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COLEOPTERA,
Meloidae (Gyllenhal 1810) -- <Images>
& <Juveniles> Please refer also
to the following links for details on this group: Meloidae = Link 1 Description &
Statistics
Those Meloidae that are referred to
as parasitic have relationships with their hosts that are not a true
parasitism, where individual larvae consume the body contents of the host and
complete development thereon. In
Meloidae, the host egg is consumed, and feeding thereafter is on the food
mass stored in the cell by the parent bee.
Early reviews on Meloidae behavior may be found in Balduf (1935) and
Clausen (1940). Clausen (1940) believed it
important to note that in host preferences, the Meloidae are limited to the
two widely separated groups mentioned above.
Adaptations required to gain access to the host stages and to develop
successfully upon them are markedly different. The lack of transitional forms, possibly on other hosts, is
surprising. However, both host groups
have in common the fact that stages attacked are most found in soil, but a
few species inhabit wood galleries (Clausen 1940/62). The overall economic value of
Meloidae is open to question. Many
species that develop in Locustidae egg pods destroy vast numbers of eggs
annually, but the actual effect on the host population is not measured in
most cases. The numerous species
developing in the cells of bees may drastically reduce the size of colonies
and thereby result in less complete pollination of surrounding plants. Although they do not attack the immature
stages of the honeybee, in Europe the triungulinids sometimes congregate on
the adults in such numbers that irritation and death ensues. This activity occurs so frequently that
hive populations are depleted. The
most serious injury inflicted by the family is by feeding of adult beetles on
foliage and blossoms of cultivated crops, which sometimes results in severe
injury. Several species of Horia develop at the expense of
xylocopid bees, so that these may be considered beneficial. Horia
maculata Swed. was introduced to
Hawaii from Guatemala in 1934 for control of Xylocopa, but establishment was not confirmed (Clausen 1940/62). There were over 2,000 species known as of 1993. They are abundant in desert and drier
regions worldwide. The characters of
these "blister beetles" are a filiform antenna; prothorax as wide
as head or narrower; elytra often overlapping at base and separated at apex;
tarsal formula 5-5-4. The body is
medium-sized, elongate, cylindrical to robust. The color is often dull gray, brown or ochre, sometimes
metallic green, blue or purple. They
are often lightly sclerotized. Meloidae adults are phytophagous
and often destructive. Some adults
apparently do not feed at all.
Immature stages are predaceous or parasitic on the provisions and
immatures of wild bees and in the egg pods of grasshoppers. The immature stages are not
destructive. Predators of Locustidae
are found mainly in the genera Zonabris
(= Mylabris), Epicauta and a few species of Tetraonyx
and Macrobasis. Just a few species are parasitic in the
cells of various bees of the families Megachilide and Andrenidae, with the
subfamily Nemognathinae being limited entirely to the latter hosts. Common species occurring on these hosts
are found in the genera Apalus, Meloe, Nemognatha, Zonitis, Hornia, Sitaris and Tricrania. Meloids have not been used with
much success in biological pest control. Biology
& Behavior
DeGeer first noted the parasitic
relationship with Hymenoptera in 1775 (cited by Clausen, 1940). Newport (1845) determined that the
triungulinids were carried into bees' nests, later describing the older
instars from cells of Anthophora. Newport (1846, 1853) provided more
detailed accounts of the biology and behavior of Meloe cicatricosus
Leach, parasitoid of Anthophora. Eggs are laid in soil, and transport of
young larvae to the nest is on the bodies of adult bees. Fabre (1857) studied Apalus muralis Foerst,
developing similarly in the cells of Anthophora. Larvae were found to be carried into the
nest by adult bees, and the larvae transferred to the egg of the bee. Valery-Mayet (1875) studied Apalus analis Schaum. (= Sitaris
colletis V.-M.), finding similar
behavior. Riley (1878b,c) studying Epicauta vittata F. and other species of the genus, discovered the
predatory group of Meloidae which feeds on eggs of Locustidae. He gave a full account of the striking
metamorphosis undergone by the developing larvae. Extensive early accounts of the biology of Meloidae were those
by Beauregard (1890), Cros (1910-1931), Roepke (1917), Milliken (1921),
Parker & Böving (1924), Zakvatkine (1931, 1934), Verbeek (1932), and
Ingram & Douglas (1932). Oviposition.-- There is a relative short
