Stanislav Trdan

Bio: Stanislav Trdan is an academic researcher from University of Ljubljana. The author has contributed to research in topics: Thrips & Heterorhabditis bacteriophora. The author has an hindex of 24, co-authored 169 publications receiving 1980 citations.

Control of the Colorado potato beetle (Leptinotarsa decemlineata [Say]) on potato under field conditions: a comparison of the efficacy of foliar application of two strains of Steinernema feltiae (Filipjev) and spraying with thiametoxam.

Abstract: The efficacy of entomopathogenic nematodes in controlling Leptinotarsa decemlineata on potato was tested in a field experiment. A Slovenian strain of Steinernema feltiae (B30) was used with the commercial product Entonem and the insecticide thiametoxam. The application of the nematodes and thiametoxam was repeated twice. In the second application half of the first dose (250.000 infective juveniles m–2) was used. Observing the population dynamics of the pest, it has become apparent that entomopathogenic nematodes significantly decreased the number of larvae, while no effect on their eggs and adults was confirmed. In controlling larvae in both years thiametoxam showed the best results in general, meanwhile treatments with EPNs showed no differences. In both years the highest yield was obtained when thiametoxam was used (2008: 24.38 t ha–1; 2009: 21.60 t ha–1), while the lowest yield was in the control treatment (2008: 7.65 t ha–1; 2009: 6.94 t ha–1). Different treatments of EPNs showed differences, and yields ranged from 16.44 (S. feltiae B30 low concentration) to 17.81 t ha–1 (Entonem high concentration) in 2008, and between 11.06 (S. feltiae B30 low concentration) and 14.88 t ha–1 (Entonem high concentration) in 2009. Both strains of entomopathogenic nematodes showed sufficient activity when controlling larvae, but unfortunately the high price of these biological agents at the moment makes it difficult for their broader implementation in the systems of potato production.

The influence of insecticides on the viability of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) under laboratory conditions

Abstract: RESULTS: The study showed that S. carpocapsae and S. kraussei are sensitive to all tested insecticides. Steinernema feltiae is compatible with azadirachtin, toxin of Bacillus thuringiensis var. kurstaki and imidacloprid, while H. bacteriophora is sensitive only to abamectin and lufenuron. The percentage of IJs that survived was statistically the highest after 6h at 15 ◦ C (82%) and 20 ◦ C (80%). At 25 ◦ C (76%) it was statistically the lowest. After 24h there were no statistically significant differences observed between 15 ◦ C (55%) and 20 ◦ C (55%), while at 25 ◦ C, the statistically largest percentage of IJs (59%) survived. CONCLUSION: Based on our research, we conclude that compatibility is not only a species-specific, but also a strain-specific characteristic. Steinernema feltiae and H. bacteriophora are compatible with azadirachtin and pirimicarb and might offer a cost-effective alternative to pest control against different vegetable pests. c � 2013 Society of Chemical Industry

How reliable are thermal constants for insect development when estimated from laboratory experiments

Abstract: The concept of thermal time, where a linear relationship between developmental rate (d) and environmental temperature (T) is assumed for plants and poikilothermic animals (∂ = a + b · T ; a is the intercept, b the slope, and ∂ the model estimate of d) (e.g., Bonhomme, 2000), has been widely used as an approximation of physiological time (Trudgill et al., 2005). This approach has been especially common in studies of insect development (e.g., Hon e k & Kocourek, 1990; Hone k, 1996), as temperature plays a major role in the course of their life. Although a linear approximation of the generally non-linear relationship between developmental rate and temperature (e.g., Briere & Pracros, 1998) is valid only within a limited range of temperatures, the simplicity of the thermal time approach makes it very valuable in practice. Thermal constants [lower developmental threshold (LDT) and sum of effective temperatures (SET)] can be estimated from the assumed linear relationship, usually determined from laboratory observations of insect development at different constant temperatures. The LDT, which is defined as the temperature at which the development of insect ceases (d = 0) (e.g., Jaro8 ik et al., 2004; Trudgill et al., 2005), can be estimated as LDT = − a/b. The SET, which is defined as the temperature difference above LTD when total development (d = 1) is reached in a single day (e.g., Jaro8 ik et al., 2004; Trudgill et al., 2005), can be estimated as SET = 1/b (Figure 1). Because the values d = 0 and d = 1, which determine LDT and SET, are extremes in developmental rates and therefore outside the range of values used for the development of the linear model, the estimation of thermal constants is a typical example of extrapolation. This stimulated us to investigate how uncertain the estimates of thermal constants actually are; we base our investigation on laboratory experiments, due to the extrapolation inherent to the computational procedure.

