The Impact of Beauveria bassiana, Trichogramma, Bt Sprays, and Spinosad on the Lepiodpteran (Crambidae) Cereal Stalk Borer- The European Corn Borer (Ostrinia nubilalis)

The Impact of Beauveria bassiana, Trichogramma, Bt Sprays, and Spinosad on the Lepiodpteran (Crambidae) Cereal Stalk Borer- The European Corn Borer (Ostrinia nubilalis)

Summary

The results of this study indicated intensive infestation of stalks, lots of European corn borer larvae in the stalks, lots of tunnels, much infestation of cobs and a yield loss of corn in the control treatments. There was also a considerable infestation of the stalks by the European corn borer larvae, a good amount of larvae and a number of tunnels, and infested cobs which consequently affected the yield in the treatment with Trichogramma pretiosum. The explanation for this is that in the control treatments there was simply the lack of control of the European corn borer in those plots. Whenever there is infestation of pests and control measures are not implemented, the results will be destruction of the crops resulting in decreased yield of the same.

In the treatment 2 (with Trichogramma pretiosum), it could be that:
a) it is always difficult to contain the Trichogramma pretiosum in the same plots. They are flying insects and are prone to wander around or fly away to distant places;
b) There is a major limitation to the use of
Trichogramma pretiosum due to reduced efficacy under conditions of heavy rainfall, sunshine and high temperatures (J. Chihrane and G. Lauge, 1996). There was a week when the temperatures were over 90 0F during this research;
c) In addition to reducing the efficacy of parasitism by Trichogramma pretiosum, high temperatures cause male sterility and reductions in the rate of wasp emergence from the capsules.

The other treatments 3, 4, 5, 6, and 7 provided a considerable amount of control of the European corn borer in almost all parameters for both years and especially in the year 2007.

Throughout this research Spinosad has emerged as the most effective biological agent in the control of the European corn borer. Treatments 3 in all parameters have shown the efficacy of Spinosad in controlling the European corn borer larvae. The general trend so far has been that these biological agents have increased the mortality of the European corn borer larvae. The infections on corn have been very severe in all the control treatments while the different treatments have imposed various degrees of restraints on the European corn borer population. In all the parameters there has been a significant difference between the control and other treatments with a P value of <0.001.

While the tradition control methods of using insecticides are sometimes environmentally hazardous, and fail to control the European corn borer larvae when the larvae are in the tunnels, these novel (underutilized) biological control methods if extensively used would provide good control measures in an integrated pest management. They would provide farmers an economically effective and environmentally sound approach to the management of the European corn borers. This is so because one of the Biological agents, Beauveria bassiana by the help of its conidia would grow into the tunnel of the stalk develop into hyphae which proliferate and kill the larvae inside the stalk. Beauveria bassiana also has no preference as to its host’s stage in life; it will attack larvae and adults. A very unique characteristic is that it affects its host upon contact, unlike many other pathogens that need to be consumed to cause infection. Upon contact the pathogen kills the host from the inside out. It produces spores, known as conidia (asexual form), that directly infect through the outside of the insect’s skin; it then proceeds to germinate. From the spores it secretes enzymes that attack and dissolve the cuticle. It also produces Beauvericin, a toxin that weakens the host’s immune system.

This research finding is relevant in boosting underutilized control strategies and increasing stakeholder adoption of integrated pest management practices and thereby reducing the use of conventional insecticide. The results are good and relevant for increasing farmers’ adoption of Integrated Pest Management practices, reducing the use of conventional, broad-spectrum chemicals for Ostrinia nubilalis control and employing less environmentally harmful insecticides. By adopting less broadly toxic chemicals in pest management, control by natural enemies of European corn borer, such as Parasitoids such as Trichogramma pretiosum and microbial pathogens may be enhanced and this would in turn reduce the need for chemical controls and make row crop farming more profitable for the farmers.

The results of the research done on the abundance and composition of the non-target arthropods in the treatment plots clearly show that the different treatments applied to various plots had no effect on the distribution and abundance of these non-target arthropods. All the P values obtained by one way ANOVA were bigger than 0.05.

Objectives/Performance Targets

The research had the following objectives:

1.To compare the efficacy of Bacillus Thuringiensis (Bt) spray, Dipel Beauveria bassiana, Trichogramma pretiosum and Spinosad for the economic control of Ostrinia nubilalis.

2.To assess the impact of these treatments on the abundance and composition of non-target arthropods.

Accomplishments/Milestones

There was more infestation by the European corn borers in the stalks of corn in the control treatment than in the other treatment plots. The control treatments had a mean of 17.0 infected stalks per plot, while the other treatments had much lower infestation levels. There was a significant difference between the control treatment and the other treatments. One way ANOVA: (DF = 6, 28, F =14.73, P < 0.001). There was very little infestation of stalks of corn from Spinosad treatment and Trichogramma pretiosum plus Spinosad with a mean of 3.4 (±0.98 SE) and 4.8 (±1.2 SE) respectively of the sampled stalks.

