SP-401 Skylab, Classroom in Space

[168] Part III - Science Demonstrations
 

Chapter 17: Life Sciences.

picture of the Apollo/Skylab capsule being hoisted aboard a recovery ship

 

[169] Between 1970 and 1972, approximately 6 million acres of trees were damaged by gypsy moths (Porhetria dispar lepidotera) in the eastern United States, and the destruction became more widespread in the years following. Oak trees are particularly susceptible to damage. White oaks, especially, showed a mortality rate of 80 percent after exposure to the moths for only 2 years.

For many years the gypsy moths were controlled by DDT. Since the use of DDT was prohibited in 1969 because of its detrimental ecological effects, the gypsy moth population grew unrestrained. No entirely satisfactory physical or chemical deterrent other than DDT has since been discovered to control the destructive pests.

 

Gypsy Moth Life Cycle

The typical life cycle of a gypsy moth starts with the laying of eggs in late summer. The eggs then undergo a 9-month dormant or hibernation period called diapause and hatch in the spring as larvae, simultaneous with budding of trees. It is the larvae that are most destructive, as they devour the shoots and leaves of the young trees. They live for about 6 weeks before entering another dormant phase of 2 weeks as pupae. July generally marks the emergence of the young gypsy moths. Each female moth will then normally produce some 700 eggs. The lifetime of the moth is less than a year, but its population growth is enormous because of the total number of eggs laid and hatched.

One of the few promising methods of suppressing the moth is by the sterile male technique, which involves rearing large numbers of insects in the laboratory and exposing the males to small doses of radiation to render them sterile. The sterile males are released and allowed to disperse throughout the general moth population. The eggs produced by females that mate with sterile males never hatch. Over a period of years, this technique could be expected to reduce the insects.

The major drawback of this technique is the length of time required to obtain new generations of sterile males. The wild population is expanding too rapidly, while the laboratory population does not develop quickly enough. A significant advantage would be to reduce the diapause for the laboratory groups, but no techniques have yet been found to accomplish such biological change.

It was hoped that the weightlessness of Skylab might induce some intracellular redistribution of material within the embryo or alter the permeability of cell membranes to cause an early end to diapause. Research performed in biological experiments on the Biosat 2 satellite in 1967 had demonstrated the feasibility of such approaches. Thus, the purpose of the experiment was to prematurely terminate the diapause of gypsy moth eggs by exposure to zero gravity. It required a cooperative effort among the Department of Agriculture's Agricultural Research Service and its Animal and Plant Health Inspection Service (APHIS) and NASA.

 


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Gypsy moths are among the worst destroyers of trees, especially the white oak.

Gypsy moths are among the worst destroyers of trees, especially the white oak. The life cycle of the pest is shown here with two females laying eggs (1), as many as 700 at a time. The eggs hatch into caterpillars (2) that begin devouring young shoots and leaves (3). A forest can be almost totally destroyed by the caterpillars (4). The caterpillars then mass together for a dormant period of 2 weeks (5) before emerging as adult moths (6) ready to repeat the life cycle. (Courtesy Charles Herron, U.S. Department of Agriculture.)

 
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Gypsy moth eggs were carried to Skylab as a part of an experiment to determine whether weightlessness would affect the life cycle of the insect.

Gypsy moth eggs were carried to Skylab as a part of an experiment to determine whether weightlessness would affect the life cycle of the insect. The demonstration was part of a plan for controlling or eliminating the moth.

 

Five hundred gypsy moth eggs were collected from forests near State College, Pa., in October 1973. They were removed from their hairy mass, cleaned, and placed in a vial labeled "wild." Another 500 eggs, from the APHIS Laboratories in Massachusetts, were packaged and labeled "tame." The wild eggs were thought to have been laid about 6 weeks prior to the laboratory eggs. Two vials, containing 200 eggs each from the same populations as the flight eggs, were maintained under similar environmental conditions for the ground-control groups.

The wild and tame vials were launched in the Apollo spacecraft with the third crew, which then checked the vials daily to determine if any of the eggs had hatched. Throughout the 84 days of the mission, only seven of the wild eggs hatched, but their diapause had been reduced significantly from 9 months to 5 months. None of the tame eggs hatched during the period.

The crew brought the vials back, and the eggs and larvae were returned to their laboratories. Nine more of the wild eggs hatched after return to Earth, with diapause between 9 and 12 months. Only one tame egg hatched, with an 8-month diapause. The moth, a female, was named Astromoth 1 and was reared to adulthood and mated with a male gypsy moth hatched on Earth. Her brood of 300 to 400 eggs was to be examined for morphological changes upon hatching. However, none of them hatched; neither did any of the ground-control eggs.

