A Novel Interaction of Nesidiocoris tenuis (Hemiptera: Miridae) as a Biological Control Agent of Bactericera cockerelli (Hemiptera: Triozidae) in Potato.

Nesidiocoris tenuis (Hemiptera: Miridae) is a generalist predator commonly used to control the whitefly Bemisia tabaci in Europe. This mirid has been found and established in South Texas, where it was initially observed feeding on nymphs of the psyllid Bactericera cockerelli (Hemiptera: Triozidae) in open tomato fields. B. cockerelli is the vector of the fastidious bacterium "Candidatus Liberibacter solanacearum" that causes diseases in several solanaceous crops, including zebra chip (ZC) disease in potatoes. There is a need to better understand how this predator impacts the control of important crop pests, such as potato psyllids. We assessed the interactions between N. tenuis and B. cockerelli in three different environmental settings. First, we estimated the numeric response of N. tenuis preying on B. cockerelli under laboratory and greenhouse conditions. Second, we evaluated the predator-prey interaction under controlled field cage conditions. Then, we exposed N. tenuis under controlled field release conditions to the natural occurrence of B. cockerelli. Finally, we assessed the compatibility between the use of N. tenuis as a biological control agent in a field study and its impact on ZC disease incidence, severity in potato tubers, and potato yield. Laboratory and greenhouse experiments resulted in diverse types of functional model responses, including exponential and linear mathematical models. Our findings revealed a significant predation effect exerted by N. tenuis, resulting in a reduction of more than fourfold in the number of B. cockerelli nymphs per cage. Specifically, the nymphal population decreased from 21 ± 3.2 in the absence of N. tenuis to 5 ± 1.6 when N. tenuis was present. Furthermore, the combination of N. tenuis with a reduced insecticide program increased potato yields, but only reduced ZC tuber incidence in one of two potato cultivars evaluated, and in one season. Findings from these studies indicate that N. tenuis could be effective as a biological control agent for B. cockerelli in potato production in South Texas. This is the first report of N. tenuis preying on immature stages of any psyllid species.

Association of Two Bactericera Species (Hemiptera: Triozidae) With Native Lycium spp. (Solanales: Solanaceae) in the Potato Growing Regions of the Rio Grande Valley of Texas.

Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is a vector of 'Candidatus Liberibacter solanacearum' (Lso), the pathogen that causes potato zebra chip. Zebra chip incidence varies regionally, perhaps because of geographic differences in species of noncrop hosts available to the vector and in susceptibility of those hosts to Lso. Native and introduced species of Lycium (Solanales: Solanaceae) are important noncrop hosts of B. cockerelli in some regions of North America. Susceptibility of native Lycium species to Lso is uncertain. We investigated the use of two native species of Lycium by B. cockerelli in South Texas and tested whether they are susceptible to Lso. Bactericera cockerelli adults and nymphs were collected frequently from L. berlandieri Dunal and L. carolinianum Walter. Greenhouse assays confirmed that B. cockerelli develops on both species and showed that Lso infects L. carolinianum. Molecular gut content analysis provided evidence that B. cockerelli adults disperse between potato and Lycium. These results demonstrate that L. berlandieri and L. carolinianum are likely noncrop sources of potato-colonizing B. cockerelli in South Texas and that L. carolinianum is a potential source of Lso-infected psyllids. We also routinely collected the congeneric psyllid, Bactericera dorsalis (Crawford), from both Lycium species. These records are the first for this psyllid in Texas. Bactericera dorsalis completed development on both native Lycium species, albeit with high rates of mortality on L. berlandieri. B. dorsalis acquired and transmitted Lso on L. carolinianum under greenhouse conditions but did not transmit Lso to potato. These results document a previously unknown vector of Lso.

Persistence of the Exotic Mirid Nesidiocoris tenuis (Hemiptera: Miridae) in South Texas.