oviposition period of 2-4 weeks in most Meloidae. The gestation period is short, being only a few days, and in
some cases eggs are laid on the day of adult emergence. The number of eggs laid varies among
species. Species which develop on
eggs of Locustidae usually produce a comparatively small number, ranging from
<100 to several hundred. These are
laid in batches in shallow burrows in the hard, dry soil of the host's
breeding area. The burrows are filled
and covered when egg-laying is finished. Eggs have an adhesive substance that keeps them together in a
mass (Clausen 1940/62). The number of eggs produced per
female in species that attack bees is considerably larger, probably owing to
the greater hazards encountered by young larvae before they reach the host
cells. Meloe cicatricosus and M. autumnalis
var. cribripennis Dej. lays 3,000
or more eggs. Other species
approximate this number. A single
batch of eggs of M. violaceus Marsh had 3-4,000, and several
additional batches, containing smaller numbers, were laid by the same female
(Cros 1931). One Meloe sp. was found to contain a total of 4,218 eggs when
dissected (Newport 1851). Meloe majalis L. was found to lay several thousand eggs in each batch
(Cros 1912, 1913). The first batch
usually contained the largest number of eggs, while those following were
successively smaller. Each batch
represented the entire quantity of mature eggs in the body of the female at
the time of egg-laying, and the abdomen consequently shrinks with this
activity. A feeding period then
follows, and the abdomen gradually becomes distended with more eggs. There is not as much uniformity in
the place of oviposition among species attacking bees as in the case of those
attacking Locustidae eggs. Parker
& Böving 1924) studied Tricrania
sanguinipennis Say, developing in
nests of Colletes. The egg batches were laid in the soil in
the vicinity of the host nests. Meloe autumnalis cribripennis
(Cros 1914), M. majalis, and Apalus muralis (Cros
1910) have similar behavior. However,
Hornia nymphoides Esch. lays batches of eggs of several hundred in the
gallery of Anthophora or in an old
cell, and Horia debeyi Fairm. places them in the
galleries of xylocopid bees (Cros 1913).
In Nemognatha chrysomelina L., the eggs are found in
small batches on the blossoms of Echinops
spinosus, and hatching coincides in
time with the complete opening of these blossoms (Cros 1912). Apalus
rufipes Gory lays eggs upon the
blossoms of Ballota hirsuta (Cros 1913). In the Nemognathinae, which are restricted
to bees, there is less care for the safety of the egg masses than in other
Meloidae (Parker & Böving 1924).
Some species of Sitaris, Stenoria and Apalus lay their eggs in uncovered piles in small grooves in the
host gallery, while others place them on leaves or stems of various
herbaceous plants. Egg incubation ranges from 4-6 days
in the case of Zonitis immaculata Ol. to ca. 4 weeks in other
species under normal temperature conditions.
Much longer periods of up to 5 months are known for species that
oviposit during colder seasons or that overwinter in the egg stage. Triungulinid Larva.-- In most
species the triungulinids disperse almost immediately after hatching, but in
certain species there is a tendency for them to remain en masse for some time
around the egg shells. Those of apalus muralis remain clustered together throughout the winter (Fabre
1857). Young larvae of most species
are able to continue their activities without food for 3-4 weeks in
summer. Rau (1930) found some
colonies of triungulinids of Hornia
minutipennis Riley in the area of Anthophora nests, and these remained
intact for 2 weeks, even outdoors in June.
However, when disturbed they attached readily to various objects. Riley (1877) while observing H. minutipennis,
found that adult females occurred in the immediate vicinity of the host
cells, and that they seldom or never left the host gallery. Rau (1930) found that adult females within
host cells may contain many young larvae.
On examination, the cells were found to be unbroken except for a tiny
hole to the outside, which was too small either for emergence or for entry of
adult beetles. Clausen (1940)
considered two possible explanations for the occurrence of triungulinids in
these cells. Either the female was
inseminated through the minute opening mentioned, or reproduction was
thelytokous. The way triungulinids gain access
to the host stages on which they develop is variable in Meloidae. Those attacking egg masses of Locustidae
are already in the soil in the breeding grounds of the host on emergence, and
thus are dependent only on their own searching to find the egg masses. Similarly, species laying eggs in
galleries or cells of bees have little trouble finding eggs. Tricrania
sanguinipennis lays eggs in the
immediate vicinity of a Coletes sp.
