Steinernema diaprepesi (Nguyen and Duncan, 2002) AM
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publication ID |
https://doi.org/ 10.3906/zoo-2104-53 |
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persistent identifier |
https://treatment.plazi.org/id/EA083A12-FFAF-FFA5-FD53-FF12FE8F6B11 |
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treatment provided by |
Felipe |
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scientific name |
Steinernema diaprepesi |
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2.7. Virulence of Steinernema diaprepesi View in CoL to Euschistus heros on two substrates with two-layer thicknesses
This study assessed the virulence of Steinernema diaprepesi AM 163 to E. heros adults on two substrates with two-layer thicknesses, aiming its control on the bared ground or on the crop remains/straw left on the ground after the crop harvesting. The study consisted of four treatments: A) 200g of sand - 1 cm layer thickness, B) 1000g of sand - 5 cm layer thickness, C) 4g of straw - 1 cm layer thickness, D) 20g of straw - 5 cm layer thickness; each treatment had its respective control. The choice of sand and straw in two-layer thicknesses aimed to find out if the nematode would go deeper in greater layer thickness, resulting in lower rate on the surface of the substrate and, consequently, in lower levels of insect mortality.
The nematode S. diaprepesi was applied with a pipette, generating a rate of 88.4 IJs/cm² (1000 IJs/insect), which provided the highest insect mortality level (74.6%), with the highest reproduction rate of the nematode per insect (5400 IJs), in the previous experiment. Each treatment had three replications, each of which represented by a 1.5 L plastic pot (12.5 cm Ø) containing the substrate, two bean pods, plus ten adult insects. The sand was previously moistened to 14% humidity, while the straw remained submerged in water for 24 h, before the water was drained and the moistened straw was transferred to the pots. Each treatment had its respective control with the application of only water.
The insects were released into the pots 24 h after the application of the nematode, in order to allow a previous distribution of the IJs in the substrates. The pots were sealed with sheer fabric and elastic bands, and incubated at 25 °C, RH 60 ± 5% and 12-h photoperiod. Evaluation was carried out seven days after the insects’ release, based on their mortality. The dead insects were transferred to White traps to confirm the infection by the nematodes. The experiment was conducted twice in time.
2.8. Comparative susceptibility of Dichelops melacanthus and Euschistus heros to the nematode Steinernema diaprepesi
This study compared two species of stink bugs adults, E. heros and D. melacanthus , in respect to their susceptibility to the nematode S. diaprepesi AM 163. Thus, the treatments consisted of the two insect species treated with the nematode and the two controls represented by the two insects treated with water. Each treatment had three replications; each replication represented by a 1.5 L plastic pot (12.5 cm Ø) containing 200 g of sand (14% humidity) (1 cm layer thickness) covered with 4 g of pre-moistened straw (soaked in water for 24 h before drainage) (1 cm layer thickness), two bean pods and 10 insect adults. The use of this double layer straw-over-sand substrate aimed to simulate the natural conditions in the field, since sand and straw allowed similar performance of S. diaprepesi against E. heros in the previous experiment.
Steinernema diaprepesi was applied with a pipette, generating a rate of 88.4 IJs/cm² (1000 IJs/insect), which provided the highest insect mortality level (74.6%), with the highest reproduction rate of the nematode per insect (5400 IJs) in the previous experiment. The pots were sealed with sheer fabric and elastic band, and incubated at 25 °C, RH 60 ± 5% and 12-h photoperiod. Evaluation was carried out seven days after inoculation, based on insect mortality. The experiment was conducted twice in time.
2.9. Comparative virulence of Steinernema diaprepesi and Steinernema carpocapsae to Dichelops melacanthus
This study compared the nematodes S. diaprepesi AM 163 and S. carpocapsae ( Weiser, 1955) IP 1 in respect to their virulence to the bug D. melacanthus , which showed greater resistance to S. diaprepesi when compared to the bug E. heros . These two nematodes were selected because they caused 100% mortality of E.heros in the first test and because they have different foraging behaviors. While S. diaprepesi displays a “cruise” behavior ( Del Valle et al., 2014), seeking its target insects, the nematode S. carpocapsae displays an “ambush” behavior (Koppenhöfer and Kaya, 1996), staying in lurk waiting for the host to approach.
