February . 1919 



GLEANINGS IN BEE CULTURE 



79 



beos iiexor i)uiu-tuio the leaves; indeed, 

 under normal conditions they never visit 

 them; nor do they puncture the flowers of 

 the apple or pear, for the nectar is easily 

 accessible on a flat disc. If, however, 

 blijjht is chiefly distributed by the wind, 

 the prickino; in of the germs, altho a great 

 advjintngo, is not an actunl necessity. 

 An Alibi for Bees. 



It is clear that all infection of the leaves 

 and twigs must be due to other agencies 

 than the honej'bee, since the latter confines 

 its visit strictly to the flowers. Further- 

 more, since bees visit the trees only during 

 blooming time, it is only during about two 

 weeks out of 14 or 15 that it can be ac- 

 cused of being a carrier of blossom blight. 

 Let us now inquire if honeybees are re- 

 sponsible for the spread of blossom blight. 

 As they do not visit the foliage they can 

 not be the agency, which, in the first place, 

 brings the blight to the bloom. In Kansas 

 orchards, Merrill states, this is done by 

 plant lice, which in large numbers enter 

 the apple buds and suck their juices before 

 they open, at the same time inoculating 

 them with blight bacteria. Thus the flow- 

 ers blight in the bud before bees begin 

 their visits. Once the bloom is blighted 

 it is no longer attractive to honeybees; for, 

 if we remove the petals of a healthy pear 

 blossom, bees will at once cease to visit it, 

 altho they will continue to visit other flow- 

 ers near by. Twenty-three pear blossoms 

 received 24 visits from honeybees in half 

 an hour; the writer then removed all the 

 petals and in the half hour following there 

 was not a single visit, altho the denuded 

 blossoms contained nectar and the bees of- 

 ten visited other flowers near them. Thus 

 bees might fly indefinitely betw.een the un- 

 contaminated blossoms without disseminat- 

 ing the blight. But it must be remembered 

 that the bloom is visited by many insects 

 besides bees, especially by flies and beetles 

 which do not exhibit flower fidelity. As 

 they alight on the leaves both in search of 

 food and by chance, and will freely visit 

 the blighted blossoms, they can not fail to 

 spread the blight among the flowers. Inci- 

 dentally it may be remarked that not all 

 blighted pear blossoms are the result of 

 fire blight. In the Hudson Valley, accord- 

 ing to Dr. E. Porter Felt, the injury is 

 caused by pear thrips. These little insects, 

 which are about 1-20 of an inch long, appear 

 on the trees as the buds start and seek shel- 

 ter in the expanding flower buds, blasting 

 the bloom, which presents a brown seared 

 appearance. 



Summary of Above Observations. 



A brief summary of the above statements 

 is as follows: 



1. Fire blight appears both before and 

 after pear and apple trees bloom, and in 

 nursery plantations which have never 

 bloomed. With such outbreaks the honey- 

 bee has no connection. 2. It has been 

 shown experimentally that fire blight is 

 spread by hosts of sucking and biting in- 

 sects, such as plant lice, leaf hoppers, the 



tarnished plant bug, and probably many 

 flies and beetles which puncture or feed 

 on leaves and flowers. 3. Since honeybees 

 restrict their visits to flowers they do not 

 carry blight from the foliage to the bloom. 

 This is done in many instances by plant 

 lice, which creep in and infest the buds 

 before they expand; and also doubtless by 

 many flies and beetles which fly freely back 

 and forth between the leaves and the 

 bloom. Honeybees will not visit blighted 

 inconspicuous bloom, but flies will often do 

 so. While honeybees may occasionally car- 

 ry the germs, they are of so little impor- 

 tance compared with other distributors that 

 their absence from orchards would proba- 

 bly not affect the prevalence of blight. 

 Pear Blight Wind Borne. 

 At this point the defense of the honeybee 

 against the accusation of carrying fire 

 blight rested up to Nov. 1, 1918. On this 

 date there appeared in Science a paper by 

 F. L. Stevens, W. A. Euth, and C. S. 

 Spooner of the University of Illinois, en- 

 titled "Pear Blight Wind Borne," which 

 advanced new and revolutionary evidence 

 in favor of bees. A brief abstract of this 

 paper given largely in the words of the 

 authors is as follows: Twelve-mesh wire- 

 screen cylinders, 15 cm. in diameter and 

 .30 cm. long were constructed to enclose 

 parts of single branches. Some of the cyl- 

 inders were slipped into closely fitting 

 sleeves of fine bolting cloth. The ends of 

 both kinds of cj^linders were covered with 

 canvas extending past the wire far enough 

 to permit secure tjdng. The exposed wire 

 of the first type of cylinder was painted 

 with a mixture of tanglefoot and benzine. 

 No insects were found in any of the cyl- 

 inders except one which was accidentally 

 permitted to dry, and in which two insects 

 were found, but the shoot did not blight. 

 The purpose of the following experiments 

 was to discover whether infection was as 

 common in the cylinders as in the open. 

 Ten cylinders enclosed flowering wood. 

 Flowers in two of the cages blighted. Forty 

 cylinders, 20 of the bolting cloth and 20 

 of the tanglefoot type, enclosed terminal 

 growth. Thirty per cent blighted, which 

 was practically the same proportion as pre- 

 vailed among the unenclosed terminal 

 shoots, as was shown by a count of a thou- 

 sand terminal shoots on these and adjacent 

 trees of the same variety and age. Since 

 insects did not obtain access to the shoots 

 the blight bacteria must have been carried 

 by the wind; and "insects were not even of 

 primary importance as carriers." This con- 

 clusion was further supported by two facts: 

 (1) there was a lack of insects in the or- 

 chard in sufficient numbers to account for 

 the large amount of twig blight — aphids 

 and leaf hoppers were entirely absent dur- 

 ing the period of infection; (2) insects were 

 entirely absent from the exuding cankers, 

 where they might receive their initial con- 

 tamination. During three years of close ob- 

 servation during blooming time not a single 

 insect was seen to visit the cankers. 



