Crude Extracts and Alkaloids Derived from Ipomoea-Periglandula Symbiotic Association Cause Mortality of Asian Citrus Psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae)

Abstract

Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is an important economic pest of citrus crops because it vectors the causal pathogen of huanglongbing (HLB; aka citrus greening). Population suppression of D. citri with insecticides has been disproportionally relied on for HLB management and a greater diversity of more sustainable tools is needed. Periglandula spp. is a fungal endosymbiont (family Clavicipitaceae) that forms a mutualistic relationship with members of plants in family Convolvulaceae. This association results in the production of ergot alkaloids that were previously documented as having psyllicidal properties. We investigated the mortality and behavior of D. citri exposed to crude extracts from morning glories in the plant family Convolvulaceae, as well as synthetic ergot alkaloids. Nymphs and adults were exposed to the crude plant extracts from Periglandula positive species of Convolvulaceae, as well as five synthetic ergot alkaloids. Treatments were prepared by exposing clippings of citrus to 100 ng/µL of crude extract from Periglandula-positive species of Ipomoea (I. imperati, I. leptophylla, I. pandurata and I. tricolor), and Turbina corymbosa, and from one Periglandula-negative species (I. alba) (100 ng/µL). Mortality of adult and nymphal D. citri was significantly higher than the control after exposure to extracts from I. tricolor and I. imperati. The synthetic ergot alkaloids, lysergol (10-100 ng/µL), ergonovine maleate (100 ng/µL), agroclavine (10-100 ng/µL), and ergosine (10-100 ng/µL) increased mortality of D. citri nymphs, while ergosine (100 ng/µL) and agroclavine (100 ng/µL) increased mortality of adults compared to water controls. Fewer D. citri adults settled on plants treated with crude extracts or synthetic ergot alkaloids than on water controls at 48 h after release. D. citri that fed on citrus leaves treated with 10 ng/μL solution of crude extract from the Periglandula-positive species Ipomoea (I. imperati, I. leptophylla, I. pandurata, I. tricolor), and Turbina corymbosa excreted significantly less honeydew compared with a negative water control and extract from Periglandula-negative species (I. alba). Our results indicate that crude extracts and ergot alkaloids exhibit toxic and sub-lethal effects on D. citri that could be useful for management of this pest.

Keywords: Convolvulaceae; Diaphorina citri; citrus greening; ergot alkaloids; mortality.

Figure 1

Exposure-dependent mortality rates among Diaphornia citri nymphs exposed to leaves treated with increasing concentrations of agroclavine (A), ergocornine (B), ergosine (C), lysergol (D), or ergonovine maleate (E). See Table 3 for statistical results. The figure depicts morality observed with the control (0 ng/µL) and at the two highest concentrations tested, 10 and 100 ng/µL.

Figure 2

Exposure-dependent mortality rates among Diaphornia citri adults exposed to leaves treated with increasing concentrations of agroclavine (A), ergocornine (B), ergosine (C), lysergol (D), or ergonovine maleate (E). See Table 3 for statistical results. The figure depicts morality observd with the control (0 ng/µL) and at the two highest concentrations tested, 10 and 100 ng/µL.

Figure 3

Effect of crude extracts from Convolvulaceae plant species (A) or synthetic alkaloids (B) on feeding by adult Diaphorina citri as measured by honeydew excretion.