Elad Chiel

Identification and Localization of a Rickettsia sp. in Bemisia tabaci (Homoptera: Aleyrodidae)

ABSTRACT Whiteflies (Homoptera: Aleyrodidae) are sap-sucking insects that harbor “Candidatus Portiera aleyrodidarum,” an obligatory symbiotic bacterium which is housed in a special organ called the bacteriome. These insects are also home for a diverse facultative microbial community which may include Hamiltonella, Arsenophonus, Fritchea, Wolbachia, and Cardinium spp. In this study, the bacteria associated with a B biotype of the sweet potato whitefly Bemisia tabaci were characterized using molecular fingerprinting techniques, and a Rickettsia sp. was detected for the first time in this insect family. Rickettsia sp. distribution, transmission and localization were studied using PCR and fluorescence in situ hybridizations (FISH). Rickettsia was found in all 20 Israeli B. tabaci populations screened but not in all individuals within each population. A FISH analysis of B. tabaci eggs, nymphs, and adults revealed a unique concentration of Rickettsia around the gut and follicle cells, as well as a random distribution in the hemolymph. We postulate that the Rickettsia enters the oocyte together with the bacteriocytes, leaves these symbiont-housing cells when the egg is laid, multiplies and spreads throughout the egg during embryogenesis and, subsequently, disperses throughout the body of the hatching nymph, excluding the bacteriomes. Although the role Rickettsia plays in the biology of the whitefly is currently unknown, the vertical transmission on the one hand and the partial within-population infection on the other suggest a phenotype that is advantageous under certain conditions but may be deleterious enough to prevent fixation under others.

Endosymbiont metacommunities, mtDNA diversity and the evolution of the Bemisia tabaci (Hemiptera: Aleyrodidae) species complex

Bemisia tabaci, an invasive pest that causes crop damage worldwide, is a highly differentiated species complex, divided into biotypes that have mainly been defined based on mitochondrial DNA sequences. Although endosymbionts can potentially induce population differentiation, specialization and indirect selection on mtDNA, studies have largely ignored these influential passengers in B. tabaci, despite as many as seven bacterial endosymbionts have been identified. Here, we investigate the composition of the whole bacterial community in worldwide populations of B. tabaci, together with host genetic differentiation, focusing on the invasive B and Q biotypes. Among 653 individuals studied, more than 95% of them harbour at least one secondary endosymbiont, and multiple infections are very common. In addition, sequence analyses reveal a very high diversity of facultative endosymbionts in B. tabaci, with some bacterial genus being represented by more than one strain. In the B and Q biotypes, nine different strains of bacteria have been identified. The mtDNA‐based phylogeny of B. tabaci also reveals a very high nucleotide diversity that partitions the two ITS clades (B and Q) into six CO1 genetic groups. Each genetic group is in linkage disequilibrium with a specific combination of endosymbionts. All together, our results demonstrate the rapid dynamics of the bacterial endosymbiont–host associations at a small evolutionary scale, questioning the role of endosymbiotic communities in the evolution of the Bemisia tabaci species complex and strengthening the need to develop a metacommunity theory of inherited endosymbionts.

The presence of Rickettsia is associated with increased susceptibility of Bemisia tabaci (Homoptera: Aleyrodidae) to insecticides.

BACKGROUND The presence of certain symbiotic microorganisms may be associated with insecticide resistance in insects. The authors compared the susceptibility of two isofemale lines, Rickettsia-plus and Rickettsia-free, of the sweet potato whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) to major insecticides from different chemical groups, including imidacloprid, acetamiprid, thiamethoxam, pyriproxyfen, spiromesifen and diafenthiuron. RESULTS While the Rickettsia-plus and Rickettsia-free lines showed no differences in their susceptibility to imidacloprid and diafenthiuron, higher susceptibility of the Rickettsia-plus line to acetamiprid, thiamethoxam, spiromesifen and especially pyriproxyfen was observed. LC(90) values indicated that the Rickettsia-free line was 15-fold more resistant to pyriproxyfen than the Rickettsia-plus line. CONCLUSION Findings indicate that the infection status of B. tabaci populations by Rickettsia is an important consideration that should be taken into account when performing resistance monitoring studies, and may help in understanding the dynamics of B. tabaci resistance, symbiont-pest associations in agricultural systems and the biological impact of Rickettsia on whitefly biology.

