Native natural enemies of plant pests in Slovenia with an emphasis on species suitable for mass rearing.

In Slovenia, only the native natural enemies of plant pests that are on the EPPO Positive List of biological control agents can be used in agricultural production to control plant pests. The List of native species of organisms for biological control, which is an important part of the Regulations on biological control, currently includes a total of 35 species of beneficial insects and mites and entomopathogenic nematodes. Compared to the number of species on the first list that was established in 2006, the number of beneficial species that Slovenian growers of food and ornamental plants can currently use in everyday practice has doubled. This is the result of intensive professional and research work in the investigation of the occurrence and distribution of natural enemy species in Slovenia, which has been systematically supported by the state for many years. Natural enemy species, which are an integral part of the EPPO Positive List of biological control agents, can be included on the list of native biological control species via a special procedure. However, many natural enemy species that are not yet included on the EPPO Positive List have been identified in the period 2007-2022. In this paper, we list 75 such species and we present 5 candidates (Cotesia glomerata [L.], Diadegma semiclausum [Hellen], Anisopteromalus calandrae [Howard], Neochrysocharis formosa [Westwood] and Kampimodromus aberrans [Oudemans]) that, in our opinion, have high potential as biological controls and will be suitable in the future for mass rearing and use in augmentative biological control.

The Role of Ascorbate-Glutathione System and Volatiles Emitted by Insect-Damaged Lettuce Roots as Navigation Signals for Insect and Slug Parasitic Nematodes.

The effect of wireworm-damaged lettuce roots on the antioxidative defense system (ascorbate-glutathione cycle, photosynthetic pigments) and movement of insect/slug parasitic nematodes towards determined root exudates was studied in a glasshouse experiment. Lettuce seedlings were grown in a substrate soil in the absence/presence of wireworms (Elateridae). The ascorbate-glutathione system and photosynthetic pigments were analyzed by HPLC, while volatile organic compounds (VOC) emitted by lettuce roots were investigated by GC-MS. Herbivore-induced root compounds, namely 2,4-nonadienal, glutathione, and ascorbic acid, were selected for a chemotaxis assay with nematodes Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora, Phasmarhabditis papillosa, and Oscheius myriophilus. Root pests had a negative effect on the content of photosynthetic pigments in the leaves of infested plants, indicating that they reacted to the presence of reactive oxygen species (ROS). Using lettuce as a model plant, we recognized the ascorbate-glutathione system as a redox hub in defense response against wireworms and analyzed its role in root-exudate-mediated chemotaxis of nematodes. Infected plants also demonstrated increased levels of volatile 2,4-nonadienal. Entomopathogenic nematodes (EPNs, S. feltiae, S. carpocapsae, and H. bacteriophora) proved to be more mobile than parasitic nematodes O. myriophilus and P. papillosa towards chemotaxis compounds. Among them, 2,4-nonadienal repelled all tested nematodes. Most exudates that are involved in belowground tritrophic interactions remain unknown, but an increasing effort is being made in this field of research. Understanding more of these complex interactions would not only allow a better understanding of the rhizosphere but could also offer ecologically sound alternatives in the pest management of agricultural systems.

Biological Parameters, Phenology and Temperature Requirements of Halyomorpha halys (Hemiptera: Pentatomidae) in the Sub-Mediterranean Climate of Western Slovenia.

In the last decade, the invasive brown marmorated stink bug Halyomorpha halys, native to East Asia, has become one of the most serious pests for agricultural crops worldwide. First detected in Europe (in Switzerland), the insect is now widely found across the European continent and many Eurasian countries. Since its first appearance in Slovenia in 2017 it has caused considerable damage to fruit and vegetable production. Understanding the biology and behavior in the local environmental conditions is of key importance for an effective pest management. Knowledge of the voltinism of the species is crucial to anticipate critical phases of pest development and for adapting control measures that target the vulnerable life stages of the pest. A 3-year study (2019-2021) of H. halys biological parameters was performed outdoors in Nova Gorica (western Slovenia), confirming that in the sub-Mediterranean climate this pest has two overlapping generations per year. The net reproductive rates observed in the studied period indicate growing populations. The highest population growth was recorded in 2019, when the net reproductive rate of increase (R0) reached 14.84 for the summer generation and 5.64 for the overwintering generation. These findings match the current situation in Slovenia, where increasing populations of H. halys and severe crop damage have been observed since 2019.

