Acaricidal and Repellent Activities of Rhizobacterial Isolates Against Tetranychus urticae (Acari: Tetranychidae) Under Laboratory and Greenhouse Conditions

Acaricidal activity of symbiotic bacteria associated with entomopathogenic nematodes against the red palm mite Raoiella indica Hirst (Acari: Tenuipalpidae)

ABSTRACT The red palm mite Raoiella indica Hirst, 1924 (Acari: Tenuipalpidae) is an important invasive pest affecting tropical crops, particularly coconut and banana, in several countries. In Brazil, pest management is limited by the reduced availability of registered chemical control products, which may favor the selection of resistant populations. Symbiotic bacteria of entomopathogenic nematodes (EPNs), such as Xenorhabdus (Thomas and Poinar, 1979) and Photorhabdus (Boemare and Akhurst 2006), are known to produce metabolites with insecticidal and acaricidal activity, but their activity against R. indica has not been evaluated yet. In this study, an exploratory laboratory bioassay was conducted to assess the acaricidal activity of 15 bacterial isolates of Xenorhabdus and Photorhabdus through topical application to adult females of R. indica. Mortality was recorded over a six-day period and compared with water and culture-medium controls. Several isolates induced mortality rates exceeding 95%, and two isolates resulted in complete adult mortality. In addition, oviposition was strongly reduced by specific isolates. Females exposed to isolates CER144 and CER09 laid on average 0.03 and 0.15 eggs per alive female per day, respectively, compared with approximately 0.85 eggs per alive female per day in both controls, indicating a reduction of over 80% in egg production. Although preliminary, these findings provide the first evidence that EPN-symbiotic bacteria represent a promising and underexplored source of compounds for the biological control of R. indica, opening perspectives for sustainable pest management in tropical and subtropical systems.

Efficacy of Entomopathogenic Fungi against Sapota Fruit Mite, Tuckerella kumaonensis Gupta (Tuckerellidae: Acari) under Laboratory Condition

A laboratory investigation was conducted during 2020 and 2021 at Biocontrol Laboratory, N. M. College of Agriculture, Navsari Agricultural University, Navsari, Gujarat, to test the efficacy of different entomopathogenic fungi against sapota fruit mite, Tuckerella kumaonensis Gupta infesting sapota. Among the various entomopathogenic fungi, the treatment of Beauveria bassiana (1×10⁸ cfu/g) @ 4g/l found significantly superior (62.03% mortality) over the rest of the treatments. However, the treatment of Lecanicillium lecanii (1×10⁸ cfu/g) @ 4g/l registered 45.41 per cent mortality and found the next best treatment against sapota fruit mite and was statistically at par with the treatment of Metarhizium anisopliae (1×10⁸ cfu/g) @ 4g/l (42.39% mortality). The treatments of Hirsutella thompsonii (1×10⁸ cfu/g) @ 4g/l found to be least effective against sapota fruit mite (31.04% mortality).

Antibacterial Properties of Origanum vulgare and Eucalyptus staigeriana Essential Oils Single or in Combination With Cloxacillin Against Corynebacterium pseudotuberculosis

Caseous lymphadenitis is a chronic infectious disease caused by Corynebacterium pseudotuberculosis that affects small ruminants, resulting in significant economic losses. In response, essential oils (EO) have emerged as promising natural alternatives for disease control. The present study evaluated the chemical composition, antioxidant capacity, and antibacterial activity of EO from Origanum vulgare (OVEO) and Eucalyptus staigeriana (ESEO) against C. pseudotuberculosis isolated from Northeastern Brazil. The antibacterial effect was assessed by disk diffusion, minimum inhibitory concentration (MIC), Minimum Bactericidal Concentration, time–kill assays, and combination tests with cloxacillin. Gas chromatography analysis identified carvacrol as the major compound in OVEO, and D‐limonene in ESEO. OVEO demonstrated strong antibacterial efficacy, exhibiting inhibition zones of up to 74 mm and MICs ranging from 31.2 to 250 µg/mL. Both EOs demonstrated bactericidal properties and exhibited additive interactions with cloxacillin (FICi 0.56–1.03). Furthermore, OVEO exhibited strong antioxidant activity (IC50 = 6.89 ± 0.58 µg/mL). These findings underscore the significance of bioactive compounds with antibacterial potential, although further studies are necessary to evaluate their applicability for managing caseous lymphadenitis.

Bioefficacy of Indian Beauveria bassiana and Lecanicillium lecanii isolates against Lipaphis erysimi (Hemiptera: Aphididae) and their safety to Apis cerana (Hymenoptera: Apidae)

Environmental issues associated with the excessive use of chemical substances have received increasing attention globally, particularly regarding their effects on non-target/beneficial insects such as pollinators. To overcome such drawbacks, alternative control methods are being increasingly evaluated. A study was conducted to assess the effectiveness of two Indian biopesticidal isolates against the mustard aphid, Lipaphis erysimi, on rapeseed crops and to investigate their potential risks to the pollinator honeybee, Apis cerana. Laboratory bioassays showed that Beauveria bassiana AS-4220 was the most effective material against L. erysimi after 24 h (LC50 = 95.5 ppm); however, neem seed oil was the most toxic to A. cerana after the same time interval (LC50 = 185.4 ppm). The highest reduction in the aphid population under field conditions was observed with B. bassiana AS-4220 at 3 × 108 spores mL− 1 ten days after field treatment (71.9%), followed by B. bassiana AS-4220 at 2 × 108 spores mL−1 ten days after field treatment (70.7%). The highest PT (persistent toxicity index) and RPT (relative persistent toxicity) values were observed for B. bassiana at 3 × 108 spores mL− 1 (799.98 and 1.06, respectively). The benefit: cost ratio among the treatments was highest for B. bassiana at 3 × 108 spores mL− 1 (4.90:1). However, the highest honeybee mortality was observed following treatment with neem seed oil at 3 mL L− 1 and B. bassiana at 3 × 108 spores mL− 1 ten days of treatment (100%). No significant inhibition of acetylcholinesterase (AChE) activity was observed in honeybees 24 h after treatment. The study demonstrates that entomopathogenic fungi effectively control L. erysimi while posing some risk to A. cerana, particularly at higher concentrations, necessitating careful timing of application . Therefore, these treatments may be used to manage L. erysimi in rapeseed crops while minimizing effects on A. cerana bees, provided that application is scheduled during periods of low foraging activity.

Assessment of Insecticidal Compatibility of Metarhizium anisopliae Isolates against Diamondback Moth (Plutella xylostella L.)

Findings indicate that compatible combinations of M. anisopliae with selective insecticides demonstrated strong potential for the environmentally sound management of P. xylostella as part of an integrated pest management programme.

Cell-free supernatants from entomopathogenic bacteria as a potential alternative for managing Tetranychus urticae in tomato