Spatial distribution is one of the most characteristic ecological properties of species. Unlike rates of growth and reproduction, which often vary more between generations within a species than they do between species, spatial distribution yields characteristics parameters that segregate species. These parameters are the population expression of the individual behavior defined by the ethologist and observed by the naturalist. They determine the spatial distribution of temporal dynamic change. Starlings flock, herrings school, and deer herd together, while eagles, sharks, and tigers hunt alone. This behavior determines their spatial patterns. The spatial patterns of insects are no less specific. Interest in this characteristic of species is both applied and fundamental. Most of the sound data available for analysis were collected by applied entomologists and hydrobiologists. Large mammals are rarely available in the numbers and species necessary for comparative analysis, although there are good data for birds. Insects are especially suitable for investigation because of the large numbers of individuals and species. Expermentation is difficult because, if the population is constrained, the natural distribution is destroyed. Hence, fundamental interest tends to be theoretical, rather than practical, or directed to behavioral response rather than to spatial pattern. Applied interest centers on formalizing systems of sampling.

Assessing and Interpreting the Spatial Distributions of Insect Populations

Studies evaluating the impact of natural enemies on their hosts fall into two broad categories. The first category involves separate host populations: one population with a particular natural enemy; the other without it. When the resulting densities and mortalities in the populations are compared, the differ­ ences are attributed to the natural enemy. Evaluations of this type quantify the impact of the natural enemy largely in terms of the amount of mortality that is caused by an agent to a given generation or set of generations of the host and the consequent overall reduction in host density; however, these evaluations do not provide descriptions of other sources of mortality that act together with the natural enemy. This approach was reviewed recently (83). The second category involves the construction and analysis of life tables for affected populations, and this is done either for single or multiple locations or generations. This particular use of life tables may be directed at two distinct types of questions regarding the action of natural enemies: (a) They may be

Life-Table construction and analysis in the Evaluation of Natural Enemies

Five hundred thirty life tables for 124 holometabolous, herbivorous insects were compiled from the literature and studied to uncover demographic patterns. Survival and sources of mortality of the preadult stages were correlated with their ecological setting, and several patterns emerged. Exophytic herbivores suffer a 5%-10% greater risk of preadult mortality than endophytics but are also nearly twice as large (pupal length, 11.8 mm vs. 6.4 mm; adult body length, 13.5 mm vs. 5.5 mm) and twice as fecund (206.1 vs. 99.3 eggs per female). Attack by natural enemies is the most frequent mortality source for immature herbivores (frequency = 48%). Plant factors are not nearly as frequent (9%) but have probably been underestimated in past life tables. The influence of plant factors is greatest in the early stages, and the influence of enemies is greatest in the later stages of development. Plant factors kill endophytic species more frequently than exophytic species (frequencies = 15% vs. 2%), whereas enemies kill ...

Survival Patterns and Mortality Sources of Herbivorous Insects: Some Demographic Trends

There is a significant and increasing interest in using fungi as biocontrol agents for insect pests in agricultural systems, and also a growing interest in the basic biology of insect-fungal associations from the perspective of parasitism, symbiosis, and infection. Vega and Blackwell are well-regarded workers in this field, and they have assembled an impressive short book of ten chapters to cover the most important topics in this field, incorporating new molecular techniques wherever possible. The book should appeal to worker in ecology, entomology, mycology, plant pathology, and biological control and pest management.

Insect-Fungal Associations: Ecology and Evolution

Density-dependent processes and key factors in insect populations

Survival and development rates were obtained for the cereal leaf beetle, Oulema melanopus (L.), at 12 constant temperatures. Rates of survival for eggs were high at temperatures ranging from 12°C to 32°C, but none hatched at 6°C or 34°C. Larvae survived at 8° to 32°C with no drastic rise in mortality at the extremes; mortality at 34°C increased with larval age. Pupal survival was low at all temperatures from 8°C to 32°C, ranging from about 3% at these limits to 40% at intermediate temperatures (14° to 30°C). Duration of egg and larval stages decreased with rise in temperature up to 30°C, and that for pupae, up to 32°C. Developmental rates plotted against temperature did not deviate significantly from fitted curves of the form 1/y = K/(1 + ea-bx).The threshold for complete development was at some point between 6°C and 8°C. Thermal requirements, with 7°C as developmental zero, were calculated at 105, 41, 36, 43, 46, and 282°D, respectively, for the eggs, the four larval instars and the pupae. Accumulated heat units (°D7) during development of O. melanopus in field plots at Ottawa did not differ significantly from those expected. Similar calculations using a base of 9°C (ca. 48°F) predicted development equally well.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0008347X0001782X

Effects of temperature on development of the immature stages of the cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae).

