Larval Brood Research Articles

Aggressive behaviour in the ant, Formica fusca

1. 1. The factors eliciting and influencing aggressive behaviour in the ant, Formica fusca, have been investigated. 2. 2. Seizing and dragging are types of aggressive response. Threat is shown to be an aggressive response which may be regarded as an incomplete seizing movement. Arguments are presented to show that threat, seizing and dragging represent increasing strengths of aggressive motivation. 3. 3. Four types of response may typically be shown towards aliens—the 3 aggressive responses and licking. The response pattern towards aliens is different from that towards returning nest-mates. More licking is shown towards the latter. 4. 4. Licking correlates negatively with total aggressive responses, but is more closely linked with threat than with seizing or dragging. The relation of licking with aggression is discussed. 5. 5. Various factors besides colony odour evoke or influence aggression. Thus, both temperature and hunger affect it. The situation “ant-entering the-nest” probably evokes aggressive responses and licking. However, colony odour remains the most potent stimulus to aggression. 6. 6. There is no evidence of an inherent difference in aggression between colonies. Increased aggression is shown at higher temperatures. Hunger also increases aggression and the significance of this is discussed. Other factors such as the presence of larval brood probably affect aggression as well. 7. 7. The origin of distinctive colony odours is discussed. Metabolic differences induced by different diets play only a small role in producing these odours in ants.

Distribution and Survival of Herring Larvae (Clupea pallasi Valenciennes) in British Columbia Waters

Through study of the distribution and survival of herring larvae of one of the main populations in British Columbia waters, it is concluded that (a) the principal cause of death in Pacific herring larvae is traceable to their passive transport by inshore water currents to the open sea, and (b) the number of larvae that are not so transported in any particular year determines the strength of the resulting year-class.Greatest concentration of larvae after hatching was found in inshore waters near the spawning grounds, and as they were carried seaward the numbers remaining decreased at an approximately constant rate. The movement of larvae, as noted through sampling, was related to the pattern of water currents, as determined by oceanographic survey. The extensive movement of larvae offshore was explained through seaward moving currents being strongest (a) in waters in which the largest larval broods were present, and (b) at the surface of the water where larvae were heavily concentrated at night. Predation, lack of food, and conditions of temperature and salinity were not considered important mortality factors in inshore areas.Sampling indicated that few larvae carried to sea returned to inshore waters. Furthermore, several pieces of evidence suggested that most larvae carried offshore did not survive. The failure to find either larvae offshore or nearly-metamorphosed juveniles near the mouth of Barkley Sound appeared significant, particularly since schools of the latter were regularly found inshore near the spawning grounds. The factors directly causing death in offshore waters were not determined, but it was suggested that death may be connected with the high salinity of the open sea. It was concluded that the strength of herring year-classes was largely determined by the numbers of larvae that remained in inshore waters during the critical period of larval life.Meteorological factors were considered capable of causing annual variations in current flow and hence in year-class strength, and the delayed effect of snow on river discharge appeared to be of greater importance than the more immediate effect of rainfall. No single meteorological factor, however, seemed to have a dominant influence.

Cyclical Changes in Numbers of Moths and Larvae of the Peach Twig Borer in California

Moth flight patterns or the peach twig borer (Anarsia lineatella Zeller), as well as the movements of larval broods into and out of foliage. fruits, and bark were studied during 1960 in two almond orchards in California. Three flights of moths were detected by means of a new sampling technique. The first flight, composed of moths resulting from the over wintered larvae, lasted from mid-April until early June. The second, composed of moths derived from first generation or May brood larvae, lasted from mid-June until late July. The third, which was much more pronounced than either of the two earlier flights, lasted from mid-August. until October. The ability to sample moth populations presents possibilities for estimating levels of infestation and predieting impending crop loss. It is known that during the spring and summer some larvae enter the hark and construct summer hibernacula. This study indicates that larvae which entered the bark during May, June, and July remained only temporarily. By the end of July most of these returned to the actively feeding stage. Larvae which entered hark during August and September remained through the winter. The data suggest that larvae which form temporary hibernacula early in the growing season are a possible source of infestation in stone-fruit orchards during the mid-summer harvest season.

