1. The history of the occurrence of Merodon equestris in various countries is related and a list of known food-plants given.2. The immature stages of the fly are described in detail.3. The biology of the fly is fully discussed and additions made to our knowledge regarding it.4. Control measures are reviewed and additional information is given, particularly with reference to the use of a poison-bait spray against the adult flies.5. Recommendations are made as to the most satisfactory combination of methods to use for the purpose of obtaining control of the fly under field conditions.6. A list of literature cited is given.
1. Reference is made to the proven capacity of aphides of the genus Capitophorus to transmit virus disease among strawberries, and attention is drawn to the confusion existing as to the actual synonymy of the insect principally concerned.2. For the first time sexual and asexual forms of the species commonly present in England have been observed together. Evidence is considered which suggests that the aphis is Capitophorus fragariae, Theo., and that American forms are in reality other, but closely related, species.3. The incidence of the aphis in the field is considered, and the biology as observed in field and laboratory is discussed.4. The economic significance of the aphis is referred to, and attention is drawn to the practical difficulties attending efforts to keep it in control, particularly in commercial strawberry-growing areas.
INTRODUCTION.THE stem eelworm, Tylenchus dipaci (Kuhn) Bastian, causes severe injury to a variety of both wild and cultivated plants, on the latter of which it is a pest of considerable economic importance. In the following paper the writer has made an attempt to add to our knowledge of the normal biology of this nematode. The small size of the eelworms and the difficulty experienced in keeping them alive under artificial conditions make the task of accurate observation a difficult one: nevertheless, it has been possible to arrive a t certain definite conclusions, which are stated in the paper. They are followed by a discussion of the existence of Biologic Strains in this species. A morphological description of the eelworm has not been included, as this has been made by many previous workers, notably by Ritzema Bos (8) and Marcinowski (7).
BIOLOGY.Life-history. The life-history is essentially the same in all those host plants, which the present writer has had an opportunity of studying. The eelworms breed with great rapidity under favourable conditions. Temperature seems to affect them only indirectly in so far as it controls plant growth. Breeding is usual only in succulent and rapidly growing, or in storage tissues. For example, all stages of the worm from egg to adult may be found in a state of activity in narcissus bulbs throughout the winter months. On the other hand, oat seedlings infected in late autumn were not found to contain any eggs, or to show any appreciable increase in the number of eelworms present, until the latter end of March, plant growth having by then become more rapid.
The larvae of certain flies belonging to the family Syrphidae have long been recognised as plant pests. Merodon equestris, Fab., was recorded in Great Britain as far back as 1869, having probably been imported in narcissus bulbs from Holland (Verrall). This fly is now universally known as the “ Large Narcissus Fly,” the larvae causing serious losses in nearly every locality where the narcissus is grown commercially. More recently flies of the genus Eumerus have been associated with a type of injury very similar to that caused by the larger fly, and the larvae have been recorded on a variety of host-plants in Europe and America. Chief among these hosts may be included narcissus, onion, hyacinth, parsnip, iris, and potato. The flies are commonly referred to as “ Lesser Bulb Flies ” or alternatively in some parts of North America, where they were first recorded as European introductions in 1904, as “ Lunate Onion Flies.”
The foregoing observations and experimental work clearly indicate that the bulb mite, Rhizoglyphus echinopus, is not a primary pest of the narcissus. At the same time there is every indication that the mite does bring about the destruction of bulbs originally damaged by other organisms or by mechanical means, which would normally recover from their original injuries. Further, the mites can undoubtedly carry fungus spores from bulb to bulb. It is therefore very desirable that every effort should be made to reduce the mite population in bulb-growing areas to a minimum. This can be effected by careful attention to the points enumerated under the heading of control measures.
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