First instars of 93 North American species of mosquitoes are studied and 56 are illustrated, 41 for the first time. Generic differences are well marked in this instar and nearly all species are separable.

Two keys to the 11 North American genera are presented; the first is constructed to show similarities between first and later instars. Each genus is described and keyed to species, and notes are given on each species. A supplementary key to the species of the southeastern states is designed for the use of a binocular microscope with magnification up to 60 ×.

Specific and generic differences are as well marked in the first as in the fourth instar. Identifications are as easy or as difficult in the first as in the fourth instar, though usually based on different characters.

An expanded key to the North American species of Aedes, incorporating those previously treated by Bohart and by Price, is attempted. The key reveals several species complexes which have not been discerned from other stages of the life cycle, namely, Aedes canadensis, nigromaculis, punctor, stimulans infirmatus and trivittatus.

A key to the first instars of the 37 species of the world-wide Anophelinae is presented, on the basis of published descriptions and figures of the exotic species.

The haemocytes of adults of the stonefly, Acroneuria arenosa Pictet, are described and figured as they appear in vivo in the wings and as fixed and stained elements in blood films prepared in four different ways. The adequacy of the blood films is judged by comparing the haemocytes there with those in vivo, and the cell complex is interpreted from both aspects. Four categories of haemocytes, the prohaemocytes, plasmatocytes, granular haemocytes, and hyaline haemocytes, are denoted and characterized within these visual limits. The validity of one category, the hyaline haemocytes, is questioned on the basis of cell counts and cell morphology but is tentatively retained. Variations in the haemocyte complex during the adult life is considered. The progressive decrease in relative numbers of circulating plasmatocytes with age is shown to be due to their adherence to the walls of wing veins and presumably to other tissues within the body.

A method is described for the laboratory rearing of adult bark beetles and their broods in whole bark. A Petri dish rearing chamber is described, which maintains bark moisture at a relatively constant level for periods of up to two months and permits observation of adults and immature stages.

A list of 169 aphid species occurring in the Province of Quebec is given. Two new species: Stegophylla quercina n. sp. from Quercus, and Heterocallis daviaulti n. g., n. sp. from Carex are described.

Insight into the source of aggregation in the spatial distribution of cocoons of the Swaine jack-pine sawfly, Neodiprion swainei Middleton was gained by the use of special techniques enabling the sampling of units of forest floor in contiguous 2 × 2-inch square samples, as well as by randomized one-square-foot samples taken over a larger area. It was concluded that cocoon distribution is initially random but marked aggregation results from the subsequent transportation of cocoons into feeding stations by predacious small mammals, mostly of the genus Sorex. The feeding stations tended to be distributed near decaying stems and stumps on the forest floor, a factor which augmented the extent of aggregation. Of cocoons not preyed upon by small mammals, slightly higher counts were recorded directly under crown canopies as opposed to open areas, at a tree density of approximately 920 per acre.