Application of Streptomyces Antimicrobial Compounds for the Control of Phytopathogens

One of the relevant problems in today's agriculture is related to phytopathogenic microorganisms that cause between 30–40% of crop losses. Synthetic chemical pesticides and antibiotics have brought human and environmental health problems and microbial resistance to these treatments. So, the search for natural alternatives is necessary. The genus Streptomyces have broad biotechnological potential, being a promising candidate for the biocontrol of phytopathogenic microorganisms. The efficacy of some species of this genus in plant protection and their continued presence in the intensely competitive rhizosphere is due to its great potential to produce a wide variety of soluble bioactive secondary metabolites and volatile organic compounds. However, more attention is still needed to develop novel formulations that could increase the shelf life of streptomycetes, ensuring their efficacy as a microbial pesticide. In this sense, encapsulation offers an advantageous and environmentally friendly option. The present review aims to describe some phytopathogenic microorganisms with economic importance that require biological control. In addition, it focuses mainly on the Streptomyces genus as a great producer of secondary metabolites that act on other microorganisms and plants, exercising its role as biological control. The review also covers some strategies and products based on Streptomyces and the problems of its application in the field.

Comparative study on microbial and botanical pesticides as biorational control of mango hopper

Mango hopper is considered as one of the most destructive pests of mango in Bangladesh which can be effectively controlled by using bio-agents and botanical pesticides. An experiment was conducted at the IPM Laboratory of the Department of Entomology, Bangladesh Agricultural University, Mymensingh, Bangladesh to study the comparative performance of three botanicals (Neem, Mahogany and Karanja oils) and a microbial pesticides (Beauveria bassiana) for the management of mango hopper (Idioscopus clypealis). The experiment was designed following completely randomized design (CRD) using 39 petridishes of 12 cm in diameter. Four insecticides each with 3 different doses (1%, 2% and 3%) were evaluated for their effectiveness. The data on the number of hopper killed were collected every day of a week. Results showed that all the three doses of Beauveria bassiana effectively controlled mango hopper. All the treatments influenced significantly in the management of mango hopper in comparison to the control. Among the botanicals 3% Neem oil was the most effective best but relatively lower performance was observed in case of 1% Mahogany oil. Observation on the effect of a microbial pesticide (Beauveria bassiana) and some botanicals on the infestation of mango hopper at different stages showed that hopper population at pea-shaped after prior to the second spray was maximum in 1% Mahogany oil (13.87) and minimum number of hopper was found in 3% Beauveria bassiana (7.33). Overall results suggested that Beauveria bassiana as a microbial pesticide performed better than botanicals in controlling mango hopper and resulting in higher yield. Asian J. Med. Biol. Res. June 2019, 5(4): 330-335

Evaluating the Efficiency of the Entomopathogenic Fungus Beauveria bassiana to Control the Brown Banded Cockroach Supella longipalpa F.

Entomopathogenic fungi can be ideal for the biocontrol of cockroaches since it is environment-friendly microbial pesticide. Susceptibility of second and fourth instar of nymphs and adults of the brown banded cockroach, Supella longipalpa (F.) (Blattodea: Blattellidae) to the entomopathogenic fungi Beauveria bassiana (Bals.) Vuill. at two concentrations 1x 107 and 1x 108 spore/ml was evaluated. Fungus was tested by using two different methods: bait and direct contact. Mortality was monitored after 3, 5 and 7 days’ post exposure. Direct contact of B. bassiana at concentration 1x 107 spore/ml produced mortality on adults 82.76% and for fourth and second instar of nymphs 82.76 and 93.10% after 7 days’ post treatment, respectively. When S. longipalpa was exposed to bait with B. bassiana the mortality percentage was 37.93% for the adults, and caused 64.29 and 58.62% mortality to the second and fourth instar of nymphs, after 7 days from treatment, respectively. Nymphs and adults of S. longipalpa treated by direct contact with B. bassiana at 1x 108 spore/ml, produced mortality on adults, fourth and second instar of nymphs 78.57, 93.10 and100% after 7 days’ post treatment, respectively. Method of bait the mortality for adults, fourth and second instar of nymphs were 51.72, 72.41 and 78.57% after 7 days’ post treatment, respectively. Results showed differences in susceptibility between nymphs and adults of S. longipalpa. Adult and nymph instars (fourth and second) mortalities due to direct contact by B. bassiana suspension (1x 107 and 1x 108 spore/ml) produce high mortalities (53.51, 93.10, 82.76% and 78.57, 100, 93.10%) respectively.

Acaricidal activity and sublethal effects of the microbial pesticide spinosad on Tetranychus urticae (Acari: Tetranychidae)

Laboratory bioassays were conducted to evaluate the toxicity of the microbial pesticide spinosad to different life stages of the two-spotted spider mite, Tetranychus urticae Koch, as well as its sublethal effects on reproduction and population growth of this important mite pest. The biopesticide was applied to bean primary leaves or leaf discs carrying spider mites using a Potter spray tower (2.7 mg/cm2 aqueous deposit). The following LC50 and LC90 (mg/L) estimates for motile stages were obtained in acute toxicity bioassays: 27.52 and 116.72 (larvae), 36.55 and 136.20 (protonymphs), 82.76 and 721.28 (female deutonymphs), and 61.47 and 457.21 (adult females). Spinosad showed no significant ovicidal action: toxic effect observed after spraying eggs (LC50 = 105.78 mg/L, LC90 = 596.95 mg/L) was the result of its residual action on larvae that hatched from the treated eggs. The effects of spinosad on life history traits and population growth of adult female survivors from treatments with 240, 120 and 60 mg/L were evaluated in two successive 7-day bioassays on untreated leaf discs. In the first bioassay, females that survived treatments as 24 h old eggs and completed their juvenile development on treated leaves had significantly lower gross fecundity, net fecundity and instantaneous rate of increase (ri) but the reduction was merely 4–6%, 9–11%, and 2–3%, respectively. Female longevity was significantly reduced (approximately by half a day) only after treatment with 240 mg/L. In the second bioassay, in which females were treated during their pre-ovipositional period, the treatments with 240 and 120 mg/L significantly reduced their gross fecundity (16–17%), net fecundity (28–31%), ri values (8–9%) and female longevity (approximately by one day). Spinosad effects on the intrinsic rate of increase (rm) and other demographic parameters were evaluated in two successive bioassays in which life tables were constructed for females that survived treatment with 120 mg/L at the egg stage (first demographic bioassay) or pre-ovipositional period (second demographic bioassay). In the first bioassay, the intrinsic rate of increase was significantly higher in treated (rm = 0.278) than control mites (rm = 0.267) as a result of higher net fertility at the beginning of reproduction of treated females. In the second bioassay, treated females had significantly lower rm than control females (0.254 and 0.283, respectively). The results obtained in this study indicate that spinosad, applied against insect pests (at field relevant rates of 60–240 mg/L), could eliminate a part of T. urticae population as well, but survivors would retain a significant potential for population recovery.