An Overview of Insects Territoriality
Jeff Brase
Territoriality has been extensively studied by biologist in vertebrates. However,
in insects the subject of territoriality is not as well explored. Although, every
aspect exhibited by vertebrates is also exhibited by insects (Baker, 1983). The
general definition of territoriality is the defense of a resource from other
organisms. An animal can defend a resource by just advertising and not using
physical encounters. Insect display these same characteristics, which are shown in
three major forms: a) physical conspicuousness; b) acoustical signaling; and c)
scent marking. An example of physical conspicuousness in insects is the coloration
of the males of many butterflies. The ultraviolet flashing when the wings are
flashed may serve as a deterrent to other males (Scott, 1974). Stridulation in
Orthoptera has been shown to influence the spacing of males (Latimer, 1981). Scent
marking is used by many insects such as a species of Hymenoptera, Jamaican Centris
spp. mark their territories around the food sources of females with pheromones
(Raw,1975). When resources are, abundant simple advertisement may be sufficient for
an intruder to be deterred. If advertisement fails then the confrontation escalates
until one contestant leaves. Insects such as ants will face each other (Wilson,
1971), or as in crickets that will click or stridulate (Otte & Joern, 1975) and some
butterflies engage is flying contest (Baker, 1972), all as a part as confrontation.
However if these types of behavior fail to deter the invader the contest often
escalates into physical combat (Baker, 1983). Only a few insects equipped biting
mouth parts or stingers are really able to cause much damage in physical conflicts.
Most generally the competition for resources like food sources, females and
oviposition sites end without physical conflict among insects. One possible reason
that territoriality in insects has not been as widely studied could be that the
physical aggression in defense of a resource is less obvious than in many animal
species.
Introduction:
A general definition of territoriality is the defense of a resource from other
organisms. Webster's dictionary defines territoriality as "the pattern of behavior
associated with the defense of a territory". These resources may take the form of
food, females and oviposition sites. In many species of insects territoriality is
a strategy used by a male to obtain increased mating (Willmer, Gilbert, Ghazoul,
Zalat & Semida, 1994). Territoriality has been extensively studied and well
documented in vertebrates. However, in insects the subject of territoriality is
not as well researched. Although, every aspect of territoriality exhibited by
vertebrates is also exhibited by insects (Baker, 1983). Wilson (1975) observed
that feeding territoriality was uncommon in the non social insects. There are many
reasons why insect territoriality is not as well known. One reason is that the
basic characteristics of these insect systems makes feeding territoriality
unnecessary or uneconomical. Another possible reason for the lack of study of
these insects due to the size and difficulty of observing them in their natural
habitat (Hart, 1987). Another problem faced by researchers when dealing with
territoriality in aquatic insects is the difficulty in deciding which resources are
being contested. Unlike other organisms with multipurpose territories in which
mates, shelter sites, and food may be simultaneously defended, some insect only
defend a food resource (Wittenberger, 1981). Also insect territoriality has not
been extensively studied because physical aggression is less obvious in insects.
Insects such as butterflies and dipterans are poorly equipped for physical
aggression (Baker, 1983).
An organism ability to hold a territory is referred to as resource holding power.
Brown (1964) stated that resource defense should not occur unless two conditions
are met. The first is that the resources must be limiting, and second, the benefits
derived from restricting the access of competitors to these resources must be
greater than the cost of resource defense. An insect can defend a resource without
showing overt physical aggression. The insect can just advertise intent of physical
aggression. There are three main forms of advertisements. There is physical
conspicuousness, acoustic signaling and scent marking. Many male butterflies use
physical conspicuousness as advertisement. The coloration of these male
butterflies, especially the ultraviolet flashing that results from the flapping
wings advertises the presence of a territorial male to other males (Baker, 1983).
