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agrestis has always been more abundant and has been largely if not entirely responsible for injuries to radish roots.
The species A. agrestis is of foreign origin, and in England where it occurs generally in gardens and fields it is known as the Field Gray Slug. It is one of the most prolific of its race. In 19051 it was stated that for four years this and other species had greatly increased all over Britain " so much so that whole fields of wheat and other plants had been destroyed. In gardens they had been even worse, and it has frequently been impossible to grow a crop of early peas or beans. Young potato sprouts and flowering plants of all kinds have suffered in a similar way.”
In the radish beds the slug agrestis fed upon both leaves and roots. In the attacks on foliage the injury has been variable, ranging from production of small holes through the leaf tissues to the entire destruction of leaves with exception of the stalks and larger veins. In the attacks on the roots the slug causes mere abrasions which appear as whitish specks on the surface of the radish and produces also holes of varying depth and circumference, ranging from one-fourth to one-half inch across. Owing to the white flesh which is exposed by the attacks of the creatures the eaten areas contrast strongly with the reddish epidermis. The slugs are nocturnal, and during the day they may be seen in protected situations about the frames or under stones or clods of earth or in the soil. They are partial
They are partial to moisture, apparently preferring cool, damp situations. During cloudy weather they may be observed in exposed situations, even during the daytime. The chief damage to radishes has usually occurred during the latter part of May or during early June, or as fleshy roots were attaining marketable size. Until 1916 injuries to radishes had never been very conspicuous, but during the past two years the damage by slugs has been important. It should also be noted that in the region about Geneva agrestis has been quite common in gardens, believed that collecting slugs by lantern light, applications of airslaked lime in situations frequented by the pests, trapping with sliced cull potatoes, and spraying with bordeaux mixture, especially if an outbreak of mildew threatens, are measures that singly or in combination would afford adequate protection.
1 Board of Agriculture and Fisheries, Leaflet No. 132.
Of the millipedes, two species have been detected in radish beds, which are Julus coeruleocinctus! Wood and Polydesmus moniliaris Koch. The former has been more abundant and, as with the slugs, it has been most injurious during the past two years, which have been characterized by cold and wet weather during the growing season. Injury by cæruleocinctus is caused by its eating holes in the fleshy roots, which are similar in appearance to those produced by slugs. The damage has not been extensive, which is fortunate, as at the present time no practical measures have been developed for protecting radishes from attack.
The practical outcome of the studies herein described is as follows: Radishes produced in the spring months in this latitude are subject to attack by one brood of maggots which in normal seasons injure roots during the latter part of May or early June. As this vegetable is grown in most home gardens these dates closely coincide with the period when radishes are making their most succulent root growth; hence the occurrence of maggots and attending injuries to the roots. By reason of this behavior of the insect two courses of action appear to be open to the grower who does not care to resort to applications of insecticides or to repressive measures - to dodge attacks by sowing either later than is customary or by sowing somewhat earlier than is the common practice. However, there is serious objection to the former step as radishes suffer from drought and heat incident to the summer and become fibrous and pungent. A recourse that is more to be preferred and which is quite practical is to practise early sowing, as timely planting of seed to secure harvesting of crop before the danger period has, in our experiments, generally resulted in the production of roots that were exempt from injury. In the adoption of this practise the caution is urged that in certain seasons, on account of weather and soil conditions, little leeway may be given as to choice of time for planting and it is not always possible to make as early sowings as are desirable to entirely safeguard the beds from attack. However, the gardener should make it a rule to plant radish seed as soon as the physical condition of the soil permits. For the protection of radishes that are to be harvested during the period of the prevalence of the insects, growing of radishes in frames covered with cheesecloth of 20 to 30 mesh has given excellent results. In addition to freedom from maggots, roots grown by this method have in most seasons given larger yields and have been more succulent and tender than those produced in
1 Identifications by Dr. R. V. Chamberlain, Museum of Comparative Zoology, Cambridge, Mass.
The cherry leaf-beetle is a native species which normally feeds on the bird, pin, or fire, cherry (Prunus pennsylvanica). Both insect and plant have the same geographical distribution. Their habitat embraces Nova Scotia and Quebec westward thru southern Canada and the northern United States to the Rocky Mountains. It extends along the Alleghany Mountains to North Carolina and in the valley of the Fraser River to the Pacific Ocean. The beetle migrates for short distances beyond its normal breeding range.
The history of the species records intermittent attacks on cultivated cherries. The most extensive outbreak as regards extent of invaded territory and abundance of the insect occurred during 1915. The beetle was superabundant in two areas: (1) Western New York, Pennsylvania and northern West Virginia; and (2) the northern portion of the southern peninsula of Michigan. The outbreak in the Appalachian region extended as far east as Cayuga Lake in New York and Williamsport, Pa., and westward to the Ohio-Pennsylvania line, the infestation being most severe in the western portion of this area. In Michigan the beetle was most abundant in the region of Grand Traverse Bay. In 1916 and 1917 the numbers of the beetles in the foregoing areas were greatly reduced.
The eggs of this beetle are ellipsoidal in shape, averaging -78 mm. in length and .70 mm. in breadth, varying in color from stramineous to yellow. From these hatch olive-colored larvæ which later change to a very dark brown with the head and ninth segment black. When full grown the larva shows considerable yellow and characteristic black spots. The mature larvæ average about 7 mm. in length. The pupæ are bright yellow and vary from 4 to 5 mm. in length. The adults upon emergence are yellow, but soon change to yellowbrown and in a few days assume a blood-red color. They vary from 4.5 to 5.5 mm. in length.
Reprint of Bulletin No. 444, December, 1917.
The time of emergence from the pupal stage varies with seasonal conditions. During 1915 the adults emerged from August 23 to September 18, but during the summer of 1916, which was warmer, the adults appeared in the breeding cages from July 31 to September 2. The adults are rather sluggish, feeding very little during the late summer and fall. By September 15 some show a tendency to seek hibernating quarters, at least on cooler days, altho most of the beetles will emerge and feed on warm, sunny days. By October I all beetles entered hibernation, from which they did not emerge during the warm weather of early October.
The hibernation period of the insect in western New York is nearly eight months, emergence occurring during the latter part of May. In 1916, the first beetles emerged on May 27 at Fredonia. During 1917 at Lily Dale, eight miles from Fredonia and at an elevation five hundred feet greater, the first beetle emerged on May 30. The time of the appearance of the beetles was about one week after the bird cherry was in full bloom. The most extensive feeding by the adults occurs during the early part of June. It is at this time that practically all injury by the species to cultivated trees is inflicted. The greatest natural dissemination of the beetles occurs during the latter part of May and early June, when they may fly considerable distances to new feeding grounds.
Egg laying in 1916 began on June 5, under natural conditions, and on June 10 in observation cages, reaching the maximum in the first week of July and ending in the cages on August 9. The eggs are deposited on or near the trunk of the tree upon which the adults are feeding, usually not more than six inches above the surface of the soil, the majority being placed at the junction of the surface of the soil and the trunk. Some of the eggs are scattered loosely on the soil but most of them are glued to rootlets, small stones or the tree trunk. They are found to a depth of about one inch in the soil. The number of eggs laid in breeding cages by an individual varied from 10 to 294 with an average of 93. The normal life of the beetles appears to vary from 11 to 12 1-2 months, altho some individuals may reach an age of nearly 14 months.
The length of the incubation period during 1916 averaged 13 days, with a maximum of 23 days and a minimum of 9 days. These differences are ascribed largely to variation in temperature, altho there is individual variation in the incubation period of eggs deposited