Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae) and Its Fungal Symbiont Ambrosiella roeperi Associated with Arecanut Kernel Decay in Karnataka, India

Xylosandrus crassiusculus (Coleoptera: Curculionidae: Scolytinae) is reported causing damage to areca palm plantations (Areca catechu L.—Arecaceae) in Karnataka (India). In particular, X. crassiusculus has been observed attacking and successfully reproducing on areca nuts; besides the new host plant record, the data provided here represent the first documented case of spermatophagy for this xyleborine beetle. All infestation symptoms of this polyphagous pest were documented and illustrated. The identity of the scolytid, besides morphologically, was confirmed by its DNA barcoding. Eggs, larvae and pupae were found within the galleries of infested kernels. All galleries of the infested kernels were characterized by the presence of whitish to greyish fungal growth. The fungus was identified as Ambrosiella roeperi, a known symbiont of Xylosandrus crassiusculus. Incidence of this symbiotic insect-fungus complex in the economic part of arecanut, i.e., the kernel, is of serious concern. In a climate change scenario, this beetle with fungal symbionts may pose a serious threat to arecanut production in India and elsewhere.

Viability and infectivity of Ceratobasidium encapsulated in alginate beads under different storage conditions

Mycorrhizal fungi are important partners of orchids because they establish close symbiotic relationships with this group of plants, and its preservation is also important for the successful conservation of orchids. In the present study, the conservation of Ceratobasidium sp., a fungal symbiont, using encapsulation in alginate beads was tested over different times, temperatures of storage and dehydrated conditions. Osmotically dehydrated and air-dried beads were stored at room temperature (20 ± 2°C), 4°C, -20°C and - 80°C. The fungal growth was verified after 4, 8, 26 and 96 weeks. A second test was carried out to evaluate the encapsulations of fungi as a form of inoculation in Trichoceros antennifer orchid to promote symbiosis and plants development. The results show that the encapsulation of Ceratobasidium in alginate beads is a viable strategy for its conservation, the beads are of easy manipulation and promote plant growth when inoculated in plant substrate. These results may be adopted as part of effective conservation strategies for mycorrhizal fungi and orchids.

Fungal Associates of Soft Scale Insects (Coccomorpha: Coccidae)

Ophiocordyceps fungi are commonly known as virulent, specialized entomopathogens; however, recent studies indicate that fungi belonging to the Ophiocordycypitaceae family may also reside in symbiotic interaction with their host insect. In this paper, we demonstrate that Ophiocordyceps fungi may be obligatory symbionts of sap-sucking hemipterans. We investigated the symbiotic systems of eight Polish species of scale insects of Coccidae family: Parthenolecanium corni, Parthenolecanium fletcheri, Parthenolecanium pomeranicum, Psilococcus ruber, Sphaerolecanium prunasti, Eriopeltis festucae, Lecanopsis formicarum and Eulecanium tiliae. Our histological, ultrastructural and molecular analyses showed that all these species host fungal symbionts in the fat body cells. Analyses of ITS2 and Beta-tubulin gene sequences, as well as fluorescence in situ hybridization, confirmed that they should all be classified to the genus Ophiocordyceps. The essential role of the fungal symbionts observed in the biology of the soft scale insects examined was confirmed by their transovarial transmission between generations. In this paper, the consecutive stages of fungal symbiont transmission were analyzed under TEM for the first time.

What Determines Host Range and Reproductive Performance of an Invasive Ambrosia Beetle Euwallacea fornicatus; Lessons From Israel and California

This study examined the polyphagous shot hole borer (PSHB) Euwallacea fornicatus (Coleoptera; Scolytinae) native to Southeast Asia and concentrated on its wide host range in two of the invaded areas, California and Israel. Among the 583 examined tree species, 55.9% were characterized as “non-reproductive hosts” and only 13.8% were characterized as “reproductive hosts,” suitable for the E. fornicatus reproduction. Families that included ≥20 species and genera with ≥10 were considered for further analysis. The highest percentage of tree species suitable for reproduction was obtained for Salicaceae and Sapindaceae, whereas the lowest percentage of tree species belonging to this category were within the Rosaceae, Myrtaceae, and Magnoliaceae. The genera Acer, Quercus and Acacia displayed the highest percentage within the “reproductive host” category, with the former significantly higher from all seven of the studied genera. We found that all Brachychiton and Erythrina were attacked and none of the examined 20 Eucalyptus spp. were suitable for E. fornicatus reproduction. The results suggest discordance between host tree phylogeny and susceptibility to the E. fornicatus, indicating that trait correlation of susceptibility of different tree species to the E. fornicatus are the results of convergent evolution and not of a common descent. A theoretical model, suggesting the different possibilities of potential tree species becoming attractive or non-attractive to E. fornicatus attack, is described. It is suggested that the beetle reproduction success rate over a wide host range, as well as the long list of species belonging to the “non-reproductive host” category, is the outcome of interactions between the beetle fungal symbiont, F. euwallaceae, and sapwood of the attacked tree. The model suggests that a tree selected by the E. fornicatus may fall in one of three groups, (i) those in which F. euwallaceae is unable to develop, (ii) those tree species that slow the development of the fungus, and (iii) those that enable F. euwallaceae to thrive. Hence, the host range suitable for beetle reproduction is determined by development of F. euwallaceae. In general, PSHB does not distinguish between host species of the “non-reproductive host” and “reproductive host” categories.

