Ovaries are one of the target organs hit by the nucleic acid antimetabolite 6-azauridine. All the malformations observed are caused by the suppression of mitotic activity, which appears to be the most sensitive to the applied drug. The inhibition of mitosis in the apical trophocytes results in depletion of the nutritive tissue in older females, followed by a disturbance of previtellogenesis and activation of oocytes. The blocked mitotic multiplication of prefollicular tissue results in exhaustion of this layer followed by a disturbance of regular egg chamber formation. The inadequate separation of oocytes by follicular cells causes the arrangement of the oocytes in paired chambers, often blocking the ovariole, or the formation of compound chambers. The oocytes sharing the compound chamber either remain separated by the ooplasmalemma or merge. Eggs with adherent dwarf oocytes or giant fused double eggs are oviposited. Endomitotic DNA replication and amitotic karyokinesis of the follicular cells are not interfered with by 6-azauridine, probably owing to the nucleic acid pools contained in the haemolymph. The lecytholitic cells resorb the ooplasm utilizing the nucleic acid-rich material.

The pulsatile organ, or "accessory heart," in the tibia of Triatoma consists of a membrane which divides the femur and tibia into a series of sinuses, a pulsatile muscle which propels the haemolymph through the sinuses, and a valvular membrane, which imposes unidirectional flow on the system. A possible innervation of the muscle is described, and simple experiments involving nerve stimulation demonstrate that the pulsatile muscle is under nervous control. Using partially isolated preparations of the pulsatile organ, it has been shown that the organ responds to dopamine and serotonin, but fails to respond to acetylcholine. The pulsatile muscle therefore resembles visceral muscle rather than skeletal muscle.

Climatic factors which may control the time of occurrence of seasonal phenomena are discussed, and in particular the role of temperature in initiating periodic cycles in animals in continental North America. The seasonal flight periods of nine species of noctuid moths at two localities in western North America are considered in terms of the lengths of the summer season at these localities. Among the species discussed, those that are in flight prior to midsummer fly earlier, and those that are in flight after midsummer fly later, in the area with a long summer than in the area with a short summer. A factor termed the "phenological date," which is based on the number of days above 42°F in a given area, is proposed as a measure of seasonal development. The factors of photoperiod and temperature that may have a controlling influence on periodic events are discussed. Variance analysis suggests that the phenological date has greater predictive value in estimating the periods of flight of the species considered than have the other factors.

Five new species of Megapenthes are described: apacheorum from Arizona and New Mexico; texanus from Texas, New Mexico, and Arizona; fuscus from Arizona; antennatus from Arizona and Durango (Mexico); and elongatus from Arizona and New Mexico. Four species are redescribed: longicornis Schaeffer, variolatus Van Dyke, megalops Van Dyke, and obtusus Van Dyke. The male genitalia of these species are illustrated, and a key to the 29 nearctic species is included. The position of aterrimus Motschulsky is discussed, Dolopiosomus Motschulsky is considered as a nomen oblitum under Megapenthes, and caprella californicus Brown is synonymized under caprella LeConte.

The fauna of the sporophores of the perennial bracket fungus Fomes fomentarius (L. ex Fr.) Kickx were examined in a 3-year study. One species of molluscs and more than 152 species of arthropods excluding mites, representing 13 orders, 70 families, and 5400 individuals, emerged from or were found on or in, 1448 sporophores detached from dead birch trees; the sporophores were collected each year in Gatineau Park, Que., kept individually in screen-topped glass jars in a laboratory, and examined for several months. Mites, which were recorded quantitatively only in the final year, added 4 orders, 19 families, and 30 species to the preceding totals. Mites were the most frequently occurring and probably the most numerous arthropods, followed by Coleoptera, Psocoptera, Collembola, Hymenoptera, and Diptera.The key organisms of the fauna were five species of beetles that were primarily responsible for tunnelling and destruction of the sporophores and would therefore exert great influence on the composition of the community. Their tunnels provided shelter and food for many smaller arthropods or facilitated their feeding. Some beetle species tunnelled the sporophores for one season and others, for several, but many living sporophores and most dead ones tunnelled by beetles were tunnelled in the same season by more than one species of beetles.There was considerable latitude in types of sporophores inhabited by various arthropods but some species were particularly attracted to living or dead, to younger or older, and to smaller or larger, sporophores. Some species were also attracted to certain regions of the sporophore more than were other species.Possible economic implications of observations made in the study are discussed.

