Žiga Laznik

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.

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.ZusammenfassungDie Wirksamkeit entomopathogener Nematoden bezüglich der Bekämpfung des Kartoffelkäfers (Leptinotarsa decemlineata) wurde im Feld an Kartoffeln untersucht. Ein slowenischer Stamm von Steinernema feltiae (B30) und das kommerzielle Produkt Entonem wurden mit dem Insektizid Thiametoxam in zweifacher Wiederholung verglichen. Bei der zweiten Anwendung wurde mit 250.000 Nematodenlarven m–2 die halbe Dosis der ersten ausgebracht. Populationsdynamische Beobachtungen am Schadtier ergaben, dass die entomopathogenen Nematoden zwar die Anzahl der Käferlarven signifikant verminderten, die Anzahl der Eier und Adulten aber nicht beeinflussten. Gegenüber den Käferlarven zeigte Thiametoxam in beiden Jahren generell die stärkste Wirkung, während sich die Wirkung der Varianten mit entomopathogenen Nematoden nicht voneinander unterschied. Die höchsten Kartoffelerträge wurden in beiden Versuchsjahren mit Thiametoxam erzielt (2008: 24,38 t ha–1; 2009: 21,60 t ha–1), während die geringsten Mengen in der Kontrolle geerntet wurden (2008: 7,65 t ha–1; 2009: 6,94 t ha–1). Die verschiedenen Behandlungen mit Nematoden wirkten unterschiedlich; die Erträge variierten zwischen 16,44 (S. feltiae B30 in geringer Dosierung) und 17,81 t ha–1 (Entonem in hoher Dosierung) im Jahr 2008, sowie zwischen 11,06 (S. feltiae B30 in geringer Dosierung) und 14,88 t ha–1 (Entonem in hoher Dosierung) im Jahr 2009. Beide untersuchten Nematodenstämme zeigten gegenüber den Larven des Kartoffelkäfers ausreichende Wirksamkeit, aber ihr derzeitig hoher Preis beeinträchtigt noch ihre verbreitetere Anwendung im Kartoffelbau.

Impact of entomopathogenic nematodes on adults of Phyllotreta spp. (Coleoptera: Chrysomelidae) under laboratory conditions

Abstract In 2005, preparations of four species of the entomopathogenic nematodes Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora, and H. megidis, were tested under laboratory conditions for their ability to kill adult flea beetles, Phyllotreta spp. (Coleoptera: Chrysomelidae). The nematode preparations were tested at doses of 200, 1000, and 2000 IJs per adult and at temperatures 15°C, 20°C, and 25°C. The numbers of beetles killed were recorded two, four, six, and eight days after treatment. The nematodes were more effective at 20°C and 25°C than at 15°C. At 20°C, the nematodes had killed between 44% (H. megidis at the lowest dose tested) and 77% (S. feltiae at the lowest dose tested) of the beetles eight days after treatment. At the two highest doses tested, the S. feltiae, S. carpocapsae, and H. bacteriophora preparations each killed at least 74% of the beetles at 25°C. Steinernema feltiae was the most effective nematode (LC50=483–1467 IJs/adult) and, as an alternative to chemical insecticides, appears to have the highest potential for controlling overwintered flea beetles (May) under field conditions. The nematodes S. feltiae, S. carpocapsae and H. bacteriophora would all be suitable for controlling adult flea beetles during warm summer months, when flea beetles occur in high numbers in Slovenia.

Activity of four entomopathogenic nematode species against different developmental stages of Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera, Chrysomelidae)

SummaryFour entomopathogenic nematode species (Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora, and H. megidis) were tested in a laboratory bioassay for the efficacy of these pathogens in controlling the larvae and adults of the Colorado potato beetle, Leptinotarsa decemlineata. The main aim of the study was to develop an efficient sustainable control method against the pest. With this we could develop a strategy of potato production with the intention of diminishing or even preventing the appearance of pest resistance to insecticides. The activity of these biological agents was assessed at three different temperatures (15, 20, and 25 °C) and three concentrations (200, 1000, and 2000 infective juveniles per individual). Mortality of three stages (young and old larvae and adults) was determined 2, 4, and 7 days after treatment. At 15 °C entomopathogenic nematodes showed the lowest efficacy against all insect stages. No significant differences in efficacy was determined at 20 and 25 °C as all nematodes caused prompt death of all stages. At all temperatures young larvae were most susceptible. However, when controlling overwintered adults for the purpose of preventing the mass appearance of Colorado potato beetle, we recommend an application of higher concentrations of S. feltiae suspension.