nest. The young larvae could not be
induced to enter the burrow directly, but rather entry was by carriage on the
body of the adult bees (Parker & Böving 1924). Male bees play an important role in the economy of Tricrania. They appear in the field ca. 1 month earlier than females, and
during this time the parasitoid larvae are active. Many of them attach to the bodies of these males. The latter are much more active than females,
and for this reason most of the parasitoid larvae are eventually found on
them. It is then necessary for the
triungulinids to transfer to the females in order to reach the brood chamber. It is thought that transfer of
triungulinids from male to female bees was at the time of mating, this
conclusion being supported by their position on the bee body, as they are
found primarily on the male venter and on the female dorsum (Clausen
1940/62). Species that oviposit entirely
apart from the host bee nests have triungulinids that frequently show a
tendency to climb upward and thus may congregate in large numbers on
blossoms. These are frequented by the
bees in their search for food, and the larvae attach themselves and are
thereby carried to the nest. Egg hatching
in Nemognatha chrysomelina coincides with the complete opening of the blossoms
and gives the maximum opportunity for the young larvae to attach to Anthidium and other bees that frequent
the blossoms of this plant. Usually attachment
is to the hairs of the carrier bee, although Cros (1927) found that larvae of
Meloe cavensis Pet. cling to the abdominal intersegmental folds. Under the previously mentioned conditions,
it is evident that the majority of triungulinids never succeed in reaching
host cells. This loss is compensated
for by the production of a proportionately larger number of eggs among
species facing such hazards (Clausen 1940/62). Obstacles encountered by triungulinids incident to gaining
entry into the bee cell in which development will occur are added to by the
necessity for transfer from the body of the female bee to the newly laid
egg. This is thought to occur at the
time of oviposition by the bee.
Probably, the triungulinids are brushed off against the cell wall and
then reach the egg by their own effort.
However, the triungulinid of Tricrania
sanguinipennis is able to descend
by a silken thread similar to that of many lepidopterous larvae, although in
this case the thread originates from the caudal end of the body (Clausen
1940/62). It is interesting that certain
species of bees are immune to parasitization by Meloidae. Parker & Böving (1924) investigated
this with T. sanguinipennis, that develops in the cells of Colletes rufithorax Swenk. but does not in cells of Andrena perplexa Smith,
even though the nests of the two species are mixed. It was especially puzzling because triungulinids were found on
the bodies of Andrena females. It was explained on the basis of different
oviposition habits of the two bee species.
In Colletes, the egg is
attached to the side wall of the cell just above the food mass. The parasitoid larva is thus able to reach
it without contacting the food mass.
However, the egg of Andrena
is placed on end in the center of the food mass, never in contact with the
cell walls. It is almost entirely
immersed in thin, watery honey, and any larvae that enter the cell are
effectively prevented from reaching the egg by the liquid barrier. After accessing the cell of the
host bee, the first act of the triungulinid is to begin feeding on the
egg. This furnishes food for the
parasitoid and at the same time eliminates the host, leaving the food supply
with which the cell is stocked for the later stages of the parasitoid. Normally the first molt occurs right after
the host egg has been consumed, and ensuing instars are boat-like which
enables them to float freely on the honey while feeding on it. That the host egg is not required for the
development of the 1st instar larva is shown by the fact that one individual
of T. sanguinipennis was reared to maturity only on pollen and
honey. Even the 1st instar larva of
several species readily accepted honey as well as host eggs and larvae (Cros
1908-1935). Often several
triungulinids access a single cell, but in no case does more than one reach
maturity. The youngest individual
because of a greater agility and aggressiveness, readily overcomes those
which have molted or which have fed sufficiently to render them sluggish. Larval maturity is usually attained
in the cell to which the larva first gained entry. Exceptions were recorded by Cros who found that Meloe autumnalis cribripennis
may consume the contents of 6 cells during its feeding period, and that the
4th instar larvae of Nemognatha chrysomelina and Zonitis sp. penetrate into a second cell to complete their
feeding. After consuming the food in
one cell of Megachile sculpturalis Smith, the larva of Z. pallida
F. penetrates the resinous partition of the adjoining one, feeds extensively
on the mature larva contained therein, and eventually returns to its original
cell, after which it repairs the break in the partition (Iwata 1933). Species that attack egg masses of
Locustidae are much more simple in feeding habits because the food consists
only of eggs and a sufficient number are available in each mass to provide
for the larva's full requirements.
Only 1-2 eggs are consumed before the first molt. Such larvae are wholly entomophagous
during their feeding period, in contrast to those species developing at the
expense of bees (Clausen 1940/62). The first 4 larval instars
represent the feeding period in most species, with the following two being
inactive and serving as a resting period or to carry the species through
winter or through periods of adverse temperature and moisture
conditions. On completion of the
scarabaeoid stage, the larva may either leave the egg capsule and transform
to the following instar in a cell in the soil near by or it may go through
its following transformations while still within the capsule. In some species the coarctate larvae is
found in a vertical position, with the exuviae forming a pad about the
abdomen's tip. The larva remains in
this instar until suitable conditions for further development occur. Milliken (1921) noted the change of Epicauta sericans Lec. from the coarctate to the colytoid stage within a
few minutes after the application of water to the body. The colytoid larva exhibits some degree of
activity for several days. Coarctate larvae represent a resting
stage in which the species is able to withstand adverse conditions to a great
extent. The integument is heavy,
providing protection from winter conditions in some species and from
extremely arid conditions in others.
