GLEANINGS IN BEE CULTURE 



February, 1919 



THE BEES ARE NOT GUILTY 



discovery of the True Agencies of 

 Spreading Fire Blight and the Exon- 

 eration of the Honeybee 



By John H. Lovell 



ABOUT a 

 score of 

 years ago 

 bees were accus- 

 ed of being a se- 

 rious factor in 

 the spread o f 

 fire blight. Al- 

 tho this charge 

 was b a s e d on 



wholly insufficient observation and experi- 

 ment," it was generally accepted, doubtless, 

 as Merrill observes, because bees are so 

 abundant in orchards at blooming time. By 

 tending to check the growth of bee culture 

 this belief has been injurious to both bee- 

 keepers and fruit-growers. But during the 

 last half-dozen years evidence has rapidly 

 accumulated, which shows that blight is 

 spread by other agencies and fully exoner- 

 ates the honevbee. 



The Nature of Fire Blight. 

 Fire blight is a bacterial disease, which 

 attacks th« twigs and ends of the branches 

 of apple and pear trees and blights the 

 leaves and flowers. If not checked it may 

 extend to the entire branch, or may finally 

 even kill the tree. Usually the infections 

 die out in a few weeks; but, here and there, 

 at the point where the dead limb joins the 

 living wood, a few survive the winter. In 

 the spring they resume their activity 

 and exude a gummy substance filled with 

 germs. They are called "hold-over can- 

 kers." From these cankers the germs are 

 widely disseminated thru the orchard, and 

 a new outbreak of blight follows. The 

 question at once arises, what agencies act as 

 carriers of the germs. It is certain that 

 the honeybee is not one of them, for it re- 

 stricts its visits entirely to the bloom of the 

 trees. There is not a single instance on 

 record of a bee visiting the exuding can- 

 kers. Nor is it claimed that they do. Dur- 

 ing three years' close observation at bloom- 

 ing time W. A. Ruth did not observe a sin- 

 gle case of an insect visiting the exuding 

 cankers. It has been suggested that ants, 

 which roam everywhere, may carry the 

 blight bacteria to plant lice feeding on the 

 leaves; but this supposition does iiot appear 

 to be based on direct observation. It is 

 probable that the wind, not insects, as will 

 be shown later, is the chief agent in their 

 distribution. 



When Outbreaks Occcur. 

 There may be repeated outbreaks of fire 

 blight in April, May, June, July, and Aug- 

 ust; but the chief months for blight are 

 May, June, and July. Thus this disease is 

 by no means confined to the blooming time 

 of the apple and pear. Clearly the ap- 

 pearance of fire blight, when there ^ is no 

 bloom on the trees, '-an not be attributed 

 to the honeybee, for it can prove an alibi; 

 it is busy elsewhere. Yet these outbreaks 

 are as severe as, or more so than those which 

 occur in blooming time. 



Leaf Hoppers Important Carriers. 

 IiT a paper on the control of fire blight 



by A. C. Burrill, 

 ])ublished in 

 Phytopathology, 

 Dec., 1915, there 

 was described a 

 series of experi- 

 ments, which 

 shows that 

 aphids, or plant 

 lice, and leaf 

 hoppers carried the infection from blighted 

 leaves to perfectly healthy shoots of the wild 

 crab apple. After five years' experience 

 Burrill believes that in the orchards and 

 nurseries of Wisconsin leaf hoppers (Em- 

 podtica mali) are the most important car- 

 riers of blight during July and August. 

 Plant Lice Chief Distributors. 

 In Kansas, according to J. H. Merrill, 

 (Bee Inspector 's Report, Iowa, 1916, page 

 33) plant lice, which are the most common 

 and widespread siK'king insects in Kansas 

 orchards, ha\'e been found to be the chief 

 distributors of blight bacteria. Aphids, 

 which had been permitted to crawl thru 

 pure cultures of fire blight, were then plac- 

 ed on terminal twigs and enclosed in cheese- 

 cloth to exclude all other insects. These 

 twigs blighted and were the only ones that 

 did. Furthermore, it has been observed 

 that in seasons diiring which plant lice are 

 most abundant, fire blight is also most 

 prevalent. In 1913 in K^ansas orchards 

 they were very common and so was fire 

 blight; but in orchards in which they were 

 controlled there was little blight. In 1914 

 there were few aphids and little blight, and 

 this reciprocal relation was again notice- 

 able in 1915 and 1916. Merrill says that 

 the amount of blight can be decreased by 

 controlling the aphids. Stewart also ob- 

 served that in apple nurseries fire-blight 

 epidemics follow rapidly in the wake of 

 aphid epidemics. 

 Sucking Insects Important Distributors. 

 In New York orchards in July, accordinrr 

 to Stewart, the tarnished plant bug and 

 several other sucking insects are important 

 distributors of blight. Finally D. H. Jones 

 has added to the list a beetle of the genus 

 f^coh/fiis, and on further observation many 

 other insect carriers will doubtless be dis- 

 covered. There is no lack of puncturing 

 and biting insects in immense numbers, 

 which, it is certain, are active in spreading 

 fire blight. 



Bees Never Puncture Leaves. 

 It will be noticed that all the insects 

 mentioned in the two preceding paragraphs 

 have mouth -parts, which can puncture or 

 bite thru the epidermis of the leaf. In this 

 way the germs are placed in the tender tis- 

 sues, multiply rapidly and produce infec- 

 tion. "Insects," says Merrill, "with suck- 

 ing mouth-parts are admirably suited to 

 this [)urpose." Stewart and Leonard state 

 that except for blossom blight the bacteria 

 can not gain an entrance in the host tissue 

 and produce infection except thru a wound 

 or the punctures made by insects. Honey- 



