Soldier production and maintenance of soldier proportions in laboratory experimental groups ofCoptotermes formosanus Shiraki
SummaryExperimental groups of 100 percent pseudergates ofCoptotermes formosanus Shiraki were set up in the laboratory and allowed to differentiate for either 4, 8 or 12 weeks. The average percentage of pseudergates differentiating into presoldiers and soldiers at these time intervals was 3.8, 14.2, and 21.9 percent, respectively. Differentiation to the soldier caste was affected both by initial group size and colony origin. Groups initially composed of 100 pseudergates produced a significantly smaller proportion of soldiers than did groups of 300, 500, or 1000. Recently collected field colonies produced soldiers at significantly higher rates than one which had been maintained in the laboratory for 8 years. The number of soldiers produced was highly correlated with the total number of all individuals at 4, 8, and 12 weeks, which indicates a precise physiological mechanism for regulating soldier proportions.Experimental groups were also set up with “normal” (24 percent), “below normal”, and “above normal” initial proportions of soldiers with pseudergates. ‘When soldiers were present in “below normal” proportions they inhibited the presoldier production, approached the norm. This species can tolerate and will maintain an exceptionally high proportion of soldiers (ca. 38 percent) which is far above the assumed “normal” proportion. Many, but not all, of the excess soldiers were probably eliminated by cannibalism. Groups severely overloaded with soldiers succumbed to microbial contamination after the excess soldiers starved to death.From these results I conclude that colonies ofC. formosanus do maintain numerically constant proportions of soldiers within broad limits. Thus, colonies might be controlled by chemically inducing the production of superfluous soldiers. Successful control would require the proportion of soldiers be so great that the pseudergates could not effectively reduce the numbers of soldiers by cannibalizing the excess individuals before their death by starvation resulted in microbial contamination of the entire colony.ResumeDes groupes expérimentaux, entièrement constitués de pseudergates deCoptotermes formosanus Shiraki, se sont différenciés librement au laboratoire pendant 4, 8 ou 12 semaines. Les pourcentages moyens de pseudergates qui se sont différenciés en soldats ou en soldats blancs ont été de 3,8 pour cent au bout de 4 semaines, 14,2 pour cent au bout de 8 semaines et 21,9 pour cent au bout de 12 semaines. La différenciation en soldat a été influencée par la taille initiale du groupe et le lieu d'origine de la colonie. Des groupes composés initialement de 100 pseudergates ont produit significativement une proportion plus faible de soldats que des groupes de 300, 500 ou 1000. Des colonies qui venaient d'être récoltées dans la nature ont fourni des taux significativement plus élevés de soldats qu'une colonie qui était gardée au laboratoire depuis 8 ans. Le nombre de soldats obtenu était en corrélation hautement positive avec le nombre total d'individus au bout de 4, 8 et 12 semaines. Ceci indique qu'il existe un mécanisme physiologique précis dans la régulation des proportions de soldats dans les colonies.Nous avons aussi constitué des groupes expérimentaux qui comprenaient des proportions «normales» (24%), «en dessous de la normale» et «au dessus de la normale» de soldats par rapport aux pseudergates. Lorsque la proportion de soldats était «en dessous de la normale», il y a eu inhibition de la production de présoldats de sorte que le développement en présoldats a progressivement diminué à mesure que la proportion de soldats par rapport aux pseudergates approchait de la «normale».Coptotermes formosanus Shiraki peut tolérer et maintenir une proportion remarquablement élevée de soldats (environ 38%), ce qui est bien au dessus de la proportion considérée comme «normale». Un grand nombre (mais pas tous) des soldats en surnombre ont été probablement éliminés par cannibalisme. Des groupes suchargés en soldats ont succombé à la contamination microbienne après que les soldats en surnombre fussent morts de faim.Je conclus de ces résultats que les colonies deCoptotermes formosanus gardent des soldats en proportion constante.
The Determination of the Castes of Social Insects
P OLYMORPHISM in the social insects and the history of the search for its causes received masterly treatment by Wheeler in his book, The Social Insects (1928). Since then there have been several attempts at experimental solutions of the problems of caste determination. The data thus far obtained are meagre, however, and statistical in nature, and it is obvious that data derived from experiments on social insects under laboratory conditions are especially difficult to evaluate. Because the problems of caste determination are of general biological interest and far from being solved, there has been a tendency to present conclusions despite paucity of evidence, and some of these conclusions have passed into the literature, although later findings have not substantiated them. Nevertheless, considered apart from these conclusions, the evidence obtained during the period since 1928 has shown a consistent trend. Until recently Wheeler had remained neutral with regard to theories of caste determination. In 1937, however, he undertook the defense of a position which is not in line with the trend of recent evidence or opinion. The time seems ripe, therefore, for a survey of the subject. The fifteen years since Wheeler's book have seen marked advances in appreciation of the nature of the problems involved in caste determination. It must be emphasized, however, that in so far as the ants and the termites are concerned, only a beginning has been made toward the solution of these problems. Indeed, I feel it necessary to emphasize that the published researches of this period, as well as my own unpublished results, serve most importantly to emphasize the difficulties involved, especially as to laboratory methods and the analysis and interpretation of results. Further advances will depend largely upon the development of adequate methods of culture, rigorous scientific controls, and the application of suitable methods in evaluating the type of data resulting from such experiments. According to Goetsch (1936), the ideal approach is through the use of isolated individuals, and no doubt every effort should be made in this direction. But it is indeed a question whether the method is a feasible one with social animals. The individuals of an insect society are so highly interdependent (Efierson, 1939a, b) that the attempt to maintain and study them in isolation involves many of the difficulties encountered inisolating the organs or the cells of complex individuals, and, in addition, some which we call psychological, forlack of amorerevealingphysiological term. For example, C. S. Lafleur tells me (in litt.) that many ants when kept in isolation exhibit symptoms of extreme nervous agitation and, unless given company, die very shortly, as a result of nervous disturbance. To such obstades to the study of social insects must be added those arising from cannibalism, endemic and epidemic bacterial diseases, and attacks of mites and fungi. Finally, there are the difficulties encountered in attempting to control moisture for organisms extremely dependent upon such a control, but accustomed at the same time to relatively great diurnal and annual shifts in temperature and helpless individually, or even in small groups, to effect such control. Control of factors and evaluation of their influence on experimental results must be accomplished by the student of caste determination, at least in the termites, when he seeks to,use isolated groups, let alone isolated individuals, as controls and experimentals. If these problems are to be solved, they must be approached with full realization of the difficulties to be surmounted. The general problem presented by the polymorphism of the social insects is, of course, the nature of the mechanisms which function in each generation of each species to cause the offspring of the same parents to develop, in relatively constant numbers, into several different types of individuals which possess the special morphological features and behavior patterns characteristic of the particular castes in the particular species, features correlated with the performance of special functions in the communal life.
Rapid determination of the effectiveness of insect resistant packaging
A technique was developed to evaluate the usefulness of odour barriers and to determine the effect of package content in consumer size packages on resistance to infestation by insects. Female Plodia interpunctella (Hubner) could distinguish sealed packets containing food from non-food items as a suitable site for oviposition. Utilization ofthis technique will reduce the time needed to evaluate new materials for use in insect resistant packaging.