The physical association between Dendroctonus ponderosae Hopk. and its associated blue stain fungi Ceratocystis montia Rumb. and Europhium clavigerum Robinson and Davidson and the yeasts Pichia pini (Holst) Phaff, Hansenula capsulata Wickerham, and H. holstii Wickerham is described in single broods reared in bolts of lodgepole pine, Pinus contorta Dougl. var. latifolia Engelm. Eggs just prior to hatch and first-instar larvae were always in contact with the microorganisms whereas newly laid eggs, second-, third-, and fourth-instar larvae were not. During pupation, blue stain fungi and yeasts colonized pupal chamber walls. Transfer of these microorganisms to the new generation of insects was ensured when tenerals contacted the microorganisms lining the pupal chamber. Ensured physical contact between these organisms supports the hypothesis of a symbiosis between them.

The diel pattern of drifting adults, pupae, pupal exuviae, and larvae of Chironomidae in a stream was established. Emergence was trimodal for the common species (Cricotopus sp. and Psectrocladius sp.), and larval drift-rates increased almost two-fold in darkness. The concurrent diel consumption of Chironomidae by coho fry was examined. The fish appeared not to make use of the peak drift-rates of larvae. Closest temporal correspondence between drift and diet was shown by adults. Forage ratios demonstrated greater consumption of chironomids than would be expected from their proportions in the drift. The order of acceptance was pupae, adults, larvae, and exuviae. High degree of utilization of an item is attributed to flotation and visibility. The major determinants of how much food is taken from the stream are identified as: marginal residence of the fish, the occupation by the fish of slow-water feeding stations, and the visibility of food items.

Three new species of ascid mites are described and illustrated: Proctolaelaps subcorticalis, Lasioseius corticeus, and Gamasellodes rectiventris. All are subcortical associates of bark beetles in North America.

Four major categories of neurosecretory cells (A, B, C, D) were distinguished in the brain of Triphaena pronuba L. by staining sections with paraldehyde fuchsin and counterstains. These comprised nine types of cells, seven of which were recognizable for analysis of their secretory products. Histochemical tests indicate that the lepidopteron brain has a multiplicity of neurosecretory cells, each type producing chemically different secretions.

A simple and inexpensive olfactometer based on that of Gaston and Shorey (1964) is described for bioassaying the sex pheromone of the eastern spruce budworm. The number of males buzzing (rapidly beating their wings while circling on the substrate) after the introduction of the sample into the airstream of the olfactometer was used as measure of response. Males held under continuous illumination showed maximum response when 2 to 3 days old. Under natural lighting males showed a circadian rhythm, with peak response shortly after dark and a minor peak in mid-morning. Since per cent response under continuous illumination exceeded the maximum response under natural lighting, it is recommended that bioassays be carried out with 2- to 3-day-old males held under continuous illumination.

A shift in the average number of an organism from an economic to a non-economic density, the goal of biological control, is usually brought about by the addition to the ecosystem of exotic "key" factors whose lethal action is more efficient and broader in scope than that of the mortality factors already operating.Such a shift in the homeostasis of a pest population can occur only when its protection from the lethal action of key factors is fortuitous. With fortuitous protection (in contrast to absolute protection) host-searching by parasite or predator populations is so unrestricted by physical barriers that no portion of the target population is continuously immune to attack.In many instances after the attainment of low-density homeostasis the controlling action of the added key factor does not appear to be either supplemental to or superimposed on the total pest mortality that had prevailed in the ecosystem but largely a substitution for that mortality through its displacement and greatly amplified replacement. Means for verifying the responsible key factor in a given locality following the importation and establishment of a possible key factor and observations on hierarchies of such factors are reviewed.

The musculature of the pterothorax of the adult male Choristoneura fumiferana (Clem.) is described in detail and the arrangement of muscles is shown to correspond closely to other lepidopterans. A comparison with the general plan of the alate segment is also attempted.

A method is described for observing, photographing, and video-taping the mouthparts of Rhodnius prolixus Stal., a blood-feeding insect, as it feeds on an artificial diet. This method was combined with another for recording the electrical resistance between the haemolymph of a feeding insect and its diet. By using a split-screen television technique simultaneous recordings were made of the changes in electrical resistance and feeding events such as mouthpart movements, salivation, and ingestion. Slow speed and stop-frame playback allowed accurate analysis and correlation of rapid events. The techniques described could be applied to many other types of investigation.

