Changes In Insect Populations Research Articles

Efficiency of Different Techniques in Collecting Insects in Environments Exposed to Palm Oil and Spent Engine Oil Effluents in Abakiliki, Ebonyi State

This study investigates the ecological consequences of palm oil and spent engine oil effluents on insect populations, employing a comparative analysis of two widely used collection techniques: pitfall traps and sweep netting. The aim was to assess the effectiveness of these methods in capturing and quantifying insect diversity and abundance in polluted environments. The research was conducted in selected sites exposed to palm oil and spent engine oil effluents, with corresponding control sites for comparison. Pitfall traps and sweep netting were deployed simultaneously to collect insects across various habitats impacted by the aforementioned effluents. The collected specimens were then identified to the lowest taxonomic level possible, and population data were analyzed to evaluate the relative impact of each effluent type on insect communities. Furthermore, statistical analyses were employed to compare the efficiency of pitfall traps and sweep netting in detecting changes in insect populations. The study revealed that pitfall traps recorded significantly higher number of insects (72.93%) than sweep nets (27.07%) in sites exposed to palm oil effluent (P<0.05). The result obtained in the site exposed to spent engine oil effluent showed that pitfall traps recorded significantly higher number of insects (80.61%) than sweep nets (19.39%) (P<0.05). This study contributes to the ecological repercussions of industrial effluents on insect populations, offering a methodological comparison that can enhance the precision of future insect-related environmental assessments.

Drivers and pressures behind insect decline in Central and Western Europe based on long-term monitoring data.

Insect declines have been discussed intensively among experts, policymakers, and the public. Albeit, decreasing trends have been reported for a long time for various regions in Europe and North America, but the controversial discussion over the role of specific drivers and pressures still remains. A reason for these uncertainties lies within the complex networks of inter-dependent biotic and abiotic factors as well as anthropogenic activities that influence habitats, communities, populations, and individual organisms. Many recent publications aim to identify both the extent of the observed declines and potential drivers. With this literature analysis, we provide an overview of the drivers and pressures and their inter-relationships, which were concluded in the scientific literature, using some of the best-studied insect groups as examples. We conducted a detailed literature evaluation of publications on Carabidae (Coleoptera) and Lepidoptera trends with data for at least 6 years in countries of Central and Western Europe, with a focus on agricultural landscapes. From the 82 publications identified as relevant, we extracted all reported trends and classified the respective factors described according to the DPSIR model. Further, we analysed the level of scientific verification (presumed vs correlated vs examined) within these papers for these cited stressors. The extracted trends for both species groups underline the reported overall declining trend. Whether negative or positive trends were reported in the papers, our semi-quantitative analysis shows that changes in insect populations are primarily anthropogenically driven by agriculture, climate change, nature conservation activities, urbanisation, and other anthropogenic activities. Most of the identified pressures were found to act on habitat level, only a fraction attributed to direct effects to the insects. While our analysis gives an overview of existing research concerning abundance and biodiversity trends of carabids and lepidopterans, it also shows gaps in scientific data in this area, in particular in monitoring the pressures along with the monitoring of abundance trends. The scientific basis for assessing biodiversity changes in the landscape is essential to help all stakeholders involved to shape, e.g. agriculture and other human activities, in a more sustainable way, balancing human needs such as food production with conservation of nature.

Extensive regional variation in the phenology of insects and their response to temperature across North America.

Climate change models often assume similar responses to temperatures across the range of a species, but local adaptation or phenotypic plasticity can lead plants and animals to respond differently to temperature in different parts of their range. To date, there have been few tests of this assumption at the scale of continents, so it is unclear if this is a large-scale problem. Here, we examined the assumption that insect taxa show similar responses to temperature at 96 sites in grassy habitats across North America. We sampled insects with Malaise traps during 2019-2021 (N = 1041 samples) and examined the biomass of insects in relation to temperature and time of season. Our samples mostly contained Diptera (33%), Lepidoptera (19%), Hymenoptera (18%), and Coleoptera (10%). We found strong regional differences in the phenology of insects and their response to temperature, even within the same taxonomic group, habitat type, and time of season. For example, the biomass of nematoceran flies increased across the season in the central part of the continent, but it only showed a small increase in the Northeast and a seasonal decline in the Southeast and West. At a smaller scale, insect biomass at different traps operating on the same days was correlated up to ~75 km apart. Large-scale geographic and phenological variation in insect biomass and abundance has not been studied well, and it is a major source of controversy in previous analyses of insect declines that have aggregated studies from different locations and time periods. Our study illustrates that large-scale predictions about changes in insect populations, and their causes, will need to incorporate regional and taxonomic differences in the response to temperature.

Declines in invertebrates and birds – could they be linked by climate change?

ABSTRACT Capsule Through case studies that link changes in invertebrate populations to changes in bird populations, we suggest how climate change may increasingly impact bird populations through variation in their invertebrate prey. Aims To assess whether invertebrate and bird population declines could be linked and suggest potentially emerging climate change impacts on wildlife. Methods We draw on field experience and case studies to illustrate how potential climate change impacts on invertebrates may cascade to affect bird populations and identify some key research gaps for urgent consideration. Results We highlight four invertebrate groups which may be sensitive to the impacts of climate change and that have the potential to impact bird populations that feed on them: soil invertebrates, foliar invertebrates, aerial insects, and aquatic invertebrates. Conclusion Our ability to understand these impacts is hampered by a lack of extensive long-term monitoring data for many invertebrates, and invertebrate data collected at scales that can be related to bird populations. We call for collaboration between entomologists and ornithologists, both non-vocational and professional, to support new empirical research and long-term monitoring initiatives to better link changes in insect populations and birds to inform future decision-making. This will be particularly important to understand likely future increasing climate change pressures on birds.