Lymantria dispar (L.) (Lepidoptera: Erebidae): Current Status of Biology, Ecology, and Management in Europe with Notes from North America.

The European Spongy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), is an abundant species found in oak woods in Central and Southern Europe, the Near East, and North Africa and is an important economic pest. It is a voracious eater and can completely defoliate entire trees; repeated severe defoliation can add to other stresses, such as weather extremes or human activities. Lymantria dispar is most destructive in its larval stage (caterpillars), stripping away foliage from a broad variety of trees (>500 species). Caterpillar infestation is an underestimated problem; medical literature reports that established populations of caterpillars may cause health problems to people and animals. Inflammatory reactions may occur in most individuals after exposure to setae, independent of previous exposure. Currently, chemical and mechanical methods, natural predators, and silvicultural practices are included for the control of this species. Various insecticides have been used for its control, often through aerial sprayings, which negatively affect biodiversity, frequently fail, and are inappropriate for urban/recreational areas. However, bioinsecticides based on various microorganisms (e.g., entomopathogenic viruses, bacteria, and fungi) as well as technologies such as mating disruption using sex pheromone traps have replaced insecticides for the management of L. dispar.

Native and Non-Native Egg Parasitoids Associated with Brown Marmorated Stink Bug (Halyomorpha halys [Stål, 1855]; Hemiptera: Pentatomidae) in Western Slovenia.

Halyomorpha halys (Hemiptera: Pentatomidae), native to East Asia, has become a globally invasive pest, as a serious threat to agricultural production and a notorious nuisance pest in urban areas. Considerable efforts have been made so far to develop effective pest control measures to prevent crop damage. Biological control of this invasive stink bug by egg parasitoids has proven to be the most environmentally sustainable long-term solution. Knowledge of the native egg parasitoid fauna is of key importance when implementing a biological control program. Therefore, the main objective of our study was to detect egg parasitoid species associated with H. halys in the Goriska region (Western Slovenia) and to evaluate their impact on the pest population under field conditions. In the years 2019 and 2020, around 4600 H. halys eggs were collected in the wild and more than 3400 sentinel eggs were exposed to detect parasitoids in the field. Five egg-parasitoid species emerged from H. halys eggs: Anastatus bifasciatus (Hymenoptera: Eupelmidae), Telenomus sp., Trissolcus basalis, Trissolcus mitsukurii (Hymenoptera: Scelionidae) and Ooencyrtus telenomicida (Hymenoptera: Encyrtidae), all of them are new records for Slovenia. The native species, An. bifasciatus, dominated in urban and suburban areas, while non-native Tr. mitsukurii prevailed in agricultural areas. Overall parasitism rates of naturally laid eggs by the parasitoid species complex in 2019 and 2020 was 3.0 and 14.4%, respectively. Rapid recruitment of native parasitoids, early detection of an effective alien parasitoid species and increasing overall parasitism rates are very encouraging results, which need to be followed and verified in future research.

Evaluation of the Field Efficacy of Heterorhabditis Bacteriophora Poinar (Rhabditida: Heterorhabditidae) and Synthetic Insecticides for the Control of Western Corn Rootworm Larvae.

