Species replacement is most commonly observed among the parasitic Hymenoptera because of their dominance in biological control. Such replacement is necessarily a reproduction phenomenon involving interspecific competition in population-saturated areas. The competitive interactions of parasitic populations are differentiated into two types, “intrinsic” and “extrinsic”, with characteristic conditions and mechanisms.

Intrinsic competition consists of interference between individuals of the interacting populations, being manifested by such factors as cannibalism, mutilation, starvation, suffocation, production of toxic or repellent excretions and secretions, and the differential susceptibility of individual hosts to parasitic attack.

Extrinsic competition concerns the interaction of populations as groups and is manifested largely by host-habitat finding, host-finding, and host acceptance.

Replacement through intrinsic competition takes place regardless of host abundance; replacement by extrinsic competition is an effect of decreased host abundance.

Diel periodicities of emergence and oviposition of Trichoptera, observed in the St. Lawrence River at Montreal, Quebec (451/2° N.), in late June and July, are closely similar. They are poorly synchronized but the peak for most species is nocturnal, falling between sunset and solar midnight. Catches in floating traps were used to measure emergence rate. As such catches (of Trichoptera) may contain parous as well as newly emerged females, attempts were made to separate these two components of the catch before analysis, thus providing records for both emergence and oviposition. Oviposition periodicity was studied independently by counting egg-masses on a floating board. Precautions needed for future critical work on emergence are mentioned.

A nuclear-polyhedrosis virus disease of Spilonota ocellana (Denis and Schiffermüller) is described. The disease was found in the majority of the Nova Scotia apple orchards sampled in a nine-year survey. Under favorable conditions the disease caused high mortalities but usually less than 10 per cent of a host population was killed by the virus.

Agathis laticinctus (Cresson) killed an average of 25 per cent of late-instar larvae.

Hot, dry weather accompanied the decline of black-headed budworm populations in 1955 and 1965. A study of weather records for southeast Alaska for the period 1945 to 1965 shows that the collapse of high populations occurred in years of unusually warm, dry weather during July. No consistent weather pattern was apparent during the years of population increases. The great reduction in budworm numbers occurred during the larval periods in both 1955 and 1965. No evidence of disease was found in either outbreak.

Two artificial (oligidic) media have been developed for the rearing of Dendroctonus pseudotsugae under xenic conditions. One medium composed of macerated, frozen inner bark of Douglas fir, brewers yeast, antimicrobial agents sorbic acid and sodium benzoate, and water, permitted 75.17%, ± 3.04 S.E., of newly hatched larvae to develop to the adult stage. A second medium, composed of powdered, lyophilized inner bark of Douglas fir, brewers yeast, sorbic acid, sodium benzoate, glucose, cellulose, water, and agar, permitted 41.72%, ± 3.14 S.E., of newly hatched larvae to develop to the adult stage. The rate of development on each medium to the fourth-instar, pupal, and adult stages was somewhat shorter than that in published developmental data for this species. Immature beetles appear to be tolerant of considerable variation in pH and physical consistency and palatability of food material but are relatively sensitive to moisture levels. The adults obtained from each of the two media appeared to be normal, and the females were capable of laying viable eggs.

Although adults from each of four study areas in California showed no morphological differences and were identified as belonging to the Neodiprion fulviceps complex, a number of biological differences in different stages of development indicate that there are three distinct populations of one species or subspecies of a species in the, N. fulviceps complex in California.

The life stages are typical of Neodiprion species. Overwintering as eggs, eclosion commences in the spring. The larvae drop to the ground after four to six feeding instars, spinning their cocoons in the duff beneath the host trees. Pre pupal larvae spend the summer in the cocoon; pupation occurs in the fall and adult emergence follows two to three weeks after.

The foliage chosen for oviposition is mainly the current year's growth. Oviposition occurs largely in the upper crown of trees less than 10 feet in height, while in trees larger than 10 feet the lower crown is preferred. The outer two-thirds of the foliage of an individual tip and the lower gravitation edges of needles are favored for oviposition.

Some of the differences supporting the belief that there are distinct species or subspecies include number of eggs per female, number of needles in each fascicle used for oviposition, number of eggs inserted in each needle, spacing of egg pockets, egg color, number of feeding instars, date of larval eclosion, larval size, and larval feeding capacity.

Males and females emerged in synchrony in the laboratory and the field. Males predominated in cocoon collections but females predominated in rearings of larvae. This discrepancy in sex ratio may be due to a differential mortality factor. (In this study no prepupae were found to go into an extended diapause.)

One adult morphological character was found that may be of significance in supporting the contention that distinct populations or subspecies occur. Females in one study area generally had more antennal segments than females in other areas. This character along with the biological differences may prove adequate to describe these populations as subspecies or even species in the future bur it was felt that additional names, at this time, would only add to the confusion in the genus. Such descriptions should wait until the entire N. fulviceps complex can be considered.

A statistical analysis of U.S.DA. studies of insect attractants provides the first direct evidence for the reality of "primary" odors (heretofore inferred indirectly from abstract principles). Molecules of a single substance may carry more than one primary osmic character and the presence of one does not preclude another, but some primaries may overlap others. Thus the molecular qualities responsible for osmic properties appear to be distributed along a continuum. Molecular vibrational frequencies are so distributed, and the far infrared absorption spectra of some attractant and non-attractant substances show correlations of the sort predicted by the theory.

The serological relationships of the larvae of a number of species of bark beetles and weevils were examined. There appeared to be no clear serological separation between the two families as represented by the test species. However, certain relationships indicated in this preliminary study suggest that more extensive testing might be useful in evaluating the current constitution of the families Curculionidae and Scolytidae. In the meantime, it is anticipated that this technique can be useful in several discrete taxonomic problems now being investigated in the family Scolytidae.

The transmission of nuclear polyhedrosis virus in populations of the forest tent caterpillar, Malacosoma disstria (Hübner), was studied in Sudbury district, Ontario. Virus was transmitted from generation to generation by infected adults. Their progeny died from virus disease during the second and third larval instars. Adult flies of Sarcophaga aldrichi Parker, a dipterous parasite, were attracted to these dead, diseased larvae, became contaminated with virus, and spread the virus to foliage on which healthy larvae were feeding. The importance of these disseminating agents in the development of virus epizootics is discussed.

Pseudopterocomma canadensis, Chaitophorus nudus and Chaitophorus nodulosus are described as new. All three infest species of poplar in North America. The affinities of each are discussed.

A lightweight and inexpensive cylindrical-sleeve insect cage is described. The cage was constructed of plastic screening and cotton fabric closed by an open-ended zipper. The cage was successfully used to collect insects from rust cankers on the stems and branches of pine trees.

The measurement of insect attraction by the number of specimens collected in a certain time, or by the duration of the attractive effect, does not distinguish between the roles of intrinsic attraction and the attractant concentration. It is shown that the number of D. melanogaster responding to a food odor is proportional to the logarithm of the attractant concentration, in conformity with the Weber–Fechner Law. The implications of this result are discussed.

The median depression on the last abdominal sternite is a useful character for distinguishing, in the field, the male from the female adult of all North American Hylobius species.

Everett and Newsom (1964) used a midline depression or sulcus on the abdominal sternites to separate the sexes of the rice water weevil, Lissorhoptrus oryzophilus (Kushel), and other weevils that are not closely related to species of Hylobius in North America. The male of Hylobius abietis L., a European relative, is distinguished from the female by a saucerlilte depression on the last sternite (Anonymous 1952). Millers et al. (1963) state that the first and second visible abdominal sterna of the male H. rhizophagus Millers are concave, and the fifth has a slight median depression; the female sterna are convex.