Neodiprion Swainei Research Articles

A Virus Disease of Swaine's Jack Pine Sawfly, Neodiprion swainei Midd. Sprayed from an Aircraft

Neodiprion swainei Middleton is the most serious defoliator of jack pine, Pinus bamksiana Lambert, in Canada. The damage to stands of this species in northern Quebec has been extensive and has resulted in considerable forest-fire hazard. Virus infected sawflies were found in the Lac Gagnon area in Quebec in 1956, and a study of the disease was begun by the Quebec Laboratory in 1957. Laboratory propagation methods were developed and resulted in the production of a quantity of polyhedral concentrate of a virulent strain. Concentrations of polyhedral bodies needed in a spray formulation to infect and kill larvae of various ages were determined in the laboratory and field tests demonstrated the potentialities of this disease as a biological control agent (Smirnoff 1960b, 1961a). These studies served as a basis for the experiment in the dissemination of the disease by aircraft described in this paper.

SOME EFFECTS OF ARTIFICIAL DEFOLIATION ON THE GROWTH OF JACK PINE (PINUS BANKSIANA LAMB.)

Young jack pine (Pinus banksiana Lamb.) were defoliated manually to measure the effects of defoliation on growth of this species, and to determine the relative efficiency of foliage of different ages with respect to growth. The removal of 2-year-old or 3-year-old foliage had no appreciable effect on tree growth, but their joint removal reduced height growth. Height growth was also reduced by the removal of 1-year-old foliage. Current foliage was found essential for the maintenance of normal height, diameter, and shoot growth; in addition, its removal induced high bud mortality, the production of profuse adventitious growth, and a reduction in the rate of shoot elongation. Trees deprived of all but current foliage showed marked reductions in height, diameter, and shoot growth. Complete defoliation resulted in tree death shortly thereafter. Growth reductions resulting from some of the treatments approximated that following defoliation by the Swaine jack-pine sawfly (Neodiprion swainei Midd.). Also, the present results are compared with those obtained by several other workers in this field.

A Technique for the Extraction of Cocoons from Soil Samples during Population Studies of the Swaine Sawfly, Neodiprion swainei Midd. (Hymenoptera: Diprionidae)

Since Neodiprion swainei Midd. overwinters within cocoons in the soil, it is necessary for the population ecologist to sample the forest floor. One-footsquare units of soil have been used for sampling cocoons in population studies of N. swainei in the Province of Quebec. After removal from the forest floor the samples were placed individually in cotton bags for shipment to the laboratory. The ordinary method to extract cocoons required that the samples be first broken up by hand, then passed over various-sized screens to eliminate the sand and other small particles. Following this, each sample was carefully manipulated and scrutinized by one worker and the cocoons removed, then similarly re-examined by another worker. Best results were obtained when the samples were dry.

Predators of Larvae of Neodiprion swainei Midd. (Hymenoptera: Tenthredinidae)

In 1958, Pilophorus uhleri (Knight) (Hemiptera: Miridae), Vespula vulgaris (L.) and V. rufa consobrina (Sauss.) (Hymenoptera: Vespidae) were recorded for the first time as being not only active predators of Neodiprion swainei larvae, but also vectors of a virus disease affecting this sawfly (Smirnoff, 1959). The latter vespid was considered to be especially important. In the summer of 1959, in the same area (St. David de Falardeau, Lake St. John region, Que.), more insect species were identified, which preyed on the first- and second- instar larvae of N. swainei. Most active were Lasioglossum (Evylaeus) sp. (Hymenoptera: Halictidae) and Crabro sp. (Hymenoptera: Sphecidae), while three species of Vespula were also observed: V. maculata (L.), V. arenaria (Fab.) and V. norwegica norvegicoides (Slad.) (Figs. 1-4). This completes the list of insects which have been observed to prey on swainei larvae. Data were also obtained on the period of greatest activity of each of these predators.

Observations on the Migration of Larvae of Neodiprion swainei Midd. (Hymenoptera: Tenthredinidae)

In the course of studies on Neodiprion swainei Midd. carried out in 1958 and 1959 in the region of Lake St. John, Que., mass migrations of Neodiprion swainei Midd. were observed. This paper gives a brief description of this phenomenon, which has never been reported heretofore, and discusses some of its implications.On hatching from the eggs which are laid on the needles of the current growth of jack pine, Pinus banksiana Lamb., N. swainei larvae crawl to the old foliage where they feed in colonies of 40 to 70 individuals. At times, when larval populations become so great that all the foliage is destroyed, mass migration begins. The larvae gather in large clusters at the top of the tree where they remain for two or three days. At this time some of the larvae moult. The larvae then abandon the tree by crawling down the tnink or by dropping to the ground. They then creep on the ground, up and down stumps, in search of jack-pine trees with foliage. The migrating larvae are pale yellow in colonr, probably as a result of their starved condition, and large nutnbers perish before they can become established on proper food. Those that manage to reach new food supplies quickly recover their original dark-green pigmentation.

Spathimeigenia spinigera Townsend (Diptera: Tachinidae), a Parasite of Neodiprion swainei Middleton (Hymenoptera: Tenthredinidae)

The sawfly Neodiprion swainei Midd. has long been recognized as a serious defoliator of jack pine, Pinus banksiana Lamb., but it was not until the relatively recent use of jack pine as a raw material for pulp that interest in the sawfly became acute. Subsequently, investigations into the natural control of N. swainei were begun in the year 1955 near the headwaters of the Gatineau River, P.Q. (47° 55′ N., 75° 25′ W.) which was considered to be near the centre of the current infestation.

Predators of Neodiprion swainei Midd. (Hymenoptera: Tenthredinidae) Larval Vectors of Virus Diseases

In the summer of 1958 a virus disease of larvae of Neodiprion swainei Midd., a serious defoliator of jack pine (Pinus banksiana Lamb.), was investigated. The experiments were carried out near St. David de Falardeau in the Lake St. John region, Quebec, where the forest is largely composed of 15- to 20-year-old jack pine. The infestation was three years old, and judging by the production of eggs, had reached serious proportions in some places.