This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
[Footnote: A paper recently read before the California Academy of Sciences.]
By DR. H. BEHR.
With the exception of Hymenoptera there is no group of insects that interfere in so many ways in good and evil with our own interests, as that group of Homoptera called Coccidæ.
But while the Hymenoptera command our respect by an intellect that approaches the human, the Coccus tribe possesses only the lowest kind of instinct, and its females even pass the greater part of their lives in a mere vegetation state, without the power of locomotion or perception, like a plant, exhibiting only organs of assimilation and reproduction.
But strange to say, these two groups, otherwise so very dissimilar, exhibit again a resemblance in their product. Both produce honey and wax.
It is true, the honey of this tribe is almost exclusively used by the ants. But I have tasted the honey-like secretion of an Australian lecanium living; on the leaves of Eucalyptus dumosus; and the manna mentioned in Scripture is considered the secretion of Coccus manniparus (Ehrenberg) that feeds on a tamarix, and whose product is still used by the native tribes round Mount Sinai.
Several species of Coccides are used for the production of wax; many more, among which the Cochenill, for dyes.
All these substances can be obtained in other ways, even the Cochenill is to a great extent superseded by aniline dyes, but in regard to one production, indispensable to a great extent, we are entirely dependent on some insects of this family; it is the Shellac, lately also found in the desert regions around the Gila and Colorado on the Larrea Mexicana. You will remember that excellent treatise on this variety of Shellac, written by Professor J.M. Stillman at Berkeley, on its chemical peculiarities.
But all these different forms of utility fall very lightly in weight, and can not even be counted as an extenuating circumstance, when we compare them to the enormous evils brought on farmer and gardener by the hosts of those Coccides that visit plantations, hothouses, and orchards.
To combat successfully against these insect-pests we have first to study their habits and then adapt to them our remedies, which you will see are more effective when well administered than those which we possess against insect pests of other classes.
I give here only the outlines of their natural history, peculiarities that are common to all, for it would be impossible to go into detail. Where there are exceptions of practical importance I will mention them.
In countries with a well defined winter the winged males appear as soon as white frosts are no more usual, and copulate with the unwieldy limbless female, that looks more like a gall or morbid excrescence, than a living animal. Shortly after the young ones are perceptible near the withered body of their mother, covered by waxy secretions that look somewhat like a feathery down.
These young ones are lively enough, they move about with agility, and it is not till high summer that they fasten themselves permanently, and lose feet and antennae, organs of locomotion and perception that are no more of any use to them. (There is a slight difference in this regard between different genera, as for instance, Coccus and Dorthesia retain these organs in different degrees of imperfection, Lecanium and Aspidiotus losing every trace of them.)
In this limbless, senseless state the females remain fall and winter. Toward the end of winter these animated galls begin to swell, and those containing males enter the state of the chrysalis, from which the males emerge at the beginning of the warm season and fecundate the gall-like females, which undergo neither chrysalis state nor any other change, but die, or we may call it dissolve into their offspring, for there scarcely remains anything of them, except a pruinous kind of down, after having given birth to the young ones.
Now we come to the practical deduction from these facts. It is clear that the only time when the scalebug can emigrate and infest a new tree is the time when it is a larva, that is, when it has the power of locomotion. In countries with a pronounced winter this time begins much later than with us, but it ends about the same time, that is, the beginning of August. I have seen the male of Aspidiotus in February, so that the active larva may be expected in March, and the active Lecanium Hesperidum I have seen last year, June 27, at Colonel Hooper's ranch in Sonoma County. We may safely fix the time of the active scalebug from March to August.
Notwithstanding the agility of the young scalebug, the voyage from one tree to another, considering the minute size of the traveler, is an undertaking but seldom succeeding, but one female bug, if we take into account its enormous fertility, is sufficient to cover with its grandchildren next year a tree of moderate size.
Besides there is another and much more effective way of transmigration by the kind assistance of the ant who colonizes the scalebug as well for its wax as it colonizes the Aphis for its honey. Birds on their feathers and the gardener himself on his dress contribute to spread them.
But even the ant can not transplant the scalebug when it is once firmly fixed by its rostrum.
It is evident, therefore, that the time for the application of insecticides is the time when all the scalebugs are fixed, that is about the end of July or beginning of August. All previous application will clean the tree or plant only for a time, and does not prevent a more or less numerous immigration from the neighboring vegetation, especially if an ant-hill is not far off.
As to the insecticide, there are to be applied two very effective ones, each with its advantages and disadvantages.
2. Lye or soap.
The petroleum is the best disinfectant. It can safely be applied to any cutting or stem, as long as it is not planted, but is one of the most invidious substances when applied to vegetation in the garden, or fields. If effectively applied, it can not be prevented from running down the bark of the tree and entering the ground, where every drop binds a certain amount of earth to an insoluble substance, in which state it remains for ever. With every application the quantity of these insoluble compounds is augmented and sterility added.
If I am not mistaken, it was near Antwerp--at least I am certain it was in Belgium--where the first experience of this kind is recorded.
In France, preparations of coal tar have been recommended and have been lately used in the form of a paint. May be that in this form the substance is not so apt to enter into combinations with the soil. At any rate, the method is of too recent a date to permit any conclusions about the final result of these applications, as the invidious nature of the substance produces, by gradual accumulation, its effects, which are not perceived until they are irreparable.
2. Lye or soap. The application of these insecticides requires more care, and is therefore more troublesome. But instead of attracting fertility from the soil, they add to it. In Southern Europe soap and water has been for many years the remedy against the Lecanium Hesperidum. The method applied by the farmers in Portugal, as described to me by Dr. Bleasdale, is perhaps the most perfect one. The Portuguese have very well observed that the colonization of scalebugs always begins at the lowest end of the trunk and pretend, therefore, that the scalebug comes out of the ground. This, of course, is not the case, but may their interpretation be an error, they have been practical enough in utilizing their observation about the invasion beginning near the roots. They knead a ring of clay round the tree, in which ring the soap water runs when they wash the tree, and besides, they fill frequently the little ditch formed by this ring.
This arrangement of course is only possible in climates of a rainy summer.
As it is our object to make our knowledge as available as possible for practical purposes, I repeat for the benefit of cultivators the advice, without repeating the reasoning:
1. Use the petroleum for disinfecting imported trees and cuttings:
2. Use soap for cleaning trees planted in your orchard.
3. If you must use the petroleum in your garden, use it in August, when a single application is sufficient.