Stridulation is known to influence the spacing out of many Orthoptera species (Otte,
1875; Baker, 1983) In addition stridulation of various beetles has been shown to
act as an antipredator device. Another possible effect of acoustical signaling is
to advertise that this area is occupied. Many parasitic flies and wasps use scent
marking for advertisement (Baker, 1983). The female applies a pheromone to a host
in which she has laid her eggs, as a way to inform other females that the host is
occupied. This behavior prevents multiple egg laying on one host, thus increasing
the chance of survival for immatures. Another example of insects using scent
marking for advertisement is the ant Jamaican centris. Individual male ants of this
species use pheromones to mark the territory in which their females feed (Raw, 1975;
Baker, 1983). This discourages other males from trespassing. In addition among the
more social ants scent marking has been used to mark colonies boundaries. As long
as there is an abundance of unoccupied territory a simple advertisement is usually
sufficient to deter an intruder (Baker, 1983). There are many factors incorporated
within territoriality.
Territorial development is an important part of territoriality. Most generally
females will only establish feeding territories while there are a few examples of
females mating territories. Since food resources not only influences female
survival but also directly determines the number of eggs that are produced, feeding
territories may have been more developed than mating territories in females
(Kaitala, 1987; Rowe and Scudder 1990). In contrast males more often establish
mating territories because the number of males directly determines female
reproductive success rather than food resources in female adulthood. Therefore
mating territories may have been much more developed than feeding territories in
males (Koga & Hayashi, 1993).
There are two types of male territories. The first and most common are territories
that contain a resource such as a food source or oviposition site. The other type
of territory is one that contains no resource. The type of territory and the
resource being defended greatly effects the behavior of the territory holder. The
territorial behavior difference between males and females of the Water Strider,
Metrocoris histrio suggests that competition for space be more severe in males than
in females. A female biased sex ratio within pools resulted from sexual
difference in territorial behavior. Since only, territorial males excluded
intruders of the same sex from holding territory in the same pool therefore, males'
territories were much larger than those of females (Koga & Hayashi, 1993).
Territory size can vary greatly among insect species and is very important to
territoriality. The territory could range from a single female being defended by a
male or hilltops occupied and defended by large butterflies. The size of a
territory is determined by how much an individual can afford in its maintenance. A
territory with average resources and small foraging area is easier to defend that a
larger territory with scare resources. There have been many models constructed to
learn how economic cost effect territoriality. These models reflect an optimum
trade off between the benefit of increased resources and the greater cost of defense
with increasing territory size ( Baker, 1983). Habitat quality is directly related
to territorial size. As the quality of a habitat increase the more likely an
organism will spend resources in defense (Brown, 1993). Another factor
associated with habitat quality is depletion rate. This is how fast a resource is
used and if it is replenished. When depletion rates are low, feeding territoriality
is not favored either because the resource is so slowly depleted that there is no
benefit or that the resource is renewed so quickly that food is unlimited. However
when resource depletion rate is high, territoriality is not as cost effective but is
more necessary. In the case of high depletion rate insects are forced to forage
over larger areas and compete vigorously for resources (Miller, 1969).
Not only does size and quality of a habitat play a part of territoriality, but body
size plays an important role in territoriality. Within the Aquarius remigis (Say)
(Heteroptera, Gerridae) the females were territorial. Winged females are
considerable larger than wingless females. Due to larger size, winged females were
more„territorial than wingless females in dimorphic populations. Females of this
species are also larger than males both in winged and wingless individuals.
However, males do exhibit a wider femur in the prothoracic legs. This supports the
hypothesis that a wide prothoracic femur is a male characteristic. This larger
femur is thought to aid the male during copulation. It enables the male to hold on
when the female resists mating (Baker, 1983). The larger females held territories
while smaller non territorial females were less site specific. Males were either
territorial, 'edge males' or moved around continuously as satellite males.
Territorial males in the middle caught more prey items than did males in the outer
edges (Rubenstein, 1984). There are a couple of hypothesis on how body size should
affect behavior. The first is if the behavior of an individual depends on is body
size, the greater the variation in body size among individuals the more they should
differ in behavior. Although we see, a variation in size there is not as much
variation in behavior. The second hypothesis is that comparisons between migratory
and nonmigratory morphs should reveal several characteristics that are often
associated with high dispersal ability, including large body size and high fecundity
(Dingle, 1988). Overall this hypothesis stands true. Size also plays a large role
in the ability of an individual to defend its territory.