A STUDY OF REPRODUCTION IN THE INTERTIDAL BARNACLE, MITELLA POLYMERUS, IN MONTEREY BAY, CALIFORNIA ,

1. The gross structure of the reproductive system of M. polymerus is described and compared with that of the southern hemisphere species, M. spinosus (studied by Bathanm, 1944-45).2. Size and reproductive activity in M. polymerus are related. All animals over 27.5 mm. in breadth (distance from rostrum to carina) are found to reproduce; smaller animals are found to contain developing embryos less frequently. No sexually mature animals less than 17.2 mm. in breadth were found.3. A fifteen-month study of the reproductive cycle in the population is described. Reproductive activity is evident during the greater part of the year. For the year of 1957, developing embryos were present in the population for a period of eight months durinig which time the shore temperature ranged from 12.3° C. to 17° C. The reproductive season for the southern hemisphere species likewise occurs during the warmest months; thus the yearly cycle of M. polymerus shows a perhaps expected mirror image of the situation occurrinig in the southern hemisphere.4. Within individuals, male and female gonads mature at approximately the same time during the year, and during the greater part of the year, an individual contains both developing eggs and seminal vesicles full of sperm.5. Stages of development of ovarian eggs and brooded embryos found simultaneously in individuals are compared. During the early and middle months of the reproductive season, ovarian eggs and brooded embryos tend to be in similar stages of development (that is, small eggs are found with early stage embryos, large eggs with late stage embryos, etc.). During the later reproductive months, a relative lag in ovarian egg development is evident.6. Embryos were raised in vitro under controlled temperatures. The embryos took an average time of thirty days for development from fertilized egg to free-swimming larva.7. Estimates are given of the number of broods of young and the number of larvae liberated by a large individual during a year, and these are compared with the results of Batham (1944-45) for M. spinosus. Studies of the larval brood period, the stages of eggs and embryos found simultaneously in individuals, and the length of the reproductive season allow an hypothesis that five to seven broods may be liberated by a large individual durinig a year. Three to four broods appears more probable for an average large animal. A pair of ovigerous lamellae may contain from 104,000 to 240,000 larvae. Batham's data (1944-45) showed that probably two broods, each containing approximately 3000 larvae, are liberated by M. spinosus during a year. Thus M. polymerus may liberate from 52 to 280 times as many larvae per year as a single large M. spinosus.8. The possibility of self-fertilization in M. polymerus is studied. Relatively isolated large animals are found to carry ovigerous lamellae less frequently than those adjacent to each other; and large animals isolated from each other by over eight inches were never found carrying embryos. From this evidence, it appears that self-fertilization does not occur in this species, and that cross-fertilization is necessary for the formation of ovigerous lamellae.

Importance of Photoperiod and Temperature in inducing Diapause in the European Corn Borer, Pyrausta nubilalis (Hbn.)

THE European corn borer was first found in Ontario in 19201 and, until recently, was primarily a single-generation species, producing one larval brood each summer and overwintering in diapause in the final larval instar. Beginning about 1941, a marked change in the seasonal history of the corn borer occurred. The numbers of larvae completing development without diapause and giving rise to second-generation larvae increased until it now constitutes a substantial part of the total borer population2. As one approach to an understanding of this divergence in seasonal history, we initiated a study on factors in diapause in the corn borer, including environment.

THE CALIFORNIA FLATHEADED BORER (MELANOPHILA CALIFORNICA VAN DYKE) IN PONDEROSA PINE STANDS OF NORTHEASTERN CALIFORNIA

This paper reports the findings of studies on the biology of the California flatheaded borer (Melanophila californica Van Dyke). Until comparatively recently this insect had been regarded as a relatively unimportant element of the western pine beetle problem. It has been shown that larval broods may spend a period of up to several years in an incipient stage in the living host tree. During this period the gallery of the incipient stage larva is healed over and the abnormal tissues thus developed interfere with normal conduction in the wood. Undetermined factors associated with the dying of the host tree initiate a fast-growing larval stage in which feeding is voracious and growth rapid.No attempt is made to set forth the role of the species in the complex known as the western pine beetle problem. It is, however, suggested that this insect, at least in northeastern California, may play a more important role in insect caused losses in commercial stands of ponderosa and Jeffrey pine than had previously been believed. The contributions to the knowledge of the biology of the species may assist in an eventual better understanding of insect–host relationships in this particular problem.