Electrophysiological and Behavioral Responses of an Ambrosia Beetle to Volatiles of its Nutritional Fungal Symbiont

Ambrosia beetles (Coleoptera: Scolytinae) cultivate their fungal symbiont within host substrates as the sole source of nutrition on which the larvae and adults must feed. To investigate a possible role for semiochemicals in this interaction, we characterized electrophysiological and behavioral responses of Xylosandrus germanus to volatiles associated with its fungal symbiont Ambrosiella grosmanniae. During still-air walking bioassays, X. germanus exhibited an arrestment response to volatiles of A. grosmanniae, but not antagonistic fungi Beauveria bassiana, Metarhizium brunneum, Trichoderma harzianum, the plant pathogen Fusarium proliferatum, or malt extract agar. Solid phase microextraction-gas chromatography-mass spectrometry identified 2-ethyl-1-hexanol, 2-phenylethanol, methyl benzoate and 3-methyl-1-butanol in emissions from A. grosmanniae; the latter two compounds were also detected in emissions from B. bassiana. Concentration-responses using electroantennography documented weak depolarizations to A. grosmanniae fungal volatiles, unlike the comparatively strong response to ethanol. When tested singly in walking bioassays, volatiles identified from A. grosmanniae elicited relatively weak arrestment responses, unlike the responses to ethanol. Xylosandrus germanus also exhibited weak or no long-range attraction to the fungal volatiles when tested singly during field trials in 2016–2018. None of the fungal volatiles enhanced attraction of X. germanus to ethanol when tested singly; in contrast, 2-phenylethanol and 3-methyl-1-butanol consistently reduced attraction to ethanol. Volatiles emitted by A. grosmanniae may represent short-range olfactory cues that could aid in distinguishing their nutritional fungal symbiont from other fungi, but these compounds are not likely to be useful as long-range attractants for improving detection or mass trapping tactics.

You don’t have the guts: a diverse set of fungi survive passage through Macrotermes bellicosus termite guts

Background Monoculture farming poses significant disease challenges, but fungus-farming termites are able to successfully keep their monoculture crop free from contamination by other fungi. It has been hypothesised that obligate gut passage of all plant substrate used to manure the fungal symbiont is key to accomplish this. Here we refute this hypothesis in the fungus-farming termite species Macrotermes bellicosus. Results We first used ITS amplicon sequencing to show that plant substrate foraged on by termite workers harbour diverse fungal communities, which potentially could challenge the farming symbiosis. Subsequently, we cultivated fungi from dissected sections of termite guts to show that fungal diversity does not decrease during gut passage. Therefore, we investigated if healthy combs harboured these undesirable fungal genera, and whether the presence of workers affected fungal diversity within combs. Removal of workers led to a surge in fungal diversity in combs, implying that termite defences must be responsible for the near-complete absence of other fungi in functioning termite gardens. Conclusions The rapid proliferation of some of these fungi when colonies are compromised indicates that some antagonists successfully employ a sit-and-wait strategy that allows them to remain dormant until conditions are favourable. Although this strategy requires potentially many years of waiting, it prevents these fungi from engaging in an evolutionary arms race with the termite host, which employs a series of complementary behavioural and chemical defences that may prove insurmountable.

Screening for susceptibility of Macadamia to E. fornicatus and its fungal symbiont Fusarium euwallaceae.

The polyphagous shothole borer (Euwallacea fornicatus, PSHB), an ambrosia beetle, with its fungal symbiont, Fusarium euwallaceae, is responsible for Fusarium Dieback (FD) in a wide range of woody hosts. In 2019, the first suspected case of E. fornicatus was reported in macadamia in South Africa. The aims of this study were to confirm the E. fornicatus report and thereafter to assess the susceptibility of commercially planted macadamia cultivars to FD caused by F. euwallaceae. The identities of the beetle and associated fungal symbionts were confirmed by means of DNA sequence analysis of the 28S ribosomal large subunit gene for beetles and the internal transcribed spacer region for fungi. Isolates identified as Fusarium species were further characterised by phylogenetic analysis of the translation elongation factor 1α and the β-tubulin gene regions. Thereafter, Koch’s postulates regarding F. euwallaceae were fulfilled on a mature Macadamia integrifolia tree planted at the experimental farm of the University of Pretoria. In order to determine susceptibility against FD, additional cultivar screening was conducted on nine commercially planted cultivars by means of pathogenicity trials using sterilized or inoculated toothpicks inserted into detached branches. Detached branch inoculations showed no significant lesion development six weeks post inoculation, except for cultivar 816. The restricted growth of F. euwallaceae observed in macadamia tissues therefore suggests that macadamia may not be a suitable host for F. euwallaceae and that the threat of FD in macadamia in the event of E. fornicatus infestation is less than for other E. fornicatus hosts. Future work on beetle attraction to macadamia is recommended for a more comprehensive understanding of the interaction between E. fornicatus and its fungal symbionts and macadamia.