Selection for and Analysis of UV-Resistant Cryptophlebia Leucotreta Granulovirus-SA as a Biopesticide for Thaumatotibia leucotreta

Abstract

Cryptophlebia leucotreta granulovirus-SA (CrleGV-SA) is used as a commercial biopesticide for the false codling moth, Thaumatotibia leucotreta, in citrus and other crops. The virus is sensitive to UV irradiation from sunlight, which reduces its efficacy as a biopesticide in the field. We selected a UV-resistant CrleGV-SA isolate, with more than a thousand-fold improved virulence compared to the wild-type isolate, measured by comparing LC50 values. CrleGV-SA purified from infected T. leucotreta larvae was exposed to UV irradiation under controlled laboratory conditions in a climate chamber mimicking field conditions. Five cycles of UV exposure, followed by propagating the virus that retained infectivity in vivo with re-exposure to UV, were conducted to isolate and select for UV-resistant virus. Serial dilution bioassays were conducted against neonates after each UV exposure cycle. The concentration-responses of the infectious UV-exposed virus populations were compared by probit analysis with those from previous cycles and from the original CrleGV-SA virus population. NGS sequences of CrleGV-SA samples from UV exposure cycle 1 and cycle 5 were compared with the GenBank CrleGV-SA sequence. Changes in the genomes of infective virus from cycles 1 and 5 generated SNPs thought to be responsible for establishing UV tolerance. Additional SNPs, detected only in the cycle 5 sequence, may enhance UV tolerance and improve the virulence of the UV-tolerant population.

Transmission Electron Microscopy Observation of Morphological Changes to Cryptophlebia Leucotreta Granulovirus following Ultraviolet Irradiation

“…Furthermore, 18% of OBs showed no signs of UV degradation after 72 h exposure to UV irradiation. Consequently, virus populations may include individuals possessing a higher tolerance to UV irradiation that can be specifically selected for through serial passage after UV exposure [28,47], as was recently reported by us in a laboratory selection procedure from the same isolate of CrleGV-SA described in this paper [48].…”

“…This crystalline structure is formed by the OB protein granulin [33]. Whilst granulin protects the OB from harsh environmental conditions and enables the virus to persist for long periods of time in the soil or similar shaded environments, it has been shown that it cannot provide sufficient protection to the NC against UV irradiation to enable prolonged survival when exposed to sunlight [8,34].…”

Review: The effect and possible mitigation of UV radiation on baculoviruses as bioinsecticides

“…Therefore, it is not recommended to utilise LdMNPV-45/0 in locations with high UV loads or at densities of forest stands. Another study reported the use of Cryptophlebia leucotreta granulovirus-SA (CrleGV-SA) as a commercial biopesticide against the false codling moth, Thaumatotibia leucotreta, in citrus and other crops (Mwanza et al 2022). This virus strain was isolated from infected T. leucotreta larvae and subjected to UV irradiation in a climate chamber with simulating field settings under laboratory condition.…”

“…This virus strain was isolated from infected T. leucotreta larvae and subjected to UV irradiation in a climate chamber with simulating field settings under laboratory condition. This UV-resistant CrleGV-SA strain was thousand-fold more virulence than the wild-type isolate (Mwanza et al 2022). Single Nucleotide Polymorphisms (SNPs) was discovered in the 5 th generation of UV-resistant CrleGV-SA which is believed to have improved the UV tolerance and pathogenicity of the virus.…”

Compatibility of the fungus Beauveria bassiana and Trichoplusia ni SNPV against the cabbage looper Trichoplusia ni: crop plant matters

“…24,25 Although studies have moved from artificial diet to more realistic scenarios involving host plants, either in laboratory-controlled conditions 16,26 or directly in the field, 27,28 they remain focused on a single plant species which limits our ability to generalise the outcome of pathogen interactions to different crop plants. Yet, host plants can directly affect entomopathogens and alter their persistence and viability on the plant 29,30 or indirectly affect them by changing insect behaviour. and thus pathogen acquisition, as well as susceptibility through changes in immunocompetence.…”