[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is to a great extent superseded by aniline dyes, but in regard to one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.