In the insect world when advertisement fails to discourage an intruder, and the
confrontation escalates into physical combat. Usually this combat does not serious
harm to either side. Physical combat occurs in many in insects such as predatory
flies with piercing mouth parts, beetles and crickets with biting mouthparts and
Hymenoptera with jaws and stingers. The physical combat among these insects usually
results in minor injuries. However, there are cases in which ants of two colonies
line up in a show of force and if one side does not back down a battle takes place.
After a time one colony will withdraw before being wiped out (Baker, 1983).
However, social insects are not the only one to cause death to their rivals. The
larva of the Orange Tip butterfly, (Anthocharis cardamines) a European pierid will
grasp a smaller larva with its mandibles and throw it off the plant. If the smaller
larva fails to release the plant, such as when it is attached by a silken pod for
ecdysis, the larva is killed and eaten (Baker, 1983). These are rare instances and
for most confrontation's advertisement is sufficient.
Territoriality in a solitary bee:
There are many examples of territoriality in insects. One such example is the
solitary anthophorid bee (Anthophora sp nov.) who uses physical conspicuousness as
advertisement of territorialility . Males establish territories in areas where
females were likely to occur. These areas included feeding sites, nesting
aggregations and visually apparent areas such as hilltops. Females are often
attracted to these aggregations by pheromones released by the males (Kimsey, 1980:
Alcock and Smith, 1987).
Territories held by male bees are classified as either holding territories or those
that patrol a home range. Those that patrol a home range have a particular circuit
or pattern that they fly. These patrolling males often try to sneak in and feed on
flowers within areas held by territorial males. These patrolling males rarely
encounter other males and if encounters occur they are usually subdued. (Baker,
1983). True territorial males may or may not have a patrol circuit.
Some males will patrol their territory while others wait and perch on a site
watching over their territory. In either case these territorial males will actively
confront any intruders. Those territorial males that flew patrol circuits were so
consistent that it was often possible to identify the same male for several
consecutive days in specific areas. Non territorial males or sneaker bees often try
on occasion to adopt a territory, but with little success. Territorial males also
patrolled sites where females nest. Many of the bees territories seem to be held
at least in part by pheromones marking. However there was no conclusive evidence of
behavioral changes associated with the scent marking of male territories (Kimsey,
1980, Marshall and Alcock 1981).. Territorial males defend flowers not only when
females are present feeding but also before the female's arrival. By defending the
food sources the territorial males are ensuring an adequate food supply for his
females. Thus, the male is securing paternity of the eggs. In addition, the male
territoriality is ensuring that the cells in which young are to be laid are better
provisioned This male behavior is a form of paternal investment in future offspring
(Willmer, Gilbert, Ghazoul, Zalat & Semida, 1994).
Territorial males increase the size of their territory as the day goes on.
Expanding it to include more flower clumps farther away. To ensure territoriality
the male will increase fight speed to cover additional area added to the territory.
The male speeds increase so that the time it takes to cover the additional territory
is the same if not less than it was for covering the initial territory. This allows
the male to maximize his residency on the central clump of flowers at the time when
females began to visit it again (Willmer, Gilbert, Ghazoul, Zalat & Semida, 1994).
With the number of flowers defended increasing throughout the day, each male
maintains this territory with just enough flower visits to fuel own flight activity.
These visits occur most frequently in the middle part of the day. This may also be
the time when cost of flight is the highest (Willlmer, 1986), in addition this is
also the period when pollen supply is at its peak. The main activity of territorial
males is maintenance of his territory.