Assessments of Fitness Effects by the Facultative Symbiont Rickettsia in the Sweetpotato Whitefly (Hemiptera: Aleyrodidae)

ABSTRACT The sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), harbors several bacterial symbionts, including the obligate primary symbiont Portiera aleyrodidarum and the facultative secondary symbionts Arsenophonus, Cardinium, Fritschea, Hamiltonella, Rickettsia, and Wolbachia. The roles of these symbionts are yet unknown. In this study, we tested for possible effects of one symbiont, Rickettsia, on some fitness parameters of B. tabaci (biotype B) by comparing whiteflies that carry this symbiont to whiteflies that do not. Preadult development of Rickettsiacarrying whiteflies was faster, but all the other parameters that were measured: longevity, total number of progeny, sex ratio, and nymphal survivorship did not differ significantly. Estimates of the intrinsic growth rate (r) were almost identical for the two groups. Cross-mating between clefts-carrying and Rickettsia-free whiteflies provided no evidence for cytoplasmic incompatibility. Vertical transmission of Rickettsia was found to be nearly complete. Our results do not clearly identify a selective advantage that would explain the high prevalence of Rickettsia in B. tabaci populations, thus, other fitness parameters and horizontal transmission routes are suggested and discussed.

Sugar feeding of parasitoids in an agroecosystem: effects of community composition, habitat and vegetation

Sugar from nectar or from honeydew can prolong parasitoids’ lifespan, enhance their fecundity and foraging ability, and thereby increase their pest suppression efficiency. Sugar sources within crop monocultures are considered to be limiting for parasitoids. Nevertheless, only few studies have measured the sugar feeding of parasitoid assemblages in agricultural areas or in surrounding non‐crop habitats. We used cold anthrone tests to compare the frequency of sugar feeding in parasitoid communities, inside pomegranate orchards and in adjacent natural areas, over two consecutive years. Overall, 40% of the 1610 sampled individuals belonging to 135 species scored positive for sugar. Sugar‐feeding frequency was lower within the orchards than in the neighbouring natural areas. The proportion of sugar‐fed wasps increased with herbaceous vegetation cover, both within and outside the orchards, suggesting that herbs are a sugar‐rich habitat. Parasitoids sampled from trees and from herbs within the orchards had similar frequencies of sugar feeding, despite differences in wasp species composition. Our results probably overestimate sugar‐feeding frequencies in the field because sugar‐fed individuals have higher longevity and hence are more likely to be sampled. We propose a simple model to approximate this over‐sampling bias and apply it to Encarsia inaron (Aphelinidae), one of the most abundant parasitoids in the samples. We conclude that sugar availability potentially limits parasitoid fitness in this agro‐ecosystem. This may be due to the low density of plants in natural areas during the Mediterranean summer, and to herbicide applications within the orchards that further suppress non‐crop herbs.

Diversity and Abundance of House Fly Pupal Parasitoids in Israel, with First Records of Two Spalangia Species.

Abstract Filth flies (Diptera: Muscidae), particularly the house fly, Musca domestica L., are global pests of livestock production. In this study, we characterized the fauna of house fly pupal parasitoids in Israel and identified factors affecting their diversity and abundance. The study, which included one round of sampling during the fall of 2013 and another round of sampling in the spring of 2014, encompassed 26 locations of common fly-breeding habitats: dairy, egg-laying, and goat farms throughout Israel. Nine parasitoid species were found: Spalangia cameroni Perkins, Spalangia endius Walker, Spalangia drosophilae Ashmead, Spalangia gemina Boucek, Spalangia nigroaenea Curtis, Pachycrepoideus vindemmiae Rondani, Muscidifurax raptor Girault and Sanders, Muscidifurax zaraptor Kogan & Legner (all Hymenoptera: Pteromalidae), and Dirhinus giffardii Silvestri (Hymenoptera: Chalcididae). This is the first record of S. gemina from the Palearctic, as well as the first record of S. drosophilae from the Middle East. The composition and relative abundance of parasitoid species varied markedly among localities, climatic regions (Mediterranean vs. desert), habitat types (dairy vs. egg-laying vs. goat farm), and seasons. Overall, parasitoid richness in egg-laying farms was two- and sevenfold higher than in dairy and goat farms, respectively, and three times higher in Mediterranean than desert climate. The significance and implications of our results for inundative biological control programs of filth flies are discussed.

