Autecology and biology of Nemoptera sinuata Olivier (Neuroptera: Nemopteridae)

Abstract

Specimens of Nemoptera sinuata were reared from eggs to second instar larvae in captivity, and observations on imagos were carried out in the Struma Valley, Bulgaria. The adults occur in open sunny places in river gorges and feed only on pollen. They are most active at noon be- tween the middle of May and the end of June. The males occur one week earlier than the fe- males. The eggs are laid directly on the ground, most often in the morning. They are spherical (rare among Neuroptera), white, opaque, with one micropyle. Up to 70 eggs are laid by a fe- male over a period of 10 days. The egg stage usually lasts from 23 to 25 days. The lid is cut off by an eggbreaker during hatching. The newly hatched larvae are 2.0-2.1 mm long, are terricolous and always buried themselves by digging to 1 cm in depth. The larvae rejected liv- ing or freshly killed arthropods, or roots and blossoms of plants. They were only observed to take water and vegetable sap. The longest surviving larva moulted in September (first instar lasts 72 days) and hibernated. It increased in length to5 mm and died in April after being reared for nine months.

Full text

Acta Zoologica Academiae Scientiarum Hungaricae 48 (Suppl. 2), pp. 293–299, 2002
AUTECOLOGY AND BIOLOGY OF NEMOPTERA SINUATA
OLIVIER (NEUROPTERA: NEMOPTERIDAE)
A. POPOV
National Museum of Natural History, Blvd Tsar Osvoboditel 1, BG-1000 Sofia, Bulgaria
E-mail: nmnhnd@bgcict.acad.bg
Specimens of Nemoptera sinuata were reared from eggs to second instar larvae in captivity,
and observations on imagos were carried out in the Struma Valley, Bulgaria. The adults occur
in open sunny places in river gorges and feed only on pollen. They are most active at noon be-
tween the middle of May and the end of June. The males occur one week earlier than the fe-
males. The eggs are laid directly on the ground, most often in the morning. They are spherical
(rare among Neuroptera), white, opaque, with one micropyle. Up to 70 eggs are laid by a fe-
male over a period of 10 days. The egg stage usually lasts from 23 to 25 days. The lid is cut off
by an eggbreaker during hatching. The newly hatched larvae are 2.0–2.1 mm long, are
terricolous and always buried themselves by digging to 1 cm in depth. The larvae rejected liv-
ing or freshly killed arthropods, or roots and blossoms of plants. They were only observed to
take water and vegetable sap. The longest surviving larva moulted in September (first instar
lasts 72 days) and hibernated. It increased in length to 5 mm and died in April after being
reared for nine months.
Key words: Nemoptera sinuata, imaginal ethology, feeding, oviposition, egg, hatching, larva
INTRODUCTION
Investigations on the autecology and the early stages of Nemoptera sinuata
OLIVIER, which are reported here, were carried out more than 30 years ago. They
included a rearing from imago to second instar larva. The observations and conclu-
sions on the behaviour, feeding and habitat of the adults and the larvae were the
subject of my thesis (POPOV 1967). These observations were not published be-
cause I expected to continue the rearing of a mature larva, prepupa and pupa.
At the time of the investigations there was no information on either the egg
and larva, the biology and habits of the larva, or the feeding and behaviour of the
imago. There were almost no detailed data on the whole family Nemopteridae
sensu MONSERRAT (1996), now comprising 90 taxa. The development and the
preimaginal stages of a number of species, mainly from the closely related family
Crocidae distributed in the southern Hemisphere, has recently been investigated by
MANSELL (1973, 1981, 1983a,betc.) and of Nemoptera bipennis (ILLIGER) and all
the Spanish representatives of both families by MONSERRAT (1983a, b, 1985a,
1996). A mature larva of Nemoptera coa (LINNAEUS) from Greece was reared to
imago by TRÖGER (1993). Their results are very similar to my observations on
Acta zool. hung. 48 (Suppl. 2), 2002
Hungarian Natural History Museum, Budapest