In other species a portion of these larvae consistently persist until
the 2nd year, and in E. erythrocephala Pall. the diapause may
extend over many years (Zackvatkine 1931, 1934). These larvae may, under certain conditions, also revert to the
coarctate form several times.
Milliken also noted this reversion in E. sericans Lec., and
the occurrence of definite supplementary molts was verified. Locust egg predators among Meloidae show a
perfect adaptation, unequaled in any other group of similar food habit, for
life under the most adverse conditions (Clausen 1940/62). Among bee-attacking meloids, the
6th instar larva is enveloped by the unbroken 4th and 5th exuviae. As no food is taken after the 4th molt,
the body volume decreases and the exuviae are thus not distended. In Nemognatha
and Zonitis, the 6th exuviae are
also retained complete, the pupa thus being enveloped in 3 larval skins,
whereas in other genera of Nemognathinae the last larval skin is found as a
pad attached to the tip of the abdomen.
Retaining exuviae in these species is correlated with the less
specialized forms of the last two larval instars, which are less adapted to
adverse conditions than are those of the species subjected to free life in
the soil (Clausen 1940/62). Life
Cycle The duration of the life cycle varies
considerably among species of Meloidae.
In E. lemniscata in Louisiana, development from egg to adult is in
35-50 days and 3 generations may be produced annually (Ingram & Douglas
1932). Meloe majalis, Hornia nymphoides and E. vittata have 2 generations
annually. Cerocoma vahli F.
requires ca. 3 yrs. for its cycle (Cros 1919, 1924). Most species seem to have only one
generation per year, which is correlated with the host cycle, with adults
appearing during the oviposition period of the host. Apalus
muralis has only one generation in
2 years, and in a number of species with an annual cycle, a high percentage
of the larvae persist until the 2nd year or longer. The various immature stages have
variable durations, especially the nonfeeding periods. Incubation may range from 4-5 days to 6
weeks, and the triungulinid, after a free-living phase that may take 3-4
weeks, spends an additional week or more feeding before it molts. Three to 5 weeks seems a normal figure for
the feeding stage. The caraboid stage
takes about one week, and the two scarabaeoid stages total about the
same. The coarctate or pseudopupal
stages are those in which hibernation or diapause occurs most frequently. Thus, they vary greatly in length, even
within a single species. Cros
determined that in H. nymphoides a portion of the eggs of
the 2nd generation may carry over to the following spring. Fabre found that the triungulinids of A. muralis
persist in dense clusters through winter, while a few species hibernate in
the adult stage in the host cells.
The scolytoid stage of E. vittata takes only a few days, while
in E. lemniscata it takes 11-21 days and is extended in Zonabris pustulata Thbg. to 10-60 days (Verbeek 1932). In Z.
zebraea the pupal stage is 2 weeks
and in Tricrania sanguinipennis it is 24 days. Ingram & Douglas (1932)
commented on an unusual variation in habit of E. lemniscata, which is
a predator of grasshopper eggs. In
the summer generation, development through the immature stages is rapid and
the scarabaeoid larva changes directly to the pupa, omitting the coarctate
and scolytoid stages. These two
stages appear in the overwintering generation or under unfavorable
conditions. These two instars are
lacking entirely in Macrobasis immaculata. For detailed
descriptions of immature stages of Meloidae, please see Clausen (1940/62). = = = = = = = = = = = = = = = References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] Bhattacharjee, P
& R. T. Brodell. (2003).
"Cantharidin". In Robert T. Brodell and Sandra Marchese Johnson,
eds. Warts: Diagnosis and Management—an Evidence-Based Approach.
London: Martin Dunitz. pp. 151–160.. Ingram, J. W. & W. A. Douglas. 1932. J. Econ. Ent. 25: 71-4. Insects
of Australia. 1991. CSIRO, Division
of Entomology, Melbourne University Press, 2nd Edition 1991, 668 p. Matthews, E. G. 1985. A guide to the
Genera of Beetles of South Australia Part.5, p. 9. Picker, M., C. Griffiths & A. Weaving.
2002. Field Guide to Insects of South Africa.
Struik Publishers, Cape Town, 444 pp. Pinto, J.
D. 1991.
The taxonomy of North American Epicauta
(Coleoptera: Meloidae), with a revision of the nominate subgenus and a survey
of courtship behavior. J. Univ.
Calif. Publ. 110 van Dyke,
E. C. 1928.
Univ. Calif. Publ. Ent. 4:
395-474. |