An exceptional family: Ophiocordyceps-allied fungus dominates the microbiome of soft scale insects (Hemiptera: Sternorrhyncha: Coccidae)

Hemipteran insects of the suborder Sternorrhyncha are plant sap feeders, where each family is obligately associated with a specific bacterial endosymbiont that produces essential nutrients lacking in the sap. Coccidae (soft scale insects) is the only major sternorrhynchan family in which obligate symbiont(s) have not been identified. We studied the microbiota in seven species from this family from Israel, Spain and Cyprus, by high‐throughput sequencing of ribosomal genes, and found that no specific bacterium was prevalent and abundant in all the tested species. In contrast, an Ophiocordyceps‐allied fungus sp.—a lineage widely known as entomopathogenic—was highly prevalent. All individuals of all the tested species carried this fungus. Phylogenetic analyses showed that the Ophiocordyceps‐allied fungus from the coccids is closely related to fungi described from other hemipterans, and they appear to be monophyletic, although the phylogenies of the Ophiocordyceps‐allied fungi and their hosts do not appear to be congruent. Microscopic observations show that the fungal cells are lemon‐shaped, are distributed throughout the hosts body and are present in the eggs, suggesting vertical transmission. Taken together, the results suggest that the Ophiocordyceps‐allied fungus may be a primary symbiont of Coccidae—a major evolutionary shift from bacteria to fungi in the Sternorrhyncha, and an important example of fungal evolutionary lifestyle switch.

Effects of pyriproxyfen on wild populations of the housefly, Musca domestica, and compatibility with its principal parasitoids

BACKGROUND The housefly, Musca domestica L., is an important pest of animal agriculture. Effective fly management requires integration of manure management, mass trapping, biological control, and selective insecticide use. Insecticidal control of houseflies is difficult due to the rapidity of resistance development, yet the insect growth regulator pyriproxyfen (PPF) is one of few insecticides that may still be effective. Here, we tested the susceptibility of wild housefly populations in the USA and in Israel to PPF, as well as the effect of PPF on housefly parasitoids of the genera Muscidifurax and Spalangia. RESULTS Most housefly populations from both countries were completely eliminated at PPF concentrations of 100 mg kg-1 (USA) and 600 mg kg-1 (Israel). One population from each country exhibited initial levels of PPF tolerance. PPF efficacy significantly decreased in cow manure. Emergence rates of parasitoids developing in PPF-treated hosts at concentrations of ≥600 mg kg-1 were significantly affected, whereas other fitness parameters were moderately to non-affected. CONCLUSIONS PPF is still an effective tool for housefly control, but resistance management practices should be employed to avoid resistance. PPF is compatible with principal housefly parasitoids at concentrations <600 mg kg-1 , and is suitable for use in integrated pest management.

Do Bacterial Symbionts Govern Aphid’s Dropping Behavior?

ABSTRACT Defensive symbiosis is amongst natures most important interactions shaping the ecology and evolution of all partners involved. The pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae), harbors one obligatory bacterial symbiont and up to seven different facultative symbionts, some of which are known to protect the aphid from pathogens, natural enemies, and other mortality factors. Pea aphids typically drop off the plant when a mammalian herbivore approaches it to avoid incidental predation. Here, we examined whether bacterial symbionts govern the pea aphid dropping behavior by comparing the bacterial fauna in dropping and nondropping aphids of two A. pisum populations, using two molecular techniques: high-throughput profiling of community structure using 16 S reads sequenced on the Illumina platform, and diagnostic polymerase chain reaction (PCR).We found that in addition to the obligatory symbiont, Buchnera aphidicola, the tested colonies of A. pisum harbored the facultative symbionts Serratia symbiotica, Regiella insecticola and Rickettsia, with no significant differences in infection proportions between dropping and nondropping aphids. While S. symbiotica was detected by both techniques, R. insecticola and Rickettsia could be detected only by diagnostic PCR. We therefore conclude that A. pisums dropping behavior is not affected by its bacterial symbionts and is possibly affected by other factors.

Contagious sterility in the parasitoid wasp Eretmocerus mundus (Hymenoptera: Aphelinidae)

Abstract The parasitoid wasp Eretmocerus mundus (Hymenoptera: Aphelinidae) is used commercially to control the sweet potato whitefly Bemisia tabaci (Homoptera: Aleyrodidae). Recently, a rapid deterioration of E. mundus populations has been documented under mass-rearing conditions. We found that deteriorating cultures consist of increasing proportions of sterile individuals, up to 90% within 6 months. Microscopic examination revealed that the gonads of wasps from both sexes are severely underdeveloped. Preliminary screening for potential pathogen candidates by means of polymerase chain reaction and denaturating-gradient gel electrophoresis did not provide any indication of possible causative agents.