned and, if these are successful, a rhodamine B-grease formulation
will be field tested.

Evaluation of adhesives for foliar application of methiocarb

The avian repellent methiocarb (4-methylthio-3,5,-xylyl N-methylcarba-
mate) has shown promise in field and laboratory tests as a potential
agent for reducing quelea (Quelea quelea) damage to African grain
crops. The efficacy and economic benefits associated with the use of
methiocarb or other chemical repellents could be enhanced if the
effective duration of the applications could be prolonged. This is
especially true where treated crops may be exposed to rainfall. The
incorporation of foliar adhesives may prolong the duration of repel-
lent applications. Hence, this study was designed to evaluate differ-
ent adhesives for such use. The first phase of the study involved
treatment of sorghum with different concentrations of methiocarb and
different adhesives. These were subsequently exposed to different
levels of simulated rainfall (see 1977 report). We had hoped to com-
plete residue analyses and bioassay tests in time for inclusion in
this report. However, results of the chemical tests, to date, have
been inconsistent. We suspect that the problem is associated with
the simulated rain system. For this reason, the initial phase of the
study will be repeated with a different system of simulated rainfall.

A related study was designed to better our understanding of the
relationship between the bird repellent methiocarb and selected
adhesives. An R50 value for the adhesive Rhoplex AC-33 was determined
for red-winged blackbirds. Using a level of 0.1 percent methiocarb
with varying levels of adhesive, the R50 level was 0.00999 percent,
with confidence levels of 0.00096 percent to 0.10361 percent. Next,
the R50 value for the adhesive was used to determine the R50 value for
methiocarb. The resultant R50 value was 0.094 percent, with