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Introduction
Belonging to the Poaceae family, sugarcane Saccharum officinarum L. is one of the main crops in Mexico, which generates an important source of jobs and dividends. Of the 849 873 ha established, 53 841 556 t are produced, with a national annual average yield level at 69.48 t·ha-1. Of the 16 cane-producing states, Nayarit ranks 8th nationally in terms of planted area and production (SIAP, 2020). In Mexico, the “white grubs” of the genus Phyllophaga (Coleoptera: Melolonthidae) are important soil pests of a wide variety of crops, such as corn (Hernández-Velázquez et al., 2010) and sugarcane (Cortez-Isiordia et al., 2017). This insect, by feeding on the cane roots, interrupts the normal absorption of water and nutrients of the plant, directly affecting its quality and yield, in addition to reducing the anchorage of the sugarcane strain, causing detachment progressively and a decrease in its longevity period (Calvo et al., 2016). The white grubs complex encompasses a great diversity of pest species with rhizophagous habits, which are mainly concentrated in the genera Phyllophaga, Cyclocephala and Paranomala (Morón et al., 1997). This complex is frequently found on land expanded by monoculture, where aggressive tillage methods and stubble burning during harvest limits the availability of organic matter as a food source, forcing the insect to consume crop roots (Castro-Ramírez et al., 2004). An example of this phenomenon is represented by Triodonyx lalanza Saylor a specie distributed in the northwestern and northeast areas of Mexico, in the states of Jalisco, Nayarit, Sinaloa, Sonora and part of Durango (Warner & Morón, 1992). It is worth mentioning that this taxon has not been related to significant damage to agricultural crops; however, in Nayarit for the harvests of 1993 and 1994, severe infestations of this species were recorded in more than 1 000 ha of sugarcane in the supply area of Ingenio Puga S.A. de C.V. in the municipality of Tepic, where it caused between 70 and 80 % of damage to the crops. These damages generated losses that were close to 14 900 t, even when large amounts of granular insecticides such as Terbufos, Chlorpyrifos and Diazinon were applied for control (Morón et al., 2010). In a more recent study by Cortez-Isiordia et al. (2017), it was reported that T. lalanza is still the predominant species in the sugarcane zone of central Nayarit. The foregoing shows the importance that these white grubs represent, as it becomes a potentially important pest for the other states where it is distributed. The use of chemical active ingredients as a main tool to combat white grubs in Mexico has been ineffective, and they also harm the beneficial fauna of the soil, leading to an ecological imbalance between the natural enemies of the soil, and an ecological imbalance between the natural enemies of this pest, without discarding the pollution it generates to the environment (Rodríguez-del Bosque & Morón, 2010). Therefore, it is necessary to resort to other management alternatives with less environmental impact; our internal ecologically safe strategy, has a great potential for the control of white grubs with entomopathogenic fungi (Deuteromycota: Ophiocordycipitaceae). This is based on the report of the isolation of numerous strains that naturally infect this insect (Hernández-Velázquez et al., 2010), and the obtaining of significant mortality rates of white grubs (50 to 96 %), in the evaluation of Metarhizium anisopliae (Metschnikoff) Sorokin and Beauveria bassiana (Bals.-Criv.) Vuill. strains, under laboratory conditions (Rodríguez-del Bosque et al., 2005; Guzmán-Franco et al., 2012; Carrillo-Benítez et al., 2013; Solís-Pérez et al., 2016). Secondly, few evaluations have been done on the effectiveness of these microbial agents against white grubs, under semi-controlled and field conditions; although it is true that some strains have shown promising levels of mortality in laboratory tests, under these conditions, there is absolute control of factors such as temperature, relative humidity, radiation, etc. that can disguise the real effect of a strain when comparing their efficacy in the field. Even more so, due to the complications represented by the control of underground pests, and in the particular case of white grubs, where these show great mobility in the soil when it perceives the effect of active insecticides (Morón et al., 2010). Therefore, it is necessary to increase studies on the real effectiveness of entomopathogenic fungi under less controlled conditions, which are similar to environmental conditions under which microorganisms will carry out their insecticidal activity after application, such as formulations as a part of an integrated pest management program. This will improve the correct effective field application formulations and the obtainment of efficient pest control. The objective of this study was to evaluate the biological efficacy of a native strain (MGCPh4) of M. pingshaense in contrast to the commercial strain Fungizium( of M.anisopliae, and with a granulated chemical insecticide (Allectus(-GR) against T. lalanza Saylor larvae in pots with sugarcane, under semi-controlled conditions.
