Cyril E. Abbott.
The Toxicity of Trimethylamine for Necrophorus orbicollis (Say).
Psyche 43:37-39, 1936.

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19361 Toxicity of Trimethylamine for Necrophorus 37 THE TOXICITY OF TRIMETHYLAMINE FOR
NECROPHORUS ORBICOLLIS (SAY).
Morgan Park, 111.
As a natural decomposition product of flesh, trimethyl- amine [N (CH3) J, is found, in varying concentrationsl, in those animal remains to which various necrophilous beetles are attracted. It is of some interest to know, then, how well a species such as Necrophorus orbicollis can withstand the toxic effects of this chemical.
For testing the resistance of the beetle to various concen- trations of the substance a glass jar with a hollow, ground- glass stopper was used. The jar had a capacity of 125 cc. ; the hollow in the stopper 5 cc. The stopper was stuffed tightly with cotton, which was then soaked with all the solu- tion it would contain without dripping. The jar was cleaned with hot water, the stopper replaced, and the whole allowed to stand for 1 minute before the specimen was introduced. The beetle was thus exposed to the chemical in its gaseous form.
The insects used were active adults, and, although but one specimen was used at a time, each experiment was repeated with two additional beetles, so that an average could be determined ; this was necessary because individuals varied in size. The data on any specimen showing an unusu- ally long or short period, as compared with the other two specimens, was discarded; the average then being taken from the two remaining.
It is somewhat difficult to determine the exact death- point for the Necrophori. Preliminary experiments indi- cated that although parts of the body may move for hours, beetles in which not more than one tarsus twitched spas- modically never recovered after removal from the jar; this was considered the "death-point," and the time elapsing



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38 Psyche [June-Sept.
between the introduction of the insect into the jar and this point constituted the time necessary to produce death. The stock solution of trimethylamine had a concentration of 33 %. It is doubtful if a greater concentration than this ever occurs in nature. Dilutions of the stock solution with water were used for the remaining tests. By making a few progressive records of the action of the chemical on the beetles, paralysis was found to occur in the following order :
1. Paralysis of posterior legs.
2. Paralysis of middle legs.
3. Paralysis of anterior legs.
(This followed so closely
upon that of the middle legs' that in concentrated atmos- pheres the time interval could not be determined.) 4. Paralysis of antennae.
5. Paralysis of mouth-parts (practically all at once). 6. Spasmodic twitching of tarsi and tip of abdomen. 7. Slow movements of leg's and head.
8. Movement of abdomen only.
(May continue for many
hours.)
9. All movement ceases.
The time durations necessary to bring about death at various concentrations of trimethylamine were as follows: 33 % - 5 minutes 10% - 22 minutes
25% - 7 minutes 5 % - 40 minutes
20% - 10 minutes. 1% - 70 minutes
T/Må IN M/NUTES
1.
Toxicity of trimethylamine for Necrophorus orbicollis.



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19361 Toxicity of Trimethylmine for Necrophorus 39 The graph (Fig. 1) indicates a little more clearly the relation between toxicity and the various concentrations of the chemical. It appears that at high concentrations death occurs very rapidly, but that as the concentration decreases the toxicity 'becomes less. Moreover, the toxicity decreases, not in direct proportion to the concentration, but in a kind of geometric proportion. At very low concentrations (1 % ) the beetles can withstand the fumes for a long time. The objection may be raised that the data here given do not represent the toxicity of given concentrations of sub- stance, but the time required for the substance to reach a toxic concentration in an inclosed space. But this is chiefly an academic objection. If seventy minutes are required for a 1 % slolution of trimethylamine to fill 125 cc. of space with enough gas to kill a beetle, the result is practically the same as if a low concentration, held constant, brought about the same result. The effect is the same in either case. There is some indication that, in low concentrations, tri- methylamine actually attracts Necrophori. Several speci-
mens kept in an experimental cage, were trapped twice as frequently with this as with pure water. Beetles also tore a piece of cotton soaked with the chemical and left in their cage.
Dead bodies lying in the open must be comparatively free from high concentrations of so volatile a substance as tri- methylamine. In a confined space the situation is different. It is the custom of collectors to trap necrophilous beetles in jars sunk in the earth and containing scrap meat. In such jars Necrophori, as well as other beetles, are often found dead, even when the decaying flesh is not sufficiently liqui- fied to produce drowning. Such jars have a strong odor of ammonia, which doubtless, in many cases, is due to the pres- ence of trimethylamine.




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