R. Jason Bishop
Colorado State University
Fort Collins, Colorado 80523
Several species within the genus Carpophilus areа known pests on a wide variety of
hosts.а This paper reviews the elements involved in the attraction of theseа sepcies
to their hosts, including host-related volatiles, aggregation pheromones , and the
interaction between the two.а Kairomonal activity between species is also discussed.а
This review is presented inа context of the value of knowledge of attraction of sap
beetles to possible control strategies for beetle populations.
ааааааа In the animal world, humans are not unique in the need to communicate.а
Communication between and among species takes on many forms, from a simple visual
cue to a complex set of chemical cues.а Among insects, communication often involves
mechanisms which prove too difficult to understand from a human perspective without
further investigation.а Humans tend to take for granted the chemical processes which
occur in nature, as well as in our own bodies at any given time.а Chemical reactions
are not always readily visible, and therefore tend to pass unnoticed.
ааааааа Chemical communication among insects presents a diversity of forms and
functions.а Among the primitively eusocial paper wasps (Polistes, Hymenoptera:
Vespidae), cuticular hydrocarbons are the primary means by which nestmates recognize
one another (Gamboa, 1987).а Lepidopteran species are known to use chemicals from a
wide range of chemical classes for mating purposes.а Females release copious amounts
of sex pheromones into the air to attract males, while males use pheromones to
induce the females into mating once they have found their target (Jacobson, 1970).а
Several species of arthropods are known to use chemicals for defense (Berenbaum,
1995).аа Chemicals are also known to be used by insects to insight mass
aggregations.а The bark beetle Dendroctonus ponderosae (Scolytidae)а is a well
documented example of such behavior (Ali, 1990).аа
ааааааа Commonly referred to as sap beetles, members of the genus Carpophilus
(Coleoptera: Nitidulidae) are cosmopolitan pests which occur on a wide variety of
hosts, including fruits and grains, both before and after harvest (Hinton, 1945).а
This paper reviews the attraction ofа sap beetles to different sources.а Sap beetles
are known to respond to male-produced aggregation pheromones as well as host-related
volatiles (Bartelt, 1993a; Blumberg, 1993).а Several species of sap beetles are
known agricultural pests, occurring on a wide variety of host plants (Bartelt,
1995).а The presence of large numbers of sap beetles on a host plant can prove
economic in terms of crop damage caused by theа feeding beetles, but impact on crop
value is primarily due to the presence of beetles in products ready for sale
(Bartelt, 1992).а In addition to damage caused by feeding, sap beetles are also
known to transmit fruit -degrading microorganisms, such as brown rot [Monolinia
fructicola (Wint.) Honey] in stored fruits (Tate, 1975). Damage of this nature to
high value crops, such as stone fruits presents a need to understand the chemistry
and biology of pheromones in nitidulid beetles so that tools for monitoring and
controlling sap beetle populations may be developed (Bartelt, 1995).
ааааааа Before moving further, it is important to review some basic terminology used
in chemical ecology.а The term semiochemical is used to describe any chemical which
conveys information between organisms (Law & Regnier, 1970).а Semiochemicals, from
the Greek semeion (= signal), can be further divided into two subcategories
(Nordlund & Lewis, 1976):а (i) allelochemicals, and (ii) pheromones.а The division
is important in that it distinguishes the receiver of the chemical message from its
ааааааа From the Greek allelon (= of one another), allomones are chemicals which
convey interspecific information. The receiver of the chemical message is of a
species different from its sender (Ali, 1990).а Allomones can be further categorized
according to the advantage ofа the behavioral response elicited by the released
compounds (Ali, 1990).а If the behavioral response is advantageous to the receiver
ofа the message, as with predators locating prey, the compound is termed aа
kairomone (Brown et al., 1970).а If the advantage goes to the originator of the
compound (i.e. defensive secretions) the allelochemical is referred to as an
allomone (Brown et al., 1970).а аFor cases in which both the originator and receiver
benefit, the allelochemical is appropriately called a synonome (Nordlund & Lewis,
1976).а Synonomes are exemplified by pollinating insects (e.g. honey bees)
responding to floral scents (Ali, 1990).
