Download The Effect of Exposure to Dry Conditions on the Eggs of Aeneolamia

1963]
Ross, Mary H., and D. G. Cochran. 1962. A body
colour mutation in the (.German cockroach. Nature
195: 518-9.
MATERIALS AND METHODS
Eggs were obtained by caging A. varia saccharina
adults in 1-pound jam jars, with two pieces of sugarcane
leaf for food and a wad of moist filter paper for egg
laying. The eggs were extracted from the filter paper
with fine forceps, counted, and set out on moist filter
paper in petri dishes.
In one experiment, 34 eggs were used which had not
hatched after 40 days' incubation at 25° to 26° C, and
which apparently were in diapause. These eggs were
randomly separated into 2 equal groups of 17 eggs
each. One group was kept in moist conditions throughout the experiment. The other group was transferred to
dry filter paper in an open petri dish and was kept dry
(r.h. 30% to 40%) for 10 days. The filter paper was
then moistened, a cover was placed on the dish, and the
eggs were kept moist thereafter until hatching was
complete.
Material for a second experiment consisted of a batch
of 44 eggs which had not hatched after 54 days' incubation at 25° to 26° C.; this batch was divided into 2
groups of 22 eggs each. One group was maintained continuously moist and the other was kept dry, as above,
for 20 days, then returned to moist conditions.
A third experiment was carried out in an outdoor
insectary at temperatures ranging from 21° to 32° C.
The Effect of Exposure to Dry Conditions
on the Eggs of Aeneolamia varia saccharina
( Homoptera: Cercopidae ) 1
I). W. FKWKES
Tate & Lyle Central Agricultural Research Station,
Waterloo Estate, Carapichaima, Trinidad, B.W.I.
The ecology of the Trinidad sugarcane froghopper,
Aeneolamia varia saccharina Distant, is greatly influenced by the moisture content of the soil, in which more
than 98% of the eggs are laid (Pickles 1933). During
the dry season (late December to mid-May), when soil
moisture is generally at a low level, the froghopper
population is largely diapausing in the egg stage. Thus
the eggs must be fairly resistant to dry conditions if
they are to survive.
1
719
SCIENTIFIC NOTES
Accepted for publication April 16, 1963.
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Fig. 1.—Effect of exposure to dry conditions on hatching of diapause eggs of Aeneolamia varia saccharina.
A. 34 eggs laid December 29, 1961, of which 17 (solid circles) were kept moist continuously and 17 (open circles)
were exposed to dry conditions for 10 days (February 7 to 17, 1962). B. 44 eggs laid December 17-18, 1961,
of which 22 (solid circles) were kept moist continuously and 22 (open circles) were exposed to dry conditions
for 20 days (February 9 to March 1, 1962).
720
ANNALS OF T H E ENTOMOLOGICAL SOCIETY OF AMERICA
(mean, 26° C.) to test the effect of exposure to dry
conditions on nondiapause eggs. One hundred fifty eggs,
laid by a group of females, were kept in moist conditions in the insectary. At 6 days after oviposition,
these eggs were separated at random into 5 equal groups
of 30 eggs each. All apparently were fertile, with the
black "hatching lid" visible beneath the hatching line
(Fewkes 1962). One batch of eggs was retained in
moist conditions. The other four batches were transferred to dry filter paper in petri dishes and were kept
dry for 2, 4, 8, and 16 days, respectively. After remoistening, all these cultures were kept moist throughout the remainder of the experiment.
RESULTS AND DISCUSSION
Exposure of diapausing eggs to dry conditions for
10 and 20 days generally accelerated their hatching: that
is, it tended to break diapause. The viability of the eggs
was not significantly affected. The eggs kept dry for
10 days hatched from the 10th to the 20th week after
oviposition, or 3 to 13 weeks after treatment. Those,
kept moist did not commence hatching until the 12th
week, and only 3 of the 17 eggs had hatched by the
20th week. Hatching of the eggs kept dry for 20 days
started later (14 weeks) than that of eggs kept moist
(11 weeks), but proceeded at a more rapid rate up to
the 20th week (fig. 1), when 86% and 45%, respectively,
of the eggs had hatched.
Exposure of nondiapause eggs to dry conditions delayed their hatching, but did not appear to affect the
viability of the eggs. In this experiment, 3 of the 150
eggs used had not hatched at 140 days and may have
been in diapause. The number of days required to
achieve a 90% hatch under the various treatments, with
days of exposure to dry conditions stated in parentheses,
were: 17(0), 18(2), 20(4), 25(8), and 36(16), respectively.
