Conidia Of Metarhizium Flavoviride Research Articles

Fluctuating Temperature and the Longevity of Conidia of Metarhizium flavoviride in Storage

Conidia of Metarhizium flavoviride were hermetically stored at 13.7% moisture content with four constant (20, 30, 40 and 50 C) and six fluctuating temperature regimes (20:30, 20:40, 20:50, 30:40, 30:50 and 40 C:50 C, all 24 h:24 h) for up to 119 days. Survival of conidia stored at both constant and fluctuating temperatures conformed to cumulative negative normal distributions and all 10 survival curves could be constrained to a common origin. The effect of constant storage temperature on conidia longevity was quantified satisfactorily by a negative curvilinear semi-logarithmic relation developed previously, in which the estimates of the constants CH and CQ were 0.0176 (SE 0.0013) and 0.000703 (SE 0.000019), respectively. The fitted relation at constant temperatures showed that Q10 for loss in conidia viability increased the warmer the temperature regime. The effect of the cooler temperature of each fluctuating temperature regime on conidia longevity was small, since the effective temperature of each regime for loss in conidia viability was always much warmer than the mean. Conidia were also stored in two further regimes: at 30 C for 21 or 35 days before transfer to 50 C. The standard deviations of the conidia survival curves at 50 C were unaffected by the duration of previous storage at 30 C. Thus change in temperature per se had no effect on conidia survival: conidia survival curve slopes were solely dependent upon the contemporary storage environment. Approaches are developed in order to predict loss of conidia viability in fluctuating temperature storage environments, and the predictions compared against independent observations.

Effects of the Sunscreen Oxybenzone on Field Efficacy and Persistence of Metarhizium flavoviride Conidia Against Kraussella amabile (Orthoptera: Acrididae) in Mali, West Africa

A field trial was performed at Mourdiah, northwest Mali, to evaluate whether the performance of Metarhizium flavoviride conidia would improve if 2% oxybenzone, an oil-soluble ultraviolet light protectant, was used. Conidia were applied in an ultra-low volume formulation against nymphs of the grasshopper Kraussella amabile . Mortality was assessed by collecting grasshoppers directly from field plots (sweep net samples) or by exposing untreated nymphs to sprayed vegetation for 48 h (field cage samples). For sweep net samples, the mortalities in M. flavoviride treatments varied between 94.5 and 99.9% up to 7 days after treatment, while control mortalities were significantly lower (20.7-55.0%). There were no significant differences between M. flavoviride treatments with or without oxybenzone. The average survival times were found to be significantly lower for fungal treatments (4.9 days) compared with the control treatment (11.8 days). W ith field cage samples, the mortality in M. flavoviride treatments declined from > 95.0% for nymphs exposed just after application to < 30.0% for nymphs exposed to treated vegetation on the 10th day after application. The control mortalities varied between 5.1 and 37.2%, and were significantly lower than fungal treatments for samples placed just after application and 10 days after application. The overall average survival times were 10.9 and 10.7 days for M. flavoviride with and without oxybenzone respectively, and 13.9 days with the control treatment. An exponential regression was fitted using cage mortality data which indicated that the half-life for conidial infectivity was 4.3 days on treated vegetation.

Limits to the Negative Logarithmic Relationship Between Moisture Content and Longevity in Conidia ofMetarhizium flavoviride

Conidia ofMetarhizium flavoviridewere hermetically stored at 50 °C and 14 moisture contents between 2.5 and 31.8% (fresh weight basis) for up to 146 d, and tested for germination on Sabouraud Dextrose Agar at 25 °C for 24 h. Survival of conidia conformed to cumulative negative normal distributions and all 14 survival curves could be constrained to a common origin. There was a negative logarithmic relation between longevity and conidia moisture content, but limits to the relation were detected: the lower-moisture-content limit was 4.6% [in equilibrium with 10.7% relative humidity (RH) at 20 °C], below which value further reduction in moisture content did not increase conidia longevity; and an upper-moisture-content limit between about 21.2 and 31.8% moisture content (between 77 and 90.0% equilibrium RH at 20 °C) above which conidia longevity no longer decreased. The observations could also be described by a negative semi-logarithmic relation between conidia longevity and equilibrium relative humidity. In this model, each reduction in equilibrium relative humidity by 11.2% within the range 10.7 to 80% RH doubled conidia longevity. The similarities in these relations, and the limits to these relations, between the conidia of this entomopathogenic fungus and the orthodox seeds of higher plants are discussed.

