Time at UIUC

Zhiyong Huang, Postdoc --> Senior Research Scientist

Time at Urbana-Champaign was too long (8.5 years). I worked with Prof. Gene Robinson, now a highly prominent scientist known world-wide.

Adaptation and validation of two sensitive assays (radiochemical assay & radioimmunoassay) for measurement of juvenile hormone in bees

I adapted and validated two very useful assays, a radiochemical assay and a radioimmunoassay, for measurement of juvenile hormone in honey bees. The radiochemical assay involves surgically removing the corpora allata (CA), the organ that produces juvenile hormone (JH), and incubate them in a medium specifically formulated for bees. The JH produced de novo can be measured by the amount of radioactivity in the organic phase because CA uses the radiolabelled methyl moiety in the penultimate step of JH synthesis. Several criteria must be met for the assay to be reliable: such as optimal incubation condition, linearity of JH synthesis within certain time period, correlation between synthesis and release, stoicheometry, and the identification of the radiolabelled compound as JH. Our adapted assay met all the criteria and has been used successfully to probe the physiological mechanisms controlling the division of labor in bees. I also validated a chiral specific radioimmunoassay (RIA) to be used in bees without extensive sample preparations. The assay is sensitive enough (detection limit: 10 pg racemic JH) to measure hemolymph JH titer in individual workers, and yields similar results as previously published RIA methods such as Strambi RIA or Goodman RIA. The adaptation and validation were published in Journal of Insect Physiology and Journal of Comparative Physiology.

Physiological mechanisms for the regulation of division of labor in workers

It has been shown that foragers have high level of juvenile hormone (JH). Topical applications of JH analogs have also been shown to induce foraging. The accepted model therefore is that high JH induces foraging, and only foragers have high JH. In a paper recently published in J. Comparative Physiology A (with G.E. Robinson and D.W. Borst) , however, we reported that high levels of JH are also found in several other groups of bees performing specific behaviors. These include guards, undertakers and soldiers. Guards and undertakers are much younger than foragers (average age of 15 vs. 25 days), yet their JH levels are similar. These results suggest that the current model of JH's role in honey bee division of labor needs to be expanded. JH may be involved in the regulation of division of labor among similarly aged bees in addition to its role in age-related division of labor. In another paper recently published in J. Comparative Physiology B (with G.E. Robinson), we report that workers in early spring and late fall had low levels of JH, despite of the fact that they were actively foraging when sampled. We also replicated this phenomenon by moving a colony of bees into a cold room and found the JH of foragers dropped significantly. We suspected that cold temperature either directly affected the JH production or caused a more efficient transfer of inhibitors among bees, hence the observed hormonal reversion. These data suggest the role of JH might be much more complex than previous suggested. For example, a constantly high level of JH might not be necessary for the foraging task, but high JH titer at some developmental stage might be necessary to cause a permanent change (such as the change reported recently by Withers et al., 1993 in Nature) which enables foraging.

A novel model on regulation of behavioral development in worker bees

It is known that honey bee workers can either accelerate, retard, or revert their behavioral development depending on colony conditions. For example, workers can become foragers when only 5-7 days old in a colony made entirely of young bees. This represents a very impressive acceleration compared to the normal foraging age, 21-30 days. The mechanism of the behavioral plasticity remained unknown, however. In a paper published in the Proceedings of the Natural Academy of Sciences (with Gene Robinson), we presented experimental evidence for a theoretical model explaining possible regulation of this plasticity. We hypothesized that older bees (foragers) have an inhibitor(s) that is transferred to other bees to inhibit their hormonal and behavioral development. The inhibitor prevents the rising of the activator: juvenile hormone (JH) that is shown to promote foraging. In the above example, precocious foragers are produced because there is no source of inhibitors in the colony. This study looks at the behavioral development in an insect society as a process similar to cell development in a higher organism and provides a heuristic, testable, model for social organization.

Experimental test of the activator-inhibitor model

I also tested extensively the prediction of the model by manipulating the proportion of foragers in a colony, and the results fits well with the predictions. For example, preventing foraging with artificial rain caused young bees to retard their development into foragers, while artificially depleting foragers (simulating predation) caused accelerated development. The developmental decisions based on our model are always ecologically correct; while decisions based on the alternative model (that bees adjust their developmental rates based on the information of freshly collected food material) are not. For example, during a prolonged period of rain, our model would predict that young bees should show delayed development since most old bees are home, a correct decision; while the alternative model would predict an acceleration in development because no fresh food is coming in.