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.

First record of Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) in Slovenia

SummaryIn October 2007 we examined 80 soil samples from 16 different locations in the central part of Slovenia (the Notranjska region) and confirmed the presence of entomopathogenic nematodes only in two soil samples. This represents the first recorded instance of an entomopathogenic nematode in Slovenia. In sample B30 we confirmed the presence of Steinernema feltiae (Rhabditida: Steinernematidae) by means of a molecular technique. In Slovenia the application of entomopathogenic nematodes was hitherto possible only in laboratory experiments, while the Rules on Biological Plant Protection made the practical application of exotic organisms in the domestic environment entirely impossible. After the first record of the entomopathogenic nematode S. feltiae we expect the aformentioned agent to become an important alternative to insecticides in plant protection against pest insects.

Evaluation of different soil parameters and wild boar (Sus scrofa [L.]) grassland damage

Presented in this paper are the correlations between different soil parameters [presence of grubs, earthworms, pH, content of P2O5, K2O and organic matter (OM) in soil] and wild boar (Sus scrofa [L.]) damage to grasslands. The soil samples and damage assessments were performed at six locations in the Kočevje region, which is a densely wooded part of South East Slovenia. A significant positive correlation was discovered between the extent of damage due to wild boar rooting in grasslands and the number of grubs (r=0.73), the weight of grubs (r=0.69) and the content of P2O5 (r=0.87) in the soil. The quantity and weight of grubs in soil were significantly influenced by soil pH, the content of CaCl2 (r=0.71/0.72), P2O5 (r=0.90/0.91), and OM (r=0.74/0.77); while the quantity and weight of earthworms in soil were influenced by the content of K2O (r=0.81/-0.84). A moderate yet insignificant correlation (r=0.48/0.56) was discovered between the number and weight of earthworms in soil and the extent of grassland damage. Grubs represent a more important source of protein for wild boars than earthworms; consequently, reducing the quantity of grubs in soil could minimise the extent of damage caused by boars.

The Effects of Different Fungicides on the Viability of Entomopathogenic Nematodes Steinernema feltiae (Filipjev), S. carpocapsae Weiser, and Heterorhabditis downesi Stock, Griffin & Burnell (Nematoda: Rhabditida) under Laboratory Conditions

To increase our knowledge on the susceptibility of entomopathogenic nematodes (EPN) species to agrochemicals, the compatibility of the infective juveniles (IJ) of the entomopathogenic nematodes Steinernema feltiae , S. carpocapsae , and Heterorhabditis downesi with 15 chemical fungicides was investigated under laboratory conditions. The effect of direct IJ exposure to fungicides for 24 h was tested in a petri dish at 15, 20, and 25 oC. The results showed that the compatibility of S. feltiae with azoxystrobin was high, and similar findings were obtained for S. carpocapsae (strain C67) and all of the tested fungicides, except for tebuconazole + spiroxamine + triadimenol, maneb, dinocap, and copper (II) hydroxide + metalaxil-M. Nematode H. downesi (strain 3173) suffered the highest mortality rate when infective juveniles were mixed with tebuconazole + spiroxamine + triadimenol. The integration of the aforementioned agents into a pest management program is also discussed.

Oulema melanopus (L.) (Coleoptera: Chrysomelidae) adults are susceptible to entomopathogenic nematodes (Rhabditida) attack: results from a laboratory study

