Pavel Kindlmann

Two‐year oscillation cycle in abundance of soybean aphid in Indiana

1 The present study evaluated the population dynamics of the heteroecious soybean aphid Aphis glycines Matsumura (Hemiptera: Aphididae) during an 8‐year period in Indiana, shortly after its detection in North America. Sampling conducted at multiple locations revealed that A. glycines exhibited a 2‐year oscillation cycle that repeated itself four times between 2001 and 2008: years of low aphid abundance were consistently followed by years of high aphid abundance. 2 Similar patterns of abundance of A. glycines and coccinellids (Coleoptera: Coccinellidae) in soybean fields, both within and between‐years, suggest that late season predation by coccinellids plays a role in the oscillatory cycle of aphids. Insidious flower bugs Orius insidiosus (Say) (Hemiptera: Anthocoridae) were numerically more abundant than coccinellids, although the lack of synchrony between aphids and predatory bugs suggests that O. insidiosus has a limited influence on between‐year variations in aphid density. 3 The inverse relationship between aphid densities before and after the start of the autumn migratory period changes direction in alternate years. High aphid density on soybean in the summer is associated with a reduced number of alate migrants produced in the autumn. Conversely, years with low density aphids on soybean in the summer are characterized by high numbers of alates that migrate to the primary host in the autumn. 4 From a pest management perspective, the 2‐year oscillation cycle of A. glycines is a desirable attribute with respect to population dynamics because it implies that aphids cause significant economic damage only in alternate years (as opposed to every year). Cultural practices enhancing the conservation biological control of Coccinellidae may help to preserve the periodicity of aphid infestation and restrict the pest status of A. glycines.

Can the barrier effect of highways cause genetic subdivision in small mammals

Roads and highways contribute enormously to habitat fragmentation, because they can inhibit or even block animal movement across them, which may result in the ultimate division of the populations adjacent to the roads into smaller isolated subpopulations. The isolation reduces gene flow and increases risk of extinction due to a decrease in the genetic diversity of the isolated population. The aim of the present study is to determine whether highways can cause genetic subdivision of the bank vole Myodes glareolus (Schreber, 1780) and yellow-necked mouse Apodemus flavicollis (Melchior, 1834). The study was carried out at three sites in the Highway D1 (Prague-Brno) in the Czech Republic, where a previous study demonstrated a barrier effect of the highway avoiding the interchange of individuals of both species. The genetic structure was determined from the analysis of six DNA microsatellites loci in M. glareolus and five in A. flavicollis. We found only weak genetic differences between populations living at opposite sides of the highway in either of the species and a low degree of subdivision, but significant positive correlation between genetic and geographical distance, which suggests isolation by distance in both species.

Does Body Size Optimization Result in Skewed Body Size Distribution on a Logarithmic Scale

Kozlowski and Weiner (1997) challenged the idea that interspecific allometries reflect unitary functional relationships between parameters that are shared by all of the species within a set. They suggested that these allometries might also be produced as a by-product of underlying intraspecific processes. In the course of their argument, Kozlowski and Weiner developed a model for the optimal adult body size and found a striking result, which is that optimizing body size produces a distribution of sizes within a taxon that is skewed to the right, even when examined on a logarithmic scale. In this note, we point out that while this result was based on a limited range of parameters, it is actually a very general outcome of optimizing body size in their model. Kozlowski and Weiner’s (1997) new model is based on the assumptions that assimilation and respiration are allometric functions of body size, aw and hw , respectively; that the production rate, P(w), is the difference between assimilation and respiration, that is, ; b b P(w) 5 aw 2 hw that the mortality rate, m(w), can be described by ; and that the optimal adult body size can l m(wx) 5 2gw be found as a solution of

Modelling Population Dynamics of Aphids and Their Natural Enemies

Aphids are serious pests of many agricultural crops. Therefore, a good understanding of their population dynamics is vitally important for crop protection. There have been several attempts made to forecast the abundance of aphids and develop expert systems to help farmers optimize prophylactic measures and minimize their costs. The advisory systems, however, did not receive general acceptance and disappointingly few forecasting systems are in use. The failure of models to predict aphid population dynamics for practical purposes is due to the extremely wild oscillations in aphid numbers caused by intrinsic (size, fecundity, mortality, migration rate) and external factors (weather, especially temperature). As a consequence, the predictions are unlikely to be robust enough for reliable forecasting, mainly because they depend on the course of weather during the season, which cannot be predicted. Here we present a critical review of existing models of aphid population dynamics, examine biological assumptions that are incorporated in the models and present one of the latest models of aphid metapopulation dynamics. We conclude that natural enemies are unlikely to affect aphid population dynamics late in the season, but may have an effect very early in the season, when aphid colonies are still small and predators might be able to reduce the numbers of these colonies. Empirical verification of this is still very weak, however, and further experiments on this aspect of predator prey dynamics should be undertaken.

Effect of temperature and nutrients on the growth and development of seedlings of an invasive plant

Little is known about how alien plants that arrive in central Europe from climatically warmer regions cope with the temperature conditions at the early stage of population development. Using Ambrosia artemisiifolia (common ragweed), an invasive annual plant as a model, we found that the rate of seedling development decreased with decrease in temperature and nutrient supply. Our results thus highlight temperature as the main determinant of common ragweeds distribution and identify nutrient availability as a factor that results in the realized niche being smaller than the fundamental niche.

