Efficacy of entomopathogenic nematodes (Rhabditida: Heterorhabditidae and Steinernematidae) against codling moth,Cydia pomonella (Lepidoptera: Tortricidae) in temperate regions

The biocontrol potential of South African isolates of Heterorhabditis zealandica, Steinernema citrae, S. khoisanae, S. yirgalemense, and Steinernema sp., was evaluated against codling moth, Cydia pomonella. Codling moth was susceptible to all six nematode isolates at a concentration of 50 infective juveniles/insect (78–100% mortality). Low temperatures (10 h at 17°C; 14 h at 12°C) negatively affected larvicidal activity (≤3%) for all isolates. All tested isolates were most effective at higher levels of water activity (a _w=1). The average a _w50-values for all isolates tested was 0.94 (0.93–0.95), except S. khoisanae 0.97 (0.97–0.98). Regarding host-seeking ability, no positive attraction to host cues could be detected amongst isolates, except for H. zealandica. Three of the isolates, H. zealandica, S. khoisanae, and the undescribed Steinernema sp., were selected for field-testing and proven to be effective (mortality >50%). Insect containment methods used during field experimentation was shown to influence larvacidal activity, as different levels of mortality were obtained using various containment methods (wooden planks vs. pear tree logs vs. mesh cages). Pear tree logs were impractical. Predictive equations were subsequently developed, enabling future trials to be conducted using either planks or cages, enabling the prediction of the expected level of control on tree logs. All tested isolates therefore showed a certain degree of biological control potential, however, none of the experiments showed clear efficacy-differences amongst isolates. The study highlighted the importance of environmental factors to ensure the successful application of these nematodes for the control of diapausing codling moth larvae in temperate regions.     

Key elements in the successful control of diapausing codling moth,Cydia pomonella (Lepidoptera: Tortricidae) in wooden fruit bins with a South African isolate of Heterorhabditis zealandica (Rhabditida: Heterorhabditidae)

The non-insecticidal control strategies currently being implemented in South African orchards for the control of codling moth, Cydia pomonella (L.) may be hampered by wooden fruit bins being infested with diapausing codling moth larvae, acting as a potential source of re-infestation. Key factors contributing to the success or failure of an entomopathogenic nematode application were investigated using the SF 41 isolate of Heterorhabditis zealandica in laboratory bioassays with wooden minibins. Under operational conditions, an application rate of 100 IJs/mL (LD₉₀₌102 IJs/mL) effectively controlled codling moth larvae in these bins, and for further laboratory bioassays, the LD₅₀ value of 18 IJs/mL (?25 IJs/mL) was identified as the discriminating dosage. Maximum mortality was attained when bins were pre-wet for at least 1 min (>90% RH) and maintained at maximum humidity (>95% RH) post-treatment for at least 3 days (LT₉₀=73 h), to ensure nematode survival and subsequent satisfactory infection of diapausing codling moth larvae. Tarping bins achieved the desired high level of humidity required. Furthermore, adjuvants (specifically Reverseal 10?) also improved an application. The study conclusively illustrated that if all the above-mentioned conditions are met, H. zealandica has the potential to successfully disinfest wooden fruit bins of codling moth.     

Post-application of anti-desiccant agents improves efficacy of entomopathogenic nematodes in formulated host cadavers or aqueous suspension against diapausing codling moth larvae (Lepidoptera: Tortricidae)

