324 



bounds by N. ( Vedalia) chermesina, which increases slowly and is not 

 operative all the year round. The practical solution in such cases 

 appears to be the introduction of quickly- maturing strains, thus 

 increasing the number of broods per annum, and their reinforcement 

 till they become dominant. 



In certain hosts such as black scale, Saissetia oleae, and Hessian fly, 

 Mayetiola destructor, the problem is complicated by the presence of 

 several species of parasites, which are supplementary up to a certain 

 point and then become competitive, so that in the event of a pest 

 being introduced into new surroundings, only that parasite which 

 most effectively controlled it in its original locality should also be 

 transferred to its new home. 



Annual Report of the Horticulture Branch for the Year 1916. — Jl. Bd. 



Agric, London, xxiv, no. 2, May 1917, pp. 142-158. 



Apple and pear growers in the south and midlands of England 

 sustained serious losses from severe infestations of the larvae of the 

 Avinter moth [Cheimatobia brumaia], various species of Tortrix, and 

 other insect pests. Several investigations of a scientific and practical 

 nature have been carried out during the past 12 months. The long 

 and detailed enquiry into the parasitism of the large larch sawfly 

 [Lygaeonematus erichsoni] has been concluded, though the results have 

 not yet been tabulated ; they are largely of a negative character. 

 This sawfly has at present almost disappeared from the infested area 

 and the economic injury to larch plantations is not noticeable. No 

 cases of scheduled pests such as Phylloxera, Colorado potato beetle 

 [Leptinotarsa decemlineata] or Aidacaspis (Diapi s) pentagona were 

 reported during the year. 



Isle of Wight bee disease now seems to have spread over the whole 

 of England ; the study of the disease has been continued and many 

 experiments conducted. Two drugs have been found fairly successful 

 in cases that have not developed beyond a certain point. In 

 order to secure definite data on this point experiments were under- 

 taken throughout a whole village under the conditions that every 

 colony in the district was to be examined for signs of Nosema apis ; 

 all colonies pronounced beyond hope of successful treatment were to 

 be destroyed ; no other treatment was to be applied during the 

 experiment ; the bees to be under the supervision of a local expert and 

 to be finally examined before conclusion of the experiment. The 

 results are not yet conclusive, but are apparently fairly satisfactory, 

 since in the treated colonies several swarms have been thrown off and 

 a large supply of honey obtained, while all the bees died in untreated 

 villages in the vicinity. Several specifics have been offered to the 

 public for which remarkable properties are claimed, but it is considered 

 that a claim to a satisfactory cure can be substantiated only on the 

 condition that microscopical examinations of specimens from a sus- 

 pected colony have revealed the presence of Nosema apis in large 

 numbers in the bees' intestines and that the treatment must be applied 

 under conditions which eliminate all possibility of other influences 

 being present. The effect of treatment can only be judged by micro- 

 scopical examination to determine the presence or absence of Nosema 

 apis. Moreover, no treatment can be considered effective unless the 



