Matthew F. Addison

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).

Abstract 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.

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)

Abstract 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.

Evaluating mulches together with Heterorhabditis zealandica (Rhabditida: Heterorhabditidae) for the control of diapausing codling moth larvae, Cydia pomonella (L.) (Lepidoptera: Tortricidae)

Abstract 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.

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

Abstract 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.

Evaluation of above-ground application of entomopathogenic nematodes for the control of diapausing codling moth (Cydia pomonella L.) under natural conditions

In South Africa, after harvest and prior to the winter months, when the entire codling moth population enters diapause, no control measures are applied in apple and pear orchards. The biocontrol potential of three imported entomopathogenic nematode (EPN) isolates, being Steinernema feltiae and two isolates of Heterorhabditis bacteriophora (Hb1, Hb2), as well as a local isolate, S. yirgalemense, were evaluated for the control of codling moth under local conditions. All concentrations of S. yirgalemense, applied by immersion in a suspension of nematodes, gave >98 % control. The in vivo-produced S. yirgalemense resulted in codling moth control of >90 %, compared to 54 % and 31 % control by the H. bacteriophora Hb1 and Hb2 isolates, respectively. In follow-up field trials, S. feltiae resulted in ³80 % control, and was more effective than both the S. yirgalemense and the H. bacteriophora (Hb1) isolates. To validate the data obtained from the field trials, subsequent laboratory bioassays were conducted evaluating temperature regimes, following the same cycle as under natural conditions, with a constant humidity of 100 %. Steinernema feltiae proved to be most effective, causing >90 % mortality, followed by S. yirgalemense, with 78 % mortality. The two H. bacteriophora isolates (Hb1, Hb2) under the above-mentioned laboratory conditions, resulted in 73 % and 59 % control, respectively. Humidity, thus, seems to be the most important factor affecting EPN efficacy during above-ground applications. From the results obtained, it can be concluded that H. bacteriophora will not be suitable for the control of codling moth, with S. feltiae proving to be a better candidate than S. yirgalemense for such control purposes.

Control of codling moth (Cydia pomonella) (Lepidoptera : Tortricidae) in South Africawith special emphasis on using entomopathogenic nematodes

In the Western Cape province of South Africa, codling moth (Cydia pomonella) is the most important lepidopteran pest of apples and pears. Currently an integrated pest management (IPM) strategy is followed. However, chemical control still plays an important role in the control of this pest. Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae have been successfully utilized as biological control agents in classical, conservation, and augmentative insect pest management programmes. In this review different biological control options for control of codling moth are considered, with special emphasis on research being done on the biological control of codling moth using EPNs. To integrate nematodes into an IPM system, it is important to conduct research under local environmental conditions for a specific crop. Application of EPNs against codling moth will target the diapausing larval overwintering population above-ground. Especially for commercial application, the unique environmental conditions in the various production areas need to be assessed to allow for the effective use of various EPN species. Orchard application, onto trees poses its own unique challenges with regard to the inundative application of EPNs. Research on the use of EPNs to control codling moth and obstacles encountered in the success of codling moth control are discussed.

Potential of Heterorhabditis zealandica (Rhabditida: Heterorhabditidae) for the control of codling moth, Cydia pomonella (Lepidoptera: Tortricidae) in semi-field trials under South African conditions

ABSTRACT Infection of codling moth, Cydia pomonella (L.), larvae by the entomopathogenic nematode, Heterorhabditis zealandica, was studied under semi-field conditions. Late-instar diapausing codling moth larvae, coccooned in perforated cardboard strips, were used in all trials to evaluate the nematode treatments involved. A morning application of 0.5, 1.0 and 1.5 MM infective juveniles (IJs) per tree resulted in 85%, 95% and 100% codling moth larval infection, respectively. Contrasting results were obtained for an evening application, with low levels of codling moth infection (<50%). Nematode treatment strips placed in direct sunlight resulted in almost no infection (<10%), opposed to strips attaining 67% infection placed in the shade.

