Browsing by Author "De Waal, Jeanne Y."

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    Effect of humidity and a superabsorbent polymer formulation on the efficacy of Heterorhabditis zealandica (Rhabditida: Heterorhabditidae) to control codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae)
    (Taylor & Francis, 2013-12) De Waal, Jeanne Y.; Malan, Antoinette P.; Addison, Matthew F.
    Adequate moisture levels are required for nematode survival and subsequent efficacy as entomopathogens. Formulation of nematodes aimed at aboveground applications may assist in maintaining such moisture levels. In this study, we report the effects of a superabsorbent polymer formulation, Zeba® on the performance of an entomopathogenic nematode, Heterorhabditis zealandica Poinar, for controlling diapausing codling moth, Cydia pomonella (L.) larvae in cryptic habitats on trees. Water activity (aw-value) on bark was considered to be an indication of moisture levels on trees in cryptic habitats where codling moth larvae are known to occur, thereby influencing nematode efficacy. H. zealandica was only able to infect codling moth larvae at aw≥0.92, with aw50=0.94 and aw90=0.96.
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    Efficacy of entomopathogenic nematodes (Rhabditida : Heterorhabditidae and Steinernematidae) against codling moth, Cydia pomonella (Lepidoptera: Tortricidae) in temperate regions
    (Taylor & Francis, 2011-09) De Waal, Jeanne Y.; Malan, Antoinette P.; Addison, Matthew F.
    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 17ºC; 14 h at 12ºC) negatively affected larvicidal activity (≤3%) for all isolates. All tested isolates were most effective at higher levels of water activity (aw=1). The average aw50-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.
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    Heterorhabditis safricana n. sp. (Rhabditida: Heterorhabditidae) : a new entomopathogenic nematode from South Africa
    (Brill Academic Publishers, 2008-11) Malan, Antoinette P.; Nguyen, Khuong B.; De Waal, Jeanne Y.; Tiedt, Louwrence
    During a survey for entomopathogenic nematodes in the Western Cape Province of South Africa, a new species in the genus Heterorhabditis was collected from a peach orchard. The nematode was trapped by the insect-baiting technique using last instar larvae of Galleria mellonella. The infective juvenile of the new species differs from the morphologically closest species, H. marelatus, in shorter body length 600 (550-676) vs 685 (588-700) μm and the shorter tail of 93 (86-108) vs 107 (99-117) μm. It differs from all other species in the vulva pattern of hermaphroditic female. The genital papillae of the male H. safricana n. sp. are typical for species in the megidis-group (three papillae in terminal group). The average length of the gubernaculum is longer than that of all other species (24 vs 19-23 μm) and the gubernaculum length as a percentage of spicule length (53.9) is less than that of H. mexicana (56), similar to that of H. floridensis (53.8), but larger than that of all others (51 or less). For molecular characterisation, the species closest to H. safricana n. sp. is H. marelatus. The length of the ITS rDNA sequence of the new species is characterised by 995 base pairs, identical to that of H. marelatus, but differs from this species by 25 aligned positions, seven of which are unambiguous autapomorphies. Phylogenetic trees show further evidence of a separate species status for H. safricana n. sp.
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    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)
    (Taylor & Francis, 2010-01) De Waal, Jeanne Y.; Malan, Antoinette P.; Levings, John; Addison, Matthew F.
    The non-insecticidal control strategies currently being implemented in South African orchards for the control of codling moth, Cydia pomonella (L.) may be hampered bywooden 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 (LD9=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.