Abstract
Management of the Mediterranean flat-headed root-borer, Capnodis tenebrionis, is critical due to the larvae’s root localization. Neonate larvae can be exposed to natural enemies before penetrating the roots. Application of Metarhizium brunneum strain Mb7 and Beauveria bassiana strain GHA formulations on rice granules was investigated for their efficacy against C. tenebrionis larvae. Mb7 application, evaluated on apricot twigs, significantly and dose-dependently reduced colonization rates of neonates, with highest mortality at 108 conidia/g soil. Neonate susceptibility to Mb7 and GHA was evaluated on potted rootstocks (GF677 almond × peach, 2729 plum) planted in entomopathogenic fungi (EPF)-premixed soil (1.3–1.6 × 105 conidia/cm3 soil) or in EPF-free soil surface-treated with 5 g Mb7 fungal granules (1.25 × 109 conidia). Larval colonization rates were reduced 7.4-fold in 2729 by both fungi; only Mb7 completely prevented colonization of GF677 by larvae. Larvae inside plant galleries exhibited mycosis with EPF-treated soils and both fungi proliferated on larval frass. Mb7 conidia germinated in the rhizosphere of GF677, and conidia of both fungi remained viable throughout the trial. Galleria baiting technique was used on EPF-treated soil to evaluate EPF infectivity over time; Mb7 and GHA persisted 180 and 90 days post inoculation, respectively. The formulation (fungus-covered rice grains), delivery method (mixing with soil) and persistence (3–6 months) of Mb7 and GHA are feasible for potential field application to control C. tenebrionis.
Highlights
The Mediterranean flat-headed root-borer, Capnodis tenebrionis (L.) (Coleoptera: Buprestidae), can severely damage ornamental and stone-fruit tree species, and is a key pest of apricot, peach, plum, nectarine, cherry, and almond, especially under arid and semiarid conditions with scarce water supply, and in organic orchards [1,2]
Susceptibility of C. tenebrionis Neonates to Mb7-green fluorescent protein (GFP) under Laboratory Conditions
The infestation rate of twigs in the control microcosms did not differ from that of twigs in the microcosms treated with 5 × 106 Mb7-GFP conidia/g soil (100% and 78.0 ± 14.1%, respectively) (Table 2)
Summary
The Mediterranean flat-headed root-borer, Capnodis tenebrionis (L.) (Coleoptera: Buprestidae), can severely damage ornamental and stone-fruit tree species, and is a key pest of apricot, peach, plum, nectarine, cherry, and almond, especially under arid and semiarid conditions with scarce water supply, and in organic orchards [1,2]. Insects 2020, 11, 319 neonate larvae crawl through the soil toward the host plant roots and penetrate them [12]. During this short searching time, the neonate larvae are exposed and vulnerable to natural enemies inhabiting the soil [7,12]. This pest is mainly controlled at the adult stage by repeated foliar sprays of chemicals
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