THE STATE ENTOMOLOGIST. 109 



ties it by no means follows that the mother beetle would deposit her 

 eggs upon the potato in a state of nature, and thereby compel her fu- 

 ture progeny to feed upon that plant. That she will do so upon her 

 natural food-plant, the horse-nettle, we know ; and, according to Mr. 

 Walter of Alabama, she will do so upon the egg-plant, which is thorny 

 like ihe horse-nettle. But apparently she is indisposed to go one step 

 further, and lay her eggs upon a smooth species of the same botanical 

 genus, namely the potato. 



Natural Remedies. — Persons not familiar with the economy of 

 insects are continually broaching the idea that, because the Colorado 

 Potato-beetle is in certain seasons comparatively quite scarce,therefore 

 it is about to disappear and trouble them no more. This is a very fal- 

 lacious mode of reasoning. There are many insects — for instance, the 

 notorious Army-worm of the north (Leucania unipuncta, Haworth) 

 — which only appear in noticeable numbers in particular years, 

 though there are enough of them left over from the crop of every 

 year to keep up the breed for the succeeding year. There are other 

 insects — for instance the Canker-worm {Anisopteryx vernata, Peck)— 

 which ordinarily occur in about the same numbers for a series of 

 years, and then, in a particular season and in a particular locality, 

 seem to be all at once swept from off the face of the earth. These 

 phenomena are due to several different causes, but principally to the 

 variation and irregularity in the action of cannibal and parasitic in- 

 sects. We are apt to forget that the system of Nature is a very com- 

 plicated one — parasite preying upon parasite, cannibal upon cannibal, 

 parasite upon cannibal, and cannibal upon parasite — till there are 

 often so many links in the chain that an occasional irregularity be- 

 comes almost inevitable. Every collector of insects knows, that 

 scarcely a single season elapses in which several insects, that are or- 

 dinarily quite rare, are not met within prodigious abundance; and 

 this remark applies, not only to the plant-feeding species, but also to 

 the cannibals and the parasites. Now, it must be quite evident that 

 if, in a particular season, the enemies of a particular plant-feeder are 

 unusually abundant the plant-feeder will be greatly diminished in 

 numbers, and will not be able to expand to its ordinary proportions 

 until the check that has hitherto controlled it is weakened in force. 

 The same rule will hold with the enemies that prey upon the plant- 

 feeders, and also with the ememies that prey upon those enemies, 

 and so on ad infinitum. The real wonder is, not that there 

 should be occasional irregularities in the numbers of particular spe- 

 cies of insects from year to year, but that upon the whole the scheme 

 of creation should be so admirably dove-tailed and fitted together, 

 that tens of thousands of distinct species of animals and plants are 

 able permanently to hold their ground, year after j r ear, upon a tract 

 of land no larger than an ordinary State. 



To illustrate the decrease in its numbers which took place in the 

 State of Iowa from 1867-8, 1 will state that Mr. ^nry Tilden, of Da- 