Control of diapausing codling moth, Cydia pomonella (Lepidoptera: Tortricidae) in wooden fruit bins, using entomopathogenic nematodes (Heterorhabditidae and Steinernematidae)

ABSTRACT Stacked wooden fruit bins are frequent overwintering sites for overwintering diapausing codling moth larvae. Control strategies against the codling moth (Cydia pomonella) (Lepidoptera: Tortricidae) in South Africa have been hampered by the reinfestation of orchards from nearby stacked infested fruit bins and by the movement of infested bins between orchards. Worldwide, wooden fruit bins are systematically being replaced with plastic bins, however in South Africa this will not be accomplished in the near future. The objective of this study was to evaluate the potential of two recycled commercially available entomopathogenic nematode (EPN) species, Heterorhabditis bacteriophora and Steinernema feltiae, as well as of a local species, Steinernema yirgalemense, to disinfest miniature wooden fruit bins under controlled conditions in the laboratory. After dipping miniature bins loaded with codling moth larvae in a suspension of 25 IJs/mL of each of the three EPN species, under optimum conditions of temperature and humidity, the highest percentage of control was obtained using S. feltiae (75%). The addition of adjuvants significantly increased S. feltiae infectivity to >95%, whereas it did not result in a significant increase in H. bacteriophora or S. yirgalemense infectivity.

A synthesis for managing invasions and pest risks simultaneously for tephritid fruit flies in South Africa

Developing a general management framework for monitoring and reporting biological invasions in agricultural contexts is crucial to assist in the planning and execution of intervention and control strategies. Here we make use of a diverse range of data sets for economically significant South African agricultural fruit fly pests to offer several potential intervention strategies and present a general management framework that unifies different but related fields of research (invasion science and pest management). We review the status of Tephritidae (Diptera) in South Africa with a strong focus on the highly invasive Bactrocera dorsalis (Hendel) and touch on the use of population genetics in pest or invasion management. Integrated modelling of landscape friction from population genetics is undertaken to test for any intrinsic resistance to pest movement across the landscape (e.g., natural or agricultural barriers). Based on the novel analyses presented here, clearly defined landscape management units can be allocated. Across South Africa, control and intervention strategies for managing both invasions of new Tephritidae and existing pest species can be unified into a common framework. Finally, we illustrate the concepts outlined above in a conceptual management decision tree for integrating pest management and invasion management simultaneously. Promoting awareness among growers and the public about fruit fly invasions and impacts is a priority to prevent future incursions of fruit flies, whereas managing Tephritidae as distinct landscape units should facilitate prevention of movement of emerging and existing pests.

Effect of Genetically Modified Bt Maize in an Artificial Diet on the Survival of Cydia pomonella (Lepidoptera: Tortricidae)

Abstract Genetically modified maize contains an insecticidal gene from the soil bacterium Bacillus thuringiensis (Bt), which is an important component in integrated pest management strategies against lepidopteran pests of maize. A project is being implemented in the Western Cape of South Africa against the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), a pome fruit pest, using an area-wide integrated pest management approach with a sterile insect technique component. The project requires rearing of large numbers of the target pest for which an artificial diet that contains maize meal as the main ingredient is used. Most of the maize produced in South Africa is Bt maize, which is known to be toxic to codling moth. The aim of this study was to assess the impact of Bt maize in the diet of codling moth on its production parameters. Codling moths were reared for a period of 44 d on artificial diets that contained 5 different concentrations of Bt maize meal and a control using non-Bt maize. The use of Bt maize in the larval diet resulted in larval mortality, delayed larval development and larvae leaving the diet prematurely. Delayed larval development seemed to be the response with most negative consequences. Since optimal rearing of codling moth is not feasible using meal from genetically modified maize with insecticidal properties, another nutritious meal lacking an insecticidal component must be substituted in the artificial diet.