Mary Ann Rankin

The Influence of Time of Day on the Foraging Behavior of the Honeybee, Apis mellifera

The honeybee time sense, or Zeitgedächtnis, is highly adaptive, allowing bees to synchronize their foraging behavior with the peak time of daily floral nectar rhythms. Each foraging group within the honeybee colony shows a high degree of fidelity to one species of flower. Across the day, the temporal accuracy of foraging visits to experimental feeding times varies considerably, being nearly exact for morning-trained foraging groups but becoming less so for foraging groups trained later in the day. The evidence gained in this study suggests that the diel change in accuracy exhibited by foraging groups, which persists after the removal of many potential environmental time cues, is an endogenously driven behavior pattern. Fur thermore, it appears that individual bees are continuously and accurately aware of the time of day, but are programmed to forage with greater anticipation to late-day food sources. Therefore, two separate processes contributing to the honeybee time sense are implicated. The first varies with time of day and determines the amount of anticipatory activity directed toward the food source. The second process is invariant across the day and is involved with the individual foragers continuous, accurate awareness of time.

Hormonal control of migratory flight in Oncopeltus fasciatus: The effects of the corpus cardiacum, corpus allatum, and starvation on migration and reproduction

Abstract The effects of starvation on the activity of the corpus allatum (CA) and on migratory flight behavior and as the effect of the corpus cardiacum (CC) on migratory behavior were examined. Juvenile hormone (JH) titer determinations were done on Oncopeltus hemolymph using the Manduca pigmentation bioassay. Starvation resulted in a decrease in measureable JH in Oncopeltus hemolymph over a period of 5–6 days after which time JH titers were undetectable. Flight behavior increased for the first 4–6 days after the beginning of starvation, then decreased to very low levels as JH titers diminished. Topical applications of the JH mimic ZR512 to starved individuals 9 days after starvation restored flight to its former high level. However, implantation of three CC into starved Oncopeltus at this time had no effect on flight. Oviposition was also inhibited by starvation. Feeding Oncopeltus on suboptimal food (green pods) resulted in a significant delay in reproduction and an increase in flight activity similar to that seen in diapausing individuals. Therefore, JH is the primary hormone responsible for the stimulation and coordination of migration and reproduction while the CC appears not to be involved in the stimulation of migratory behavior in this species. Food shortage or suboptimal food appears to be important in initiating the spring migratory flight by maintaining the hemolymph JH titers at a level below the threshold for ovarian development but above that necessary to stimulate migratory flight.

Wing dimorphism in Gryllus rubens: genetic basis of morph determination and fertility differences between morphs

SummaryThe genetic basis of wing morph determination and fertility differences between wing morphs were studied in the wing-dimorphic cricket, Gryllus rubens. Using pair corsses, a significant effect of genotype on morph determination was documented in F3 progeny of field-collected crickets. The effect of genotype was significantly stronger in females than in males. Results are consistent with an earlier study (Zera and Tiebel 1988) showing that wing development is more strongly buffered from environmental variation in females. Segregation patterns were consistent with a polygenic mode of inheritance and provided no evidence for the existence of genes of major effect, maternal effects, or sex linkage. Only a weak morph x sex association was observed. These results contrast those of Walker (1987) where sex-linked loci of major effect on morph determination were identified in crosses between long-wing and short-wing-selected strains of G. rubens. Short-winged female G. rubens began ovipositing earlier and oviposited significantly more eggs than long-winged females during the first 24 days after adult eclosion. The greater reproductive output of the short-winged morph was due entirely to greater oviposition during the first two weeks after adult eclosion. Preliminary results indicate that flight may further accentuate the reduced reproductive output of long-winged versus short-winged females. These data provide the foundation for investigating the endocrine basis of morph-associated fertility variation in G. rubens and its mechanistic relationship with morph determination.

Juvenile hormone and ecdysteroid titres during critical periods of wing morph determination in Gryllus rubens

Abstract Juvenile hormone and ecdysteroid titre developmental profiles were compared between Gryllus rubens that were genetically-determined to develop into long-winged vs short-winged adults. Hormone titres were measured during the penultimate and last stadia, two periods during which wing length development is sensitive to exogenous juvenile hormone. No large differences in juvenile hormone titres were observed between nascent wing morphs during any stage in development. Slightly elevated titres were observed in long-wing vs short-wing-destined crickets during the middle third of the penultimate stadium. However, titre differences were opposite those inferred from earlier experiments involving topical application of juvenoids. An earlier decline in the juvenile hormone titre was also suggested in presumptive long-winged crickets during the last stadium. The earlier decline in macropters is consistent with previous juvenile hormone topical application experiments as well as with morph specific differences in juvenile hormone esterase activity. Peak ecdysteroid titres were higher in presumptive macropterous vs brachypterous males, while an elevated ecdysteroid titre occurred for a longer duration in macropterous females during the penultimate stadium. In both sexes, ecdysteroid titres were higher in presumptive long-winged vs short-winged morphs throughout the last stadium; peak titres were significantly higher in macropterous vs brachypterous females but not males. Both the longer duration of elevated ecdysteroid titres and the higher hormone titres in presumptive long-winged crickets are consistent with a regulatory role of ecdysteroids in wing morph determination.