Modeling Overdispersion, Autocorrelation, and Zero-Inflated Count Data Via Generalized Additive Models and Bayesian Statistics in an Aphid Population Study.

Count variables are often positively skewed and may include many zero observations, requiring specific statistical approaches. Interpreting abiotic factor changes in insect populations of crop pests, under this condition, can be difficult. The analysis becomes even more complicated because of possible temporal or spatial correlation, irregularly spaced data, heterogeneity over time, and zero inflation. Generalized additive models (GAM) are important tools to evaluate abiotic factors. Moreover, Markov chain Monte Carlo (MCMC) techniques can be used to fit a model that contains a temporal correlation structure, based on Bayesian statistics (BGAM). We compared methods of modeling the effects of temperature, precipitation, and time for the Brevicoryne brassicae (L.) population in Uberlândia, Brasil. We applied the proposed BGAM to the data, comparing this to the GAM model with and without autocorrelation for time, using the statistical programming language R. Analysis of deviance identified significant effects of the smoothers for precipitation and time on the frequentist models. With BGAM, the problem in variance estimations for precipitation and temperature from the previous models was solved. Furthermore, trace and density plots for population-level effects for all parameters converged well. The estimated smoothing curves showed a linear effect with an increase of precipitation, where lower precipitation indicated no presence of the aphid. The average temperature did not affect the aphid incidence. Autocorrelation was solved with ARMA structures, and the excess of zero was solved with zero-inflation models. The example of B. brassicae incidence showed how well abiotic (and biotic) factors can be modeled and analyzed using BGAM.

Potential effects of elevated carbon dioxide on leaf-feeding forest insects

The elevated concentration of atmospheric CO2 may result in a decline of leaf nutritional quality (especially N) and an increase in some kinds of defensive secondary components (such as phenolics). The changes in the phytochemistry of trees, combined with the effect of elevated CO2 per se, have a potential negative influence on insect herbivores. Here, we review the effect of elevated CO2 on the performance of leaffeeding forest insects at individual-level and community-level. The elevated CO2 per se have little influence on the metabolism of insects. Over half of the tree-insect experimental systems show that the performance of individual insect become poorer under high-CO2 grown trees; but the others show that the insects have just little or no response to the treatments. The direction and magnitude of the changes in the performance of insects could be mediated by various factors. The effects of treatment are strongly species-dependent. The magnitude of changes in the phytochemistry, the sensitivity and adaptive capacity of insects to the poorer leaf quality, the differences in plant growth conditions and experimental methods, and the mediated effects of other environmental factors (such as soil nutrient availability, light, temperature, O3) were all closely related to the final performance of insects. However, the larvae’s consumption usually increased under enriched CO2 treatment, which was widely thought to be a compensatory response to poorer plant quality. The experiments on forest community-level found identically a reduction in herbivory, which was contrary to the results from small-scale experiments. The changes in insect population and the actual response of consumption by leaf-feeding forest insects under CO2 enrichment remain unclear, and more field-based experiments need to be conducted.

Effects of Dimethoate on Small Mammal Populations

The effects of an insecticide, dimethoate, on small mammal populations comprising three species, the prairie vole (Microtus ochrogaster), the house mouse (Mus musculus), and the prairie deer mouse (Peromyscus maniculatus), were investigated by means of live trapping grids in an Indiana clover field. House mice decreased in num- bers after spraying while prairie voles increased and deer mice remained at the same density level. Density of insects declined greatly after spray- ing, but no evidence was found to indicate that the insecticide caused direct mortality in any of the mammal species or had any additional effect on the habitat. It is postulated that the abrupt decline in insects was related to a drift in the mammal population composition from an omnivore to a herbivore species. The present paper reports on an intensive study of small mammal populations in a clover field before and after experimental spraying with dimethoate, an organic phosphate insecticide, at levels that might be used in routine agriculture. Changes in insect populations, in weather, in vegetation, and in the amount of residue present were followed in an attempt to evaluate the possible indirect effect of the insecticide on the clover field ecosystem. Only by considering the ecosystem as a whole can possible indirect effects of sublethal

Changes in insect populations in the field in relation to preceding weather conditions.

An attempt has been made to measure changes in a mixed insect population under natural conditions in the field, and to see to what extent they are quantitatively related to previous weather conditions. To obtain a measure of the population, insects were caught in a light-trap at Harpenden, about 25 miles north of London, every night for four years from 1933 to 1937, and again for four years from 1946 to 1950. In all about 1,440,000 insects, mostly Diptera, were captured on about 2850 nights. The measure of population level in any one month was the geometric mean catch per night, obtained by calculating the arithmetic mean of log ( n + 1), where n is the number of insects caught in one night. This figure has to be corrected for the effect of prevailing weather conditions on activity. The departure of each month, on the logarithmic scale, from the average value for all repetitions of the same month gives a measure of how the population in this particular month is differing from the level to be expected for that time of the year. These departures were then made the basis of six-factor multiple regressions, in which the population change was the dependent variable, and the rainfall and minimum temperature departures from normal in each of the three preceding months were the independent variables. It is shown that a very high proportion of the mean changes of the population in the field can be accounted for by the effect of rainfall and minimum temperature in the three previous months. An examination of the regressions in the different seasons shows that rainfall has a high positive effect in the summer and autumn but little or no effect in the winter. Minimum temperature, on the contrary, has its lowest effect in the summer, so that the relation between population and minimum temperature one month previous is negative in the summer, and with temperature two months previous is negative in the autumn. The analysis of the available data has so far only been carried out on the total insect population, against rainfall and minimum temperature. Work is continuing on other weather conditions, other time intervals, and also on special groups of insects, but it is unlikely that the method can be applied with any great accuracy in the near future to single species of insects.