Ecosystems that are managed for resource production are under continual structural change. Changes imposed by local management aggregate to produce regional patterns and new regionwide responses. Anthropogenic influences on hemispheric and global processes add another level of change. The result is a bewildering variety of real or anticipated changes unique to experience. For example, in the spruce/fir and budworm interaction of eastern North America, a syndrome of causes affects the vulnerability of renewable resources, and the triggers of change can never be predicted. Yet, it is possible to identify key features that affect resilience of ecosystems and robustness of regulation and to reject other possibilities. This approach provides a way to assign priorities for research and for contingency planning to adapt to change.

New technology allows the rapid mapping of point or polygon variables, the correlation of maps, and the use of maps as variables in computer models. An illustration is the use of map correlation to investigate how changes in abundance of adult grasshoppers relate to rainfall in Alberta: maps of monthly rainfall, monthly hours of sunlight and annual grasshopper counts (8391 survey records) from a 5-year period were contoured and correlated. The methods of smoothing are described. Correlograms of Moran's I over distance show spatial autocorrelation of grasshopper abundance on a geographic scale. The grasshopper counts were autocorrelated to 20–30 km on most maps, and the relationship of correlograms to contour mapping is discussed. Quotient maps were produced: each population–abundance map was divided by the map from the previous year, and the results were correlated with monthly rainfall maps. There was significant association between areas of increase and levels of rainfall. Population tended to decline in areas of above-average rainfall. A simple model enabled a forecast of grasshopper distribution from the previous year's grasshopper population, monthly rainfall maps, and sunlight hours during the previous August.

Three populations of the pea aphid, Acyrthosiphon pisum (Harris), from locations between 27 and 36°S in eastern Australia were studied at five constant temperatures from 10 to 28 °C. A three-parameter, nonlinear equation accurately described developmental rate as a function of temperature for each of the five lines from each population. Maximum adult weight was attained at 20 °C. Wingless aphids developed faster and were heavier than winged aphids. There were no significant differences in developmental times among populations, and adult weights among populations differed only at 25 °C. These weight differences and other nonsignificant differences among populations showed no trends with the long-term average temperatures at the collection sites. This finding indicates that developmental rate and adult weight have not been adapted to temperature in the 5 years since the aphids were introduced. The maximum rate of development, optimum temperature for rapid development, developmental threshold, and optimum temperature for high adult weight were higher for the Australian populations than for North American populations, but these differences do not reflect adaptation to different environmental temperatures. We conclude that Australian populations of A. pisum did not originate in North America.

The effects of weather on the spruce budworm parasitoid, Apanteles fumiferanae Vier., are examined. A phenological model based on temperature-dependent rates of development and longevity is developed and validated with field data. The model is then used to explore the effects of age-specific mortality on phenological behaviour of the parasitoid and the seasonal synchrony between the parasitoid and its host over several years. The results show that the parasitoid adult ecloses well before the host reaches an age susceptible to parasitism but that the egg maturation period and the longevity of the parasitoid diminish the consequences of the apparent asynchrony. The historical data reveal that the relative phenological characteristics of A. fumiferanae and its host vary little from year to year. In the second part of the study, temperature is shown to have a strong effect on adult parasitoid activity and on the rate of oviposition.

Individual meteorological factors, particularly temperature and wind, directly influence the dispersal of arthropods, as do weather systems — formation and movement of air masses, cold and warm fronts, and air flows associated with topographical features such as mountains, valleys, bodies of water. Models have been recently developed that simulate the effects of many of these systems on airborne dispersal of insects. Also, some attention has recently been directed toward the behaviour of arthropods during weather conducive to dispersal. Clearly, both winged and wingless forms of arthropods respond to certain stimuli for dispersal and behave specifically to enhance the potential for migration. Recent progress toward understanding the interplay between insect movement and mesoscale weather is particularly relevant to pest management.