A nymph of an homopteran preserved in Cretaceous amber from Cedar Lake, Man., is described. It presents features of two recent families, Cercopidae and Cicadellidae, and so is recognized as a new family of intermediate position. Jascopidae new family contains only Jascopus notabilis n. gen., n. sp.

Duplicate benthic stream samples were collected from three sites on Sandy Creek (Lake Ontario Watershed) in Western New York, 8 and 22 September, 1970. Samples taken on 8 September were preserved in 10% formalin. Samples taken on 22 September were not preserved. Insect specimens were removed from both sets of samples by flotation with a sucrose solution of 1.12 sp. gr. Preserved and unpreserved samples were compared for efficiency of recovery of insect larvae. Mean recovery for preserved samples was 90.78% compared with 83.03% for unpreserved samples. The range of recovery values for unpreserved samples (66.7%) was more than twice as great as that of preserved samples (29.5%). A paired t-test for means of all taxa showed no significant difference (P < 0.001) between recovery values for preserved and unpreserved samples. In fact, preservation may enhance the recovery of certain groups—Zygoptera, Hemiptera, Trichoptera, and Chironomidae. Apparently samples may be preserved without sacrificing recovery of any specific groups of insect larvae.

Medetera aldrichii Wheeler larvae enter galleries of Dendroctonus ponderosae Hopkins through the beetle entrance holes. Observed larval densities of the fly were greatest in the May–June period following beetle attack. Densities were consistently greatest in the portion of the tree 5–10 ft aboveground; averaging around 3–4/sq. ft. The fly larvae probably cause a major share of the beetle mortality between August and the following May. The fly larvae pupate near beetle-created openings that lead from the galleries to the exterior.

Larvae of the marsh fly, Sepedon tenuicornis Cresson, were used to determine (1) number and approximate volume of snails killed before pupation, (2) time required to make the first kill as a function of distance and snail density, and (3) vulnerability of snails of different sizes to larvae of different sizes.Results1. Mean number of snails killed (by 34 larvae): 8.1 ± 2.5, (S.E.) Volume: 544 ± 256 mm3.2. Regression line relating time required to kill as a function of snail density: T (minutes) = 65.3–111.6 × (snail density).Regression line relating time to kill and snail densities of 0.6 and 1.2 snails/cm as a function of distance from snails: T = 0.79–0.33 × (distance).Data from a snail density of 0.3/cm could not be pooled because of high day-to-day variation in larvae.3. Vulnerability of snails can be expressed for each larva length by the equation: Fraction of snails killed = a + b × (snail size).

Values of a and b are as follows:

The egg and five nymphal instars of Podisus placidus Uhler and Stiretrus fimbriatus (Say) are described and illustrated. The nymphal instars can be separated on the basis of head width or pronotal width. No overlap was encountered in the nymphal instars studied.P. placidus overwinters as an adult. Egg development in the laboratory took approximately 6.0 days. The average time spent in each of the five nymphal stages was 5.4, 4.6, 4.9, 4.7, and 7.6 days, respectively. Development of S. fimbriatus eggs took approximately 9.5 days. The average time spent in each of the five nymphal instars was 5.1, 4.3, 4.1, 4.3, and 8.2 days, respectively. Adults of S. fimbriatus were parasitized by Cylindromyia fumipennis (Bigot) (Tachinidae).

In an attempt to evaluate the importance of physical and biotic factors affecting the distribution of species of the cutworm genus Euxoa, a multivariate regression analysis, as based on a light-trapping survey in western North America, has been conducted. The possible contributory factors have been grouped into four major categories relating to geography, habitat, period of flight, and sample size. Sample size is a composite value reflecting both suitability of habitat and suitability of weather conditions at the time the sample was taken. Geographic factors considered were latitude, altitude, and longitude; habitat factors were mean annual temperature, mean July temperature, mean January temperature, mean annual rainfall and plantform; factors relating to period of flight were calendar date, mean temperature on date of sample, photoperiod, and the phenological date. Except for photoperiod, the variables listed were considered in a quadratic as well as a natural function in the regression analysis. With the number of species of Euxoa as the dependent variable and the factors listed above as the independent variables a total reduction of 76.0% in the residual variance was obtained. When only four variables, sample size, mean annual temperature, mean annual rainfall, and phenological date were employed in a similar regression analysis, however, a reduction of 68.7% in the residual variance was obtained. On the basis of present evidence, it appears that temperature and rainfall are primary factors governing the abundance of species of Euxoa in a given habitat.