Habitat heterogeneity as the key determinant of the abundance and habitat preference of prey species of tiger in the Chitwan National Park, Nepal

Studies on the relationship between habitat heterogeneity and animal abundance are essential for understanding what determines biodiversity. Transect-based direct observations of eight principal prey species of tiger in the Chitwan National Park (CNP) were used to determine their abundances and habitat preferences. Chital was the most abundant prey species of tiger (Panthera tigris). Each of the prey species had significantly different habitat preferences except sambar deer and chital. Habitat preference was measured using Manly’s preference index, which revealed that short grassland, mixed forest, and riverine forest were the most preferred habitats of the prey species. The results indicate that large species of deer tend to be found in more diverse habitats than small species, except muntjac. The abundance of the principal prey species of tiger was positively correlated with habitat heterogeneity. The habitat, which contributes significantly to the heterogeneity of the landscape, is grassland in large patches of forest. The ongoing increase of forest cover in the CNP has led to a reduction in the area of grassland, which may negatively affect the abundance of the prey species of tiger. Hence, it is suggested that the restoration of landscape heterogeneity is the best way to manage the habitats in the CNP.

Effect of synthetic and plant-extracted aphid pheromones on the behaviour of Aphidius colemani

Parasitoid females use several chemical cues to locate hosts. A better knowledge of how they respond to a complex of these cues in a small range may help us to understand how to manipulate the parasitoids in the field. Here, the response of the aphid parasitoid Aphidius colemani to a mixture of odours of synthetic and plant‐extracted nepetalactone (a component of aphid sex pheromone) and to (E)‐β‐farnesene (aphid alarm pheromone) was investigated. The behavioural responses of A. colemani to three semiochemical groups with different concentrations were studied in a square arena. Parasitoid females were significantly attracted by the semiochemicals, when their concentrations were high, in which case the females spent more time in squares with semiochemicals. The majority of females preferred plant‐extracted nepetalactone, when it was in high concentration, but they consistently did not respond to (E)‐β‐farnesene.

Effect of human disturbance on the prey of tiger in the Chitwan National Park – Implications for park management

Chitwan National Park is surrounded by large settlements of people who exploit the areas where tigers and their prey occur. In this study, we measured the associations between the abundance of the prey of tiger with habitat, topographic, predator and human disturbance variables, using canonical correspondence analysis. We show that the abundance of hog deer is closely associated with areas of tall grassland and floodplains, while that of other ungulate species is associated with that of forests and short grasslands. Primates were mainly abundant in riverine and mixed forests. Abundances of most species, except hog deer and wild pig, were more closely associated with areas of forests than with open areas, because the latter were mainly occupied by humans and livestock. The presence of the species studied was closely associated with habitat and disturbance variables. Proximity of water holes was more closely associated with the presence of ungulates than primates. There were close associations between human disturbance and abundances of primates and muntjac, possibly because these species are more tolerant and adapted to human disturbance. However, the major prey species of tiger were negatively associated with human disturbance. As a consequence, human disturbance has resulted in a decline in the abundance of tigers and the lack of prey could result in their extinction in the Chitwan NP. Therefore, in terms of the conservation and management of the park, minimizing human disturbance of wildlife habitats and restoration of a buffer zone forest should be the prime objectives.

Relationship between the abundance of aphids and their natural enemies in cereal fields and landscape composition

We investigated, over the course of two years, the association between the abundance of aphids and their natural carabid enemies and landscape, which may help in the development of effective strategies for reducing the incidence of aphid outbreaks in agricultural crops. This was undertaken in 12 wheat and 12 maize fields each year in an agricultural landscape in western France. Our study area was characterized by hedgerows surrounding arable fields and permanent grassland. Some areas have not changed much for several decades, while field enlargement and removal of hedges occurred in some areas following agricultural intensification. This paper aims to determine if the abundance of aphids in crops (either directly, or indirectly via their natural enemies) is associated with the landscape around fields and if so, is it dependent on the landscape scale considered. We observed that the abundance of aphids in fields was associated with landscape composition at a large scale (500 m and 800 m). There was a positive correlation between the abundance of aphids and the proportion of the area under woodland and grassland at these scales. There was a negative correlation between the abundance of carabids and the proportion of grassland and hedgerow around crop fields. The species richness of carabids was positively correlated with the proportion of hedgerows. We found that the abundance of aphids in wheat fields was negatively and in maize fields positively associated with the proportion under grass strips. At a large scale carabid abundance in both types of culture was positively correlated with the proportion under grass strips.

Prevalence of honeybee viruses in the Czech Republic and coinfections with other honeybee disease

Six bee viruses, which occur in Apis mellifera, were monitored in the Czech Republic between 2006 and 2009. Samples of larvae and pupae collected from hives where American foulbrood was detected were screened for bee viruses and in the 125 samples of larvae, there was no confirmed case of a larva infected with both American foulbrood and a bee virus. Of 145 samples infected with the protozoan Nosema apis, there were 23 cases of coinfections with the BQCV virus, 18 with the DWV virus and 11 with the ABPV virus. All coinfections with three or four viruses were also statistically significant apart from the one between ABPV with CBPV and DWV. The PCA ordination diagram indicates that BQCV occurs mainly with Nosema apis and DWV mainly with ABPV.