The 2007 results were somewhat similar to the results obtained in 2006. There was no noticeable difference between the Control treatment and treatment with Trichogramma pretiosum. But there was a significant difference between the Control treatment and other treatments (One way ANOVA – DF = 6, 28, F = 9.83 and P < 0.001). There was more infestation of the stalks in control treatment and treatment with Trichogramma pretiosum with an infestation mean of 20.0 (± 0.0 SE) and 19.6 (± 0.4 SE) respectively. The trend seems to be very similar with that of 2006.

The greatest number of larvae per stalk was found in the control treatment followed by the treatment with Trichogramma pretiosum. The control treatment had a mean of 34.8, while the other treatments had less than that. There was a significant difference between treatment with Spinosad and treatment with Trichogramma pretiosum plus Spinosad with the other treatments. One way ANOVA – DF =6, 28, F = 14.37 and P < 0.001. There were fewer larvae per stalk in Spinosad treatment with a mean of 9.8 (± 0.58 SE) and Trichogramma pretiosum plus Spinosad with a mean of 8.6 (± 1.86 SE) than in any other treatments.

The 2007 results were almost similar to the 2006 results. The highest number of larvae was found in the control treatments with a mean of 29.4 followed by the treatment with Trichogramma pretiosum mean of 25.8. There was a significant difference between treatments with Spinosad and the other treatments. One way ANOVA – DF =6, 28, F = 7.03 and P < 0.001. There were fewer larvae per stalk in Spinosad treatment with a mean of 6.0 (± 1.48 SE) followed by treatment with Trichogramma pretiosum plus Spinosad with mean of 10.8 (± 1.16 SE) than in the Control treatment which had a mean of 25.8 (± 3.38 SE).

There were more tunnels in the stalks of corn from both control treatment and treatments with Trichogramma pretiosum with a mean of 24.2 (± 3.8 SE) and 25.4 (± 2.44 SE) respectively. There was a significant difference between the Control treatment and treatments with Spinosad and Trichogramma pretiosum plus Spinosad. One way ANOVA – DF = 6, 28, F = 9.09, and P = < 0.001. Treatments with Spinosad and Trichogramma pretiosum and Spinosad had low numbers of tunnels (mean of 6.6 (± 0.4 SE) and 7.6 (± 7.6 SE) respectively) per plant compared to the rest of the treatments.

In 2007, there were more tunnels in the control treatment with a mean of 44.8 cm (± 3.06 SE) followed by the treatment with Trichogramma pretiosum with a mean of 36.6 cm (± 3.82 SE) than any other treatments. There were few tunnels in Treatment with Spinosad with a mean of 11.8 cm (±1.28 SE). There was a significant difference between Control treatment and treatment with Spinosad. One way ANOVA – DF = 6, 28, F = 14.18, and P < 0.001.

There was no significant difference between Control treatment and the treatment with Trichogramma pretiosum. Both treatments had long tunnels means of 32.6 cm (± 2.3 SE) and 32 cm (± 5.4 SE) respectively. However, Control treatments and treatment with Trichogramma pretiosum differed significantly with treatments with Spinosad, Beauveria bassiana and Bt spray and Trichogramma pretiosum plus Spinosad. One way ANOVA – DF = 6, 28, F = 6.96 and P = < 0.001. The shortest length of tunnels was recorded in treatment with Spinosad Trichogramma pretiosum, with a mean of 6.8 (± 1.7 SE) and also in treatment with Spinosad with a mean of 14 (± 3.3 SE).

In 2007, the longest tunnels were also in Control treatments and in treatment with Trichogramma pretiosum with a mean of 46 (± 1.9 SE) and 39 (± 3.86 SE) respectively. The shortest lengths of tunnels were in Treatment with Spinosad with a mean of 12.4 (± 1.5 SE). There was a significant difference between the length of tunnels in Control treatment and the lengths of tunnels in other treatments (One way ANOVA – DF = 6, 28, F = 15.88 and a P<0.001).

The highest infestation of the cobs was recorded in Control treatment with a mean of 17.4 (±2.0 SE) and treatment with Trichogramma pretiosum which had a mean of 13.4 (± 1.3 SE). There was no significant difference between Control treatment and treatment with Trichogramma pretiosum.

The lowest infestation of the cobs was in treatment with Spinosad. There was a significant difference between Control treatment and other treatments. One way ANOVA – DF = 6, 28, F = 7.08 and P < 0.001. There was also low infestation of cobs in treatments with Bt sprays and treatment with Trichogramma pretiosum plus Spinosad.

In 2007, the highest infestation of cobs was in Control treatment with a mean value of 14.2 (± 0.73 SE) followed by treatment with Trichogramma pretiosum with a mean of 11 (± 1.14 SE). There was no significant difference between Control treatment and treatment with Trichogramma pretiosum. There was a significant difference though between the Control treatment and other treatments. One way ANOVA – DF = 6, 28, F = 20.19, with a P < 0.001. The lowest infestation of cobs was recorded in treatment with Spinosad.