Three species of entomopathogenic nematodes from Slovenia (Steinernema feltiae B30, S. carpocapsae C101, and Heterorhabditis bacteriophora D54) and commercial product Entonem (S. feltiae as active ingredient) were tested under laboratory conditions for their ability to kill adult cereal leaf beetles (Oulema melanopus). The nematode strains were tested at 250, 500, 1000, and 2000 infective juveniles/adult and at 15, 20, and 25°C. The numbers of beetles killed were recorded 2, 4, and 6 days after treatment. S. carpocapsae strain C101 was the most effective and showed itself to be a good alternative to chemical insecticides (at 2 DAT 100% mortality was recorded), and appears to have the highest potential for controlling overwintered cereal leaf beetles under field conditions. The temperature had the greatest influence on the efficacy of the entomopathogenic nematodes; both S. feltiae strains proved to work better at the lowest temperature, however the strain H. bacteriophora D54 had its best efficacy at the highest temperature. S. feltiae and S. carpocapsae have been efficient at lower suspension concentrations, which enables their more economical usage against the cereal leaf beetle in integrated agriculture practice in the future.ZusammenfassungDrei entomopathogene Nematodenstämme aus Slowenien (Steinernema feltiae B30, S. carpocapsae C101 und Heterorhabditis bacteriophora D54) sowie das S. feltiae enthaltende kommerzielle Produkt Entonem wurden im Labor hinsichtlich ihrer mortalen Wirkung auf adulte Stadien des Rothalsigen Getreidehähnchens (Oulema melanopus) überprüft. Die Nematoden wurden in Dichten von 250, 500, 100 und 2000 Infektionslarven pro adultem Käfer bei 15, 20 und 25°C getestet. Die Anzahl getöteter Getreidehähnchen wurde 2, 4 und Tage nach der Behandlung bestimmt. S. carpocapsae C101 war mit einer 100%igen Mortalität nach 2 Tagen der wirksamste Nematodenstamm und stellt damit eine praktikable Alternative zu chemischen Insektiziden dar. Er scheint das höchste Potential der untersuchten Stämme zur Bekämpfung überwinternder Getreidehähnchen im Feld zu besitzen. Die Temperatur besaß den größten Einfluss auf die Wirksamkeit der entomopathogenen Nematoden; die Wirkung der beiden Stämme von S. feltiae war bei 15°C, die von H. bacteriophora D54 dagegen bei 25°C am höchsten. S. feltiae und S. carpocapsae wirkten auch bei geringeren und damit kostengünstigeren Suspensionsdichten, was ihre zukünftigen Anwendungs-chancen gegenüber Getreidehähnchen im integrierten Pflanzenbau erhöhen könnte.

Failure of entomopathogens to control white grubs (Coleoptera: Scarabaeidae)

White grubs are the root-feeding larvae of scarab beetles (Coleoptera: Scarabaeidae), and they are among the most destructive pests of turfgrass, pastures and horticultural plants in many parts of the world. A two-year field experiment was conducted to control different white grub species in an organically utilised meadow with dry forage conservation. The efficacy of Beauveria brongniartii, Beauveria bassiana, Bacillus thuringiensis var. kurstaki, B. thuringiensis var. tenebrionis and Heterorhabditis bacteriophora was tested against the white grubs in comparison with untreated control (only water suspension was used). The application of biological control agents was conducted twice (April and August). Our observations show that several biological control agents are capable of controlling the populations of the first and second instar larvae of different scarab grub species. The efficacy of most biological control agents, however, declines when larvae reach the third instar stage. The most promising combination tested in our study is that of entomopathogenic fungi and H. bacteriophora for controlling the first- and second-stage instar larvae. In addition, the summer application proved to be more suitable for control of the first-stage instar larvae than the spring application.

The influence of herbicides on the viability of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae)

ABSTRACT Entomopathogenic nematodes (EPNs) are agents that can be used for the biological control of pests associated with pesticides in a tank mix. Compatibility studies need to be conducted to analyse which products are compatible with EPNs. The survival of infective juveniles (IJs) of four species of EPNs (Steinernema, Heterorhabditis) was determined after exposure to eight chemical herbicides. The effect of direct IJs exposure to herbicides for 1, 4 and 24 h was tested in a Petri dish at 15, 20 and 25 °C. The study showed that Steinernema kraussei was the most tolerant among the tested EPN species, while S. carpocapsae was the most sensitive to all tested herbicides. The lowest mortality of IJs was at 15 °C (19%). Our investigation showed, overall, the herbicides negatively affected EPN survival. The results confirmed that the compatibility is a species-specific characteristic, influenced by the temperature and time of exposure. Application of two different control ingredients (insecticide and herbicide) at the same time would reduce cost and time consumption in pest/weed control.