On the Ravages of the Turnip Fly.

XIX. On the Ravages of the Turnip Fly (Halt' xa nemo- rum), with Experiments. By T. S.*

[Read 1st February, 1836.1

THE most abundant species of beetle which feed upon the turnip are those noticed in the present paper, but there are at least two other, probably more, kinds which also devour thin vegetable, (Haltica sirnilis and Haltica fEava), though not by any means so common.

Of the two species, some of whose habits are now to he de- tailed, both appear to be equally abundant in this district : they are both equally active, disappearing upon the slightest sound or motion, retreating either under the surface of the leaves upon which they are feeding, or vaulting to a considerable distance from them, returning again in a few minutes, if the sound or motion be not con- tinued. The parent insects pair in July, if not in the earlier months. They are to be seen in the earliest fine days of February, (one spe- cies at least, H. nernorzim), and do not disappear before the end of October, if the weather be warm : but they do not appear to feed much after the latter end of September. They seem capable of enduring long abstinence, as three specimens of H. oleracea were shut up in a box on the 24ath of September, and, being forgotten, were not seen again for five weeks, when they were found alive and active; so that probably an idea entertained by some agri- culturists of starving them, would be found difficult to act upon. I have never been able to find any under the bark of trees in the winter. They feed chiefly by night, when they may be found in great numbers on the surface of the young plants, sixty having been counted on a row of plants, just out of the ground, eighteen inches long, and one inch broad. In the day-time they retire, for the most part under the cotyledons, or young leaves, of the plants.

In order to ascertain whether the eggs were deposited upon the seed, as suggested by Rusticus, in the " Entomological Ma- gazine," I tried the following experiments, similar, indeed, to his own.

* The writer hereof has communicated his name to the Councilof theEntomo- logical Society.

On the Ravages of the Turnip Fly. 109

1834,. EXPERIMENT 1. July 12th. Some light sandy loam, richly manured, was exposed

to a light temperature, and, when cold, placed in flower pots, previously boiled in water. Seeds of the following varieties of turnip :

No. 1. Red Pudding, 2. White Tankard, 3. Yellow Scotch, 4. Short-topped Swede, 5. Green Round, 6. Early Round, 7. Early Stone,

were then selected, and sown in separate pots, the pots covered with gauze, and placed in a green- house.

EXPERIMENT 2. Seeds of No. 2 were sown in the same kind of soil,

as in Exp. 1, but not baked, and the pots were plunged, unprotected, in the open ground.

EXPERIMENT 3. Seeds of Nos. 1 and 6 were sown in the same kind of

soil, baked, and plunged, uncovered, in the open ground.

EXPERIMENT 4. Seeds of Nos. 3 and 9 were sown in unbaked soil, and

the pots placed in the greenhouse : seeds of No. 7 in baked, and No. 5 in mixed, earth, were also placed in the greenhouse : all the pots unprotected, and not prepared by boiling in the three last experiments.

-15th. Seeds coming up in most of the pots.

EXPERIMENT 5. All the varieties of seed sown in rows, eighteen inches

long, in unmanured soil, in the open air. -20th. Specimens of Haltica nemorum found upon Nos. 2, 1,

and 6, in Expts. 2 and 3. -22d. One beetle (H. oleracea) found upon a plant of No. 6,

(Exp. l), pot protected. Seeds of Exp. 5 coming up.

-24th. Green beetles (H. oleracea), and striped beetles (H.

110 On the Ravages of the Turnip Fly.

nemorzim), found upon all these last plants, but in greatest abundance at night.

1834. EXPERIMENT 6 . July 24th. Placed some of the beetles, found upon the plants of

Exp. 5, under glasses upon plants, growing in small phials, in common soil.

July 25th. Plants of Nos. 3, 4, 5, and 7, of Exp. 4, unprotected, not touched at present, No other beetle seen upon the plants of No. 6, in Exp. 1, the solitary speci- men having been removed when first seen.

None eaten, and no appearance of beetles.

Thinned, also, the unprotected plants (Expts. 2 and 3) in the open ground : many eaten.

Aug. 7th. Thinned the plants of Exp. I a second time: none eaten, Thinned, also, the plants of Expts. 2 and 3 : many eaten. Nos. 3, 4, 5, and 7, (Exp. 4), not touched : no fly visible.

- 8th. Plants of Exp. 5 thinned, and transplanted ; numbers of beetles upon them, and much eaten : sixty were found upon one row.

Sept. 24th. Some beetles ( H . olevacea) found feeding upon turnips: three enclosed in a box. A very large beetle of this kind found.

-- 25th. Haltica nemovum seen. Turnip plants very little eaten after this time.

Oct. 31st. A specimen of H. nevnorum seen.

Mar. 28th. Repeated Exp. 5 . April 7th. Seeds of Nos. 4, 5 , 6, and 7, coming up. - 9th. Beetles of H. nemorum, and H. oleraceu, feeding upon

the young plants. - 10th. Seeds of Nos. 1 and 3 coming up, -20th. Many beetles feeding. Sowed mustard, cabbage, and

--22d. Sowed fresh seeds of all the varieties of turnip enu- Many beetles feeding on the first

-28th. Beetles found upon all the young plants of turnip,

-28th. Thinned the plants of Exp. 1.

1835.

radish seed.

merated above. sown plants.

cabbage, radish, and mustard.

These insects may be found upon the first sown plants of mus-

On the Ravages of the Turnip Fly. 111

tard and radishes in the earlier months of spring, the leaves of which are constantly perforated by them in almost every garden. From their extreme activity, it seems almost impossible to apply any destructive agent to them, but probably sulphur, in a dry hot season, scattered over the plants early in the morning of a clear day, would destroy them, as a t a temperature of from 75 to 85 it would undergo slow combustion, and 'form sulphurous acid gas, which is very deleterious to almost all kinds of insects. Lime, if applied very late in the evening, or very early in the morning, before the dew was 0% might have some effect upon them. They seem to be equally abundant in wet as in dry weather ; but, in the former case, the growth of the turnip is greater than the con- sumption by the fly, and the insects are probably not quite so active. Watering the plants, therefore, would appear to be the easiest remedy under some circumstances.

The specimens confined under glasses appeared to be injured by the damp arising from the soil in which the plants grew, and most of them escaped upon replacing the plants for their food; after some weeks' confinement, some of both species (confined each separately) paired under confinement, but the bottles unfor- tunately, containing the earth in which eggs might have been deposited, were lost.

The foregoing experiments appear to me to prove the conclu- sions of Rusticus to be erroneous so far as the deposition of the egg is concerned, and to render it evident that the beetles are to be found in the immediate vicinity, ready to devour the plants a s soon as they make their appearance. If I mistake not, the young plants of hedge-mustard (Erysimum alliaria) are frequently per- forated by these insects, and probably charlock (Xinapis arvensis), and other wild plants, supply them with their earliest food.

SAFFRON WALDEN.