The yield was quite lower in the Control treatment with a mean of 7847.11 (±1196 SE) kilogram per hectare, than the rest of the treatments, followed by that of treatment with Trichogramma pretiosum with a mean yield of 9942.04 (± 484.88 SE) Kilograms per hectare. One way ANOVA – DF = 6, 28, F = 2.49 and P < 0.046. The highest yield was in treatment with Trichogramma pretiosum plus Spinosad with a mean yield of 10797.56 (± 664.03 SE) kilograms per hectare followed by that of Spinosad with a mean yield of 10756.89 (± 376.22 SE) kilograms per hectare (Figure 8). There was a significant difference in the yield between the Control treatment and treatments with Spinosad, Beauveria bassiana and Trichogramma pretiosum plus Spinosad (One way ANOVA; DF = 6, 28, F =2.49 and P<0.046.

In 2007, the yield was slightly lower in treatment 1 than in the other treatments. In the control treatment the yield mean was 10360.28 (±293.8 SE) kilograms per hectare while in the other treatments the yield was higher than that. The highest yield was in treatment with Spinosad, with 11515.8 (± 110.2 SE) kilograms per hectare followed by treatment with Trichogramma pretiosum plus Spinosad with a mean yield of 11335.28 (± 153.2 SE) kilograms per hectare. There was no significant difference between the yield in the Control treatment and the yield in other treatments. One way ANOVA; DF = 6, 28, F = 1.49, and P= 0.217.

Yield losses due to the European corn borers can vary from year to year according to the levels of infestation, and I think are generally unpredictable from one year to the next.

Yield losses are primarily physiological losses from reduced plant growth. Stalk tunneling results in shorter plants with fewer and smaller leaves. Movement of water and nutrients can be restricted over the entire kernel- filling period. During the period of kernel growth, there is between 5 and 6% loss in grain yield for each larva per plant. During corn development stage, the loss per plant is about 2 to 4% (Mason C. E. et. Al. 1996). Most yield losses can be attributed to the impaired ability of the corn plants to produce normal amounts of grain due to physiological effect of larvae feeding on the leaf and conductive tissues.

Results of Insect Sampling

During 2006 and 2007 sampling of insects was done in all the 35 plots. Most arthropods sampled from different plots with various treatments were in the order of Coleoptera (Coccinella septempunctata, Popillia japonica and Diabrotica virgifera virgifera), Hemiptera (Euschistus variolarius), Hymenoptera (Andrena imitatrix Cresson), and Orthoptera (Neoconocephalus and Melanoplus femurrubrum). The reason may be for having sampled few orders of arthropod could be that the changes in corn plants growth levels could have potentially affected the arthropod orientation and interaction with the plants, and not the microbial agents. For arthropods that feed on pollen (at that stage pollen had fallen off) the changed plants could for example offer less pollen as food source. A decrease in arthropod species availability would eventually affect other arthropod populations that fed on those arthropods from the decreased population. Andrena imitatrix Cressons need both suitable nesting sites and pollen plants (Gathmann et al. 1994). Parasitoids depend on spatially and temporally co-occurrence of hosts and nectar (Russell 1989). Some monophagous insect herbivores may spend their whole life on one host plant, feeding, copulating and ovipositing (Zwolfer and Harris 1971; Tscharntke 1999), and these could be the ones that were sampled.

In both years the collection was dominated by the Diabrotica virgifera virgifera in all the plots while the least were the bees and the moths. The following were the average insects that were sampled in all the plots. Analysis of variance (ANOVA) was used to determine if any significant difference occurred between treatments. The data were statistically analyzed by using Minitab 14, one-way ANOVA and differences between parameters could have been obtained by using Tukey post-hoc comparison test, but there were no significant differences between the control treatment and the other treatments. The analysis showed no significant differences between the insects sampled from the control treatments and the other treatments. The P values obtained by one way ANOVA were greater than 0.05.

The number of Diabrotica virgifera virgifera was quite high in all the plots, Minitab 14: One way ANOVA – DF =10, 24. F = 0.77. P = 0.657.

So far the statistical analysis done regarding the abundance and composition of the non target arthropods in all the plots for both years, showed no significant difference.

The results clearly show that the different treatments applied to various plots had no effect on the distribution and abundance of these non-target arthropods.

Impacts and Contributions/Outcomes

This research finding is relevant in boosting underutilized control strategies and increasing stakeholder adoption of integrated pest management practices and thereby reducing the use of conventional insecticide. The results are good and relevant for increasing farmers’ adoption of Integrated Pest Management practices, reducing the use of conventional, broad-spectrum chemicals for Ostrinia nubilalis control and employing less environmentally harmful insecticides. By adopting less broadly toxic chemicals in pest management, control by natural enemies of European corn borer, such as Parasitoids such as Trichogramma pretiosum and microbial pathogens may be enhanced and this would in turn reduce the need for chemical controls and make row crop farming more profitable for the farmers.

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