Abstract
ABSTRACT: Asian citrus psyllid, Diaphorina citri, is considered the most important citrus pest worldwide, as it transmits Huanglongbing – serious citrus disease. New efficient and sustainable strategies to control this pest have been investigated and the use of entomopathogenic fungi has become a promising alternative. The objective of this study was to evaluate the effects of adjuvants a) Tween 80 at 0.01 % (v/v); b) Silwet L77 at 0.025 % (v/v) and c) KBRAdj at 0.075 % (v/v) on adhesion, germination and pathogenicity of Isaria fumosorosea ESALQ-1296(5 × 106 conidia mL–1). Female adults of D. citri used in this experiment were sprayed on Citrus limonia seedlings. The sprayed insects were analyzed through scanning electron microscopy (SEM) to identify the most susceptible integument regions for fungus attachment and the effect of adjuvants used. In the pathogenicity test, adjuvants Silwet L77 and KBRAdj presented a higher efficiency than Tween 80. Fungi adhered predominantly to the ventral posterior (abdomen) region in comparison with the dorsal anterior (thorax) region. In addition, adjuvants Silwet L77 and KBRAdj presented faster germination ( 72 h). Conidial germination in the dorsal part of the thorax of the insects was observed only with adjuvant KBRAdj 72 h post inoculation.
Highlights
Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) is considered the most important citrus pest worldwide due to the transmission of bacteria ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’, causal agents of citrus Greening disease or Huanglongbing (HLB) (Bové, 2006; Chu et al, 2016)
Field trials were performed to test the efficacy of this strain in commercial citrus orchards during one year and the results showed that I. fumosorosea Escola Superior de Agricultura “Luiz de Queiroz” (ESALQ)-1296 was as effective as the chemical insecticides in most trials
Mortality caused by KBRAdj and Silwet L77 alone did not differ statistically with I. fumosorosea ESALQ-1296 + Tween 80 resulting in 37.0 ± 11.2 % and 37.0 ± 11.2 %, respectively
Summary
Diaphorina citri Kuwayama (Hemiptera: Liviidae) is considered the most important citrus pest worldwide due to the transmission of bacteria ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’, causal agents of citrus Greening disease or Huanglongbing (HLB) (Bové, 2006; Chu et al, 2016). The first step in fungi infection corresponds to the adhesion of reproductive structures (conidia) to insect cuticle, which occurs through physical and chemical mechanisms between the pathogen and the host insect (Hajek and Eastburn, 2003; Holder and Keyhani, 2005; Travaglini et al, 2016; Vestergaard et al, 1999) In this sense, the use of chemical adjuvants in fungal formulations is an alternative to improve contact and adhesion of conidia to the external region of the insect. Field trials were performed to test the efficacy of this strain in commercial citrus orchards during one year and the results showed that I. fumosorosea ESALQ-1296 was as effective as the chemical insecticides in most trials. We investigated how adjuvants can affect the fungus performance by improving adhesion, germination and penetration on adults of D. citri
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