. Circular. Insect pests; Insect pests. theless, when confined in the warm season of tlie year to a small re- ceptacle, not at all tenacious of life. It results from this fact, for example, that it is almost impossible to ascertain the leniith of the life of the house fly in the adult condition. These breeding experi- ments in confinement showed that the house fly will lay its eggs freely on fresh horse manure in an undisturbed condition. When the ma- nure is spread out the flies will not lay their eggs on it. They can very rarely be induced to lay their eggs upon anything but horse manure and
. Circular. Insect pests; Insect pests. theless, when confined in the warm season of tlie year to a small re- ceptacle, not at all tenacious of life. It results from this fact, for example, that it is almost impossible to ascertain the leniith of the life of the house fly in the adult condition. These breeding experi- ments in confinement showed that the house fly will lay its eggs freely on fresh horse manure in an undisturbed condition. When the ma- nure is spread out the flies will not lay their eggs on it. They can very rarely be induced to lay their eggs upon anything but horse manure and cow manure, and their preference for the former is very marked. Although eggs were laid upon cow manure, the larvse were unable to mature in this substance. The experiments, in fact, indicated that horse manure is by far the most favored breeding place of this species. Continuous observations in- dicated that the larva> molt twice, and that there are thus three distinct larval stages. The periods of development were found to be about as fol- lows: Egg from deposition to hatching, one-third of a day; hatching of larva to first molt, one day; first to second molt, one day; second molt to pupa- FlG. 4.—The green bottle fly (LitclUa cn'sar): a, i- fU«p„ /^Lia-g- i^iii->.ifimi i.^ adult? 6, head from front; c, antenna—all enlarged tlOn, inrec (la^S, pupaiion lO (from Ann. Kept. U. S. Dept. Agrie., 1890). issuing of the adult, five daVS : total life round, approximately ten days. There is thus abundance of time for the development of twelve or thirteen generations in the climate of Washington every summer. The number of eggs laid by an individual fly is undoubtedly large, averaging about li20, and the enormous numbers in which the insects occur is thus plainly accounted for, especially when we consider the abundance and universal occurrence of appropriate larval food. In order to ascertain the numbers in wdiich house fly larva^ occur in horse manure piles, a quarter of
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