LAUSR

Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is a key pest of citrus in South Africa. In addition to the fruit damage caused, export markets such as the United States, South Korea and China regulate T. leucotreta as a phytosanitary organism in addition to restricting the use of pesticides on exported fruit (Grout & Moore 2015; SA-DAFF 2015). The bulk of citrus in South Africa is exported (Citrus Growers’ Association 2015). Thus, the control of T. leucotreta is crucial. Consequently, the citrus industry adopts a zero tolerance approach controlling the pest, being strongly reliant on integrated pest management (Moore & Hattingh 2012). Numerous control options are available, but are largely limited to use against the above-ground life stages of this pest: eggs, neonates and adults (Moore & Hattingh 2012; Grout & Moore 2015). Isolates of the entomopathogenic fungal species Metarhizium anisopliae (Metchnikoff) Sorokin (G 11 3 L6 and FCM Ar 23 B3, referred to as Ma1 and Ma2 respectively) and Beauveria bassiana (BalsamoCrivelli) Vuillemin (G Ar 17 B3, referred to as Bb1) have been identified as capable of inducing greater than 80 % mycosis of late fifth instar T. leucotreta upon their exposure to soil inoculated with these fungal spores under controlled laboratory conditions at a concentration of 1 × 107 conidia/ml (Goble et al. 2010, 2011; Coombes et al. 2015). These isolates originated from soil samples collected from conventional citrus orchards and isolated using the insect baiting technique (Goble et al. 2010). The possibility of applying these isolates in the field to control the soil-dwelling life stages (wandering late instars, prepupae and pupae) of T. leucotreta as a complementary strategy to aboveground control options was suggested (Coombes et al. 2015). However, environmental factors (abiotic and biotic) in the field are complex and have the potential to hinder fungal efficacy (Inglis et al. 1997; Jaronski 2010; Foster et al. 2011). A trial to assess the efficacy of these isolates against T. leucotreta late fifth instars using plastic cages (5-l containers, 20 × 20 × 30 cm, with breathable mesh inserts) was conducted in an organic 22-year-old Palmer Navel orange citrus orchard (Eastern Cape, South Africa) (33 37’S 25 40’E). Soil texture was classified as loam (16 % clay, 38 % silt and 46 % sand) with a soil pH of 7.7. Average soil temperature and moisture within the upper 10 cm soil surface was measured as 21.3 °C and 36.5 %, respectively. The trial was initiated on 13 March 2014 and terminated one month thereafter. The efficacy of each isolate was determined at three concentrations [2.5 × 1013 (low), 5 × 1013 (intermediate) and 1 × 1014 (high) spores/ha] and in the presence of a lucerne hay mulch at the intermediate concentration. A mulch treatment was included, as the orchard was mulched regularly with sheep’s wool and lucerne. Mulch was added to each respective cage as a thin complete-coverlayer prior to fungal application. Controls and a treatment applied with a commercially produced fungal formulation (Broadband®, a.i. B. bassiana strain PPRI 5339) (BASF, South Africa), were included. The trial design was a completely randomised design replicated eight times. Cages were buried in the upper soil layers underneath the canopy of citrus trees (on the south-facing side and 1 m from an irrigation sprinkler) and filled with the soil removed during hole-digging. Fungi, with the exception of Broadband®, were massproduced as dry aerial conidia by Agrauxine (Loches, France) and applied as an aqueous suspension (water supplemented with 0.01 %