The results indicate that both diapause and nondiapause eggs of A. varia saccharina are fairly resistant to
dry conditions. This is of interest, as it is known that
even during the dry season a variable proportion of nondiapause eggs is laid (Fewkes 1962). The termination
of diapause by exposure to dry conditions has not been
reported for any other insect. It seems quite possible
that, in the field, this may lead to the synchronous
hatching of eggs of A. varia saccharina at the onset of
the wet season. Further study is required to elucidate
the physiological mechanisms involved.
REFERENCES CITED
Fewkes, D. W. 1962. In: Tate & Lyle, Central Agric.
Res. Sta., First Quarterly Rept., January 1962.
Pickles, A. 1933. Entomological contributions to the
study of the sugar cane froghopper. Trop. Agric,
Trinidad, 10: 286-95.
Survival of Isolated Insect Tissues
Following Radiation1
WESLEY LARSEN
College of Southern Utah, Cedar City
Tissues used in this experiment were obtained from
embryos of the cockroach Blabems craniifer Burmeister.
Dorsal closure and heart formation take place at 39 days
of development in this species of cockroach. The heart
starts beating posteriorly even before it is completed
anteriorly. Contractions are regular and at a rate of
about 35 per minute.
1
This research was supported by A.E.C. Contract No. AT
(ll-l)-1030. Accepted for publication February 7, 1963.
[Vol. 56
METHODS AND RESULTS
After 40 days of embryonic development, oothecae
were removed from gravid females that had been
anesthetized with ether and surface sterilized with a
solution of 0.05% HgCla in 50% ethyl alcohol. In turn,
the oothecae were surface sterilized, rinsed in distilled
water, and placed in sterile Ringer solution. Individual
eggs were separated from their ootheca, micropylar tips
cut off, and the embryos squeezed out of the chorion
through the cut opening at the tip of the egg. Fragments
of heart, 1 to 2 mm long, were excised with iridectomy
scissors and placed in culture dishes containing medium
T.C. 199 fortified with 2% bactopeptone. Most heart
fragments when transferred from Ringer to T.C. 199
picked up air bubbles that caused them to float on the
surface of the liquid. This phenomenon facilitated observation. Streptomycin and mycostatin (Squibb nystatin)
were added without apparent inhibitory effect on the
tissue; at least, there was no change in the rate of heart
contraction or in appearance of the cells. The fragments
were maintained at 25° C. Several fragments continued
to beat for 160 days in the synthetic medium.
Each heart fragment consists of a muscular tube, a
dorsal epithelial layer, and fat body cells lateral to the
heart tube. As a fragment aged the amount of fat body
tissue gradually diminished until after 65 days had
passed little of the fat body around the heart tube and
beneath the epithelium remained. The fat body tissue
was either utilized as energy or disintegrated into the
culture medium. Evidence points to the former supposition, since fat-body tissue persisted on fragments that
failed to contract but that remained in the medium for
the same period of time as those that were active. A
fragment covers a body area of two or three segments,
and, although the contraction was synchronized for
several weeks following excision, in older specimens each
segment beat independently of the others.
Excised tissues other than heart fragments also were
used in this preliminary study, some only to ascertain
their survival in medium T.C. 199, the remainder to
serve as material for irradiation. An isolated head of a
40-day embryo displayed contraction of the dilator
cibarii muscles of the clypeus for 170 days after severance from the remainder of the body. The mandibles
on this same head had become pigmented and chitinized
during that time interval, changes that take place in the
normal embryo at between 65 and 75 days of development. An entire 28-day embryo with the yolk and embryonic membranes removed was alive after 150 days.
Dorsal closure had taken place in the posterior portion
of the body, the heart pulsating regularly in that region.
Growth in the size of the embryo did not occur. Isolated
Malpighian tubules show writhing movements in the
culture medium. Sections of hindgut exhibit both
peristaltic and gross movements.
A series of 24 hearts was given dosages of X-irradiation varying from 1,000 to 12,000 roentgens. All, except
six which succumbed to bacterial infection, continued to
live and contract for 150 days after the treatment.
Whole embryos and adults have a lethal point of about
7,000r.
Another series of 22 hearts, 11 clusters of Malpighian
tubules, and 11 portions of hindgut was treated with
Cobalt-60 dosages up to 93,000 rads. The tubules continued to pulsate for 15 days, hearts to beat for 23 days,
and hindguts to carry on gross movements for 60 days
after maximum treatments.
This extreme resistance to gama radiation may be due
to the very low oxygen requirements of these tissues.
In an attempt to find some clue as to the oxygen requirement, six gravid females containing eggs that were
1, 17, 22, 27, 33, and 36 days old were placed in a gallon
jar holding a lighted candle. The jar was tightly
sealed, and the candle consumed some of the oxygen.
The sealed jar also held a Bray dish containing a