The relationship between yellow sticky trap catches of Pholetesor (= Apanteles) ornigis (Weed) and its emergence during the first two of its three yearly emergence periods was examined using four trap locations in five commercial apple orchards in Norfolk County, Ont., during 1984 and 1985. Orchards were divided into two zones: the border row of trees (= peripheral zone) and all trees within the border row (= interior zone). Traps were positioned within and below the tree canopy in the two zones.The sensitivity of the yellow traps to first male and female spring emergence was similar. Trap location had no obvious effect on the relationship between first spring emergence and first spring trap catch of males and females. The traps were similar in sensitivity to peak male and female spring emergence. Trap location affected the relationship between peak male emergence and peak male trap catch during the spring emergence period; the number of parasites caught on traps placed below the tree in the interior zone was the best indicator of peak male emergence. Trap location did not affect the relationship between peak female emergence and peak female trap catch during the spring emergence period.The yellow traps were more sensitive to male than to female first emergence during the first summer emergence period. During this emergence period, trap location had no obvious effect on the relationship between first emergence and first trap catch of males and females. The traps were more sensitive to peak male than to peak female emergence during the first summer emergence period. The number of male parasites caught on traps placed within the tree in the peripheral zone gave the best indication of peak male emergence during the first summer emergence period. The most accurate indication of peak female emergence was given by the number of female parasites caught on traps placed within or below the tree in the interior zone of the orchard.During the spring emergence period, few parasites were caught after emergence was complete, whereas during the first summer emergence period, relatively large numbers of parasites were sometimes caught up to 2 weeks after emergence was complete.The application of the results for monitoring P. ornigis emergence is discussed.

Outbreak patterns of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), over western North America historically appear to be synchronous, particularly in British Columbia, Washington, Oregon, and northern Idaho. Populations of the insect increase to outbreak and collapse in a variable cycle, averaging 9 years between peaks. A review of all outbreaks suggests repeated, widespread, nucleopolyhedrosis viral epizootics are responsible for the collapse of the population and, hence, the cycle. The virus appears to survive in the soil between outbreaks and to be carried incidentally to foliage where it is occasionally consumed by larvae. Ingestion of a single particle is probably sufficient to cause infection. Populations of the moth increase until density reaches the point where larvae to larvae infection is established. The viral inoculum builds rapidly following that point and spreads widely so that distant populations at all densities become infected, and collapse in the same year. The epizootic continues for another year. Then foliage contamination disappears, and populations reach their lowest densities before starting the cycle again.

Foragers from the species Acromyrmex octospinosus (Reich) were given a choice between four different plant discs in the laboratory: Manihot esculenta (Crantz.) (cassava) varieties A and B; Ipomea batatas (L.) (sweet potato); and Dioscorea cayenensis cayenensis (Lam.) (yellow yam). Disc pick-up was not random among 8 of 11 individual foragers nor for the whole colony. Variations in preference were observed between days of the experiment and between foragers for the same day. Some foragers were not seen every day of the experiment. Variations between foragers might be an effect of age or genetic make-up. The existence of such variation may be adaptive for the colony as it ensures a better sampling of the plants available around the nest and avoids problems that would arise from the disappearance of a plant if it were the exclusive source of substrate for the colony.

Pseudaletia unipuncta (Haw.) males, experimentally deprived of hairpencils (male-specific scent organs), were less acceptable to females than were intact males. The degree to which females discriminated against males lacking hairpencils depended on the experimental protocol. When females were placed with males before scotophase onset, they tended to evade repeatedly and/or terminate genital contact with hairpencil-less males before eventually copulating, although this tendency was not statistically significant. When males were introduced after females had initiated calling, females refused hairpencil-less males significantly more often than intact ones. The incidence of copulation by hairpencil-less males was also lower than that of intact males, significantly so in one of the two populations tested. Neither copulation duration nor the dimensions of the cuticular portion of the spermatophore were correlated with the presence of hairpencils. Yet in all cases, females that mated with hairpencil-less males were more fecund and laid more fertile eggs than those mated to intact males. Hairpencil eversion could not be seen during courtship, nor did females show any obvious change in calling behaviour in response to scent from a freshly excised hairpencil. However, gas chromatographic analysis of hairpencils showed a decrease in titre of two scent components, acetic acid and benzaldehyde, just before the moment of genital contact between male and female, indicating that the pheromone was released at this time. These results suggest that P. unipuncta male pheromone facilitates female acceptance of males. The hypothesis that male pheromone carries information about the quality of a courting male is discussed in relation to recent work on arctiids, nymphalids, pierids and pyralids. An appendix of lepidopteran species possessing male scent structures is included.

Maternal influences on an insect population must be assessed within a numerically and spatially restricted enclave; it is difficult to demonstrate the impact within a large polymorphic group whose qualitative and quantitative evolution is subject to a number of conflicting influences. When a variety of selective factors is involved, the problem is to isolate, from the polymorphism, the portion that can be attributed to maternal effects.In short-lived organisms such as insects, direct maternal effects on the progeny have an advantage over slower, indirect responses to selective pressures. Direct effects allow progeny to adapt sooner to ecological trends that began or were operating during the parental generation. The peculiarities of insect embryonic development allow maternal influences to act directly on the F1 adults through their deferred effects on the imaginal discs. Species that deposit organized egg masses provide the best material for studying maternal effects.Behaviour at oviposition can lead to special types of progeny distributions that affect the offspring's survival. In parasitoids, for example, maternal behaviour can introduce a kind of "arena selection" generating superparasitism by aggregative oviposition.The next generation's ecological response that is produced by maternal effects is mediated by changes at the behavioural, metabolic and ovarian levels during the mother's reproductive activity. In this way, she provides a key part of the next generation's functional polymorphism.

