Abstract
Simple SummaryThe false codling moth is an indigenous pest of the citrus industry in southern Africa. It is a major threat as it can cause substantial fruit damage through larval feeding. The microorganisms associated with insects are often studied for their potential to kill their host instead of how they could aid them. However, in recent years, this aspect of their interaction has received much attention. The codling moth has been shown to have a close relationship with the naturally occurring yeast found within their digestive tract. These beneficial yeasts help the adult female moths locate a suitable host for egg laying. During their larval phase, these yeasts help them develop faster and increase their chance of survival. These interactions could be manipulated for the purposes of biological control, as one might be able to combine these yeasts with existing biological control agents to improve their effectiveness. These yeasts may also provide additional methods for monitoring field populations of insect pests. In this study, we identified yeasts that occur naturally in the guts of false codling moth larvae and investigated whether any of them are beneficial to their host.Thaumatotibia leucotreta is endemic to southern Africa and is highly significant for various fruit industries, including the South African citrus industry, due to its classification as a phytosanitary pest. Mutualistic associations between C. pomonella, closely related to T. leucotreta, and yeasts have previously been described and reported to reduce larval mortality and enhance larval development. Here, we determined which yeast species occur naturally in the gut of T. leucotreta larvae and investigated whether any of the isolated yeast species affect their behaviour and development. Navel oranges infested with T. leucotreta larvae were collected from geographically distinct provinces in South Africa, and the larvae were processed for analysis of naturally occurring associated yeasts. Six yeast species were isolated and identified from the guts of these T. leucotreta larvae via PCR amplification and sequencing of the ITS region of rDNA and D1/D2 domain of large ribosomal subunit. Larval development and attraction assays were conducted, and T. leucotreta larvae that fed on Navel oranges inoculated with yeast had accelerated developmental periods and reduced mortality rates. Neonate T. leucotreta were also attracted to YPD broth cultures inoculated with yeast for feeding. Oviposition preference assays were conducted with adult T. leucotreta females. Navel oranges inoculated with yeast were shown to influence the oviposition preference of adult females. Yeasts harbour the potential for use in biocontrol, especially when combined with other well-established control methods. This study provides a platform for future research into incorporating yeast with current biological control agents as a novel option for controlling T. leucotreta in the field.
Highlights
Microbes are the most abundant living organisms on earth, and apart from being found within the general environment, they are known to colonise other living organisms such as insects [1]
The guts of 30 T. leucotreta larvae were screened for yeast, which resulted in the isolation of six yeast species
The isolated yeast species were successfully identified via the gene sequence analysis of the internal transcribed spacer (ITS) region and D1/D2 domain of the large subunit (LSU) (Table 1)
Summary
Microbes are the most abundant living organisms on earth, and apart from being found within the general environment, they are known to colonise other living organisms such as insects [1]. Associations between Lepidoptera and microbes have rarely been described even though they are the second-most diverse insect order with some of the most devastating agricultural pests worldwide [17,18] Unlike their bacterial counterparts, interactions between insects and yeasts have been understudied, despite their importance to insect fitness and behaviour [9,19,20]. The metabolites produced by yeasts contributed towards adult C. pomonella moths recognising and finding their host plant [26] Identifying this mutualistic association between C. pomonella larvae and yeasts from the genus Metschnikowia has led to the development of novel biocontrol strategies [27–29]. Most notably is the betabaculovirus, Cryptophlebia leucotreta granulovirus (CrleGV), which is an effective microbial control agent against T. leucotreta [36] It has previously been demonstrated, in laboratory assays and field trials, that combining yeast with baculoviruses has resulted in the significant increase in larval mortality [27,28]. Sequences were assembled and analysed in MEGA X [38], with any ambiguous nucleotides being corrected before the sequences were identified by comparison to the GenBank database of nonredundant sequences using BLAST
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