The results of the experiment were inconclusive. The wadding near the cap of each vial may have prevented adequate oxygen from reaching the eggs. Or, perhaps the regulated humidity of both Skylab and the ground controls was too low, causing the egg shells to harden so that the larvae could not crack through. The fact that none of the ground-control eggs hatched indicated that spaceflight was responsible for the limited success.

Diapause did terminate after 5 months, about half the normal time, for 7 of the 17 flight eggs that hatched. This does indicate some promise for successful results, and the Department of Agriculture is interested in further experiments on Space Shuttle flights. However, in the past few years, other population-control techniques such as new insecticides, parasites, and insect viruses have demonstrated greater effectiveness than the sterile....

 


Astromoth 1 survived the rigors of being flown into space and returned to Earth as an egg.

Astromoth 1 survived the rigors of being flown into space and returned to Earth as an egg. She hatched out and was later mated with an Earth-born male gypsy moth. Unfortunately, none of her eggs hatched.

 

[172] ...male technique for restraining the gypsy moth population. The significant result of this experiment was the demonstration that zero gravity can induce alterations in some biological processes of life forms accustomed to Earth's gravitational field.

 

Fish Otolith Organ

To obtain a better understanding of the vestibular or otolith organ, which enables an animal to maintain its balance or normal orientation to the gravity force of its natural environment, two small fish were launched with the second Skylab crew. Since, under spaceflight conditions, it is not possible to obtain all of the necessary physiological data about vestibular function from men alone, additional data from animals were desired.

The experimental animals selected had to meet several fundamental requirements. They had to be small and require little or no care by the crew. Also, they had to respond quickly and consistently with regard to their vestibular function. Their vestibular system had to be similar to that of higher forms of life, and they must have been the subject of correlative studies on Earth. The obvious candidate was a small fish. The fish selected for Skylab was the common mummichog (Fundulus heteorclitus), which is found along the Atlantic coast of the United States.

Two fingerlings and 50 fertile eggs were carried to Skylab by its second crew. After 3 days in orbit, their plastic acquarium was opened, and the fingerlings were observed to be swimming in an odd, circular pattern. The fish looped sideways, keeping their backs to the light. Loops of small radius alternated frequently with loops of larger radius. The fish swam in left loops about as much as they swam in right loops. This looping swimming decreased slowly in orbit until a normal pattern of swimming prevailed. Within 21 days, the two fingerlings appeared to have adapted to weightlessness, but they would still loop when their plastic acquarium was shaken.

The eggs started hatching after 19 days, with the majority of them doing so during the fifth and sixth weeks of the mission, approximately 2 weeks after the control eggs on Earth hatched. Visual orientation was immediate upon hatching; the young fish kept their backs toward the light as their Earth-hatched cousins also did. However....

 


Fertile eggs of the mummichog fish were flown to Skylab as part of an experiment to determine the role of the otolith organs in maintaining balance.

Fertile eggs of the mummichog fish were flown to Skylab as part of an experiment to determine the role of the otolith organs in maintaining balance.

 

[173] ....they also exhibited the abnormal swimming in tight circles only when the bag aquarium was shaken.

It appears that the Skylab fish utilized visual orientation, turning their backs to the light, as a substitute for gravity. Earth studies on a centrifuge have indicated that the orientation of fish is influenced both by the direction from which the light comes and the direction of the pull of gravity. In Skylab's zero gravity, the fish kept their backs to the light with no measurable deviation. The phototropic (orientation toward light) orientation and the relatively flat aquarium probably explain why they swam in loops. The fish were probably responding to signals from extremely fine hairs in their otolith which straighten out in the absence of gravity. They reacted by swimming in a forward loop which was distorted into a sideways loop by the tendency to keep their backs to the light. Additional experimentation will be needed to explain fully the strange looping and the apparent phototropic response of the fish. The fish hatched in orbit apparently adapted to the zero gravity while still in the egg.

 


The Skylab aquarium simulated a natural environment for the fish, except for gravity, by providing a dark background (bottom of pond) and a lighted surface (sky).

Two mummichog minnows were also sent into space to observe their reactions to weightlessness. They are barely visible, while eggs can be seen near the top of the photograph.

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The Skylab aquarium simulated a natural environment for the fish, except for gravity, by providing a dark background (bottom of pond) and a lighted surface (sky).

Two mummichog minnows were also sent into space to observe their reactions to weightlessness. They are barely visible, while eggs can be seen near the top of the photograph.


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