Ecology of the Hover Fly Episyrphus balteatus
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| Lizenz | Keine Open-Access-Lizenz: Es gilt deutsches Urheberrecht. Der Film darf zum eigenen Gebrauch kostenfrei genutzt, aber nicht im Internet bereitgestellt oder an Außenstehende weitergegeben werden. Dieser Film enthält Musik, für die die Verwertungsgesellschaft GEMA die Rechte wahr nimmt. | |
| Identifikatoren | 10.3203/IWF/C-7011eng (DOI) | |
| IWF-Signatur | C 7011 | |
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| Produktionsjahr | 1997 |
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| IWF-Filmdaten | Video ; F, 16 min |
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Transkript: Englisch(automatisch erzeugt)
00:16
Ecology of the hoverfly epi-surface baltiatus.
00:24
Flowering meadows are important habitats for nectar and pollen feeding insects. Umbelliferous flowers such as hogweed and angelica offer an ample source of nectar.
00:44
Butterflies, longhorn beetles, parasitic wasps and flies are all equally attracted. Composite flowers provide pollen and are frequently visited by the hoverfly epi-surface baltiatus.
01:18
Protein rich pollen serves as nourishment and helps mature the ovaries.
01:24
Slow motion cinematography reveals details of pollen collecting and feeding. The pollen is picked up by the labellum of the proboscis and transported into the pharynx. When the females have completed their maturation feeding, they forage for aphid infested plants along field and forest margins.
02:13
Agricultural crops such as wheat and bean plants are also searched for the presence of aphids.
02:36
Foraging females seek visual and olfactory stimuli associated with aphid colonies.
02:41
Honey dew droplets disposed of by aphids become indicative olfactory cues for patches that will provide prey for predatory hoverfly larvae.
03:15
Parthenogenesis, life birth, several offspring per female per day and reproductive rates of
03:21
more than 60 offspring per female all promote rapid multiplication of the aphid colony. This newly born aphid will immediately seek a suitable site for sucking plant sap.
03:42
After four molts and two weeks of juvenile development, it will also produce offspring. The aphid colony, shown in time-lapse photography, grows exponentially, providing abundant prey for predatory hoverfly larvae.
04:03
The presence of aphids is determined in three steps. Hovering beneath the aphid colony, the female pulls down scent-laden air. While dabbing aphids with her legs, chemoreceptors on the tarsi come in contact with aphid-derived chemicals.
04:29
After landing, dabbing aphids with her proboscis confirms, through gustatory stimuli, the presence of aphids.
04:47
To oviposit, the female moves over the colony with extended ovipositor and places an egg into a niche. Grooming behaviour often precedes oviposition. Slow-motion cinematography reveals intensive grooming, particularly of the compound eyes and antennae.
05:16
The fly rotates its head up to 180 degrees so that all zones become accessible for grooming by the legs.
05:25
Massaging the ovipositor with the hind legs initiates further ovipositions. If the aphids are widely spaced, the female will place an egg in the middle of the colony. Meccano and chemoreceptors on the ovipositor help determine the most suitable oviposition site.
05:54
Previously laid eggs do not alter the oviposition behaviour.
06:01
The female quantifies the size of the aphid colony and determines the number of eggs to be laid accordingly. Embryonic development under favourable conditions is complete after three days. Stabbing movements of the mouth parts and forward thrusting of the body rupture the chorion dorsally near the micropyle.
06:27
Already during hatching, the larva tests with protruded antennae for the presence of aphids. Remaining in the chorion, it waits for the tactile stimulus of a passing aphid that will trigger preying behaviour.
06:46
Also after hatching and despite abundance of prey, the larva waits for the tactile stimulus of an aphid. Preying behaviour comprises waiting for prey, perceiving the tactile stimulus, testing with the
07:14
antennae for the source of the stimulus, pursuing and capturing the fleeing prey.
07:32
To start with, adhesive substance released from lateral glands glues the left leg and left antenna of the aphid to the thorax of the larva.
07:42
Subsequently, the larva attaches itself to the head of the aphid and begins with stabbing movements of its piercing mouth parts to perforate the aphid's cuticle.
08:02
In this example too, preying behaviour was triggered by tactile stimuli from a passing aphid. The aphid unsuccessfully attempts to escape by twisting movements.
08:21
The larva has attached itself to the ventral side of the aphid and overcomes its prey, which exceeds the larva in both weight and volume. The third instar measures about one centimetre in length and has much greater food requirements.
08:42
This may have led to the evolution of extraordinary preying behaviour. Crawling up the stem of a bean plant, the larva approaches the edge of an aphid colony. Physical contact with aphids triggers the preying behaviour.
09:00
The larva moves over the colony constantly oscillating the thorax. With each oscillation, the antennae come in contact with the colony. As long as the antennae sense aphids, the larva excretes a glue which is constantly being released from glands of the forebody.
09:24
In this manner, a sticky cover is created. The aphids are connected to each other and fixed to the plant.
09:42
Subsequently, one aphid after another is consumed. Stabbing movements of the head and transfer of haemolymph indicate that the larva has begun to consume an aphid.
10:03
Of the former aphid colony, only the empty cuticles are left behind.
10:26
During its development, the larva has consumed several hundred aphids. With the excretion of faecal matter, the two-week larval stage is complete. Peristaltic gut movements force the dark faecal fluid through the anus.
10:52
The fluid will dry and remain as black spots on the plant, a symptom of the larva's former preying behaviour. To initiate pupation, the larva attaches itself to the plant.
11:13
Within 48 hours, a droplet-shaped white puparium is formed.
11:22
After 14 days, metamorphosis of the larva to the adult is complete. Exclusion begins. As the fly's head presses forward, the ventral and dorsal lid of the puparium are pushed apart.
11:41
The antennae become free and take up their natural position. With peristaltic movements, the fly pushes itself forward.
12:01
As the wing base becomes visible, the legs are freed. Grasping the plant, they help to pull the fly out of the puparium.
12:42
Swallowed air expands the gut and the abdomen. 20 minutes later, the wings are fully spread. Two hours later, the fly is capable of flight and ready to forage for food.
13:03
Umbelliferous flowers with readily accessible nectar are particularly attractive and often visited by many flies.
13:56
Flight apparatus and wingbeat frequency of more than 300 vibrations per second make hoverflies very agile flyers.
14:11
Wings and holtias vibrate with the same frequency but in anti-phase.
14:27
Sun-drenched forests provide the microclimate most suitable for mating. Shafts of sunlight penetrating the forest canopy are highly attractive to hoverflies.
14:45
In hovering flight, the male waits for a passing female which he will pursue and mate in flight. As flowers wither and the summer draws to a close, hoverflies become rare.
15:03
Mated females of the last generation overwinter. In early spring, they re-emerge and forage for pollen on willow catkins. Still rare in the spring, hoverflies will again be abundant in the summer and become frequent visitors of flowering meadows.