Journal of Pest Science https://doi.org/10.1007/s10340-020-01223-9 ORIGINAL PAPER Efective control of Frankliniella occidentalis by Metarhizium anisopliae CQMa421 under feld conditions Jun Li1,2,3 · Jiaqin Xie1,2,3 · Deyu Zeng1,2,3 · Yuxian Xia1,2,3 · Guoxiong Peng1,2,3 Received: 30 May 2019 / Revised: 22 February 2020 / Accepted: 6 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Annual economic losses of eggplant due to western fower thrips (Frankliniella occidentalis) infestations are considerable. F. occidentalis is difcult to control due to rapid proliferation rates and resistance to chemical insecticides. A more efective biological control strategy is urgently required. To assess the potential efcacy of M. anisopliae CQMa421 in the biologi- cal control of F. occidentalis on eggplant, we evaluated its virulence and insecticidal activity in the laboratory and feld. 7 The laboratory results indicated that the LT50 of M. anisopliae CQMa421 against F. occidentalis at 2 × 10 conidia/ml was 5.5 days. The results from the experimental feld trial showed that a single spray of M. anisopliae CQMa421 reduced thrips by 50–70% compared to the control; this was signifcantly lower than for the chemical insecticide imidacloprid. However, the results from demonstration feld trials where consecutive sprays were made indicated that M. anisopliae CQMa421 controlled the pests at a level equivalent to that obtained with a chemical insecticide. The fndings clearly demonstrated the feasibility of using M. anisopliae CQMa421 as an alternative to chemical insecticides in the control of F. occidentalis under feld conditions. Keywords Metarhizium anisopliae · Western fower thrips · Eggplant · Virulence · Field trials · Biological control Key message • Application of Metarhizium anisopliae CQMa421 can control Frankliniella occidentalis under feld conditions. • The efcacy of M. anisopliae CQMa421, when applied • There is a lack of efective biocontrol tactics for western several times over a growing season, was as good as that fower thrips which are important pests of feld vegetable obtained from a spray program based on multiple chemi- crops in China. cal insecticides. • M. anisopliae CQMa421 could be a viable alternative to chemical insecticides. Communicated by S. Reitz. Special issue on novel management tactics for the western fower thrips. Introduction * Yuxian Xia Western fower thrips, Frankliniella occidentalis Pergande [email protected] (Thysanoptera: Thripidae), is a devastating pest of vegetable * Guoxiong Peng crops (Kirk and Terry 2003; Kutuk 2017; Zhang et al. 2019). [email protected] F. occidentalis feeds on the contents of plant cells, which 1 School of Life Sciences, Chongqing University, Huxi reduces photosynthetic capacity and can transmit several Campus, No. 55 Daxuecheng South Road, Shapingba important plant viruses. Economic losses result from direct District, Chongqing 401331, China feeding damage, reduced production and damaged fruits 2 Chongqing Engineering Research Center for Fungal (Wetering et al. 1999; Kutuk 2017). Insecticides, Chongqing 401331, China Currently, the main strategy used to control F. occiden- 3 Key Laboratory of Gene Function and Regulation talis is the large-scale application of chemical insecticides. Technologies under Chongqing Municipal Education In China, chemical insecticides make up 90% of all control Commission, Chongqing 401331, China Vol.:(0123456789)1 3 Journal of Pest Science agents used. High dosages and mixtures of various chemical Materials and methods insecticides are applied frequently to vegetable crops. This heavy reliance on chemical insecticides caused the resistance Preparation of fungal cultures and conidial of F. occidentalis to chemical insecticides such as abamectin suspensions (resistance raised 45.5-fold), spinosad (resistance raised > 104- fold), acrinathrin (resistance raised 43-fold) and benzoylurea M. anisopliae var. anisopliae strain CQMa421 was obtained (resistance raised 3.2–220-fold) has rapidly evolved (Wan et al. from the Genetic Engineering Research Center, College of 2018; Meng et al. 2018; Suzuki et al. 2017; Bielza et al. 2008). Life Science, Chongqing University, China. Conidia of were Additionally, eggs and pupae are hidden in plant tissues and produced as previously reported (Peng et al. 2008). Briefy, soil, protecting them from direct exposure to the pesticides mycelia were cultured in 1/4 SDAY liquid medium at 28 °C (Jensen 2000). The heavy usage of chemical insecticides is for 3 days using fermentation reactor and inoculated 10% also a hazard to ecosystems and human health (Ventura et al. culture (v/w) to autoclaved rice with water content 40–50%. 