Nemoptera sinuata. The pollenophagy of the adults of N. sinuata was observed for
the first time and my suggestion (POPOV 1967), that the structure of the mouthparts
in the whole family Nemopteridae sensu lato proves feeding only on pollen, was
confirmed by field observations of some authors, e.g. MONSERRAT (1985b)on
N. bipennis and PICKER (1987) on Palmipenna aeoleoptera PICKER. Also my pro
-
posal (POPOV 1973) that Nemopterinae and Crocinae should be regarded as dis-
tinct families, if essential differences in all stages were confirmed after the discov-
ery of the larvae of other genera, was realized by MONSERRAT (1996).
IMAGO
The observations on the imago of N. sinuata were carried out in 1965–1967
in the field in Kresna Gorge along the valley of Struma River in southwestern Bul-
garia and in captivity in Sofia. For this purpose living nemopterids were trans-
ferred to broad glass tubes containing blooming flowers. They were reared be-
tween glass and cloth screen with blossoming plants in glass jars with water.
The imago of N. sinuata occurs in meadows and open sunny places with
Mediterranean and Submediterranean vegetation in sheltered river gorges. The
adults prefer the yellow blossoms or racemes of plants, such as Achillea coarctata
POIR. (Asteraceae), Alyssum murale WALDST.etKIT. (Brassicaceae) and Hyperi-
cum rumeliacum BOISS. (Hypericaceae).
The flight period usually lasts from the middle of May to the end of June with
the earliest and latest collecting dates May 2nd and July 8th. The phenological
maximum is in the first ten days of June. The males occur one week earlier than the
females.
The flight of N. sinuata is easy and graceful, but slow. The flapping is done
only with the forewings, while the hindwings remain static. The coloration of the
wings provides effective camouflage and the adults are difficult to see. The imagos
begin to fly in the morning and are most active at noon in sunny weather. In cloudy
weather they remain perched on the blossoms with their forewings wide open and
their hindwings directed at an angle of 40–45° and slightly twisted towards the
ends. When it rains, they retreat below the blossoms with their forewings up above
the back.
N. sinuata is a diurnal insect. It flies, feeds and lays eggs only during the day.
When reared in a room or in a cage, the adults always fly and settle on more illumi-
nated or sunlit spots.
The specimens reared under different conditions in captivity lived from 5 to
13 days. Taking into consideration that they were caught in the middle of the flight
294 A. POPOV
Acta zool. hung. 48 (Suppl. 2), 2002

period of the species in the same locality and that all females had already been fer-
tilized and were laying eggs, it can be assumed that in the field the life span of the
adults is nearly 20 days.
The observations in 1965 showed that the imago of N. sinuata feeds exclu-
sively on pollen. It inserts its mouth parts into the floret cornet of Achillea and tears
off the pollen bags. The clypeus and labrum of the insect become covered with pol-
len. The imago occasionally collects pollen with the tarsi of the forelegs, wiping
the tarsi through its mouthparts and swallowing the pollen. The mouthparts of N.
sinuata and Nemopteridae s. l. as a whole have a tearing function rather than chew-
ing and are structured to feed only on pollen (Fig. 1). The main role in feeding is
played by the maxillae and the labium, while the almost immovable mandibulae
and labrum have no part at all. The maxillae move simultaneously and quickly up
and down due to the strongly movable articulation between the stipes and the
palpifer. The same movements are executed by the strongly elongated labium.
During feeding the rostrum projects into the floret, opening it, and the distal parts
of the maxillae and the labium, namely both galeae and both pairs of palpi, with
their upward movements draw out the pollen grains from the bottom of the chalice
to the mouth opening. The pollenophagy in N. sinuata was also confirmed by the
analysis of the gut contents and the excrements of the imago. Both the pro-
ventriculus and the ventriculus were filled with whole grains, and the excrements
with their shells, which are the same as the reference sample of pollen grains of
Achillea coarctata. Thus the pollenophagy in nemopterids was recorded for the
first time and accepted by analogy for the whole family because of the structure of
the mouthparts. This was confirmed by the finding of pollen in the gut contents of a
number of species by TJEDER (1967) and by observations on other species by other
authors (see Introduction).
AUTECOLOGY AND BIOLOGY OF NEMOPTERA SINUATA OLIVIER (NEUROPTERA) 295
Acta zool. hung. 48 (Suppl. 2), 2002
12
Figs 1–2. Nemoptera sinuata: 1 = feeding on a raceme of Achillea coarctata; 2 = eggs

