Assadi et al. Egyptian Journal of Biological Pest Control (2021) 31:47 Egyptian Journal of https://doi.org/10.1186/s41938-021-00395-5 Biological Pest Control RESEARCH Open Access Effect of the native strain of the predator Nesidiocoris tenuis Reuter and the entomopathogenic fungi Beauveria bassiana and Lecanicillium muscarium against Bemisia tabaci (Genn.) under greenhouse conditions in Tunisia Besma Hamrouni Assadi1*, Sabrine Chouikhi1, Refki Ettaib1, Naima Boughalleb M’hamdi2 and Mohamed Sadok Belkadhi1 Abstract Background: The misuse of chemical insecticides has developed the phenomenon of habituation in the whitefly Bemisia tabaci (Gennadius) causing enormous economic losses under geothermal greenhouses in southern Tunisia. Results: In order to develop means of biological control appropriate to the conditions of southern Tunisia, the efficacy of the native strain of the predator Nesidiocoris tenuis Reuter (Hemiptera: Miridae) and two entomopathogenic fungi (EPF) Beauveria bassiana and Lecanicillium muscarium was tested against Bemisia tabaci (Gennadius). Indeed, the introduction of N. tenuis in doses of 1, 2, 3, or 4 nymphs per tobacco plant infested by the whitefly led to highly significant reduction in the population of B. tabaci, than the control devoid of predator. The efficacy of N. tenuis was very high against nymphs and adults of B. tabaci at all doses per plant with a rate of 98%. Likewise, B. bassiana and L. muscarium, compared to an untreated control, showed a very significant efficacy against larvae and adults of B. tabaci. In addition, the number of live nymphs of N. tenuis treated directly or introduced on nymphs of B. tabaci treated with the EPF remained relatively high, exceeding 24.8 nymphs per cage compared to the control (28.6). Conclusions: It can be concluded that the native strain of N. tenuis and the EPF tested separately were effective against B. tabaci. Their combined use appears to be possible. Keywords: Bemisia tabaci, Biological control, Nesidiocoris tenuis, Geothermal, Beauveria bassiana, Lecanicillium muscarium * Correspondence: [email protected] 1Dryland and Oases Cropping Laboratory, Arid Regions Institute, Street El Jorf, 4119 Medenine, Tunisia Full list of author information is available at the end of the article © The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Assadi et al. Egyptian Journal of Biological Pest Control (2021) 31:47 Page 2 of 11 Background Geothermal Crops in Chenchou Tunisia-Gabès (TCPG) Despite its importance, the geothermal greenhouse sec- (latitude, 33° 53′ 13.3″ North; longitude, 9° 53′ 37.1″ tor faces several phytosanitary constraints, including the East; elevation 78 m). The insects were reared for 2 years whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyro- from March 2016 until March 2018. The whiteflies col- didae) the devastator of several agricultural crops. This lected from the biological greenhouse using a manual as- insect is one of the most destructive pests in the world pirator were introduced into previously prepared (Oliveiraa et al., 2001). It transmits more than 200 plant tobacco plants in pots in a glasshouse. Three weeks later, viruses (Polston et al., 2014) and causes severe economic the mirid bug was collected from TCPG’s greenhouse damage to more than 60 crop plants. In southern and subsequently released on plants infested with B. Tunisia, this whitefly causes harmful damage to crops tabaci. heated by geothermal waters (Bel Kadhi, 2004). Control of this pest has been based primarily on the Preparation of entomopathogenic fungi use of conventional broad-spectrum chemical pesticides. Two biological formulations based on EPF were tested As a result, B. tabaci developed resistance against differ- on B. tabaci under controlled conditions. One was based ent groups of insecticides following their intensive use on Lecanicillium muscarium strain Ve6 (19-79) with a (Sain et al., 2019). In addition to marketing problems, water-soluble granular formulation of 1010 spores/g, and the use of chemicals in a heated greenhouse could pose the other was based on Beauveria bassiana strain R 444 poisoning problems for farmers (Bel Kadhi, 2004). The in wettable powder with a concentration of 2 × 109 co- development of biological control methods is crucial, nidia/g. since the introduction of biological control agents in pest management programs provides a more stable re- sults (Aggarwal et al., 2016). The use of as many natural Experimental