Vol. 97, May 1965. Page 496, line 1 of Abstract — Archidipteron should read: Palaeodipteron

Page 502, line 15 — discondylic should read: dicondylic

Osmia atriventris Cr. and Megachile relativa Cr. are the most abundant bees accepting trap nests in the Black Sturgeon Lake area of Ontario. Hylaeus ellipticus (Kby.), H. verticalis verticalis (Cr.), Hoplitis albifrons albifrons (Kby.), and H. cylindrica (Cr.) are common while Hylaeus basalis (Sm.), Osmia proxima Cr., M. inermis Prov., and M. gemula Cr. are comparatively rare. All except Osmia atriventris are univoltine and overwinter as prepupae. O. atriventris is both univoltine and biennial. The major flight and nesting period for all bees is during July although M. relativa is active throughout August. Hylaeus spp. construct nests of silken membranous, secreted materials; Hoplitis spp. utilize macerated plant materials and pebbles to divide their nests; Osmia spp. partition their nests with macerated green plant material; and Megachile spp. line and plug their nests in typical leafcutter fashion. All bees provision their nests with pollen moistened with varying amounts of nectar. The sexes are probably almost equally divided in all species. Major parasites are Gasteruption assectator assectator (L.) for Hylaeus spp.; Chelynia subemarginata (Cr.) for Hoplitis spp.; Sapyga sp., for Osmia atriventris; and Coelioxys modesta Sm., and C. lucrosa for Megachile relativa. Melittobia chalybii Ashm. destroyed a few cells occasionally.

Superparasitism created a food shortage and thereby reduced survival and size of adult Nasonia vitripennis (Walk.) (Hymenoptera: Pteromalidae) reared on pupae of the house fly, Musca domestica L. Superparasitism also reduced the percentage of females in the adult progeny but had no effect on rate of development, ability to emerge, or incidence of diapause in N. vitripennis.

p. 1496, heading, top of page–For “Tabaninoe” read “Tabaninae”.

Nineteen species of carabid beetles are added to the list of those found in agricultural lands near Belleville in 1959–62, and eight previously determined to genus only are herein identified to species. Notiophilus intermedins Lth. is reported from Ontario for the first time, and a second record is made of Bembidion obtusum Ser., a European species doubtfully established in North America.

A gynandromorph of Aedes punctor, collected while it was sucking blood, is described and figured.

In certain insects there exist eocrepuscular diel periodicities of activity in which the sunrise peak occurs at a higher light intensity than does the peak at sunset. This may happen because the indicator-process chosen by the observer to designate the activity is not the first in a behavioural sequence released by light of a critical intensity.

Larval characterizations for the genera of North American Brachycentridae are revised and two new genera created, bringing to five the total number now recognized on this continent. Previous concepts of larval morphology in Micrasema are emended. Discovery of the larval stage of Brachycentrus (Amiocentrus) aspilus Ross necessitates elevation of this subgenus to generic status. Association of larvae with the two North American species placed in Oligoplectrum necessitates removal of one, O. dimicki (Milne), to Micrasema. Discovery of all stages of a new species on Mount Hood, Oregon, necessitates creation of a new genus. A provisional larval key to the genera of the North American Brachycentridae is proposed and the phylogenetic relationships of the genera are discussed. Validity of the Asian genus Oligoplectrodes is questioned.

The western species of Rhagio other than the dimidiatus group are reviewed, with a key to their identification. R. chillcotti, new species, is described from British Columbia (type), Washington, and Oregon. Confirmation of previous identifications of Bigot’s species is given and lectotypes are designated.

The construction of a temperature gradient area based upon a heat exchange grid is described. The main feature of the gradient apparatus is that it provides a flexible, yet temporally stable and evenly sloped gradient, which can be maintained in replicated troughs for many months with minimum attention. The control of the R.H. gradient in troughs containing a food medium is also discussed. Data relating to the life histories of Tribolium examined in the gradient is offered to exemplify the type of results obtainable.

It has come to my attention that results I reported (DeMars 1963) were incorrect.