EGG
The eggs are usually laid in the morning. The female, with half open wings
and a drooping abdomen, perched on blossoms or racemes of plants, e.g.Achillea.
An egg appears every two minutes and after 4–6 eggs the female moves on to an-
other raceme. The eggs fall directly to the ground or on dry vegetation. They are
not adhesive, but elastic and bounce when coming into contact with a hard surface,
as for example a piece of wood.
The eggs (Fig. 2) are spherical, snow-white, opaque, lustreless, with a diame-
ter of 0.83–0.90 mm and with one micropyle. It should be mentioned that the genus
Nemoptera is one of the few genera among all Neuroptera with spherical shape to
the eggs. The chorion is highly sculptured, with irregular hexagonal convexities on
the surface, which touch one another. About 30 convexities have been counted on
the periphery of the egg and about 180 convexities on the whole egg surface. When
seen from above, the micropyle has the form of a disk; in profile it looks like a cor-
net with no opening in it.
According to the observations in the laboratory, the number of eggs laid by
one female is up to 70. Eggs are laid for about 10 days during the total life span of
20 days of the female. Within the first five days the number gradually drops from
14 to 9 eggs per day.
The egg stage covers 20–26 days on the basis of the rearings in 1965–1967,
most frequently 23–25 days at air temperatures of 19–27° in the laboratory. The
duration of the egg phase depends on the temperature. For example, 16 eggs were
put in a refrigerator for 10 days at 6° and the larvae were hatched with 12 days de-
lay. While at 30–32° temperatures the hatching occurs after 19 days.
LARVA
After the fifteenth day the egg becomes light pink and then grey on one side.
The embryo lies in the form of a semicircle in the egg. A polar lid with the
micropyle in the centre is opened during hatching. The lid is cut off by an egg-
breaker on the larval clypeus. The egg-shell breaks by pressure from the dorsal sur-
face of the larva. The split becomes almost a complete circle and the lid separates
without breaking from the egg. The larva pulls out the dorsal part of the thorax
first, then the head in two or three minutes and the abdomen at the end. Filling its
tracheae with air, the larva becomes bigger in one to two hours and begins to move
slowly, until it hides.
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The newly hatched larva is 1.7–1.8 mm long or 2.0–2.1 mm long including
the jaws. It is dorsally grey, with an oblong transverse dark spot on both sides of the
median line of every thoracic and abdominal segment and a large, almost black
spot on the head. The body densely is haired with long and short setae: macro-
trichia, dolichasters and micrasters. The length of some of the macrotrichia is equal
to almost one third of the body length. The head is trapezium-shaped to rectangu-
lar, 0.38 mm long and 0.55–0.65 mm wide, and occupies together with the jaws
more than one third of the body in length. The slowly movable head moves only in
a vertical direction. The jaws are large, broad, gradually curved inwards, sharply-
pointed at the apices, with a flat and rounded outer margin covered with long
macrotrichia, with 9 short dolichaster-like setae on the inner margin. The eye spot
consists of 7 stemmata. Antennae are composed of one small basal segment and
one large, curved, rounded and dilated segment. Palpi labiales are very short,
four-segmented. Legs are short, with hard spines. The abdomen is broad and ten-
segmented. The first instar larva of N. sinuata from Bulgaria is very similar to that
of N. bipennis reared by MONSERRAT (1996). The former differs from the latter in
the shape of the black spot on the head and in its wide and short abdomen.
I could not find any living larvae in the field, to define their habitat. When
reared in captivity in 9 microhabitats (soil, sand, peat, leaves, etc.), the larvae al-
ways buried themselves by digging to 1 cm depth. They are consequently assumed
to be terricolous.
For the entire duration of rearing (9 months) no answer was found to the
question of how the larvae feed. They were offered the common caterpillars of Plo-
dia interpunctella (HÜBNER), larvae of Tenebrio molitor LINNAEUS, imagos of
Drosophila FALLÉN,Musca domestica LINNAEUS,Sitophilus granarius (LIN-
NAEUS), as well as field-collected Collembola, Acarina, Psocoptera, Psyllina, For-
micidae and various families of Diptera. The larvae of Nemoptera paid no attention
either to living, or to freshly killed small arthropods, or to cut out pieces of those
with body fluids. The result was also negative with Enchytraeidae, Tubifex LA-
MARCK, segments of Lumbricidae, living snails, as well as with mellow roots of
herbaceous plants or their blossoms. The larvae were only observed to dip the api-
ces of their jaws into drops of water and into the sap of newly cut carrots or pota-
toes. The typical predatory feeding habit as well as the parasitic one is not charac-
teristic at least for the first instar larva of N. sinuata. The hypothesis of MONSER-
RAT and MARTINEZ (1995) on possible myrmecophily of Nemopteridae s. str. in
the larval stage seems quite probable bearing in mind the rejection of a wide range
of prey by the larvae of N. sinuata in Bulgaria and of N. bipennis and Lertha sofiae
MONSERRAT in Spain, as well as the experiments for harvesting of eggs and even-
tually of young larvae by some ant species in their nests. The successful feeding of
AUTECOLOGY AND BIOLOGY OF NEMOPTERA SINUATA OLIVIER (NEUROPTERA) 297
Acta zool. hung. 48 (Suppl. 2), 2002