method enemies as possible in agricultural production systems Effect of N. tenuis on B. tabaci can replace the use of pesticides (Trdan et al., 2020). The study of the efficacy of 5 doses of treatment with N. Among other natural agent antagonists of the whitefly B. tenuis nymphs was carried out on Nicotiana tabacum tabaci, Nesidiocoris tenuis Reuter (Hemiptera: Miridae) plants, previously prepared in pots and installed in cages is a predatory zoophytophagous bug, naturally present in in a glasshouse, under controlled conditions, at a tomato crops in the Mediterranean basin (Perdikis and temperature of 27 ± 1°C and RH of 75 ± 5%. Arvaniti, 2016). It is used to control whiteflies (Hemip- Fifteen wooden cages measuring 1 × 1 × 1.2 m, cov- tera: Aleyrodidae), tomato leaf miner, and mites (San- ered on all three sides with an insect proof canvas (20/ chez et al., 2014 and Yano et al., 2020). Similarly, the use 10 threads/cm), were prepared and installed in a glass- of EPF is a relevant tool in biological control of whitefly house compartment. Each cage containing 5 tobacco (Faria and Wraightb, 2001). Some EPF, such as Beau- plants was assigned to one of the 5 doses of 0, 1, 2, 3, 4, veria spp., Metarhizium spp., Lecanicillum spp., and and 5 N. tenuis nymphs per plant. All 3 cages corres- Isaria spp., were developed as mycoinsecticides (de Faria pond to one treatment, and the whole was arranged in a and Wraight, 2007). They are often used as an effective randomized complete block design. At the 6–7 leaf alternative for controlling insect pests throughout the stage, the plants in each cage were infested by adults of world (de Faria and Wraight, 2007). In the quest for an B. tabaci. A week after the infestation, control of the integrated pest management program, based on the use population level of B. tabaci began. When the pest of biological control agents, appropriate to the condi- population reached 9 individuals/leaf, inoculation by N. tions of geothermal greenhouse, in southern Tunisia and tenuis nymphs was carried out. A week later, until the meeting the “Global Gap” standards that govern the ex- 14th week, monitoring of the population level of nymphs port niche, this study evaluated the efficacy of the two and adults of B. tabaci was carried out (Calvo et al., EPF B. bassiana and L. muscarium and the native preda- 2009). Using a hand-held magnifying glass, an on-site tory bug N. tenuis. In addition, the effect of these fungi analysis of a randomly selected leaf on each plant on the survival of the predator was studied. allowed the number of adults and larvae of B. tabaci and N. tenuis to be counted. Counting was done early in the Methods morning and turning the leaves gently to avoid disturb- Insect ance of mirid bug and whitefly adults. B. tabaci and the native predator N. tenuis were col- The follow-up of the test was stopped at week 14, lected from oases in southern Tunisia. The predator and when it was noted that the vegetative state of the plants the pest were reared on a tomato crop in the same no longer allows the normal development of the whitefly greenhouse of 9 × 30 m managed in organic mode, lo- due to lack of food, which can distort the efficacy of N. cated at the Technical Center for Protected and tenuis. Assadi et al. Egyptian Journal of Biological Pest Control (2021) 31:47 Page 3 of 11 Efficacy of B. bassiana and L. muscarium on B. tabaci with B. tabaci. Twenty-four hours later, the plants were The pathogenicity of B. bassiana and L. muscarrium was treated by the fungi. For each treatment, 10 plants were tested against the population of B. tabaci on Cucumis protected by a cage, replicated by 5. The whole was ar- sativus, “Vigorex variety”. To do this, cucumber plants ranged in a randomized complete block design. Each were transplanted into 2-l plastic pots, filled with or- cage was treated by 0.8 l using a 1-l sprayer. In the sec- ganic peat, and fertilized with a standard nutrient solu- ond step, to evaluate the effect of fungi already installed tion. Twelve wooden cages measuring 1 × 1 × 1.2 m, on a nymphal population of B. tabaci on the survival of covered on all three sides with an insect proof canvas N. tenuis nymphs, whitefly infested plants were treated (20/10 threads/cm), were prepared and installed in a by different EPF. Nymphs of N. tenuis, at a rate of 3 in- glasshouse compartment. In each cage, 5 cucumber dividuals per plant, were introduced at different times plants were introduced.