In Table I the values for samples 4 through 7 in column 4 (Larvae-Dead-Rad.) should read 1, 10, 7, and 4 instead of 10, 7, 4, and 0. In Table II the values for sample 13 in columns 8 and 12 (Beetles of all stages-Live and Total-Rad.) should read 102 instead of 103.

Populations of the apple aphid, Aphis pomi De Geer, on apple were followed from 1959 to 1961, in Northern California. Population trends were generally upwards during early June and downwards through the remainder of the year. In 1959 a second population rise occurred during August. Populations were correlated with growth pattern of the host.

Also of importance in the characteristic decline of the apple aphid during July and August are the emigration of alate forms and predator activity. High temperatures were not thought to be an important mortality factor during the early summer months.

In the January 1965 issue of the Canadian Entomologist, under Affiliated Societies, Acadian Entomological Society, the Secretary-Treasurer was listed as Mr. C. A. Miller. This should have read Mr. G. R. Underwood.

The genus Parapandemis is recorded from Canada, and P. borealis n. sp. is described from New Brunswick, Ontario, and Alberta.

Community organization is defined as the mean number of trophic links connecting species of different trophic levels in a community. For the special purposes of this paper, competition is assumed to occur whenever two species are known to eat the same food species. Community stability is defined as the reciprocal of the mean, for all species, of the standard error of logarithms of annual collection sizes. It is thus a measure of stability over time of the species populations in a community. Several authors writing about the relationship between community organization and community stability have insisted that the stability of a complex ecological system increases with the number of avenues by which energy can flow through it. This theory does not seem consistent with the observation that some insect pest species of notorious instability are attacked by a great number of entomophagous species. In this paper we seek additional evidence bearing on the relationship between community organization and stability, using computer analysis of data collected by the Canadian Forest Insect Survey on forest Macrolepidoptera and their food plants. After considering our results, and those of other workers, we postulate the following hypothesis. Stability at any herbivore or carnivore trophic level increases with the number of competitor species at that level, decreases with the number of competitor species that feed upon it, and decreases with the proportion of the environment containing useful food. If this hypothesis is valid, too much competition in the entomophagous trophic level will not allow the species in that level to be instable enough to control an unstable pest. Therefore, the best type of biological control agent is one that has no direct competitor species. Also, the most unstable biological control agents, and hence those capable of controlling an unstable pest, will be polyphagous.

The incidence of attacks by Dendroctonus ponderosae Hopk. (= monticolae) was recorded by square-foot quadrats from the total bark surface of 60 lodgepole pine trees, Pinus contorta Dougl. var. latifolia Engelm., according to location on the tree, proximity to branches, and degree of bark roughness. The frequency distribution of attack density was bimodal, but the bimodality was an artifact of sampling from a population having a varying mean density. A log (x + 1) transformation of the data permits the use of parametric tests. Alternative non-area sampling techniques showed that the spatial distribution of attacks within a small area tended toward regularity, probably following the distribution of bark niches. The greatest variance in attack density was associated with height, followed by areas, trees, diameters and aspects. Bark roughness was an important influence of distribution but number of branches was not.

The six-spotted leafhopper, Macrosteles fascifrons (Stål), is the only known host of Pachygonatopus minimus Fenton; parasitism has reached 37%. The female adult is also a predator of the leafhopper. In the adult stage of the parasite the sexes differ in form, color and habits; the male is winged and the female wingless. The egg is laid in the abdomen of the host. As the larva develops it protrudes through an intersegmental membrane. There are five larval instars. The first four are sedentary and attached to the host; the fifth is an active feeding stage. The larva spins a cocoon within which it pupates. The period from egg to adult is about 28 days. P. minimus does not provide effective control of the leafhopper.

The aqueous exudation from the sagittiform sensilla of Dermacentor andersoni Stiles larvae and nymphs, when placed in xylene and kerosene, indicates that the sensilla are more permeable than the rest of the cuticle to water. Potassium hydroxide also penetrates preferentially at these sites, reacting with haem pigments to form a pink colour in Dermacentor and Boophilus larvae. These observations, together with the complex structure of the sensilla, suggest that the sensilla are hygroreceptors.