Traditional and modern methods for the identification of thrips (Thysanoptera) species

Abstract: Many thrips are pests of commercial crops due to the damage they cause by feeding on developing flowers or vegetables. Thrips may also serve as vectors for plant diseases, such as tospoviruses. Their small size and predisposition towards enclosed places makes them difficult to detect by phytosanitary inspection. In this review, several methods available for identifying thrips, including their advantages and disadvantages, are discussed. A combination of different methods gives the most reliable identification. Relatively new morphometric, molecular and biochemical methods for identifying thrips species represent valuable alternatives for situations in which correct identification with classical morphological methods is very difficult, time consuming or virtually impossible. However, traditional morphological methods should not be neglected, especially because adequate identification using morphological keys is usually an indispensable first step in the development and validation of these new modern methods. In addition, modern systems may still require specimen identification to the genus level via morphological keys, or such keys may be recommended to confirm the results of modern identification methods.

Quantifying the damage of red deer ( Cervus elaphus ) grazing on grassland production in southeastern Slovenia

Abstract: The influence of red deer (Cervus elaphus) grazing on grassland production for forage conservation at the forest border during the vegetation period was studied on three locations (Mala gora, Cvislerji, and Mackovec) in the Kocevje region (SE Slovenia). The experiment lasted from the 25th of March until the 8th of October 2002. Portable cages were used to exclude red deer from grazing the herbage. At four sampling dates in the season, herbage air dry matter (DM) yield was measured at three different observations (cage-protected plot, cage-protected plot only two to three weeks before sampling date, otherwise freely grazed (removed), and unprotected plot). The results from the experiment showed that red deer grazed on grassland through the entire season and that the regeneration capability of sward was the highest in summer, middle in spring and smallest in autumn. On unprotected plots, an average reduction of 50% of herbage DM yield was found with the most damaged sites also up to 80% reduction.

Partial least squares regression as an alternative to current regression methods used in ecology

Abstract: This paper briefly presents the aims, requirements and results of partial least squares regression analysis (PLSR), and its potential utility in ecological studies. This statistical technique is particularly well suited to analyzing a large array of related predictor variables (i.e. not truly independent), with a sample size not large enough compared to the number of independent variables, and in cases in which an attempt is made to approach complex phenomena or syndromes that must be defined as a combination of several variables obtained independently. A simulation experiment is carried out to compare this technique with multiple regression (MR) and with a combination of principal component analysis and multiple regression (PCA+MR), varying the number of predictor variables and sample sizes. PLSR models explained a similar amount of variance to those results obtained by MR and PCA+MR. However, PLSR was more reliable than other techniques when identifying relevant variables and their magnitudes of influence, especially in cases of small sample size and low tolerance. Finally, we present one example of PLSR to illustrate its application and interpretation in ecology.

Impact of wild boar (Sus scrofa) in its introduced and native range: a review

Abstract: Wild boar are now present on all continents except Antarctica and can greatly affect community structure and ecosystem function. Their destructive feeding habits, primarily rooting disturbance, can reduce plant cover, diversity, and regeneration. Furthermore, predation and habitat destruction by boar can greatly affect animal communities. Effects of wild boar on fungi and aquatic communities are scarcely studied, and soil properties and processes seem more resistant to disturbance. Wild boar also affect humans’ economy as they cause crop damage and transmit diseases to livestock and wildlife. In this review, we found that most of the published literature examines boar effects in their introduced range and little is available from the native distribution. Because most of the research describes direct effects of wild boar on plant communities and predation on some animal communities, less is known about indirect effects on ecosystem function. Finally, predictive research and information on ecosystem recovery after wild boar removal are scarce. We identified research gaps and urge the need to lower wild boar densities. Identifying commonalities among wild boar impacts on native ecosystems across its introduced range will help in the design of management strategies.

Phenology of forest caterpillars and their host trees: the importance of synchrony.

Abstract: For many leaf-feeding herbivores, synchrony in phenology with their host plant is crucial as development outside a narrow phenological time window has severe fitness consequences. In this review, we link mechanisms, adaptation, and population dynamics within a single conceptual framework, needed for a full understanding of the causes and consequences of this synchrony. The physiological mechanisms underlying herbivore and plant phenology are affected by environmental cues, such as photoperiod and temperature, although not necessarily in the same way. That these different mechanisms lead to synchrony, even if there is spatial and temporal variation in plant phenology, is a result of the strong natural selection acting on the mechanism underlying herbivore phenology. Synchrony has a major impact on the population densities of leaf-feeding Lepidoptera, and years with a high synchrony may lead to outbreaks. Global climate change leads to a disruption of the synchrony between herbivores and their host plants, which may have major impacts for population viability if natural selection is insufficient to restore synchrony.