Caloric reserves in natural populations of a blackfly, Simulium decorum (Diptera: Simuliidae), and a deerfly, Chrysops ater (Diptera: Tabanidae)

Simulium decorum and Chrysops ater immatures were collected in northern New Hampshire during 1982 and were reared to adults in the laboratory to describe follicular development, to quantify total available caloric reserves, and to determine longevity. Females of both species produced eggs without blood meals and sucrose solutions during the first ovarian cycle. Differences in mean fecundity (mean range, 152–215) were noted for the Chrysops obtained at three sites below a trout-rearing pond. A chemical test consisting of a sulfuric acid solution of sodium bichromate was used to quantify caloric reserves in the newly emerged blackflies and deerflies. Available reserves for S. decorum females, ≤4 h or 24 h after eclosion, were about sevenfold greater than those of the males. There were no significant differences in available reserves for adult deerflies. Although males and females of both species utilized stored reserves for survival during early adulthood, sugars greatly enhanced longevity.

CHEMICAL WEED KILLERS: I. RELATIVE TOXICITY OF VARIOUS CHEMICALS TO FOUR ANNUAL WEEDS

Toxicity tests on four annual weeds, Thlaspi arvense L.; Brassica arvensis L. Ktze.; Chenopodium album L.; and Avena fatua L.; showed no definite evidence of a specific susceptibility of a given species to a given substance. The relative resistance of these four weeds to most substances, judging from the certainly lethal dose, was in the order 1:1:2:7. Of the 76 chemicals tested, the following most toxic compounds killed all four species at the dosages employed; selenic and chloric acids, sodium hydroxide, arsenic pentoxide, sodium arsenite, sodium and ammonium chlorate, ammonium thiocyanate, sodium cyanide, zinc chloride, sodium bichromate, sodium selenite, copper nitrate, sodium sulphide, formic acid, gasoline, phenol, creosote, tetralin, sodium benzoate, aniline, benzene and furfural. The residual toxic effect on the soil, three to four weeks after treatment, showed that of the 35 more toxic chemicals tested, only selenic acid and the five chlorates used had any appreciable effect at low and intermediate dosages, while eleven other substances depressed growth following the application of high dosages.

The determination of organic carbon in soils

(1) It is proposed to estimate the amount of organic carbon in soils by determining the amount of sulphur dioxide produced in the ordinary Kjeldahl digestion. The gaseous products of reaction are passed through standard iodine solution, and the excess iodine titrated with standard sodium thiosulphate. Details of the method are given.(2) The results obtained with a number of soils of differing character and origin are compared with the figures obtained for organic carbon by dry combustion. The sulphur dioxide method gives results which average 89.6 ±1.03 per cent, of the combustion figures. It is proposed therefore that the percentage of organic carbon found by this method should be corrected by the factor 100/89.6 = 1.116.(3) The percentage recovery of carbon indicated by the proposed method is rather higher for pure substances but still falls short of 100 per cent.(4) The proposed method is applicable to carbonate soils without the necessity for any correction for inorganic carbon.(5) It is likely that soils containing inorganic reducing substances such, as sulphides will give high results by the proposed method.(6) Absorbing the sulphur dioxide in 25 per cent, sodium bichromate, it is possible to determine the carbon dioxide by passing the gases through standard baryta in a Reiset tower. The organic carbon thus indicated agrees with that by the sulphur dioxide method.(7) From data with certain peats, it appears that the factor 1.724 for converting organic carbon to organic matter is too low.