534 



'jtmm Mvmmmi^MM mwrn jensKifMir. 



!l.A.O,A.^^A^.^A.^AJ 



LARVAL FOOD. 



A Consiidcratioii of the Food of 

 Larval Bees. 



Address at the British Bee-Keepers' Association 

 Br MB. THOS. WM. COWAN. 



In April, 1887, I brought before 

 your notice a worlvof some importance 

 inasmuch as it was one that was about 

 to clear up a rather difficult problem, 

 that had caused a good deal of con- 

 troversy. The work I allude to was 

 that of Dr. A. de Planta, which gave 

 the results of his chemical investiga- 

 tions into the nature of larval food. 

 To fully appreciate the value of these 

 reseai'ches, it would be as well if I 

 gave you, as briefly as possible, the 

 history connected with the subject. It 

 has been general!}' the accepted idea 

 that the food given to the larvje was 

 partly digested in the chyle stomach. 

 This was the theory of Dufour, and 

 was even mentioned by Swammerdam 

 before. 



Leuckart also held this view at first, 

 but when the glauds were discovered 

 he thought he was not quite satisfied 

 with the semi-digestive theor}', and 

 suggested that the larvre were fed with 

 a secretion from the diflerent glands. 



In the honey-bee there are four 

 pairs of glands : two pairs in the upper 

 part of the head, and called systems 1 

 and 2 ; one pair in the thorax called 

 system 3 ; and one pair in connection 

 with the jaws, called system 4. These 

 glands have been described by diS'er- 

 ■ ent observers, but it was Schiemenz 

 who, in 1883, published the most com- 

 plete work on the subject. Schiemenz 

 was a pupil of Leuckart, and was re- 

 quested by him to investigate tlie 

 glands of bees, especiallj- with respect 

 to their being the produ(!ers of brood 

 food. The work as far as regards the 

 description of the glands is most ac- 

 curate, and shows an immense amount 

 of energy and perseverance, for I must 

 tell yoti that investigating such deli- 

 cate organs as the glands of bees re- 

 quires considerable patience and ma- 

 nipulative skill. 



Although this part of the work is 

 accurate, when he comes to treat of 

 the functions performed by these 

 glands he seems to have gone quite 

 astray, and I believe it is because he 

 started upon the work with the pre- 

 conceived idea that these glands 

 actually produced the brood food, as 

 Leuckart had suggested. But he is 

 not the only one, for others who have 

 copied Schiemenz and Leuckart have 

 fallen into the same error. 



Then Leuckart discovered, in 1855, 

 that the worker larvs3 were fed with 

 one kind of food the first three days of 

 their existence, and stated that after 

 tliat they were fed on pollen and 

 honey, or, in other words, that they 

 were weaned after the third day. 

 Larvos intended for queens were, on 

 the other hand, provided with an 

 abundance of the same rich food dur- 

 ing the whole of this larval existence. 

 Drone larvre were supposed to be 

 weaned in the same way as worker 

 larvfe. This theory was to a certain 

 extent supported by the analysis by 

 Schlossberger of the larval food, but 

 he having food given to him from the 

 diiferent cells all mixed, and suppos- 

 ing it to be the same throughout, ana- 

 lyzed it in one mass, consequently his 

 analysis was of no practical value 

 whatever. 



On the other hand, there was another 

 school of thought headed by Dufonr. 

 Those belonging to this school tliouglit 

 that the food of the larvae was partially 

 digested by the nurse-bees, aud that 

 these bees are the young bees in the 

 hive. It was for a long time difficult 

 to understand how this was done, but 

 Schonfeld took up the matter, and 

 from 1854 was at work at it, making 

 investigations and experiments without 

 number. His investigations have been 

 described in the Bienen-Zeitung from 

 the years 1854 to 1883. 