Material and Methods
Establishing the experimental plot
The study was realized in pots with sugarcane established outdoors. Stems of approximately 15 cm and containing healthy buds of the variety (MEX-80-1410) were planted. These were previously subjected to a disinfection process in a suspension of sodium hypochlorite (NaClO) at 1 % for 10 min and sterile distilled water. The stems were planted individually in black polyethylene bags, 24 cm long by 26 cm in diameter, containing 10 kg of sandy loam soil previously sterilized in an autoclave at 121°C and 1.2 bar of pressure, for 2 hours and 10 days in advance. The bags were perforated to favor the drainage and the humidity of the pots, and they were maintained with the addition of water every third day, holding a pH of 7.0 and a hardness of 100 ppm of total dissolved solids (TDS) of calcium carbonates (CaCO3). For the measurement of pH, a Ketotek( potentiometer was used and for the measurement of TDS, a Runjie( conductivity meter was used.
Obtaining Triodonyx lalanza larvae
Third-instar larvae of T. lalanza were obtained from an infested sugarcane plot. The collection of larvae was carried out from the samples of 0.25 m2 in the root zone of the cane; the specimens obtained were placed individually in transparent polyethylene bags 8 cm wide by 25 cm long, with approximately 20 g of soil from the collection site to avoid dehydration during transfer to the laboratory. During processing, the larvae were deposited individually in transparent plastic cups with a capacity of 200 mL, containing approximately 150 g of soil previously sterilized in an autoclave 10 days before. The determination of the species of white grubs was carried out based on the description of Morón et al. (1999). For the feeding of the larvae, 10 g of carrot in small slices were added, properly sterilized in a suspension of NaClO at 1 % and sterile distilled water to eliminate the excess of this solution. The soil was moistened with approximately 25 mL of distilled water for each cup, with the help of a plastic manual sprinkler for domestic use with a capacity of 1 000 mL. Subsequently, the larvae underwent a “quarantine” process at a temperature of 28(2°C for 60 days, with observations made every seven days, to discard dead larvae or those infected by entomopathogenic agents, replace the carrot slices and maintain soil moisture. The larvae that were healthy after this incubation period were used for the study.
Treatments evaluated and quality determination
Four treatments consisted of two biological insecticides (the MGCPh4 isolate, and the commercial insecticide Fungizium() a granulated chemical insecticide and a control treatment with plants infested with white grubs, without application of insecticide. The MGCPh4 isolate corresponds to a native strain molecularly identified by sequencing the EF-1( gene as M. pingshaense (Chen and Guo) (GenBank access code OK626215.1) obtained from a Phyllophaga sp. in sugarcane. This strain showed greater virulence on third-instar larvae of T. lalanza, in a previous pathogenicity bioassay, under laboratory conditions (data submitted). The commercial biological insecticide Fungizium( corresponds to a strain of M. anisopliae of an unknown host, with an emulsifiable concentrated formulation, at a concentration of 1x1011 conidia·L-1 of the commercial product. The chemical insecticide corresponded to Allectus(-GR, a granular formulation of neonicotinoid pyrethroid (i.a. bifenthrin + imidacloprid) from the FMS Agrochemical of Mexico. The M. pingshaense strain was reproduced in rice as a substrate, based on the methodology proposed by Monzón (2001). A quality test was performed on each Metarhizium strain, consisting of the concentration and viability of conidia, with the technique proposed by Vélez et al. (1997).
Infestation of white grubs and application of treatments
Ninety days after planting the cane, the infestation was carried out, adding 10 healthy third-instar larvae of T. lalanza per pot. Larvae that showed little vigor and did not burrow into the soil were replaced by more vigorous and active ones. Seven days after the infestation, the insecticides were applied. The two strains of Metarhizium were applied at a dose of 1x105 conidia·cm2, while the chemical insecticide was applied at a dose of 30 kg·ha-1. The amount applied per treatment was calculated based on its concentration i.a./kg, as in the case of the native strain of M. pingshaense and the granulated chemical insecticide, and i.a./L, in the case of the liquid insecticide Fungizium®, and based on to the planting density and population of sugarcane on average (Table 1). The weight of the portions to be applied for the native strain and the granulated chemical insecticide was carried out on an analytical balance and placed in 8x15 cm polyethylene bags for transfer and application in the experimental plot. Both the native strain and the granulated chemical insecticide were applied near the root zone of the cane, while the liquid insecticide was applied by “drench” route with a manual sprayer, where 60 mL of fungus suspension was added per pot. To maintain soil moisture, approximately 2 L of water per pot was added every third day, with a pH of 7.0 and 100 ppm of TDS.