Circadian locomotor rhythms in individual honeybees

ABSTRACT. The circadian locomotor (walking) rhythms of individual forager honeybees (Apis mellifera ligustica L.) were measured under a variety of conditions. In constant dark the rhythms exhibited endogenous periodicities that were less than 24 h, whereas under constant light the periods tended to be greater than 24 h. Individual honeybees readily entrained to photoperiods, displaying a diurnal pattern of entrainment with most of the activity occurring in late photophase. Evidence is presented which suggests that foraging behaviour and general locomotor behaviour may be governed by two different circadian clock systems.

SOME FACTORS AFFECTING PRESUMED MIGRATORY FLIGHT ACTIVITY OF THE CONVERGENT LADYBEETLE, HIPPODAMIA CONVERGENS (COCCINELLIDAE: COLEOPTERA)

Hippodamia convergens migrates long distances to and from mountain-top aggregation sites. It undergoes an imaginal diapause associated with a 6-9 month aestivo-hibernation at the aggregation sites. Laboratory tethered-flight tests can be used as an assay for migratory behavior. Beetles that fly 30 min on a tether will nearly always fly much longer.Long tethered flight is pre-reproductive in females, though apparently not in males. Starvation or poor quality food will greatly enhance migratory behavior. However, the tendency to display migratory behavior is greatly reduced in both sexes after about 7 days of optimum food. Even starvation at that time will not stimulate an increase in long-flight behavior. It would appear that some type of physiological committment to reproduction which excludes or greatly reduces the tendency to migrate is made at that time. Photoperiod has little effect on migratory behavior when food is poor. But under optimal feeding conditions, short photoperiod enhances long flight be...

Hormonal control of vitellogenin synthesis in Oncopeltus fasciatus

Abstract Previous work indicated the existence of two vitellogenins (A and B) in the haemolymph of Oncopeltus fasciatus, and that vitellogenin B was juvenile hormone (JH)-dependent whereas A was not ( Kelly and Telfer , 1977). We have extended these results using several electrophoretic techniques in combination with limited proteolysis of key proteins to show that (1) vitellogenin B is present in eggs in a modified form while vitellogenin A cannot be detected in eggs. (2) Vitellogenin A may be a precursor of B since it has a molecular weight of 200,000D, approximately three times that of vitellogenin B (68,000D) and analysis by limited proteolysis shows that two proteins to be nearly identical. (3) Neither ovariectomy nor treatment with the anti-allatotropin, precocene II prohibits the appearance of vitellogenins A and B in the haemolymph. (4) Injection of ecdysone or 20-hydroxyecdysone into adult, male Oncopeltus fasciatus induces the appearance of both vitellogenin A and B in the haemolymph, suggesting the possible involvement of ecdysteroids in the control of vitellogenin synthesis in this species. (5) We have no evidence for JH control of the synthesis of vitellogenin, however, the ratio of vitellogenin A to B in the haemolymph is higher in the precocene-treated females.

DIFFERENT PATHWAYS IN ARTHROPOD POSTEMBRYONIC DEVELOPMENT

To investigate the consequences of canalization and plasticity in arthropod developmental pathways, we developed a model that predicts eight possible combinations among three larval developmental parameters. From the descriptions of insect and spider postembryonic development, it is apparent that not all aspects of juvenile development are plastic and that species differ in which traits are plastic. Most strikingly, only four of the possible eight combinations of canalized and plastic parameters have been found in nature. Using this model, we show that the identity of the canalized developmental parameters and the degree of genetic variation in the value at which a given parameter is fixed have important implications for the ecology and evolution of complex life cycles.

VARIATION IN THE CHEMICAL COMPOSITION OF ORB WEBS BUILT BY THE SPIDER NEPHILA CLAVIPES (ARANEAE, TETRAGNATHIDAE)

Abstract The adhesive droplets in the orb webs of araneoid spiders contain, among other constituents, an aqueous solution of organic low-molecular-weight compounds. The chemical composition of this solution has been investigated for pooled web collections from several species, but little is known about how the composition might vary among individuals or among environments. To begin addressing these questions, we analyzed serial collections of orb webs spun by individual juvenile Nephila clavipes from three different populations held first under field conditions and then under laboratory conditions. Our results indicate that the composition of the organic low-molecular-weight solution is not fixed. We found significant differences in the droplet composition among individuals, among populations, and with the transfer of spiders to laboratory conditions. The possible origins and consequences of these differences are discussed.

DIURNAL CHANGES IN THE ACCURACY OF THE HONEYBEE FORAGING RHYTHM

The ability of honeybees to time foraging visits to an artificial nectar source was analyzed with respect to the time of day of food source presentation. A consistent regimen of orientation and training to the food source, which was available only during a specific one-hour period of the day for each particular experiment, allowed quantitative comparisons to be made among groups of bees trained at different feeding times. Bees trained early in the day showed the most precise time-keeping ability whereas those trained to midday or late afternoon food sources were signif icantly less accurate. In all of the experiments, the bees anticipated the onset of the training period, but the duration ofthe anticipatory component ofthe response was dependent upon the training time. Similarly, other parameters (coefficients of skew ness and kurtosis and the shut-down in the number of arrivals immediately after the end of the training time) describing the distribution of foraging flights in time varied according to times in the diurnal cycle when the food source was offered. These results suggest that honeybees more efficiently exploit a daily floral nectar source if it is available early in the morning than if it is offered late in the day. Possible mechanisms underlying the observed differences in temporal orientation are discussed.