Codling moth (CM), Cydia pomonella (L.) is the most serious pest of apple and other pome fruit worldwide. In temperate climates, diapausing cocooned larvae make up 100% of the population. Control of this stage would reduce or eliminate damage by first generation CM in late spring and early summer. Entomopathogenic nematodes (EPNs) are good candidates for control of CM in the cryptic habitats where the larvae overwinter. The two predominant limiting factors for EPNs are adequate moisture and temperatures below 15°C. Formulation that maintains moisture and enables survival of EPN infective juveniles (IJs) until they can infect overwintering larvae would significantly improve their utility for protection of apple, pear and walnut. In laboratory studies conducted in moist mulch (consisting of apple and conifer wood), Galleria mellonella (L.) larvae infected with Steinernema carpocapsae (Weiser), S. feltiae (Filipjev), or Heterorhabditis bacteriophora Poinar and coated with starch and clay, produced mean mortalities of 42, 88, and 24%, respectively in CM larvae. Mulched field plots treated with formulated S. carpocapsae- or S. feltiae-infected G. mellonella larvae, then followed by an application of wood flour foam as an anti-desiccant, resulted in 56 and 86% mortality, respectively. Comparative tests of aqueous suspensions of S. carpocapsae IJs applied to cardboard bands on apple tree trunks followed by water, fire retardant gel or foam resulted in 11, 35, and 85% respective mortalities. Identical tests with S. feltiae resulted in 20, 19, and 97% respective mortalities. Our research with cadaver formulations of EPNs in mulch and aqueous suspensions on tree trunks combined with anti-desiccant agents, demonstrated significant improvement in larvicidal activity for diapausing cocooned CM larvae.     

中国昆虫病原斯氏和异小杆线虫的研究概况(英语)

昆虫病原斯氏和导小杆线虫作为生物防治因子已受到世界各国的广泛重视,并得到了商品化的发展.自50年代,特别是7O年代末,我国从原捷克斯洛伐克、澳大利亚、美国等地引进了大批昆虫病原斯氏和异小杆线虫.同时也从土壤或自然寄主中分离出许多本国线虫种或品系,并对此类线虫进行了全面的研究,在昆虫病原线虫的种类调查和鉴定、田间大面积应用、安全性、共生细菌、大量繁殖等方面取得了可喜的进展.本文将综述这些方面的研究概况.     

Cocoon-spinning larvae of Oriental fruit moth and Indianmeal moth do not produce aggregation pheromone

1 Mature larvae of the Oriental fruit moth (OFM) Grapholita molesta (Lepidoptera: Tortricidae) and the Indianmeal moth (IMM) Plodia interpunctella (Lepidoptera: Pyralidae) leave their food source in search of suitable pupation sites in which to spin cocoons. These sites are typically well-concealed cracks and crevices within the environment. Such cocooning behaviour is also observed in larvae of the codling moth (CM) Cydia pomonella (Lepidoptera: Tortricidae), which aggregate prior to pupation in response to a pheromone blend produced by cocoon-spinning conspecific larvae.
2 In laboratory experiments, we tested whether cocoon-spinning OFM and IMM larvae produce aggregation pheromones and whether CM larvae are cross-attracted to closely-related OFM larvae.
3 Fifth-instar OFM and IMM larvae were not attracted to, or arrested by, cocoon-spinning conspecifics. Moreover, fifth-instar CM larvae were not cross-attracted to either cocoon-spinning OFM or IMM larvae.
4 Analyses of volatiles released from cocoon-spinning OFM and IMM larvae revealed that both OFM and IMM lack components that are present in the aggregation pheromone of CM larvae. This information may help explain why CM larvae are not cross-attracted to cocooning OFM or IMM larvae.     

Pathogenicity of five species of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) to the ixodid tick Dermacentor silvarum Olenev (Acari: Ixodidae)

We determined the mortality of adult tick Dermacentor silvarum Olenev after it was exposed to five entomopathogenic nematode species: Steinernema carpocapsae BJ (Sc BJ), S. glaseri NC32 (Sg NC32), S. ceratophorum D43 (Sc D43), S. feltiae Otio (Sf Otio) and Heterorhabditis bacteriophora E-6-7 (Hb E-6-7). All five species had lethal effects on adult ticks, and caused significant decreases in the amount of eggs laid by engorged female ticks (P < 0.05). Among them, Hb E-6-7 and Sc BJ were the most pathogenic to female adult ticks, with mortalities ranging from 70 to 90% (P < 0.05). Engorged females were more susceptible than unfed and partially fed females. The cumulative mortalities of engorged females exposed to Hb E-6-7 and Sc BJ for 14 days were 90%, with LT₅₀ at 6.3 and 7.0 days, respectively. Dose-dependent effect was observed in the oviposition of the ticks after they were exposed to nematodes at concentrations of 1000–5000 IJs/dish. When the concentration was higher than 5000 IJs/dish, dose dependent effects disappeared (P > 0.05). All five nematode species were lethal to unfed male ticks, and there was significant difference in mortality when compared to the control group (P < 0.05); however, the pathogenicity varied among them.     