Experimental design and evaluation of larval mortality
A completely randomized experimental design was considered with 10 larvae per pot or experimental unit, with 10 repetitions for a total of 100 larvae per treatment. The control treatment without the application of insecticides was infested with the same number of larvae per pot, with 10 repetitions for a total of 100 larvae included.
The percentage of mortality was evaluated every 10 days after the application of the insecticides, for 60 days, which was determined by the following formula proposed by Barrera et al. (2013).
Where,
% M= Percentage of mortality of larvae per treatment
NDFILE= Number of dead or fungus-infected larvae at the end of the study
NLLBS= Number of larvae living at the beginning of the study
Table 1 Treatments used in the evaluation of mortality of third instar larvae of Triodonyx lalanza in sugarcane pots.
| Treatment | Active ingredient | Formulation | Dose per hectare | Concentration (i.a./kg inert solid) | Amount applied* |
|---|---|---|---|---|---|
| Strain MGCPh4 | M. pingshaense | Rise granules | 82 kg (1x1013 conidia) | 1.22x1011 c.kg of rice | 2.05 g/pot |
| Allectus®-GR | Bifenthrin + Imidacloprid | Granulated | 30 kg of product | Bifenthrin (3g/kg product) Imidacloprid (4g/kg product) | 0.75 g/pot |
| Fungizium® | M. anisopliae | Emulsifiable concentrate | 1x1013 conidia | 1.06x1011c.L of product | 2.5 mL/pot |
| Witness | No app | No app |
c.kg (conidia.kg), c.L (conidia.L). *For the maximum recommended dose per hectare. The calculation was based on an average of 40 000 plants/ha of sugarcane. The amount of fungus applied by each strain was determined based on its yield of conidia.g rice and conidia.mL.
During the larval mortality evaluation process, the soil was carefully removed from the pots to be deposited in plastic trays to inspect the amount of dead and/or mycosed larvae. The mortality criterion consisted in the application of the physical stimulus on the ventral surface of the thorax, those larvae with no movement were considered dead (Sotelo-Galindo et al., 2008), while those that presented a rigid appearance with pale white coloration (Valencia-Cortés et al., 2011), were considered infected by the pathogenic agent. To confirm the death of the larvae by the fungus, they were individually confined in plastic cups of 200 mL capacity with approximately 150 g of moistened soil, and properly sterilized seven days before. Subsequently, they are incubated in a room in total darkness to promote the sporulation of the fungus on the insect’s corpse.
A test of normality and homogeneity of variances was carried out for the mortality data obtained with the Kolmogorov-Smirnov and Bartlett tests, respectively. In addition, a correction of mortality efficiency was made, with respect to the larvae killed in the treatment of seedlings without insecticide using the Schneider-Orelli formula (Puntener, 1981):
Where,
% MC = Percentage of corrected mortality of larvae per treatment
% MEU = Percentage of mortality in the experimental unit
% MECU = Percentage of mortality in the experimental control unit
Statistical analysis was performed for the percentage variable of dead larvae in the program SAS (2002), where a variance analysis (ANOVA) and a comparison of means were performed using the Tukey test (HSD) (0.05), both for normal and corrected mortality data.
Results
The quality test carried out for both biological treatments showed that the MGCPh4 strain presented a concentration of 1.22 x 106 conidia·g-1, and a germination percentage of 100 % at 48 h after sowing in SDA medium (Sabouraud Dextrose Agar). For its part, the Fungizium® strain showed a concentration of 1.06 x 108 conidia·mL-1, and a germination percentage of 98 %.