2019; Yan et al. 2018). The conidia were harvested with griddle (100 orders) after Entomopathogenic fungi are important control factors for 15 days of growth and then allowed to air-dry at room tem- pests in the natural environment. They infect and kill pests by perature. A batch of conidia more than 80% germination on penetrating the integument through physical force and enzy- solid medium was used for following experiments. In fol- matic degradation of the insect cuticle, proliferation within the low-up trials, working suspensions were prepared in sterile host and secreting toxins (Ortiz-Urquiza et al. 2015). Owing 0.01% Tween-80 solution (Sigma Chemical Co. Ltd., UK). to these multiple modes of action, it is more challenging for insects to build resistance against these biocontrol agents. Bioassays Entomopathogenic fungi, including Metarhizium brunneum Petch and Beauveria bassiana (Balsamo) Vuillemin, have The suspension of M. anisopliae CQMa421 conidia in been developed as mycoinsecticides to control pests and mini- 0.1% Tween-80 solution (Sigma Chemical Co. Ltd., UK) mize the damage they cause (de Faria and Wraight 2007). A was adjusted to the following serial concentrations: 8 × 105, strain of Metarhizium brunneum Petch (formerly known as 4 × 106, 2 × 107, 1 × 108 and 5 × 108 conidia/ml. The 0.1% M. anisopliae), which was isolated from Cydia pomonella, is Tween-80 solution was as control. The suspensions were pathogenic to F. occidentalis, and its use to control thrips in sprayed onto leaves of eggplant seedlings with 2–3 leaves laboratories and greenhouses has been reported (Vestergaard (1 ml per leaf) using a Potter Precision Spray Tower (Burk- et al. 1995; Saito and Brownbridge 2018; Zhang et al. 2019). ard Manufacturing, UK). F. occidentalis adults were col- These results suggest that M. anisopliae has the potential to lected from eggplant fowers under feld condition, chilled control F. occidentalis on eggplant under feld conditions. M. and placed at 8–10 °C for 10 min and then 20 individuals anisopliae var. anisopliae CQMa421, isolated from muscar- placed onto 3 leaves of the eggplant seedlings. The seed- dine cadavers of rice leafroller (Cnaphalocrocis medinalis), lings were transferred into Petri dishes (15 cm diameter) has a wide range of hosts and has been successfully applied to and placed into illuminated incubators at 26 ± 1 °C with a control plant hopper, Nilaparvata lugens, Sogatella furcifera cycle of 16 h light/8 h dark in 60–80% relative humidity. and Laodelphax striatellus on rice in China (Hong et al. 2017). Four replicates of each treatment were conducted. F. occi- Eggplant, Solanum melongena L., one of the most eco- dentalis mortality was checked daily for 7 days. To verify nomically important vegetables in Asia (Van Eck and Snyder the carcasses killed by M. anisopliae, all of them were put 2006), and approximately one-third of the global acreage is in a Petri dish (diameter 3.5 cm) and cultured at 26 ± 1 °C grown in the region (from the Food and Agriculture Organi- for 3–4 days in an incubator. zation of the United Nations). Eggplant is susceptible to F. occidentalis. To determine whether M. anisopliae CQMa421 Field trials and data collection could be used to control F. occidentalis on eggplant, the fun- gus was frst evaluated in the laboratory and small-scale feld Experimental feld trials trials, followed by a large-scale trial in feld-grown eggplant. About 0.2-hectare (ha) area of S. melongena (var. Jing- qie No. 6) infested with F. occidentalis was selected for the experimental trial. The trial area was divided equally into 20 plots with 10 m × 10 m. Distance of 1 m was set up among the plots. Four plots were assigned at random to each treatment. M. anisopliae CQMa421 suspensions con- taining 4 × 106, 2 × 107 and 1 × 108 conidia/ml were sprayed 1 3 Journal of Pest Science at a rate equivalent to 45 l/h onto the eggplants using an thrips extracted from per fower. In the experimental trials, the electric sprayer (Lanou Ltd., Corp., China). Imidacloprid relative control efcacy (%) of each treatment was based on (working concentration 0.15 g/l, Admire ® 70% WG, Bayer, the population density of F. occidentalis on eggplants and was Germany) and water acted as positive and negative controls, calculated as follows (Tong and Feng 2016): respectively. F. occidentalis on fower samples were counted 1 − D D D D ×% before spraying with the insecticides and 7 and 14 days after tj c0 t0 cj spraying, using sampling and processing protocols described Here Dc and Dcj represent the numbers of F. occidentalis below. 0 observed in the control on the day before spraying and the j D D Demonstration feld trials th day after spraying, respectively. t0 and tj represent the numbers of F. occidentalis observed after treatment with M. anisopliae CQMa421 or imidacloprid on the