Management of wood-boring beetles by injection of Heterorhabditis indica in Persea americana and Theobroma cacao

Authors: Myers, Roxana; Mello, Cathy

Submitted to: Society of Nematology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/14/2024
Publication Date: 9/10/2024
Citation: Myers, R.Y., Mello, C.L. 2024. Management of wood-boring beetles by injection of Heterorhabditis indica in Persea americana and Theobroma cacao. Society of Nematology Meeting. 56:103. https://doi.org/10.2478/jofnem-2024-0036.
DOI: https://doi.org/10.2478/jofnem-2024-0036

Interpretive Summary:

Technical Abstract: Invasive insect pests are increasingly becoming a problem to the agricultural industry and delicate ecosystem of the Hawaiian Islands. A recent introduction, Acalolepta aesthetica, the Queensland long-horned beetle (QLB) is a large polyphagous wood-boring cerambycid that attacks a wide range of tropical tree species. Preliminary trials using a native isolate of Heterorhabditis indica demonstrated that the nematode could navigate galleries created by QLB larvae, infect, and cause mortality within trunks and branches of infested trees. A field trial was initiated to manage this pest in avocado, Persea americana, and cacao, Theobroma cacao, orchards by injecting the nematodes in an aqueous suspension into openings in the trunk caused by QLB larval feeding and tunneling. Inoculum rates ranged from 20,000 to 240,000 IJs/tree depending on the levels of QLB infestation and amount of the aqueous nematode suspension the galleries could hold. Initial evaluation of the treatment’s efficacy was established by observing for new signs of larval activity such as fresh frass, wood shavings, and oozing sap one month after application of H. indica. Treatments were conducted monthly in trees that continued to show signs of QLB larval feeding. In avocado, four weeks after the initial application 33% of the nematode treated trees showed no signs of recent QLB activity. This increased to 75% one month after the second application. Following the third treatment of H. indica, 85% of trees no longer appeared to have active infestations. In the cacao orchard, where the infestation was more severe prior to starting the nematode applications, 50% of the trees no longer had signs of QLB larval feeding after the first treatment. However, signs were still observed on the remaining infested trees after two additional treatments of H. indica possibility due to the large number of QLB larvae initially colonizing those trees. Due to the cryptic habitat of this pest, it cannot be confirmed that the absence of signs of QLB activity is entirely the result of mortality caused by H. indica without felling and dismembering the trees. Additional data will be collected on the number of QLB adult emergence holes that occur on nematode inoculated trees when adult beetles exit their host trees during mating season.