Territorial bee males aggressively confront most other bees encountered in his
territory. Males also exhibited aggressive behavior toward flies, dragonflies or
any other insects who happened to venture into his domain (Willmer, Gilbert,
Ghazoul, Zalat & Semida, 1994). When a territorial male encounters another male of
the same species within his territory a chase results. The territorial male
continues to chase until the intruder leaves the territory. Sometimes the
confrontation escalates to a point when the two bees are grappling and fighting,
with one or both males falling to the ground (Willmer, Gilbert, Ghazoul, Zalat &
Semida, 1994). Aggression patterns of territorial males vary according to site.
When a territorial male confronts an intruder around defended flowers, the encounter
includes chasing and only a brief physical contact. While at emergence or nesting
sites the encounter commonly results only in multiple flights around an intercepted
male. When a male bee encounters a female often, a chase occurred and sometimes
attempted or actual copulation occurs. Non copulating encounters involved a fast
approach from any angle with an abrupt physical contact unless the female flew off,
where as males seeking copulation hovered behind a flower feeding female and
attempted to land on her more gently in alignment from the rear (Willmer, Gilbert,
Ghazoul, Zalat & Semida, 1994).
Territoriality of the Weaver Ant:
Another example of territoriality in insects that use scent marking for
advertisement is the weaver ant, Oecophylla longinoda (Latreille). These ants are
territorial, but not as individual but as a whole colony. The colony as a whole
defends the territory. These ants get their name from binding leaves together with
silken threads in the tops of trees to form their nest. These ants are predators
and they occupy different areas of the territory at different times of the day.
This behavior is regulated somewhat by circadian rhythm. The ants' activity changes
„ one is diurnal and the other is nocturnal (Willlmer, 1986). Some ants are active
during the day and some are active at night within the territory. The territories
of the weaver ant are divided into two areas. The central territory or main area
that is usually within two meters of the nearest nest. The other area is called the
secondary territory that is the zone outside the central territory that is usually
on the ground. These territories were occupied with various number of ants at
different times during a twenty four hours period. The central territory had a
maximum number of workers between 09.00 and 17.00 hours. The secondary territory
was occupied by fewer workers throughout the day and with even fewer individuals
during the night. Another difference between the two areas was the type of prey
caught. In the central area the prey consisted of winged insects whereas in the
secondary territory the workers captured insects running across the territory
(Dejean, 1986). These territories were always occupied by workers, the only
difference was the number in which they were occupied. High diurnal levels of
individuals were associated with predatory activity and guarding and low nocturnal
numbers were attributed to guarding alone. These ants expanded their territory
during the exploration of a food sources that are constantly being renewed.
Territory size is determined by the number of ants within a colony. This is related
to the resource holding power and cost benefits of maintaining the territories
(Dejean, 1986). Other factors that affects the size of the colony territory is
neighboring competition and the resources available.
Territoriality of the water strider:
Large females of the water strider, Aquarius remigis (Say) (Heteroptera, Gerridae)
are territorial in populations with winged individuals and in those with individuals
of two wing morphs. Most generally the winged females were the largest and most
territorial. These large females held territorial areas while the smaller females
were less site specific. The female territories consisted of food resources while
the male territories were mainly for mating. The territories held by territorial
males were larger than the ones held by females. Territorial males required a
larger area to give then a better access to receptive females. Males of this species
were either territorial or moved around continuously as satellite males.
Territorial males in the middle caught more prey items than did the satellite males
on the edge areas (Koga & Hayashi, 1993).
Unlike other insect species body size seems to be involved only slightly with
territoriality in the water strider. There are no significant differences in body
size between territorial males and the satellite males. The only noticeable
difference was in the femur width of the prothoracic legs used to grasp the female
during mating. Territorial males had a larger femur assumed to be a sexual
advantage. Although, the water strider females were larger than males in overall
body size, their femurs were smaller. This supports the idea that wide femur is a
male characteristic. Body size does seem to be a great advantage in the competition
for a resource, since prey capture rates are higher among territorial individuals
(Rubenstein, 1984).
