SCIENCE AND INDUSTRY. 
insects in the future. The biological method of fighting insects has 
been fully developed. This, broadly speak‘ng, embraces the use of all 
natural organic checks—bacterial and fungous diseases, as well as 
parasitic and predaceous insects. Although fungous and_ bacterial 
diseases have been used to a slight extent, most of the work has been 
* done with the entomophagous insects. These, according to their mode 
of attack, have been divided into predatory and parasitic (or endo- 
phagous). The former devour other insects or their eggs or larve. 
The parasitic insect enters the body, egg, larva, or pupa of its victim, 
and destroys it, or may remain for part or all of its existence on the 
surface. Parasitism is a condit‘on which exists widely throughout the 
animal kingdom. Hunger and the quest for shelter have probably 
led to the habit of existing as unbidden guests. One insect, the para- 
site, lives in or on another—the host—securing the necessities of life - 
from the host, which gives up part or all of its vital forces to the 
_ parasite. Very few species of insects are exempt from this unwilling 
entertainment of parasites.. It often happens that the parasites them- 
(a) (b) ; (c) 
Hippodamia convergens, a ladybug which devours the “ green bug?’ a, adult ; 
: 6, larva; c, cluster of eggs. (After Hunter.) 
selves are infested with other parasites, which we call secondary, which 
reduce very appreciably the effectiveness of the first or primary parasite. 
The secondary parasites, also termed hyperparasites, may be also 
parasitized. In the control of injurious insects, then, primary and 
tertiary parasites are beneficial, while secondary are harmful. Among 
insects are to be found all variations of parasitism. The external 
parasite, such as the sheep tick or the bird louse, spends the whole of 
its existence upon the host. In the case of a Chalcid, such as Nasonia — 
brevicornis, a parasite of the blowfly larva, the eges are laid within 
the larva, where the chalcid will dwell until it emerges as a fully 
developed winged insect—it is an internal parasite for part of its 
existence. There are many advantages gained by the parasite, such as 
abundant food, safety, and warmth; but there may be certain disadvan- 
tages. The parasite tends to degenerate through the disuse of organs 
(disuse atrophy). The sheep tick was once a winged fly, but has 
i’ 
