Spatial separation of semiochemical Lurem-TR and entomopathogenic fungi to enhance their compatibility and infectivity in an autoinoculation system for thrips management

Abstract

Background: The effect of spatial separation of the semiochemical Lurem-TR, which has been found to inhibit conidia of entomopathogenic fungi when put together, on the persistence of conidia of Metarhizium brunneum and M. anisopliae was evaluated in the greenhouse and field in order to develop an autodissemination strategy for the management of Megalurothrips sjostedti on cowpea crop. Influence of spatial separation of the semiochemical on thrips attraction and conidial acquisition by thrips from the autoinoculation device was also investigated in the field.

Results: Persistence of conidia of M. brunneum and M. anisopliae increased with distance of separation of Lurem-TR. Direct exposure of fungus without separation from Lurem-TR recorded the lowest conidial germination as compared with the other treatments. Attraction of thrips to the device also varied significantly according to distance between device and semiochemical, with a higher number of thrips attracted when Lurem-TR was placed in a container below the device and at 10 cm distance. There was no significant difference in conidial acquisition between spatial separation treatments of conidia and Lurem-TR. Attraction of other insect pests to the device did not significantly vary between treatments. Positive correlations were found between conidial acquisition and thrips attraction.

Conclusion: This study suggests that spatial separation of fungal conidia from Lurem-TR in an autoinoculation device could provide a low-cost strategy for effective management of thrips in grain legume cropping systems.

Keywords: Metarhizium anisopliae; Metarhizium brunneum; bean flower thrips; grain legumes; kairomones; lure-and-infect.

Figure 1

Experimental design for the evaluation of the effect of distance separation of Lurem‐TR on M. brunneum conidial persistence in the greenhouse.

Figure 2

Description of the spatial separation of Lurem‐TR for evaluation of M. anisopliae conidial persistence in an autoinoculation device in the field. Treatments: T₁ – direct exposure of conidia to Lurem‐TR; T₂ – conidia separated from Lurem‐TR placed inside a small container fixed just below the device; T₃ – conidia separated from Lurem‐TR at 10 cm above the device; T₄ – conidia separated from Lurem‐TR at 20 cm above the device; T₅ – control, device without Lurem‐TR.

Figure 3

Effect of spatial separation of Lurem‐TR from M. brunneum (Met52) on conidial germination. Treatments: L0, L5, L10 and L20 are respectively petri dishes with conidia directly exposed, 5 cm above, 10 cm above and 20 cm above Lurem‐TR. Lmin and Lmax represent the minimum and the maximum effect of Lurem‐TR on inhibition of spore germination when placed in closed boxes with or without Lurem‐TR.

Figure 4

Effect of spatial separation of Lurem‐TR on conidial viability of M. anisopliae in autoinoculation devices. Bars denote means ± one standard error at P = 0.05 (Tukey's HSD). Means (± SE) of three replicates of five autoinoculation devices. Treatments: T₁ – direct exposure of conidia to Lurem‐TR; T₂ – conidia separated from Lurem‐TR placed inside a small container fixed below the device; T₃ – conidia separated from Lurem‐TR at 10 cm above the device; T₄ – conidia separated from Lurem‐TR at 20 cm above the device; T₅ – control, device without Lurem‐TR.

Figure 5

Effect of spatial separation of Lurem‐TR and M. anisopliae on overall attraction of M. sjostedti. Bars denote means ± one standard error at P = 0.05 (Tukey's HSD). Means (± SE) of three replicates of five autoinoculation devices. Treatments: T₁ – direct exposure of conidia to Lurem‐TR; T₂ – conidia separated from Lurem‐TR placed inside a small container fixed below the device; T₃ – conidia separated from Lurem‐TR at 10 cm above the device; T₄ – conidia separated from Lurem‐TR at 20 cm above the device; T₅ – control, device without Lurem‐TR.