Summary:
Territoriality in insects is not as clearly studied as in vertebrates. Some of the
reasons for this is the difficulty in studying insects in their natural environment
due to size. Insects exhibit the behavior of territoriality by defending resources
such as feeding sites, females and oviposition sites. The defense of these
resources includes the use of advertisement that can takes the form of either
physical conspicuousness, acoustic signaling and scent marking. Insects can use one
or all of these forms of advertisement. In a few instances when advertisement fails
the insect will engage in physical combat and only in a few cases do these
engagements end in death. There are many aspects of territorial behavior such as
body size, habitat quality, and cost of defense. Territoriality behavior is a wide
subject with lots of potential for further study.
Bibliography:
Alcock, J. and Smith, A. P. 1987. Hilltopping, leks and female choice in the
carpenter bee Xylocopa (Neoxylocopa) varipuncta. J. Zool., Lond., 211: 1-10.
Baker, R. R. 1972. Territorial behaviour of the nymphalid butterflies, Aglais
urticae (L) and Inachis io (L). J. Anim. Ecol. 41:453-469.
Baker, R. R. 1983. Insect Territoriality. Ann. Rev. Entomol. 28: 65-89.
Brown, J. L. 1964. The evolution of divrsity of avian territorial systems. Wison
Bull. 76: 160-169.
Brown, J. 1993. Group Territoriality and Habitat Quality: What are the Issues?
TREE, 8:187.
Dejean, A. 1986. Predation by the ant Oecophylla longinoda in Zaire. 37th Annual
AIBS Meeting. 10-14 August 1986, Amherst, Massachusetts. ATB Abstracts. p. 16.
Hart, D., 1987. Feeding Territoriality in Aquatic Insects: Cost-Benefit Models and
Experimental Test. Amer. Zool., 27: 387-399.
Kaitala, A., 1987. Dynamic life history strategy of the water strider Gerris
thoracicus as adaptation of food and habitat variation. Oikos 48: 125-131.
Kaitala, A. and Dingle, H. 1993. Wing dimorphism, territoriality and mating
frequency of the waterstrider Aquarius remigis (Say). Ann. Zool. Fennici 30: 163-
168.
Kimsey, L. S., 1980. The behavior of male orchid bees (Apidae, Hymenoptera,
Insecta) and the question of leks. Anim. Behav., 28: 996-1004.
Koga, T. and Hayashi, K. 1993. Territorial Behavior of Both Sexes in the Water
Strider Metrocoris histrio (Hemiptera: Gerridae) During the Mating Season. J.
Insect Behav. 6: 65-77.
Latimer, W. 1981. Acoustic competition in bush crickets. Ecol. Entomol. 6:35-45.
Miller, R. S. 1969. Pattern and process in competition. Adv. Ecol. Res. 4:1-74.
Otte, D., Joern, A. 1975. Insect territoriality and its evolution: population
studies of desert grasshoppers on creosote bushes. J. Anim. Ecol. 44: 29-54.
Raw, A. 1975. Territoriality and scent marking by Centris males in Jamaica.
Behaviour 54: 311-321.
Rowe, L. and Scudder, G. 1990. Reproductive rate and longevity in the water strider
Geras buenou Can. J. Zoo.. 68: 399-402.
Rubenstein, D. I. 1984. Resource acquistion and alternative mating strategies in
water striders. Amer. Zool. 24: 345-353.
Scott, J. A. 1974. Mate-locating behaviour in butterflies. Am. Midl. Nat. 91:103-
117.
Wilson, E. O. 1971. The Insect Societies. Cambridge, Mass: Harvard Univ. Press 548
pp.
Wilson, E. O. 1975. Sociobiology: The new synthesis. Belknap Press, Cambridge,
Massachusetts.
Willlmer, P. G., 1986. Foraging patterns and water balance: probles of
optimization for xerophilic bee, Chalicodoma sicula. J. Anim. Ecol., 55: 941-962.
Willmer, P. G., Gilbert, F., Ghazoul, J., Zalat, S.,& Semida, F., 1994. A novel
form of territoriality: daily paternal investment in an anrtophorid bee. Anim.
Behav., 48: 535-549.
Wittenberger, J. F. 1981. Animal social behavior. Duxbury Press, Boston,
Manssachusetts.