From practical experiments he found 

 that if he mixed indigestible substances 

 in the syrup on which bees were fed, 

 that these substances reappeared in 

 the larval food, even within six hours, 

 showing that this food could be noth- 

 ing but chyle, and not a secretion ; for 

 if it were a secretion, as these indiges- 

 tible substances were not able to pass 

 through the walls of the stomach, they 

 could not have appeared in a glandu- 

 lar secretion, and thej' would not have 

 been found in the larval food. Tlieir 

 jiresenee in tlie food conKrmed Dnfour's 

 theory, and completely upset that of 

 Leuckart and his school. 



Schonfeld did more — he demon- 

 strated how the food was ejected into 

 the cells. The honey-stomach is a 

 globular sac with the oesophagus at 

 one end, and an opening to the chyle 

 stomach at the other end. This open- 

 ing has a valve called bj' Burnieister 

 stomach-mouth (or mngenmund), and 

 schonfeld showed that by means of this 

 mouth the 1>ee is able to take honey 

 and pollen when it requires it, or wlien 

 it is closed can force the honey through 

 the oesophagus into the cells. 



Below this stomach-mouth is a neck 

 and an infolding of the upper part of 

 the chyle stomach. This, Schiemenz 

 supposed was a valve, but Schonfeld 

 has shf)wn that it has quite another 

 use, and is actually brought into play 



when ejecting brood food. When 

 honey is l)eing forced ont.the stomach- 

 mouth is closed, and the muscular 

 pressure on the walls of the honey-sac 

 causes the honey to pass through the 

 cesophagus. On the other hand, when 

 brood food has to be ejected the 

 stomach-mouth is open, and it is 

 brought up to the opening of the 

 ossophagus, so that the chyle stomach 

 communicated directly with this, and 

 the food passes into the cesophagus 

 without passing through the honey- 

 sac. In such a case the neck folding 

 into the chyle stomach is drawn out, 

 and the infolding takes place in the 

 honey-stomach. 



It is very natural to suppose that 

 these investigations caused a good deal 

 of controversj', and there remained 

 only one thing to be dcjne, and that 

 was a chemical analysis of the food of 

 the larva3 in various stages. This work 

 was untiertaken by Dr. de Planta, who 

 was not at all satisfied with Schloss- 

 bcrger's analysis. He has been at 

 work for several years in tiying to set- 

 tle the question, and has had consid- 

 erable difficulty in carrying out his in- 

 vestigations. It was not an ea.sy mat- 

 ter to obtain the large quantities of 

 food he required, and keep a careful 

 account of the food at different days 

 of development of the larvos. 



You may form some idea of the 

 magnitude of the work when I remind 

 you that I stated in 1887 that he had 

 to operate on VIM queen-cells, 4,000 

 drone-cells, and 10,000 worker-cells. 

 Since then he has been carrying on 

 his experiments, and has operated on 

 4.000 more worker-cells, because his 

 results being so difl'crentto what larval 

 food was supposed to be by Leuckart, 

 he determined ta continue his experi- 

 ments. Leuckart stated that the larvas 

 were weaned by having pollen and 

 honey added to their food after the 

 third day, but Dr. Planta failed en- 

 tirely to find any pollen in the food of 

 worker larvse, and in repeating his 

 experiments he confirmed his previous 

 ones in this respect. 



Now his analysis shows that the dif- 

 ferent larval foods vary in the follow- 

 ing proportions : 



QnBEN. Percent. 



Albumen 4.?. 14 



Fat 13.5.5 



Sugar aO 39 



DRONES. 

 trnder4 (iays. Over4day8. Averafje. 



Albumen 5.^.91 31.67 43.79 



Fat 11.90 4.74 S.32 



Sugar 9.57 38.49 24.03 



WOKKERS. 



Under 4 days. Over 4 days. Average. 



Albumen 53.38 27.87 40,62 



Fat 8.38 3.69 6.03 



Sugar 18.09 44.93 31.51 



This table shows the great variation 

 of the food, not only in the different 

 bees, but also at different stages of 