Field evaluation of entomopathogenic nematodes for the biological control of the annual bluegrass weevil,Listronotus maculicollis (Coleoptera: Curculionidae), in golf course turfgrass

The ability of entomopathogenic nematodes to suppress larval populations of the annual bluegrass weevil, Listronotus maculicollis, was investigated under field conditions over a 3-year period (2006–2008). Combination of nematode species, application rate and timing produced strong numerical yet few statistically significant reductions. Steinernema carpocapsae Weiser, S. feltiae Filipjev, and Heterorhabditis bacteriophora Poinar applied at 2.5×10⁹ IJs/ha reduced first generation late instars between 69 and 94% in at least one field trial. Steinernema feltiae provided a high level of control (94%) to low densities (~20 larvae per 0.09 m²), but gave inadequate control for higher densities (24 and 50% suppression). No significant differences were found among treatment timings. However, applications timed to coincide with the peak of larvae entering the soil (fourth instars) generally performed better than applications made prior to (preemptive) or after the majority of the population advanced from the fourth instar. Nematode populations declined sharply between 0 and 14 days after treatment (DAT). Although nematode populations later increased (at 28 DAT), indicating an ability to recycle within hosts in the environment, they were nearly undetectable 56 DAT when the second generation host larvae were present in the soil. Applying commercially available nematode species at standard field rates cannot reliably reduce L. maculicollis immature densities on golf courses, nor will single applications suppress multiple generations. Future research will need to identify application strategies to improve biocontrol consistency.     

Entomopathogenic nematodes for control of Phyllophaga georgiana (Coleoptera: Scarabaeidae) in cranberries

A series of laboratory and greenhouse experiments evaluated the entomopathogenic nematodes Steinernema scarabaei Stock & Koppenhöfer, Heterorhabditis bacteriophora Poinar, and H. zealandica Poinar for control of second- and third-instar cranberry white grub, Phyllophaga georgiana Horn (Coleoptera: Scarabaeidae), in cranberries. Steinernema scarabaei was the most effective species with 76–100% control at a rate of 2.5×10⁹ IJ/ha in the greenhouse experiments. H. zealandica and especially H. bacteriophora were generally less effective and required rates of 5×10⁹ IJ/ha for acceptable control. Larval stage had no effect on H. zealandica and H. bacteriophora performance, whereas S. scarabaei was more effective against third instars than second instars in the laboratory but not in the greenhouse experiments. Steinernema scarabaei, should it become commercially available, could be an effective alternative to chemical insecticides for P. georgiana management.     

Five new species of Thripidae (Thysanoptera) endemic to New Zealand

Abstract

Three new species of genus Thrips are described—austellus, coprosmae, and phormiicola—which are closely related to the common New Zealand species T. obscuratus (Crawford). The systematic and zoogeographic significance of this endemic species-group is discussed. Physemothrips hadrus n.sp. is described from the South Island; the only other member of this genus is from Macquarie Island. Anaphothrips zelandicus n.sp. is described from the South Island and the Chatham and Antipodes islands, A. woodi Pitkin is recorded from New Zealand, and the relationships of these two species to the Australian fauna are discussed.     

Isolation and pathogenicity of some South African entomopathogenic fungi (Ascomycota) against eggs and larvae of Cydia pomonella (Lepidoptera: Tortricidae)