Regarding the bioassay in pots, all the treatments evaluated caused larval mortality between 15 and 33 %, at 60 days of evaluation. The first mortality rates among the three insecticides were obtained 20 days after inoculation, with 3 and 5 %, and the highest rate of effectiveness occurred at 30 and 40 days, for which the percentage of mortality for each insecticide evaluated behaved as follows; Allectus(-GR showed the highest percentages, 12 and 11 %, followed by the native strain MGCPh4 with 9 and 7 %, and finally the commercial strain Fungizium( with 6 and 3 %, at 30 and 40 days of evaluation, respectively. After 40 days, mortality levels gradually decreased until reaching 0 % at 60 days after application. In the control treatment, a 4 % of mortality was registered 10 days after the start of the experiment, with a maximum accumulated mortality of 11 % at 30 days of evaluation, remaining unchanged until 60 days of evaluation; highlighting that the larvae mortality for this treatment was due to natural and management causes, totally unrelated to fungal and/or chemical infection. In any case, the level of mortality obtained in this treatment is within the permissible limits of mortality for the treatments considered as control (not greater than 20 %) (Sazo et al., 2006; O’Callaghan et al., 2012).
The normality test for the data of the percentage of dead larvae indicated that they followed a normal distribution) (p = 0.056, Kolmogorov-Smirnov), as well as a homogeneity of variances between treatments (p = 0.00958, Bartlett). Regarding the corrected mortality data, the statistical analysis showed a normal distribution (p = 0.117, Kolmogorov-Smirnov), as well as a homogeneity of variances between treatments (p = 0.2429, Bartlett). The analysis of comparison of means of the normal mortality data, for the variable percentage of dead larvae, showed significant differences (F(3,36) = 8.55, p = 0.0002), highlighting the Allectus®-GR treatment with the highest mortality rate (33 %), compared to the rest of the treatments, followed by the native strain MGCPh4 with 22 % mortality. Regarding the analysis of means comparison of data for corrected mortality, it showed significant differences (F(3,36) = 3.59, p = 0.0228) highlighting the Allectus®-GR treatment with the highest corrected mortality rate (23.14), followed by the native strain MGCPh4 with 13.07 % (Table 2).
Table 2 Percentage of mortality of third instar larvae of Triodonyx lalanza by treatments in sugarcane pots.
| Treatment | Percentaje of death larvae/days after inoculation | % Total | Mean (±SD) | % Mc | Mean (±SD) | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| 10 | 20 | 30 | 40 | 50 | 60 | |||||
| MGCPh4 | 0 | 3 | 9 | 7 | 3 | 0 | 22 | 2.20 (±1.13)ab | 13.07 | 1.30 (±1.16)ab |
| Fungizium® | 0 | 4 | 6 | 3 | 2 | 0 | 15 | 1.50 (±1.50)b | 7.01 | 0.70 (±0.67)b |
| Allectus®-GR | 0 | 5 | 12 | 11 | 5 | 0 | 33 | 3.30 (±1.05)a | 23.14 | 2.31 (±1.33)a |
| Withness | 4 | 5 | 2 | 0 | 0 | 0 | 11 | 1.10 (±1.28)b | 11 | 1.10 (±1.28)ab |
% Mc = Percentage of corrected mortality. Means with the same literal are not significantly different according to the Tukey (HSD) test (α 0.05). SD= Standar deviation.
Discussion
The mortality percentages of larvae obtained, in relation to the virulence of the biological insecticides used in this study, were similar to those reported by Nájera-Rincón (2010) who, when evaluating the effectiveness of B. bassiana strains applied to rice in maize experimental plots, obtained between 16 and 18 % mortality of third instar larvae of Phyllophaga vetula Horn, at 40 days of evaluation. On their part, Castro-Ramírez & Ramírez-Salinas (2010), when evaluating the effectiveness of two strains of B. bassiana applied to rice in corn pots, they obtained 28 % mortality of third-instar larvae of three species of Phyllophaga; Phyllophaga ravida (Blanchard), Phyllophaga obsoleta (Blanchard) and Phyllophaga tumulosa (Bates), at 40 days of evaluation. However, Ruíz-Vega et al. (2012), when evaluating a strain of M. anisopliae applied to rice in corn pots, obtained a 62.5 % mortality of third instar larvae of P. vetula, 53 days after inoculation, and up to 87.5 % mortality, through the combined action of the Metarhizium strain, with the entomopathogenic nematode Hetrorhabiditis bacteriophora Poinar at 20 days of evaluation. On the other hand, Bayardo-Platas (2004) when evaluating the virulence of the commercial strains Fitosan-M( (M. anisopliae) and Sehu-Biocop Bb( (B. bassiana), against third instar larvae of Phyllophaga in experimental plots of Christmas trees of the genus Pseudotsuga, it was observed that the fungus M. anisopliae showed a greater effect than the fungus B. bassiana, by maintaining an average density of 8.3 live larvae/soil sample, less than the control, in the M. anisopliae treatment, and an average density of 13.6 live larvae/soil sample, less than the control, in the treatment with B. bassiana, at 56 days of evaluation. Likewise, he pointed out that the highest rates of effectiveness were obtained within 21 and 42 days, in both treatments.
