Using sticky card traps to evaluate entomopathogen fungi occurrence in insect populations: A cautionary tale

Authors: ALVES, LUIS FRANCISCO - UNIVERSIDADE ESTADUAL DO CEARA; LOBLEIN, JACQUELINE - UNIVERSIDADE ESTADUAL DO CEARA; Patt, Joseph - Joe

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2020
Publication Date: 5/31/2021
Citation: Alves, L., Loblein, J., Patt, J.M. 2021. Using sticky card traps to evaluate entomopathogen fungi occurrence in insect populations: A cautionary tale. Florida Entomologist. 104(1):56-57. https://doi.org/10.1653/024.104.0110.
DOI: https://doi.org/10.1653/024.104.0110

Interpretive Summary: The leaves of yerba mate are brewed to make a tea that is very popular in South America. A pest called the yerba mate psyllid (pronounced: sill-id), causes swelling and disfiguration in yerba mate leaves. This can cause heavy crop losses. No insecticides are approved for use on yerba mate and consumers prefer tea that is grown ‘naturally’. Therefore, alternatives to insecticides must be devised to control this psyllid in yerba mate orchards. A strain of a fungus that attacks the yerba mate psyllid has been identified. This strain has been named ‘Unioeste 44’ and it may provide an effective control of this psyllid in yerba mate orchards. To estimate the efficiency of Unnioeste 44 treatments, psyllids need to be collected from treated orchards, returned to the lab and then incubated in a humidity chamber so that the level of fungal infection can be determined. Yellow sticky card traps are used to monitor psyllid populations and these traps are suitable for trapping psyllids for infection studies. However, the yerba mate psyllid is a tiny and fragile insect and removing it from the adhesive surface of the trap for incubation is tedious and ineffective. To make this process more efficient, we demonstrated that an entire trap with its contingency of trapped psyllids could be incubated as a unit and that the Unioeste 44 fungus developed spore bodies on the psyllid cadavers. The cadavers with spore bodies on the trap surface could be examined and quantified easily and quickly with a microscope. For this test, psyllids were inoculated with Unioeste 44 spores and then transferred to cages (30 cm H × 12 cm W), containing a yerba-mate seedling. Control cages contained untreated psyllids. After two days, sticky card traps were placed in the cages to recover the psyllids. The traps were replaced every two days and recovered traps were then placed in lidded plastic boxes whose bottoms were covered with a layer of polyurethane foam moistened with distilled water. The boxes were incubated at 26 ± 2 °C and a 12 h light: 12 h dark light regimen. As part of this study, we tested two different types of sticky card traps for the purpose of selecting the most effective trap for recovering infected psyllids. Both kinds of traps measured 5 cm H x 7 cm W. One was a commercially available yellow sticky card trap from ISCA Technologies and the other was a homemade trap made from a yellow card coated with Colly™ insect glue. Equal numbers of traps were placed in the cages and it was shown that both traps were equally attractive to the psyllids with capture levels of 89% and 93% observed, respectively, on the traps coated with CollyTM insect glue and on the commercial traps from ISCA Technologies. Unexpectedly, the percentage of psyllid cadavers that developed spore bodies was highly significatively greater on the ISCA traps (mean = 78%) than on the traps coated with CollyTM insect glue (mean = 2.0%). Our conclusion is that certain ingredient(s) in the CollyTM glue were fungicidal and prevented the fungus from developing in the psyllid cadavers. This result showed that care must be taken to select an entomological glue that will not inhibit mycosis when planning tests to estimate entomopathogen infection levels in target pest populations.

Technical Abstract: The leaves of yerba mate (Ilex paraguariensis) are brewed to make a tea that is very popular in South America. Immatures of the yerba mate psyllid (Gyropsylla spegazziniana) cause galling and disfiguration in yerba mate leaves, which can result in heavy crop losses. There are no insecticides approved for use on yerba mate and consumers prefer tea that is grown ‘naturally’. Therefore, alternatives to chemical control measures must be devised to control G. spegazziniana in yerba mate orchards. A strain of the entomopathogic fungus Beauveria bassiana that attacks G. spegazziniana has been identified (Unioeste 44); this strain may provide an effective biocontrol of this psyllid in yerba mate orchards. To estimate the efficiency of Unnioeste 44 treatments, psyllids need to be collected from treated orchards, returned to the lab and then incubated in a humidity chamber so that the level of fungal infection can be determined. Yellow sticky card traps are used to monitor G. spegazziniana populations and these traps are suitable for trapping psyllids for infection studies. However, G. spegazziniana is a tiny and fragile insect and removing it from the adhesive surface of the trap for incubation is tedious and ineffective. To make this process more efficient, we demonstrated that an entire trap with its contingency of trapped psyllids could be incubated as a unit and that the cadavers mycosed in situ. The mycosed cadavers on the trap surface were examined and quantified easily and quickly with a dissection microscope. For this test, psyllids were inoculated with Unioeste 44 conidiospores and then transferred to cages (30 cm H × 12 cm W), containing a yerba-mate seedling. Control cages contained untreated psyllids. After two days, sticky card traps were placed in the cages to recover the psyllids. The traps were replaced every two days and recovered traps were then placed in lidded plastic boxes whose bottoms were covered with a layer of polyurethane foam moistened with distilled water. The boxes were incubated at 26 ± 2 °C and a 12 h L: 12 h D photoperiod. As part of this study, we tested two different types of sticky card traps for the purpose of selecting the most effective trap for recovering infected psyllids. Both kinds of traps measured 5 cm H x 7 cm W. One was a commercially available yellow sticky card trap from ISCA Technologies and the other was a homemade trap made from a yellow card coated with Colly™ insect glue. Equal numbers of traps were placed in the cages and it was shown that both traps were equally attractive to the psyllids with capture levels of 89% and 93% observed, respectively, on the traps coated with CollyTM insect glue and on the commercial traps from ISCA Technologies. Unexpectedly, the percentage of psyllid cadavers that mycosed was highly significatively greater on the ISCA traps (mean = 78%) than on the traps coated with CollyTM insect glue (mean = 2.0%). Our conclusion is that certain ingredient(s) in the CollyTM glue were fungicidal and prevented the fungus from developing in the psyllid cadavers. This result showed that care must be taken to select an entomological glue that will not inhibit mycosis when planning tests to estimate entomopathogen infection levels in target pest populations.