Virulent entomopathogenic fungal strains against Cydia pomonella (Lepidoptera: Tortricidae) were isolated and identified in the Western Cape Province of South Africa. Thirty-nine isolates belonging to six species were obtained using the insect bait method. Generally, Metarhizium robertsii (Ascomycota: Hypocreales) was the most frequently encountered species representing 51% of the total number of isolates collected from the soil samples. This is the first report of M. robertsii from southern Africa. Mortality data from an immersion bioassay indicated that the 39 fungal isolates were pathogenic against fifth instar larvae of C. pomonella inducing 47–85% insect mortalities. Two M. robertsii strains, MTL151 and GW461, induced 85% larval mortality and were selected for further evaluations. The exposure of freshly laid eggs to wax papers that were pre-treated with fungal spores ranging from 10³ to 10⁸ spores ml^?1 of MTL151 and GW461 resulted in a significant reduction of egg hatchabilities, from 95 to 66% and 93 to 71%, respectively as spore concentration increased. First instar larval neonates were exposed to apples that were pre-sprayed topically with varied conidia suspensions (10³?10⁸ spores ml^?1). The mean percentage of participating apples with larvae in their cores/flesh significantly reduced from 53 to 10% (MTL151) and 76 to 10% (GW461) of 10 apples, and a concurrent decrease in the incidence of apple fruit rot was observed as conidia concentration increased. Up to 90% of apples treated with 1 × 10⁸ spores ml^?1 had no larvae present in their cores and this result compared favourably with the commercial pesticide Fruitfly®, containing the active ingredient cypermethrin (20 g/l) used at a recommended dose of 0.25 ml/250 ml of water.     

苹果蠹蛾成虫产卵特性

苹果蠹蛾Cydia pomonella(L.)是全球温带地区果园主要害虫之一,是中国的重要检疫性有害生物,对我国苹果、梨等水果的安全生产造成极大危害及威胁。为详细了解苹果蠹蛾的产卵特性,从而为进行有效的监测与防控提供基础信息,作者于2006年在甘肃省山丹县梨果园中对树冠不同高度与朝向的蛀果率进行了调查,并于2010在内蒙古阿拉善左旗对梨树果枝上不同部位的产卵量进行了详细调查。主要研究结果如下:1)树冠2.5m以上的蛀果率显著高于2.5m以下的蛀果率,树冠东面的蛀果率最高,南面的蛀果率最低;2)在整个果园中,靠近北侧的果树上果实受害程度要高于南侧果树上的果实受害程度,整个果园中蛀果率由北向南逐渐降低;3)叶片上的卵数最多,占总卵数的73.1%,果实上的卵数次之,占总卵数的14.6%,枝条上的卵数最少,占总卵数的12.2%;4)在产卵的叶片上,卵主要产在叶背面,叶片背面卵量是叶正面的6.65倍。鉴于以上研究结果,在开展化学防治或颗粒体病毒防治时,应注意充分喷施果树上层树冠,且在对果实进行处理的同时,叶片和枝条也需要充分喷药。     

Pathogenicity of Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei (Rhabditida: Heterorhabditidae, Steinernematidae) Against 12 White Grub Species (Coleoptera: Scarabaeidae)

We compared the pathogenicity of the entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema glaseri, and S. scarabaei against third instars of 12 white grub species. The Japanese beetle (Popillia japonica) was highly susceptible to all nematode species. Oriental beetle [Exomala (=Anomala) orientalis], European chafer (Rhizotrogus majalis), Asiatic garden beetle (Maladera castanea), and the May/June beetles Phyllophaga crinita, Ph. congrua, and Ph. (Subgenus Phytalus) georgiana were highly susceptible to S. scarabaei but had mediocre to low susceptibility to H. bacteriophora and S. glaseri. The black turfgrass ataenius (Ataenius spretulus) was very susceptible to H. bacteriophora but had mediocre susceptibility to S. glaseri and S. scarabaei. Northern (Cyclocephala borealis) and southern masked chafer (C. lurida) had mediocre and southwestern masked chafer (C. pasadenae) and green June beetle (Cotinis nitida) had low susceptibility to all nematode species.     

Mapping of pachytene bivalents of female codling moth Cydia pomonella (Linnaeus) (Lep., Tortricidae)

Spread pachytene nuclei of codling moth Cydia pomonella (Linnaeus) (Lep., Tortricidae) females of a Syrian strain (SY) were used to investigate chromomere patterns of chromosome bivalents and determine their length. The karyotype of female codling moths consists of 28 chromosome bivalents, of which seven are clearly distinguishable using chromosome length and the number and size of the chromomeres in the pachytene stage. One autosome bivalent has two nucleolar organizing regions (NORs) that are located at the opposite ends of the chromosome and appear as distinct structural landmarks. In female codling moths, the WZ sex chromosome bivalent was easily identified in pachytene oocytes according to the heterochromatic thread of the W chromosome. This study contributed to the knowledge and identification of pachytene chromosomes of female codling moths.