The study consisted of three treatments represented by the insect treated with the two nematodes and the control (insects treated with water). Each treatment had three replications, each of which represented by a 1.5 L plastic pot (12.5 cm Ø) containing 200 g of sand (14% humidity) covered with 4 g of pre-moistened straw (soaked in water for 24 h before drainage), two bean pods and 10 adult insects.
The two nematodes were applied with a pipette, generating the rate of 88.4 IJs/cm² (1000 IJs/insect), which provided the highest insect mortality level (74.6%), with the highest reproduction rate of the nematode per insect (5400 IJs), in the previous experiment. The pots were sealed with sheer fabric and elastic band and incubated at 25 °C, RH 60 ± 5% and 12-h photoperiod. Evaluation was carried out 7 days after inoculation, based on the insect mortality. The experiment was conducted twice in time.
2.10. Efficacy of Steinernema diaprepesi to reduce Euschistus heros population in greenhouse
The study assessed S. diaprepesi AM 163 in respect to its efficacy to reduce E. heros population under greenhouse conditions, expecting to predict its efficacy in the field since both greenhouse and field have similar conditions. Thus, the study consisted of only two treatments: application of the nematode and control.
Each treatment had four replications distributed randomly in blocks, each consisting of a cement box (63 x 83 x 53 cm) filled with soil, containing two plots (treatments). Each replication was represented by a PVC tube (25 cm in diameter × 21 cm in height), deepened 2 cm in the soil of the box, containing 8g of pre-moistened straw (24 h soaked in water before drainage) covering the soil (pre-moistened with 12 L of water/cement box), two bean pods and 10 adult insects. The nematode S. diaprepesi was applied over the straw inside the tubes with a Becker, generating a rate of 88.4 IJs/cm² (4332 IJs/insect), which provided the highest insect mortality level (74.6%), with the highest reproduction rate of the nematode per insect (5400 IJs), in the previous experiment. For the control tubes, only water was applied.
The experiment was irrigated daily by micro sprinklers. During the experiment, the temperature ranged between 18 to 25 °C, and evaluation was carried out seven days after the release of the insects into the tubes, based on insect mortality. The dead insects were transferred to White traps in order to confirm the infection by the nematode. The experiment was conducted twice in time.
2.11. Statistical analysis
The laboratory experiments were carried out in a completely randomized design, while the greenhouse experiment was carried out in random blocks. For all tests, except for the “virulence of EPNs”, “virulence of bacteria”
and “efficacy of S. diaprepesi ”, the data were corrected using the Abbott formula ([survivors in the control - survivors in the treatment] / survivors in the control) × 100) (Abbott, 1925) considering the insect mortalities in the respective controls. Then, the corrected data were subjected to normality tests, while the homogeneity of variances were subjected to Shapiro–Wilk and Barlett tests. For the tests that followed the assumptions, Student’s t test was performed when there were only two variables, while analysis of variance (ANOVA) was performed when there were more than two variables. Subsequently, the Tukey 5% test was performed.
For the experiment with “ S. diaprepesi at different rates against E. heros ”, data were corrected by Abbott formula and analyzed by logarithm regression between nematode rates and insect mortalities. To analyze the number of IJs generated per insect, generalized linear model (GLM) was used with Quasipoisson distribution and “log” connection. Subsequently, analysis of variance was performed, followed by comparisons of means using Tukey test at 5%.
All percentage data (frequencies) were transformed into arcsine √x / 100 before analysis ( Southwood, 1978). Analyzes were performed using the software SPSS 16.0 (SPSSInc., Chicago, IL, USA) as well as the R 3.6 (R Core Team 2019), through the packages lme4 ( Bates et al., 2015), emmeans ( Searle et al., 1980), drc ( Ritz et al., 2015) and hnp ( Moral et al., 2017).
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