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera, Chrysomelidae), is an important insect pest of maize in North America and Central and Eastern Europe. In Central Europe, the larvae emerge in May and its three instars feed intensively on maize roots in June, causing plant lodging that leads to a loss of economic yield. A three-year field experiment (2016-2018) was conducted to compare the effectiveness i) of soil-applied granular insecticide based on the active ingredient tefluthrin, ii) of maize seeds dressed with thiacloprid, and iii) entomopathogenic nematodes Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae, product Dianem) against WCR larvae. An additional treatment with alcohol ethoxylate (i.e., soil conditioner) mixed with entomopathogenic nematodes was performed in 2017 and 2018 to check for any increase of entomopathogenic nematodes' effectiveness. Field tests were carried out in two fields infested naturally with a WCR pest population, one in Bucecovci (Eastern Slovenia) and the other in Smartno pri Cerkljah (northern Slovenia), exhibiting dissimilar pedo-climatic conditions and soil pest densities. The treatments were performed in five replicates per experiment in each year. The efficacy of the treatments was very similar at both locations, despite the approximately five-fold lower WCR soil pest densities in northern than in eastern Slovenia, as well as being constant over time. The largest number of WCR beetles was observed in the negative control, followed by that of beetles subjected to thiacloprid treatment (insignificant decrease taking into account the entire three-year dataset). Treatments with tefluthrin (44.1 ± 11.7%), H. bacteriophora (46.2 ± 7.4%), and H. bacteriophora + alcohol ethoxylate (49.2 ± 1.8%) significantly decreased the numbers of emerging beetles. Treatments of thiacloprid, H. bacteriophora, and H. bacteriophora + alcohol ethoxylate additionally led to significantly increased maize plant weights. Furthermore, entomopathogenic nematodes were able to persist in maize fields for almost five months at both experimental locations in silty and sandy loam soils. It was concluded that the control of WCR larvae in maize using the entomopathogenic nematode H. bacteriophora is as effective as a tefluthrin treatment, and could thus offer a sustainable Diabrotica v. virgifera biological control management option in Europe.

Attraction Behaviors of Entomopathogenic Nematodes (Steinernematidae and Heterorhabditidae) to Synthetic Volatiles Emitted by Insect Damaged Potato Tubers.

Entomopathogenic nematodes (EPNs) play a role in indirect defense of plants under attack by root herbivores. Several investigations have shown that EPNs are attracted or repelled by various volatile compounds (VOCs) released from insect damaged plant roots. We hypothesized that the directional responses of EPNs to the VOCs would be affected by foraging strategy and would vary among species, VOC type, and VOC concentrations. We tested the chemotactic responses of four commercial EPN species (Steinernema feltiae, S. carpocapsae, S. kraussei, and Heterorhabditis bacteriophora) to seven compounds released from insect (Melolontha hippocastani)-damaged (decanal, nonanal, octanal, undecane, 6-methyl-5-hepten-2-one, and 1,2,4-trimethylbenzene) and undamaged (2-ethyl-1-hexanol) potato tubers. Our results suggest that EPNs are able to distinguish herbivore-induced VOCs from those that are typical for healthy potato tubers. In our investigation, nonanal, octanal, and decanal had a greater influence on the movement of EPNs than other tested synthetic volatiles. Decanal was an attractant for H. bacteriophora and S. kraussei at both tested concentrations (as a pure compound and at a concentration of 0.03 ppm). The results suggest that the susceptibility to perception of chemical stimuli from the environment is a species-specific characteristic that prevails over the influence of the foraging strategy.

Combining electrostatic powder with an insecticide: effect on stored-product beetles and on the commodity.

BACKROUND: The opportunity to reduce the amount of pirimiphos-methyl applied to grain by formulating it in an electrostatic powder was investigated. The insecticidal efficacy of pirimiphos-methyl in EC formulation or formulated using electrostatic powder (EP) as an inert carrier was investigated against Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.) and Tribolium confusum Jacquelin du Val. Furthermore, the adhesive properties of EP to rice, corn and wheat, together with the effect on bulk density and bread- and pasta-making properties, were investigated. RESULTS: The results showed that pirimiphos-methyl formulated with EP provided better efficacy against adults when compared with EC formulation for O. surinamensis and T. confusum, but there was no difference for R. dominica. Progeny production was consistently lower in grain treated with the EP formulation than in grain treated with the EC. Tests showed that EP adhered to the kernels for longer on hard wheat than on maize or rice. In most commodities, EP did not alter the bulk density. Finally, the addition of EP did not affect flour- and bread-making properties, nor the pasta-making properties. CONCLUSIONS: The results of the present study suggest that an EP could be used to reduce the amount of pirimiphos-methyl applied to grain for effective pest control, with no detrimental effects on grain quality. © 2016 Society of Chemical Industry.

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

BACKGROUND: In order to increase our knowledge on the susceptibility of entomopathogenic nematode (EPN) species to agrochemicals, the compatibility of the infective juveniles (IJs) of the EPN (Steinernema and Heterorhabditis) with eight chemical and bio-insecticides was investigated under laboratory conditions. The effect of direct IJ exposure to insecticides for 6 and 24 h was tested in a Petri dish at 15, 20 and 25 °C. 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 6 h at 15 °C (82%) and 20 °C (80%). At 25 °C (76%) it was statistically the lowest. After 24 h 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. © 2013 Society of Chemical Industry.

