Pheromones are substances that serve as chemical signals between members of the same sp

Pheromones are substances that serve as chemical signals between members of the

same species. They are secreted to the outside of the body and cause other individuals

of the species to have specific reactions. Pheromones, which are sometimes called

line "social hormones," affect a group of individuals somewhat like hormones do an individual

(5) animal. Pheromones are the predominant medium of communication among insects

(but rarely the sole method). Some species have simple pheromone systems and produce

only a few pheromones, but others produce many with various functions. Pheromone

systems are the most complex in some of the so-called social insects, insects that live

in organized groups.

(10) Chemical communication differs from that by sight or sound in several ways.

Transmission is relatively slow (the chemical signals are usually airborne), but the

signal can be persistent, depending upon the volatility of the chemical, and is sometimes

effective over a very long range. Localization of the signal is generally poorer than

localization of a sound or visual stimulus and is usually effected by the animal's moving

(15) upwind in response to the stimulus. The ability to modulate a chemical signal is limited,

compared with communication by visual or acoustic means, but some pheromones may

convey different meanings and consequently result in different behavioral or physiological

responses, depending on their concentration or when presented in combination. The

modulation of chemical signals occurs via the elaboration of the number of exocrine

(20) glands that produce pheromones. Some species, such as ants, seem to be very articulate

creatures, but their medium of communication is difficult for humans to study and

appreciate because of our own olfactory, insensitivity and the technological difficulties

in detecting and analyzing these pheromones.

Pheromones play numerous roles in the activities of insects, They may act as alarm

(25) substances, play a role in individual and group recognition, serve as attractants between

sexes, mediate the formation of aggregations, identify foraging trails, and be involved in

caste determination. For example, pheromones involved in caste determination include

the "queen substance" produced by queen honey bees. Aphids, which are particularly

vulnerable to predators because of their gregarious habits and sedentary nature, secrete

an alarm pheromone when attacked that causes nearby aphids to respond by moving away.

What does the passage mainly discuss？

A．How insects use pheromones to communicate

B．How pheromones are produced by insects

C．Why analyzing insect pheromones is difficult

D．The different uses of pheromones among various insect species