ааааааа Chemicals released by organisms for intraspecific communication are called
pheromones.а Derived from the Greek, (pherein = to transfer; horman = to excite)
pheromones are defined as substances which, when secreted to the outside by one
individual and received by a second individual of the same species, will elicit a
specific response (Karlson & Butenandt, 1959).а The categories of pheromones are
numerous.а For the purposes of this paper, only those pheromones which cause
conspecifics to increase their density in the vicinity of the pheromone source will
be discussed.а Such chemicals are known as aggregation pheromones (Ali, 1990).аа
Aggregations likely serve to draw together the sexes, whereby increasing the
probability ofа mating and exchanging genetic material (Ali, 1990).аа Exceptions can
be found.а Among parthenogenic aphids (Homoptera), for example, aggregating serves a
"safety in numbers" role. Bark beetles (Scolytidae), congregate in large numbers as
a means to facilitate mating, but also to overcome the chemical defenses of their
host plants (Birch, 1984).а This "mass attack" of host material allows beetles to
colonize the host despite the trees' efforts to ward them off.
Attraction of Sap Beetles to Pheromones and Host-Related Volatiles
ааааааа As stated previously, sap beetles can be found on a wide variety of hosts.а
Although many Carpophilus species are characterized by their affiliation with a
specific host or group of related hosts, review of the literature indicates that the
beetles are not restricted in their host range.а For example, Carpophilus davidsoni
(Dobson), a small reddish brown sap beetle occurring in Australia, New Zealand, and
Micronesia is known to infest Australian sweet corn, figs, and peaches (Bartelt,
1994).а Carpophilus obsoletus (Erichson), a small dark brown sap beetle, which
occurs throughout tropical, subtropical, and milder temperate regions of the world,
also attacks corn, but is a more serious pest of dried fruit commodities such as
dates (Petroski, 1994).а The driedfruit beetle, Carpophilus hemipterus, a more
prolific species, is a pest on fresh and dried fruit, many fresh and stored grains,
spices, drugs, and seeds (Dowd, 1991; Hinton, 1945).а The corn sap beetle,
Carpophilus dimidiatus (F).а can be found on corn, peanuts, cacao, and various
spices, either fresh in the field or in storage (Connell, 1975).а The dusky sap
beetle, Carpophilus lugubris (Murray) is a beetle pest that is seen to infest a wide
variety of ripening fruits and vegetables, particularly sweet corn (Harrison, 1974).а
Finally, the confused sap beetle, Carpophilus mutilatus (Erichson), feeds mostly on
fallen and decomposing fruits, but can also be found on ripening fruit that has
suffered damage (Bartelt, 1993a).а It is clear, then, that sap beetles occur on a
wide range of hosts, with some specificity relative to each species, but with some
overlap as well.а Host selection is not a simple proposition for sap beetles.а
Selection of appropriate host material is based on many chemical components and
their interactions (Bartelt, 1993b).а Sap beetles respond to a wide range of host-
related volatiles as well as aggregation pheromones.а Furthermore, several species
of sap beetles show increased response to interactions of the host-related volatiles
and pheromones (Bartelt, 1992).
ааааааа Before one can look at the aggregation pheromones responsible for drawing in
large numbers of beetles, it is important to first discuss host-related attractants,
as the nitidulid beetles seem to be involved in a variety of interactions that go
beyond simple pheromonal attraction under field conditions (Bartelt, 1993b)..а For
the most part, sap beetles are drawn to volatiles from fermenting fruit and grains
(James, 1993).а As discussed with C. mutilatus, sap beetles will also infest those
hosts that may be ripening, but have first taken on damage (Bartelt, 1993a).
Suitable hosts will draw in large numbers of beetles, and in a given complex of
beetles occurring on a host, the composition of species can be fairly uniform in
terms of numbers present.аа High numbers of several species of beetlesа can occur
simultaneously in others instances.аа The complex of beetles occurring on fermenting
fruit exemplifies the point (James, 1993).а High numbers of several Carpophilus
species can be found infesting fermenting fruit, particularly if said fruit is
damaged (James, 1993).а Interestingly, numbers tend to favor some species over
others in traps baited with host-related volatiles (Blumberg, 1993; Lin, 1992;
Bartelt, 1992).а The notion that certain species can be attracted more readily than
others in the presence of specified host-related volatiles has important
implications for control options.
ааааааа A suite of seven volatile compounds has been identified from the head space of
fermenting whole-wheat bread dough as particularly attractive to C. lugubris (Lin,
1992).а The chemicals were isolated and identified using wind-tunnel bioassays as a
means to determine the composition of the attractants as well as the proportions
needed for each component (Lin, 1991).а These chemicals were then synthesized and
incorporated into bait attractants used in sap beetle traps where C. lugubris was
present in economic numbers (Lin, 1991).а Similar studies have also been done on the
attractiveness of fermenting fig juice volatiles to C. hemipterus (Bartelt, 1992).а
In both cases the synthetic volatiles proved attractive to the target beetles,
however more potent attractantsа were desirable (Blumberg, 1993).а Synergism between
host-related volatiles and aggregation pheromones turned out to be the element
necessary to add potency to attractants used in traps.