Meanwhile, when contrasting the mortality results obtained in this study by the chemical insecticide Allectus(-GR, Morón et al. (2010) mentions that, through bioassays carried out by Hernández-Rodríguez & Ramírez-Campos (data not published) , which consisted of evaluating the effectiveness of five chemical insecticides; Terbufos, Chlorpyrifos, Carbofuran, Isazophos and Diazinon, for the control of third instar larvae of T. lalanza, under greenhouse, pot and field conditions, obtained somewhat contradictory results. In the test carried out in a greenhouse by applying high doses; 1 g of active compound of Terbufos, Carbofuran, Isazofos and Diazinon, for every 250 g of soil, obtained more than 70 % mortality of larvae, 12 days after application; however, in the test with Chlorpyrifos they obtained less than 60 %. Regarding the bioassay carried out in pots, through the application of large doses of insecticides, 4 to 15 g in buckets with 12 kg of soil, they observed that, after 13 days, Diazinon showed 0 % mortality, while tests with Carbofuran, Chlorpyrifos, Isazophos and Terbufos caused between 4 and 20 % mortality. However, in the evaluation carried out under field conditions, only Isazophos, applied at a dose of 25 kg·ha-1, caused more than 50 % mortality, within 20 and 30 days after application. On the other hand, Bayardo-Platas (2004), through the evaluation of three commercial insecticides: Brigadier( 20G (Bifenthrin), Furadan( 350L (Carbofuran) and Lucater( 5G (Terbufos), observed that all treatments were effective for the control of white grubs, maintaining lower average densities of larvae, in contrast to the control during the evaluation. These densities corresponded to 6.48, 5.01 and 7.43 live larvae/soil samples, for the Bifenthrin, Carbofuran and Terbufos compounds, respectively, at 56 days of evaluation, achieving their highest effectiveness rates at 21 and 35 days after their application. However, Ruíz-Vega et al. (2012) by evaluating the commercial chemical treatment Granudin( 4 % (Diazinon) applied at a dose of 25 kg·ha-1, obtained 100 % mortality of larvae, 20 days after application. Based on the above, it can be said that the difference between the low mortality obtained in this study and the high mortality rates reported by Morón et al. (2010) and Ruíz-Vega et al. (2012), could be due to various factors, such as the dose and amount of insecticide applied in each of the tests, the difference in the immune response of each white grub in relation to its weight and size, as well as the capacity of each larval species to evade the effect of the active ingredients. For example, the doses of active chemicals used in the bioassays reported by Morón et al. (2010), consisting of 4 to 5 g per pot, with 12 kg of soil, and up to 40 g/10 kg of soil, were much higher than the amount of chemical insecticide applied in this study (0.75 g per pot, with 10 kg of soil), equivalent to the dose of 30 kg·ha-1; on the other hand, the high mortality reported by Ruíz-Vega et al. (2012), rather than possibly being due to the greater degree of virulence on the part of its strain, or to the greater effectiveness on behalf of the chemical insecticide, the factor that may possibly be related is the degree of susceptibility and the capacity that each species of white grubs possesses to avoid the effect of the active ingredients, depending on its size and fresh weight. For example, in this case, the fully developed third-instar larvae of T. lalanza presents a large size (8 mm width of the cephalic capsule) and a fresh weight of up to 3.5 g, values that exceed up to four or five times more, the size of the main plague larvae of the Phyllophaga complex reported in Mexico (Morón et al, 2010), in which P. vetula is found, a species evaluated by Ruíz-Vega et al. (2012). Therefore, the large size of T. lalanza gives it the development of a much thicker and chitinized cuticle, which acts as an immune barrier to infection by the fungus, and less susceptibility to the insecticide (Lu & St Leger, 2016). In this regard, Morón et al. (2010) point out that, when the larvae of T. lalanza are affected by insecticides, they exhibit a great physiological reaction to discard part of the toxicant orally or rectally, and a great behavioral response to move away from the soil impregnated with poisons, since during the tests carried out by Hernández-Rodríguez and Ramírez-Campos (data not published), it was observed that, as part of the evasive reactions of the larvae of T. lalanza upon assimilating the dose of active chemicals, they became immobilized to vomit or defecate with great intensity the poison, to later resume its activity. Another of the evasive actions they observed was that the larvae, upon perceiving