The analysis of intrageneration change in eastern ontario populations of the alfalfa weevil, hypera postica (coleoptera: curculionidae)

Tetrastichus julis (Walker), a European larval endoparasite of the cereal leaf beetle, Oulema melanopus (L), has become widely established in southern Ontario. In 1975, rates of parasitism in 14 counties varied from 15% in the east to 95% in the west Dispersal into Ontario was natural and is attributed to extensive colonization of the parasitoid in Michigan and other parts of the U.S. midwest. Reasons for its success in Ontario are suggested.

Establishment and spread of tetrastichus julis (hymenoptera: eulophidae), a parasitoid of the cereal leaf beetle in ontario

Since the late 1970's, populations of the alfalfa weevil, Hypera postiea (Gyll.), in the Quinte area of eastern Ontario have fluctuated within narrow limits at average densities below the economic threshold. Fifteen life tables compiled during a recent 5-year period were compared to similar data for an earlier period spanning the original outbreak cycle. Analysis of the components of mortality using a variance/covariance matrix of the separate mortalities, expressed as k -values, showed that a fungal disease of the larvae remained as the principal factor governing population trends. Although the disease behaves in a density-dependent manner, it is not entirely compensating in its action and this accounted for the wide population fluctuations (and economic damage) that persisted through the mid-1970's. However, since 1977, the weevil has been parasitized in significant numbers by the euphorines, Microetonus aethiopoides Loan and M. eolesi Drea, whose activity strongly reinforces that of the disease. With their influx to the Quinte area, weevil survival has declined by more than 50% and its populations have been effectively stabilized at subeconomic levels.

Analysis of Numerical Change in Subeconomic Populations of the Alfalfa Weevil, Hypera postica (Coleoptera: Curculionidae), in Eastern Ontario

Following its invasion of eastern Ontario during the mid-1970's, numbers of the alfalfa blotch leafminer, Agromyza frontella (Rondani), increased rapidly to economic proportions and then receded to near tolerable levels. Thirty-three life tables were compiled from population and mortality data collected during this colonization phase. Analysis of the components of mortality using a variance/covariance matrix of the separate mortalities, as expressed as k values, showed that maggot mortality within leaf mines was the key factor that determined population trends. Maggot mortality was the result of two contemporaneous processes fluctuating with a similar order of magnitude: exploitation and interference competition among instars, and predation by a complex of indigenous nabids and mirids. Although the former process was density dependent, its regulatory potential was damped by the inverse response of the predators, whose activity diminished the competitive interaction. Prepupal mortality was high but relatively invariant. Mortality from other causes was low and contributed little to population trend. Life tables for the larval stage in central Quebec resembled those for Ontario.

Population Dynamics of Alfalfa Blotch Leafminer, Agromyza frontella (Diptera: Agromyzidae), in Eastern Ontario: Analysis of Numerical Change During the Colonization Phase

J. C. Guppy

Papers

Effects of temperature on development of the immature stages of the cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae).

The analysis of intrageneration change in eastern ontario populations of the alfalfa weevil, hypera postica (coleoptera: curculionidae)

Establishment and spread of tetrastichus julis (hymenoptera: eulophidae), a parasitoid of the cereal leaf beetle in ontario

Analysis of Numerical Change in Subeconomic Populations of the Alfalfa Weevil, Hypera postica (Coleoptera: Curculionidae), in Eastern Ontario

Population Dynamics of Alfalfa Blotch Leafminer, Agromyza frontella (Diptera: Agromyzidae), in Eastern Ontario: Analysis of Numerical Change During the Colonization Phase