Synergism Between Host-related Volatiles and Pheromones
ааааааа Having specific attractants available for trap-out strategies is a promising
alternative to traditional chemical control of sap beetle populations, however, as
previously mentioned, traps with higher efficacy are desirable (Blumberg, 1993).аа
Synergistic effects of host-related volatiles used in combination with aggregation
pheromones have been tested in the field for both C. lugubris and C. hemipterus
(Lin, 1992; Bartelt, 1992).ааа In both investigations, significantly higher numbers
of beetles were reported to have been present in traps containing both the
aggregation pheromone of the target beetle, as well as host-related attractants,
than in traps containing each constituent individually (Lin, 1992; Bartelt, 1992).аа
One exception to this interaction was observed in C. antiguus (Bartelt, 1993b).а
This beetle was unusual in that the pheromone was quite attractive in the field
without a synergist (Bartelt, 1993b).
ааааааа Using wind-tunnel bioassays, aggregation pheromones have been identified for a
number of species of sap beetle (Bartelt, 1991; 1993a; 1994; 1995).аа Sap beetle
pheromones consistently turned out to be characterized as polyene hydrocarbons.а
Both beetle-derived pheromones as well as synthetic versions are attractive to
conspecifics , howeverа kairomonal effects of the pheromones between species has
even been investigated (Bartelt, 1993b).а Although a novel pheromone has been
identified for C. antiguus, these beetles respond quite well to C. lugubris
pheromone (Bartelt, 1993b).а Bartelt (1993b) suggests the kairomonal effect to be
quite important.а Both C. lugubris and C. antiguus respond best to their own
pheromones, however the responsiveness of C. antiguus to C. lugubris pheromone is
advantageous (kairomonal) in that a new host source is made available for C.
antiguus.а Without the presence of C. lugubris on corn ears, C. antiguus would not
normally be able to feed on kernels as it is not big enough or strong enough to
penetrate the husk (Bartelt, 1993b).а Being that corn is a suitable food source for
C. antiguus, it appears that this species uses C. lugubris pheromone to find the
ears (Bartelt, 1993b).а Using wind-tunnel bioassays, Bartelt et al. (1993b) were
able to evidence the kairomonal action of C. lugubris pheromone.аа Tests showed
significant response of C. antiguus to C. lugubris pheromone, but very weak
interspecific responses to other pheromones (Bartelt, 1993b). Kairomonal effects add
yet another dimension to the chemical interactions taking place in the attraction of
sap beetles to host material.а All dimensions are now in place and control
strategies can be developed.а
Implications for Control Strategies
ааааааа With the knowledge of the various elements involved in attracting sap beetles
it now seems possible to tailor control strategies for specific beetles or complexes
of beetles which may be occurring in economic numbers.а For example, in a date
garden being used as a test site it was observed that the most abundant species, C.
mutilatus, did respond significantly to the pheromone of C. hemipterus (Bartelt,
1992).а When a synergist was added, C. mutilatus still showed attraction to the
baits, but not in as dramatic proportions as C. hemipterus (Bartelt, 1992).а
Additionally, C. lugubris, C. obsoletus, and C. humeralis showed synergistic
attraction to the C. hemipterus pheromone, with only C. obsoletus responding to the
pheromone alone (Bartelt, 1992).а It was also shown that C. freemani responds
significantly to the C. hemipterus pheromone, but not as well as to its own
pheromone used synergistically with bread dough (Bartelt, 1992; Bartelt, 1990b).а By
manipulating various elements of trap design, one could conceivably become quite
ааааааа The kairomonal action discussed between C. lugubris pheromone and C. antiguus
presents a similar situation in which possible control strategies could be developed
using specific attractive interactions.а If both C. lugubris and C. antiguus are
present in a stand of corn, it is conceivable that trapping of both speciesа could
be achieved through use of C. lugubris pheromone and a synergist (Bartelt, 1993b).ааа
ааааааа It is clear that by adjusting various elements of a trap design one might be
able to easily target specific species of sap beetle or entire complexes.а With the
knowledge of synergistic effects of pheromones and host-related volatiles as well as
the kairomonal effects of aggregation pheromones the potential to do so is evident.а
Investigation into the biologies of sap beetle species involved is also critical.а
One must first understand the relationships between a given species and its own
pheromone alone, and in combination with host-related volatiles.а Interactions with
pheromones of other species must also be elucidated to further understand the
ecology of sap beetles and their host selection.
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