Viability of Stored Conidia of Metarhizium flavoviride Gams and Rozsypal, Produced under Differing Culture Regimes and Stored with Clays

Conidia of Metarhizium flavoviride were cultured under a range of conditions and stored , with or without clays and silica gel , as powder or in oil . Fungal biomass was produced in shake flasks in liquid media containing nutrients before being added to sterilized rice for conidial production . Conidia pre - cultured under a low C:N ratio , or dried over a 9 - day period compared with 2 days before being placed in storage , showed greatest loss of viability . Conidia stored at 10 o C survived better than those stored at + 30 o C . A range of clays had no significant effect on storage of dried conidia but montmorillonite K10 clay was often harmful in terms of conidial viability . Conidia survived better when stored as dry powder than when stored in a mixture of mineral and vegetable oils . The addition of silica gel proved beneficial even when dried conidia were being stored .

Effect of Formulation and Application Method on the Efficacy of Aerial and Submerged Conidia of Metarhizium flavoviride for Locust and Grasshopper Control

Effect of Formulation and Application Method on the Efficacy of Aerial and Submerged Conidia of Metarhizium flavoviride for Locust and Grasshopper Control

Effect of Formulation and Application Method on the Efficacy of Aerial and Submerged Conidia ofMetarhizium flavoviridefor Locust and Grasshopper Control

A study was carried out to investigate the relative infectivity of aerial and submerged conidia of Metarhizium flavoviride to Schistocerca gregaria and Zonocerus variegatus. The effect of formulation and application method on initial infectivity and field persistence of these conidia was investigated. Strain IMI 330189 was highly virulent to S. gregaria but showed relatively low virulence to Z. variegatus. Direct contact with conidia from the initial spray application resulted in 100% mortality of S. gregaria for all formulation and application combinations. The mean survival time of infected locusts was significantly shorter for treatments using a knapsack sprayer containing submerged conidia in water plus 10 ml litre−1 ‘Codacide’™ (seven days), than treatments with aerial conidia in oil using ULV techniques (8.9 days) or submerged conidia in modified (water plus adjuvants) ULV (MULV) (nine days) or in water-based (VLV) applications (9·3 days). Both aerial and submerged conidia persisted long enough in the environment to effect significant mortality via secondary pick-up of spray residue from vegeta-tion. Persistence was greatest in the ULV and MULV treatments, where the oil component of the formulations provided greater protection of the conidia from environmental stresses. The consequences of secondary pick-up of conidia from the different treatments on total mortality from a single application were examined using a simple host–pathogen model. This predicted that the ULV treatment would be much more effective than the other treatments under conditions where direct contact with the spray was limited. The results of these investigations are discussed in the context of development of optimum spray strategies for control of locusts and grasshoppers, and other pests, under different environmental conditions.

Control of Zonocerus variegatus by Ultra-low Volume Application of an Oil Formulation of Metarhizium flavoviride Conidia

An oil-based formulation of Metarhizium flavoviride conidia, applied at 2 1012 spores ha-1 in 1 l ha-1 gave good control of Zonocerus variegatus in 1-ha plots in southern Benin. In a three-replicate, randomized, complete block (RCB) trial in Mono province, a significant reduction in insect counts between treated and control plots was observed 10-15 days after application; treatment reduced the population by about 90%. A four-replicate RCB trial in Oue me province also gave high mortality. Although a significant difference between treated and untreated plots was observed 10-18 days after application, insect dispersal out of cassava fields towards oviposition sites interfered with a clear demonstration of control. Significantly more Z. variegatus cadavers with M. flavoviride infection were found in treated plots than control plots.

The Effect of Different Temperatures on the Viability of Metarhizium flavoviride Conidia Stored in Vegetable and Mineral Oils

The viability of freshly harvested conidia of Metarhizium flavoviride (Gams & Rozypal) stored in mineral, vegetable, or animal oils at 25°C was assessed over a period of 4 months. Viability was reduced to below 40% in all but two oils after 4 weeks storage; kerosene, soyabean (Sigma), and peanut were the only oils with a conidial viability of over 30% after 6 weeks storage. In a second experiment, storage at 5 and 15°C resulted in enhanced conidial viability of up to 71.9% with kerosene and 92.1% with soyabean after 14 weeks storage.