Drench Application of Systemic Insecticides Disrupts Probing Behavior of Diaphorina citri (Hemiptera: Liviidae) and Inoculation of Candidatus Liberibacter asiaticus.

Michele Carmo-Sousa,Rafael Brandão Garcia,Nelson Arno Wulff,Marcelo Pedreira Miranda,Alberto Fereres

doi:10.3390/insects11050314

Michele Carmo-Sousa, Rafael Brandão Garcia + Show 3 more

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https://doi.org/10.3390/insects11050314

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Abstract

Candidatus Liberibacter asiaticus (CLas) is a phloem-limited bacterium that is associated with the Huanglongbing (HLB) disease of citrus and transmitted by the psyllid, Diaphorina citri. There are no curative methods to control HLB and the prevention of new infections is essential for HLB management. Therefore, the objective of our study was to determine the effects of systemic insecticides, such as the neonicotinoids imidacloprid, thiamethoxam, and a mixture of thiamethoxam and chlorantraniliprole (diamide) on the probing behavior of CLas-infected D. citri and their effect on CLas transmission. The electrical penetration graph (EPG-DC) technique was used to monitor the stylet penetration activities of CLas-infected D. citri on sweet orange [Citrus sinensis (L.) Osbeck] ‘Valencia’ treated with systemic insecticides. Systemic insecticides disrupted the probing behavior of CLas-infected D. citri, in a way that affected CLas transmission efficiency, particularly by negatively affecting the stylet activities related to the phloem phase. All insecticides reduced (by 57–73%) the proportion of psyllids that exhibited sustainable phloem ingestion (waveform E2 > 10 min), with significant differences observed on plants treated with thiamethoxam and thiamethoxam + chlorantraniliprole. The transmission rate of CLas with high inoculum pressure (five CLas-infected D. citri per plant and a seven-day inoculation access period) to untreated control plants was 93%. In contrast, CLas transmission was reduced to 38.8% when test plants were protected by systemic insecticides. Our results indicated that all insecticides tested presented a potential to reduce CLas inoculation by an average of 59%; therefore, these insecticides can be used to reduce the spread of HLB.

Highlights

Citrus is one of the most important fruit crops worldwide; the citrus diseases caused by the pathogens transmitted by arthropod vectors are mainly responsible for the increasing citrus production costs
Ca. L. asiaticus (CLas) transmission was reduced to 38.8% when test plants were protected by systemic insecticides
Our results indicated that all insecticides tested presented a potential to reduce CLas inoculation by an average of 59%; these insecticides can be used to reduce the spread of HLB

Summary

Introduction

Citrus is one of the most important fruit crops worldwide; the citrus diseases caused by the pathogens transmitted by arthropod vectors are mainly responsible for the increasing citrus production costs. The Huanglongbing (HLB), known as citrus greening disease, is the most devastating citrus disease threatening citrus production worldwide; this disease is associated with the phloem-limited bacteria, Candidatus Liberibacter spp. such as Ca. L. asiaticus (CLas), Ca. L. africanus (CLaf), and Ca. L. americanus (CLam) [1]. HLB was first reported in the Americas in the State of Sao Paulo, Brazil, in 2004 [2,3] and later in the State of Florida, USA, in 2005 [4].

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