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. Laboratory experiments in which nematode concentration was investigated indicated a positive linear relationship between the concentration of nematodes applied and the level of control obtained, with the highest level of mortality recorded at 80 IJs/larva, requiring at least 4 h of conditions conducive to nematode activity to ensure infectivity and subsequent efficacy. Further experimentation showed that the use of the Zeba formulation, together with the nematodes, improved the level of control obtained at 60% and 80% RH in the laboratory and that it also enhanced the survival and infection-ability of the nematodes in the field. The study conclusively illustrates that the tested formulation assisted in maintaining adequate moisture levels on the application substratum, as required for nematode survival and subsequent efficacy.
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 (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.
The potential of using an entomopathogenic nematode, Heterorhabditis zealandica Poinar, together with different test mulches (pine chips, wheat straw, pine wood shavings, blackwood and apple wood ...chips) to control diapausing codling moth, Cydia pomonella (L.) larvae was evaluated. Mesh cages were identified as a suitable larval-containment method. High levels of codling moth mortality were obtained when using pine wood shavings as mulch (88%) compared to pine chips, wheat straw, blackwood and apple wood chips (41–88%). Humidity (>95% RH) has to be maintained for at least 3 days to ensure nematode survival. It was also proven that nematodes had the ability to move out of infected soil into moist mulch, to infect the codling moth larvae residing at heights of up to 10 cm. Field experiments showed the importance of climatic conditions on nematode performance. Low temperatures (<15°C) recorded during the first trial resulted in low levels of control (48%), as opposed to the 67% mortality recorded during the second trial (temperatures ranged between 20 and 25°C). Low levels of persistence (<10%) were recorded in the mulches post-application. The study conclusively illustrated some of the baseline requirements fundamental to the success of entomopathogenic nematodes together with mulches for the control of codling moth.
Although agriculture is crucial to economic growth in South Africa, the industry faces several challenges, including the effects of pests and diseases that contribute to crop loss. Such losses ...severely affect the maintenance of food security. Therefore, a major challenge is finding effective, environmental-friendly control measures for insect pests. Potatoes are among the four most widely consumed vegetable crops worldwide. However, a potato crop can be infested by various pests, like the devastating leaf miner, Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae). The leaf miner species has, since the early 2000s, become an important pest of various vegetable crops in South Africa. The species is highly invasive, causing up to 70 % damage of solanaceous crops. The damage that is caused by the leaf miner is direct, resulting from the female flies feeding on the leaf mesophyll during oviposition, and the larvae mining the leaves. Indirect damage is induced through pathogens entering through perforations that act as vectors of plant diseases. Biocontrol agents, e.g. entomopathogenic nematodes (EPNs), entomopathogenic fungi (EPF), and parasitoids have shown potential against L. huidobrensis. This review investigates the biology and morphological identification of L. huidobrensis, its host range in the Western Cape, and the potential of associated biocontrol agents, like EPNs, EPF and parasitoids, as future control options.
Entomopathogenic fungi (EPF) are effective and environment-friendly insect biological control agents. Ultraviolet (UV) light is known to have an effect on the survival of fungal conidia, and natural ...sunlight is potentially one of the most damaging factors undermining EPF persistence and pathogenicity. This study aimed to test the infection potential of an isolate of Beauveria bassiana and five Metarhizium species after exposure to different light treatments, on soil and leaf surfaces under laboratory and field conditions, using Thaumatotibia leucotreta (Lepidoptera: Tortricidae) as the test host. Conidia were exposed either to growth light alone, which emits the same visible light as the sun, but excluding UV light, or directly exposed to UV light for 12 h. The results indicated no negative effect on the infection potential of the conidia of most species tested. The conidia of the two Metarhizium pinghaense (5HEID and TH149) isolates showed the greatest tolerance to visible light and UV radiation exposure on both soil and leaf surfaces. Exposure of M. pinghaense isolates to visible light on soil surfaces showed pathogenicity of > 80% for both isolates, and of between 58% and 88% after exposure to UV light. On leaf surfaces, three Metarhizium isolates, M. pinghaense (5HEID and TH149) and M. majus (TH153) had > 90% pathogenicity following exposure to UV light, and M. pinghaense (TH149) and M. robertsii (6EIKEN) showed greater tolerance of > 70%, under laboratory conditions. However, the pathogenicity of the EPF isolates was very low in field trials, indicating that further trials on the use of formulations and adjuvants with the isolates are needed to improve long-term persistence and efficacy under field conditions.
Formulation of entomopathogens refers to the mixing of various inert ingredients, like clays and mineral oils, with the active ingredients which are the entomopathogens. Successful formulation ...enhances the survival of the entomopathogen and also eases their transportation, storage, preparation and application. The aim of this study was to develop a formulation to maintain the longevity and pathogenicity of the mass-produced conidia of local Metarhizium pinghaense and M. robertsii, for above-ground future commercial field application against Pseudococcus viburni. The objectives were to develop a cost-effective protocol for formulation of infective propagules and to test their effectiveness under laboratory conditions. The conidia of both isolates were formulated using four different oils (liquid paraffin, coconut, canola and olive oils) as liquid carriers, and diatomaceous earth as a mineral carrier. Conidial viability and pathogenicity were assessed over a period of eight weeks. In the study, it was observed that the conidia formulated in oil carriers maintained a high conidial viability and survival rate of >95 % over a period of eight weeks for both isolates, relative to when formulated in mineral carriers, or when stored as dry conidial powder. The conidia in all the oil formulations were also observed to induce high mortality, ranging between 60 % and 90 % for M. pinghaense, and between 70 % and 90 % for M. robertsii, when used against P. viburni. The ability of conidia of both isolates to maintain viability and pathogenicity, following storage in the oil formulations, increased the likelihood of the local isolates being successfully integrated as biological control agents for management of P. viburni under field conditions.
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