the third instar larva of Nemoptera coa in captivity by TRÖGER (1993) only ap-
pears to contradict the hypothesis. Feeding on ant larvae may be necessary and
obligatory for only the first and eventually the second instar larvae of Nemoptera.
The longest reared larva moulted on 23rd September; the instar lasts 72 days.
The second instar larva has a more elongated body, darker coloration and a rela-
tively smaller head, corresponding to one fifth of the body. Every segment has a
small tubercle laterally with tufts of black macrotrichia.
The larvae move slowly and clumsily, and only forwards. They cover about
6 cm over 30 seconds. The larvae always try to bury themselves, going forward
with their head. When touched, they become immovable and appear to be dead.
This lasts from half a minute to one minute or rarely two minutes.
The longest living larva was left to hibernate at the end of November. A small
bowl with sand was put in a bigger bowl with regularly moistened sand at tempera-
tures between +5° during the night and 10° during the day. The larva spent the win-
ter in the sand in the form of a crescent without making any nest around itself. After
being taken out of the sand, it would become active after several minutes. After the
hibernation, it still did not accept food. The larva died on 9th April next year after
being reared for nine months. Although no feeding was observed, the larva in-
creased in size from 2 mm at hatching to 4.1 mm at moulting to 4.8 mm before hi-
bernation and to 5 mm in the end of its life.
In conclusion, the known first half of the life cycle afforded an opportunity to
speculate on the development of N. sinuata. It probably passes through a second
moulting at the beginning of summer, hibernation of the third larva, forming of a
cocoon in April and emerging of the imago after one month total duration of the
prepupal and pupal stages.
*
This report was presented on the Sixth International Symposium on Neuropterology held in
Helsinki in 1997. Only an abstract of it has been published in the Proceedings of the Symposium
(POPOV 1998) because I intended to include the original data in a detailed comparative review on the
eggs, larvae and development of nemopterids. As that has not been realized, the full report is pub-
lished in the present volume.
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Revised version received 20th April, 2001, accepted 7th July, 2001, published 30th July, 2002
AUTECOLOGY AND BIOLOGY OF NEMOPTERA SINUATA OLIVIER (NEUROPTERA) 299
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