Digital image processing was used to analyse chromatin distribution patterns of fat body nuclei of five populations of Dendroctonus pseudotsugae Hopkins taken from standing (UST) trees, stressed standing (SST) trees and downed (DT) trees. At the population level, chromatin distribution patterns of DT beetles were closely grouped, whereas those from the other beetles were not. Individual nuclei from the DT and UST populations could be correctly assigned to their groups with great accuracy (96% and 90%, respectively), but only 65% of the individual nuclei from the SST population could be accurately classified, the SST population was intermediate, and nuclei from many of its members resembled those from one or other of the two extreme groups. Digital image processing quickly revealed very minute differences in the distribution patterns that would be impossible to detect by conventional microscopy. This method of analysing chromatin distribution patterns, therefore, is a useful technique for identifying qualitative differences among populations long before more obvious external manifestations of the differences appear.

The reproductive compatibility between diapausing (DP) and nondiapausing (C) strains of the citrus red mite, Panonychus citri (M.), was determined by crossing experiments. Mating between the two strains was unrestricted, but copulation between C females and DP males was often broken off prematurely, whereas copulation in the reciprocal cross was of normal duration. Diapausing males showed a strong preference for guarding quiescent female deutonymphs of their strain prior to copulation, whereas C males did not. However, males of either strain showed no preference between adult females, resulting in only a partial, one-sided premating isolation between strains. No adult females were produced in the progeny from either interstrain cross, showing reproductive incompatibility is complete. Hatchability of the eggs from the cross between DP females and C males was significantly lower than that from the cross between C females and DP males, or from the intrastrain crosses, suggesting that even though some of the eggs in the former cross were fertilized, they died during embryonic stages. This possibility was supported by the observation that, for DP females mated with a C male, the second intrastrain mating was almost totally ineffective. Also, for C females mated with a DP male, a second intrastrain mating was often ineffective, but to a lesser extent than for DP females. When the two strains coexisted, effective mating was severely curtailed for both strains. The results explained the low proportion of females from overwintered DP eggs in a pear orchard in which the two strains coexisted the previous autumn.

Quercetin, a growth-inhibiting compound that is produced by many plants, was incorporated into an artificial diet and fed to Heliothis virescens (Boddie) larvae. Eggs were collected from females that had developed on this diet and from females that had developed on unadulterated artificial diet. Neonates from these eggs were placed on diets containing quercetin or other commonly occurring plant compounds (rutin, gossypol, gramine). Offspring from parents that had developed on quercetin-containing diet grew more slowly on diets containing quercetin, rutin, or gossypol, than did larvae from parents reared on unadulterated diet. Larvae from both types of parents grew at the same rate when reared on gramine-containing diet. Maternal, but not paternal, diet led to decreased growth of offspring on quercetin-containing diet. When reared on quercetin- and rutin-containing diets, offspring from parents that had developed on tobacco or soybean grew more slowly than larvae from parents reared on unadulterated diet.

Gastropods commonly show enormous variation in growth rate, even among identically reared siblings. This was investigated using a small isolated population of Deroceras laeve (Müller) — a species with low genetic variability. A high degree of variation in growth rate was evident, even among offspring from unmated mothers. This confirmed our hypothesis that this variation does not require high genetic polymorphism. Four additional hypotheses concerning the causal mechanism(s) for this variation were investigated: (1) Maternal influence through variation of egg quality was rejected as a possible cause for the variation since animals from mothers raised on either high- or low-quality diets did not differ significantly in growth or maturation rates (when egg size was controlled). (2) The possibility that animals might have their growth trajectory fixed by early nutritional experience was tested by initially rearing slugs on either high- or low-quality diets, and then reversing their food. Such "nutritional imprinting" was not supported. (3) Intraspecific interaction among individuals was not supported as a cause of variation either since stunted slugs did not show improved growth when isolated from conspecifics, and there was equal variation among individuals reared from the egg in isolation. (4) Variation in the egg size was the only characteristic investigated that significantly changed rates of juvenile growth and the timing of maturation. Larger eggs produced slower-growing slugs that matured later, and egg size seemed to account for the full range of observed variation. The ultimate function of the mechanism remains to be determined, but possibilities include adjusting the performance of offspring to resource supply, ensuring availability of mature individuals to breed during favourable microclimates, reducing competition among members of a cohort, or ensuring sexual heterogeneity for hermaphroditic breeding.