Identification of the inhibitor that regulates plasticity in behavioral development

In the last three years at UIUC (1994-1997), I was concentrating my research efforts in understanding the mode of action and the actual identity of the inhibitor(s). We knew that the inhibitor is not very volatile, it cannot travel through double screens, but can be transmitted through single screen through which workers can antennate and feed one another. We suspected that the inhibitor resides in the mandibular glands. We showed that the mandibular gland extracts can delay behavioral development in bees if they are fed to the workers.

Publications from UIUC:

8. Huang, Z.-Y., G.E. Robinson, S.S. Tobe, K.J. Yagi, C. Strambi, A. Strambi & B. Stay. 1991. Hormonal regulation of behavioral development in the honey bee is based on changes in the rate of juvenile hormone biosynthesis. Journal of Insect Physiology 37: 733-741

9. Robinson, G.E., C. Strambi, A. Strambi & Z.-Y. Huang. 1992. Reproduction in worker honey bees is associated with low juvenile hormone titres and rates of biosynthesis. General & Comparative Endocrinology 87: 471-480

10. Huang, Z.-Y. & G.E. Robinson. 1992. Honey bee colony integration: Worker-worker interactions mediate plasticity in endocrine and behavioral development. Proceedings of the National Academy of Sciences USA 89: 11726-11729 (cited in the text book "Animal Behavior" by J. Alcock) [pdf]

11. Goodman, W.G., Z.-Y. Huang, G.E. Robinson, C. Strambi & A. Strambi. 1993. A comparison of two juvenile hormone radioimmunoassays. Archives of Insect Biochemistry & Physiology 23: 147-152

12. Huang, Z.-Y., G.E. Robinson & D.W. Borst. 1994. Physiological correlates of division of labor among similarly aged honey bees. Journal of Comparative Physiology A 174: 731-739

13. Robinson, G.E., R.E. Page & Z.-Y. Huang. 1994. Temporal polyethism in social insects is a developmental process. Animal Behavior 48: 467-469

14. Huang, Z.-Y. & G.E. Robinson. 1995. Seasonal changes in juvenile hormone in worker honey bees. Journal of Comparative Physiology B 165: 18-28

15. Bloch, G., D. W. Borst, Z.-Y. Huang, G.E. Robinson & A. Hefetz. 1996. Effects of social conditions on juvenile hormone-mediated reproductive development in Bombus terrestris workers. Physiological Entomology 21: 257-267

16. Huang, Z.-Y. & G.E. Robinson. 1996. Regulation of honey bee division of labor by colony age demography. Behavioral Ecology & Sociobiology 39: 147-158

17. Cnaani, J., D.W. Borst, Z.-Y. Huang, G.E. Robinson & A. Hefetz. 1997. Caste determination in Bombus terrestris: differences in larval development and rates of JH biosynthesis. Journal of Insect Physiology 43: 373-381

18. Trumbo, S.T., Z.-Y. Huang & G.E. Robinson. 1997. Division of labor between undertaker specialists and other middle age workers in honey bee colonies. Behavioral Ecology & Sociobiology 41: 151-163 [pdf]

19. Robinson, G.E. & Z.-Y. Huang. 1998. Colony integration in honey bees: genetic, endocrine, and social control of division of labor. Apidologie 29: 159-170 (Invited review)

20. Schulz, D.J., Z.-Y. Huang & G.E. Robinson. 1998. Effect of colony food shortage on the behavioral development of the honey bee, Apis mellifera. Behavioral Ecology & Sociobiology 42: 295-303 [pdf]

21. Pankiw, T., Z.-Y. Huang, M.L. Winston & G.E. Robinson. 1998. Queen mandibular gland pheromone influences worker honey bee (Apis mellifera L.) juvenile hormone titers and foraging ontogeny. Journal of Insect Physiology 44: 685-692 [pdf]

22. Huang, Z.-Y., E. Plettner & G.E. Robinson. 1998. Effect of social environment and mandibular gland removal on division of labor in worker honey bees. Journal of Comparative Physiology B 183: 143-152 [pdf]

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