The Rio Grande Valley is one of the most productive agricultural areas in the U.S and is located in the southernmost part of Texas. In October 2013, we detected an exotic plant bug, Nesidiocoris tenuis Reuter (Hemiptera: Miridae: Bryocorinae) occurring in the region. Nesidiocoris tenuis has zoophytophagous habits; however, in the absence of insect prey, it feeds on its plant hosts. After its morphological and genetic identification, this study monitored the population of N. tenuis in its introduction phase in commercial fields and corroborated its establishment in research fields for three years. Populations of N. tenuis were high during the fall and low during winter. This study found that N. tenuis populations were higher in tomato fields as compared to adjacent pepper, okra, and squash fields, indicating its host preferences during the introduction phase. Recurrent population growth patterns suggest that N. tenuis was established in Rio Grande Valley with permanent populations in tomato fields. In addition, N. tenuis populations were affected by tomato cultivar selection and by plastic mulch color. The presence of N. tenuis could establish a new trophic insect relationship for vegetable production. However, it is unknown if the presence of N. tenuis may help to control pests of economic importance, such as whiteflies in cotton, or become a pest on sesame, an emerging crop.

Mortality of Potato Psyllid (Hemiptera: Triozidae) on Host Clippings Inoculated With Ergot Alkaloids.

Our previous study provided correlative evidence that morning glory species harboring endophytic fungi (Periglandula) are resistant to potato psyllid [Bactericera cockerelli (Sulc)], whereas species free of fungi often allowed psyllid development. In this study, we manipulated levels of ergot alkaloids in host tissues by inoculating clippings from potato plants with extracts from morning glories that harbor Periglandula [Ipomoea leptophylla Torrey, Ipomoea imperati (Vahl) Grisebach, Ipomoea tricolor Cavanilles, Ipomoea pandurata (L.) G. F. Meyer, and Turbina corymbosa (L.)] and one species (Ipomoea alba L.) that does not harbor the endophyte. Ergot alkaloids (clavines, lysergic acid amides, and ergopeptines) were detected in potato clippings, thus confirming that leaves had taken up compounds from solutions of crude extracts. Psyllid mortality rates on inoculated clippings ranged between 53 and 93% in treatments producing biochemically detectable levels of alkaloids, when compared with 15% mortality in water controls or the alkaloid-free I. alba. We then tested synthetic analogs from each of the three alkaloid classes that had been detected in the crude extracts. Each compound was assayed by inoculating clippings of two host species (potato and tomato) at increasing concentrations (0, 1, 10, and 100 µg/ml in solution). Psyllids exhibited a large and significant increase in mortality rate beginning at the lowest two concentrations, indicating that even very small quantities of these chemicals led to mortality. Feeding by nymphs on artificial diets containing synthetic compounds resulted in 100% mortality within 48 h, irrespective of compound. Further testing of ergot alkaloids to characterize the mode of action that leads to psyllid mortality is warranted.

Survival and development of potato psyllid (Hemiptera: Triozidae) on Convolvulaceae: Effects of a plant-fungus symbiosis (Periglandula).

Plant species in the family Solanaceae are the usual hosts of potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Psylloidea: Triozidae). However, the psyllid has also been shown to develop on some species of Convolvulaceae (bindweeds and morning glories). Developmental success on Convolvulaceae is surprising given the rarity of psyllid species worldwide associated with this plant family. We assayed 14 species of Convolvulaceae across four genera (Convolvulus, Calystegia, Ipomoea, Turbina) to identify species that allow development of potato psyllid. Two populations of psyllids were assayed (Texas, Washington). The Texas population overlaps extensively with native Convolvulaceae, whereas Washington State is noticeably lacking in Convolvulaceae. Results of assays were overlain on a phylogenetic analysis of plant species to examine whether Convolvulaceae distantly related to the typical host (potato) were less likely to allow development than species of Convolvulaceae more closely related. Survival was independent of psyllid population and location of the plant species on our phylogenetic tree. We then examined whether presence of a fungal symbiont of Convolvulaceae (Periglandula spp.) affected psyllid survival. These fungi associate with Convolvulaceae and produce a class of mycotoxins (ergot alkaloids) that may confer protection against plant-feeding arthropods. Periglandula was found in 11 of our 14 species, including in two genera (Convolvulus, Calystegia) not previously known to host the symbiont. Of these 11 species, leaf tissues from five contained large quantities of two classes of ergot alkaloids (clavines, amides of lysergic acid) when evaluated by LC-MS/MS. All five species also harbored Periglandula. No ergot alkaloids were detected in species free of the fungal symbiont. Potato psyllid rapidly died on the five species that harbored Periglandula and contained ergot alkaloids, but survived to adulthood on seven of the nine species in which ergot alkaloids were not detected. These results support the hypothesis that a plant-fungus symbiotic relationship affects the suitability of certain Convolvulaceae to potato psyllid.