US ENT 16-A1
Stellenbosch University. Department of Conservation, Ecology and Entomology
Addison, P A
Malan, A P
Pringle, K L
Objectives and Rationale
Katydids (Plangia graminea) and weevils (Phlyctinus callosus), BFW, are sporadic pests of vineyard in the Western Cape province of South Africa. They primarily feed on foliage, which during pest outbreaks, may result in reduced vigour and stunted development. An increase in their density and distribution have been reported, and no agrochemicals are currently registered for their control. Previous research identified possible biological control agents, including entomopathogenic fungi (EPF) and parasitic wasps. The aim of this study was to (i) evaluate the efficacy of EPNs and EPF against katydids and weevils; (ii) to determine an estimate of katydid geographical distribution and to (iii) record observations made in field and laboratory populations.
Field collected insects were screened against 12 in vivo-cultured EPN species at 200IJ / insect, in a laboratory environment, incubated at 25°C and >95% RH for 48 h, after which mortality was assessed. Geographical distribution was estimated by plotting reported and verified katydid occurrence sites. In total, 70 soil samples were collected from deciduous fruit orchards and vineyards in the Western Cape. The soil samples were baited with mealworms, Tenebrio molitor (Coleoptera: Tenebrionidae) to trap EPNs and EPF. A field trial to determine the performance of Steinernema yirgalemense, applied at different concentrations, followed. The EPF were either applied alone, in simultaneous combination with S. yirgalemense, or 1 and 2 weeks after fungal application; the EPNs were also applied alone.
Seven locally isolated EPN species achieved significant mortality, of which the best performing nematodes achieved > 90% mortality. Katydids were reported from 36 locations, primarily in the Cape Winelands region of the Western Cape, of which 12 were confirmed by site visitation. EPNs were isolated from 17 % (12) of the samples, with Heterorhabditis bacteriophora and H. safricana as the only two EPN species isolated. In the field trials, S. yirgalemense gave 69 % and 78 % mortality for BFW larvae, at two concentrations respectively. The results showed that all EPN’s screened controlled the different life stages of the Banded Fruit Weevil (BFW). It also showed that 100% larval and adult mortality was obtained when S. yirgalemense was applied 1 or 2 weeks after Beauveria bassiana 1 and B. bassiana 2. It was recommended that the next step would be to field test these products (the best performing EPN species) on a larger scale to assess the practicality and efficacy and also to evaluate their in vitro produced counterparts where available.
Key Conclusion or Discussion
Katydid nymphs have proven susceptible to EPN infection. The efficacy of in vitro-cultured EPNs in field trials, in combination with adjuvants and as part of an IPM program, would further provide clarification on the value of EPNs as biological control agents. Both entomopathogens have shown outstanding potential to control the BFW when used alone, and in combination, could provide an economically viable control strategy against the BFW.
Recommendation to Industry / Key take-home message
Laboratory trials have shown the viability of using alternative control methods to chemicals. The next step would be to field test these products on a larger scale to assess the practicality and efficacy.
Dlamini, B. 2016. Biological control of banded fruit weevil, with focus on entomopathogenic fungi and nematodes. Paper presented at HORTGRO Science Technical Symposium, 30 May – 2 June 2016, Simondium, South Africa.
Dlamini, B E, Malan, A P and Addison, P A. 2017. Entomophathogens from local agricultural soil and their potential to control the banded fruit weevil (BFW), Phlyctinus callosus (Schoenherr) (Col,coptera: Curculionidae). Paper presented at the ESSA/ZSSA Conference, 3-7 July, Pretoria, South Africa.