Short CommunicationBio-efficacy of the indigenous entomopathogenic fungus, Beauveria bassiana in conjunction with desiccant dust to control of coleopteran stored product pests
Graphical abstract
Introduction
Using eco-friendly stored product pest management tactics is imperative to safely reduce quantitative and qualitative losses of agricultural products. Globally, conventional chemical contact insecticides and fumigants (phosphine, methyl bromide) are widely used as grain protectants (Agrafioti and Athanassiou, 2018). Resistance to synthesized insecticides is well documented in sawtoothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) (Lee and Lees, 2001, Agrafioti and Athanassiou, 2018) and in cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) (Kang et al., 2013), primarily pests of stored beans and cereals, respectively (Singh and Emden, 1979). To minimize adverse effects of chemical insecticides, researchers are attempting to develop alternatives that are environmentally friendly substitutes (Batta and Kavallieratos, 2018). Use of entomopathogenic fungus (EPF) and diatomaceous earth (DE), both of which are eco-friendly options, has been shown to have potential in managing stored product insect pests (Lord, 2001). The entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales), is globally distributed and is one of the best studied of the entomopathogenic fungi (EPF). Isolates of native EPF possess considerable genetic diversity and have been shown to be an ample reservoir of potential biocontrol agents to be conserved or inundatively released into the agroecosystem for insect control (Quesada-Moraga et al., 2007).
Diatomaceous earth affects insects via cuticular abrasion and lipid layer adsorption (Lord, 2001, Badii et al., 2014), but are slow-acting in contrast with other grain protectants (Korunic et al., 1998). On the other hand, earlier studies showed that epicuticular abrasion through DE application may improve B. bassiana efficacy (Lord, 2001). Hence, we hypothesized that indigenous B. bassiana that are compatible with a DE formulation would potentially act effectively in controlling stored product beetles when utilized in a co-application program. We focused on B. bassiana strain efficiency when combined with commercial DE (as biophysical stress factors) and ensure that neither of the two compounds produced adverse side effects on F1 progeny when utilized in stored-product control programs.
Section snippets
Grain material and insect preparations
Both beetle colonies (cowpea weevil and sawtoothed grain beetle) were maintained on sterilized adapted local host plants in the laboratory. C. maculatus was reared on cowpeas (Vigna unguiculata L. var. Parastoo) and mung beans (V. radiata L. var. Gohar) according to Bandara and Saxena, (1995). O. surinamensis was reared and adults were maintained on cracked wheat (Triticum aestivum var. Sardari), and barley (Hordeum vulgare L. var. Nosrat). Each species was cultured in ventilated 1.5 L plastic
Insecticidal activity of B. bassiana and DE on C. maculatus and O surinamensis
Dry conidia and inert dust dose-response experiments were conducted simultaneously to obtain an accurate estimate of sublethal concentrations of B. bassiana IRAN441C and DE SilicoSec® for assessment of their insecticidal activity to adult beetles on different commodity. For each beetle species, LC25 and LC50 values of strain 441C and DE on each commodity are shown in more detail in Table 1. Results of the LDR test (95% CL) showed no differences in adult C. maculatus and O. surinamensis
Discussion
The lethal agents B. bassiana IRAN441C and DE produced acceptable insecticidal activity in C. maculatus and O surinamensis adults in dry powder dose-response applications. Strain 441C (from host Rhynchophorus ferrugineus) was obtained from Saravan, Sistan-Baluchestan Province, Iran, a hot, dry desert climate. Isolates from hot-temperate agroecosystems were reported to be highly virulent to H. armigera larvae (Kalvnadi et al., 2018). Disparities in adult beetle sensitivity to 441C might be
Conclusion
The use of B. bassiana-IRAN441C strain combined with the commercial SilicoSec® DE-products was additive and resulted in higher adult mortality than B. bassiana alone or DE alone. B. bassiana and DE are cost-effective solutions for programs designed to protect stored commodities against C. maculatus and O. surinamensis and, used together, have potential to replace conventional insecticides in stored product pest management. Production of a repellent effect due to migratory morph induction or
Acknowledgments
We thank the Health Research Center, Baqiyatallah University of Medical Sciences for financial support. We are also grateful to Elham Kalvandi for assistance with laboratory experiments. We thank the Iranian Research Institute of Plant Protection (IRIP) for strain of B. bassiana IRAN441C.
Conflicts of interest
The authors have no conflict of interest.
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