Nontarget effect of entomopathogenic nematodes on larvae of twospotted lady beetle (Coleoptera: Coccinellidae) and green lacewing (Neuroptera: Chrysopidae) under laboratory conditions.

The nontarget effect of Steinernema feltiae, Steinernema carpocapsae, Heterorhabditis bacteriophora, and three mixed suspensions of two species of entomopathogenic nematodes on the larvae of the twospotted lady beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae), and on the larvae of the lacewing Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae), were studied in a laboratory bioassay. The assay was performed at three temperature (15, 20, and 25 degrees C) and at three different concentrations of the suspension (500, 2,500, and 5,000 infective juveniles [IJs]/ml). The larvae of A. bipunctata were more susceptible to nematode attack than the larvae of C. carnea. Four days after treatment, significantly the lowest mortality of A. bipunctata and C. carnea larvae was recorded at 15 degrees C, whereas no significant differences were noted between 20 and 25 degrees C. At 500 IJs/ml, the nematodes had significantly the lowest nontarget effect on the larvae of both aphid predators, whereas no significant differences in this regard were established between 2,500 and 5,000 IJs/ml. We conclude that the entomopathogenic nematodes under investigation exhibit a pronounced nontarget effect on the larvae of both predators mentioned.

Seasonal dynamics of three insect pests in the cabbage field in central Slovenia.

From the beginning of April until the beginning of November 2006, a seasonal dynamics of three harmful insect species--Swede midge (Contarinia nasturtii [Kieffer], Diptera, Cecidomyiidae), flea beetles (Phyllotreta spp., Coleoptera, Chrysomelidae), and diamondback moth (Plutella xylostella [L.], Lepidoptera, Plutellidae)--was investigated at the Laboratory Field of the Biotechnical Faculty in Ljubljana (Slovenia). The males were monitored with pheromone traps; the males of Swede midge were trapped with the traps of Swiss producer (Agroscope FAW, Wädenswill), while the adult flea beetles (trap type KLP+) and diamondback moths (trap type RAG) were trapped with the Hungarian traps (Plant Protection Institute, Hungarian Academy of Sciences). The pheromone capsules were changed in 4-week intervals, while the males were counted on about every 7th day. The first massive occurrence of diamondback moth (1.6 males/trap/day) was established in the second 10 days period of April, and the pest remained active until the 2nd 10 days period of September. The adults were the most numerous in the period between the end of May until the middle of June, but even then their number did not exceed three males caught per day. In the first 10 days period of May, the first adult flea beetles were recorded in the pheromone traps, while their notable number (0.8 males/trap/day) was stated in the third 10 days period of May. Absolutely the highest number of the beetles was recorded in the second (19 adults/trap/day) and in the third (25 adults/trap/day) 10 days of July, and the pest occurred until the beginning of October. The first massive occurrence of Swede midge (0.4 males/trap/day) was established in the second 10 days period of May, while the highest number of males (8/trap/day) were caught in the second 10 days period of July. In the third 10 days period of October, the last adults were found in the traps. Based on the results of monitoring of three cabbage insect pests we ascertained that in the central Slovenia the Swede midge has 3-4 generations, the flea beetles has 1-2 generations, and the diamondback moth has 4 generations.

Susceptibility of four different vegetable brassicas to cabbage whitefly (Aleyrodes proletella L., Aleyrodidae) attack.

Cabbage whitefly (Aleyrodes proletella L.) is one of the most noticeable pests on cultivated Brassica species in the continental part of Slovenia. In year 2000 a susceptibility of four different vegetables of Brassica genus to cabbage whitefly attack had been examined. The highest number of imagoes and larvae was found on kale, significantly less on savoy cabbage and Brussels sprouts and only individual specimen on cabbage. Due to relatively small parcels, the most appropriate way of determining potential economic importance was to count imogoes and larvae on plants (visual inspection). On the other hand, monitoring with sticky yellow boards gave less satisfactory results.