the poison, tried to go out of the soil, or else, they buried themselves deep in the pots. It is worth mentioning that this last behavior could be confirmed in this study since, during the mortality evaluation process, 40 days after the application of the three insecticides it was observed that many of the larvae were positioned at the bottom of the pot, in the lower part of the rhizosphere of sugarcane, while during the evaluation in the control treatment, this behavior did not occur. Considering the above, with respect to the immune capacity of each larval species based on their size and weight, the similarity and closeness of the mortality levels obtained by the biological strains in this study with the mortality exerted by the Beauveria strains, in the tests developed by Nájera-Rincón (2010), and Castro-Ramírez & Ramírez-Salinas (2010) result interesting. Since the size and weight of the third instar larval species of Phyllophaga that were used in these two tests is three times less than that of the third instar larvae of T. lalanza, why did these authors not obtain higher mortality indices? this may be due to a lower degree of virulence exerted by the Beauveria strains, compared to the Metarhizium strains, a phenomenon that has been demonstrated in several virulence bioassays against white grubs (Flores et al., 2002; Bayardo-Platas, 2004; Sotelo-Galindo et al., 2008; Solís-Pérez et al., 2016).
When contrasting the mortality rates of each of the treatments evaluated in this study, the highest percentage of mortality obtained by Allectus(-GR in comparison to the native strain of M. pingshaense and the commercial strain Fungizium(, are related to the advantage of its three mechanisms of action (by contact, ingestion and by systemic activity via xylem), in contrast to strains of entomopathogenic fungi, which can act only by contact. Another factor that may have influenced a greater effect of Allectus(-GR is its high degree of solubility, in agreement with Loera-Gallardo et al. (2010), that consider that among the main factors that affect the toxicity index of chemical insecticides is their degree of solubility, a property that influences directly in its distribution and mobility in the soil, and therefore in its level of effectiveness. On the other hand, the higher percentage of mortality caused by the native strain MGCPh4, compared to the commercial strain Fungizium(, may be due to the different degrees of virulence of each fungus, in relation to its pathogen-host specificity; that is, the MGCPh4 strain, when isolated from a Phyllophaga larva as original host, had a greater capacity to exert greater control over white grubs, compared to the Fungizium( strain, whose original host is unknown. In relation to this fact, Falconi et al. (2011) maintain that strains of entomopathogenic fungi tend to show a higher degree of virulence in individuals that corresponds to their original host, compared to strains isolated from other taxonomic groups. This same phenomenon was obtained by Flores et al. (2002) who, when evaluating the effectiveness of fungal strains against white grubs, observed that the isolates obtained from Phyllophaga larvae showed higher mortality rates in contrast with the strains that were isolated from hosts of the order Lepidoptera and Hemiptera. Based on the above, it can be said that, in some cases, not all commercial strains of entomopathogenic fungi exert a broad-spectrum control effect, so it must be considered that to use a commercial strain that guarantees efficient control over a pest, the species to be controlled must match with the taxonomic group of the original host of the commercial strain. In other words, and based on what was argued by Khan et al. (2012), a specific biological strain is needed to control each group of pest insects.
Conclusion
The Allectus®-GR chemical treatment statistically caused the highest mortality percentage of third instar larvae of T. lalanza, with 33 % and a corrected mortality of (23.14 %), followed by the native strain MGCPh4 of M. pingshaense, which recorded a percentage of larval mortality of 22 %, and a corrected mortality of 13.07 %. The results obtained in this study provide fundamental information on the important biocontrol capacity of larvae exerted by the native strain of M. pingshaense in contrast to a chemical insecticide; also, the development of this test under semi-controlled conditions allows us to know the real effectiveness of said strain, against the great displacement capacity that the third instar larvae of T. lalanza naturally exhibit, to evade the active compound of the fungus. However, this fact shows the ability of the M. pingshaense strain to repel white grubs from the root zone of the sugarcane plant.
