Development and Interrogation of a Transcriptomic Resource for the Giant Triton Snail (Charonia tritonis)

Gastropod molluscs are among the most abundant species that inhabit coral reef ecosystems. Many are specialist predators, along with the giant triton snail Charonia tritonis (Linnaeus, 1758) whose diet consists of Acanthaster planci (crown-of-thorns starfish), a corallivore known to consume enormous quantities of reef-building coral. C. tritonis are considered vulnerable due to overexploitation, and a decline in their populations is believed to have contributed to recurring A. planci population outbreaks. Aquaculture is considered one approach that could help restore natural populations of C. tritonis and mitigate coral loss; however, numerous questions remain unanswered regarding their life cycle, including the molecular factors that regulate their reproduction and development. In this study, we have established a reference C. tritonis transcriptome derived from developmental stages (embryo and veliger) and adult tissues. This was used to identify genes associated with cell signalling, such as neuropeptides and G protein-coupled receptors (GPCRs), involved in endocrine and olfactory signalling. A comparison of developmental stages showed that several neuropeptide precursors are exclusively expressed in post-hatch veligers and functional analysis found that FFamide stimulated a significant (20.3%) increase in larval heart rate. GPCRs unique to veligers, and a diversity of rhodopsin-like GPCRs located within adult cephalic tentacles, all represent candidate olfactory receptors. In addition, the cytochrome P450 superfamily, which participates in the biosynthesis and degradation of steroid hormones and lipids, was also found to be expanded with at least 91 genes annotated, mostly in gill tissue. These findings further progress our understanding of C. tritonis with possible application in developing aquaculture methods.

Plant-feeding may explain why the generalist predator Euseius stipulatus does better on less defended citrus plants but Tetranychus-specialists Neoseiulus californicus and Phytoseiulus persimilis do not

The generalist predator Euseius stipulatus (Athias-Henriot) and the Tetranychidae-specialist predators Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot play a key role in the regulation of Tetranychus urticae Koch in Spanish citrus orchards. Previous studies have shown that sour orange (Citrus aurantium L.) and Cleopatra mandarin (Citrus reshni hort. ex Tan.) display extreme resistance and susceptibility to T. urticae, respectively. When offered a choice between these two genotypes infested by T. urticae, E. stipulatus preferred Cleopatra mandarin, whereas the specialists did not show any preference. The present study was undertaken to check whether these preferences could be related to the feeding of E. stipulatus on the host plant and/or to differences in prey feeding on the two plants. Our results demonstrate that E. stipulatus is a zoophytophagous mite, which can engage in direct plant feeding in sour orange and Cleopatra mandarin, whereas neither N. californicus nor P. persimilis do so. Whereas Cleopatra mandarin provided a higher-quality prey/feeding substrate for E. stipulatus, which may be related to its phytophagy, no differences were observed for the two specialists. As higher constitutive and faster inducible defense against T. urticae in sour orange relative to Cleopatra mandarin plants result in sour orange supporting lower T. urticae densities and plant damage, our results demonstrate that pest regulation by specialist natural enemies may be more effective when prey feed on better defended plants.

The Millipede-Predation Behavior of Promecognathus and Exceptional Cyanide Tolerance in Promecognathus and Metrius (Coleoptera: Carabidae)

Promecognathus (Carabidae) includes beetles that are specialist predators whose prey are polydesmidan millipedes that produce highly toxic hydrogen cyanide and benzaldehyde as a defense, and it is unknown how Promecognathus overcomes these chemicals. We observed Promecognathus laevissimus (Dejean, 1829) and P. crassus (LeConte, 1868) in the laboratory and found that they did not use behaviors to avoid the chemical defenses of their prey, Xystocheir dissecta (Wood, 1867) (Polydesmida: Xystodesmidae). We tested benzaldehyde as a feeding deterrent and found noticeable deterrence in all carabid beetles tested except Promecognathus species and Metrius contractus (Eschscholtz, 1829). A total of 18 carabid species were exposed to cyanide vapors in an enclosed chamber for 10 min to determine their relative tolerances. Promecognathus and M. contractus were unaffected by HCN exposures 7–15 times greater than quantities that knocked down all other species. Promecognathus laevissimus and M. contractus were then exposed to high levels of HCN for 2 h, and while individuals of M. contractus succumbed, all P. laevissimus were still moving after 2 h. It is possible that Promecognathus evolved a high tolerance to cyanide as part of a suite of adaptations related to millipede predation. However, we have no plausible explanation for the high tolerance in Metrius, for which there is no evidence of millipede feeding. This is the first documented case of predatory insects that exhibit high tolerance and potential resistance to cyanide. Possibly, these beetles have a detoxification mechanism that is not cyanide specific, as their tolerance level far exceeds any dose they would encounter in their natural habitat.

Climbing rice plants above the waterline: escape of freshwater snails from underwater predation by snail-eating specialists

Freshwater molluscs have physical defences such as shells to protect their inner soft bodies from underwater predators. However, some predators have specialized mouthparts that can destroy the snail’s tough and/or spiral shells. Therefore, these snails could have evolved specific defences against their specialist predators. We observed the freshwater snail Austropeplea ollula (Pulmonata: Lymnaeidae) frequently climbing rice plants above the water in paddy fields in Shimane, central Japan. We also found the beetle larvae of Hydrophilus acuminatus (Coleoptera: Hydrophilidae), which are known as snail-eating specialists, in waters of the same paddy fields. We hypothesized that A. ollula climbs rice plants above the water to escape underwater predation by H. acuminatus and that the escape behaviour of snails may be specifically triggered by chemical cues from snail-eating specialists and/or killed conspecifics. To test both these hypotheses, we conducted laboratory experiments. The results demonstrated that chemical cues (e.g. body fluids) from killed conspecifics could trigger A. ollula to crawl above the waterline. Furthermore, chemical cues (e.g. scent and digestive enzymes) from H. acuminatus could promote the behaviour. Therefore, A. ollula can successfully escape from H. acuminatus by climbing the rice plants above the water.

Coexistence of three specialist predators of the hemlock woolly adelgid in the Pacific Northwest USA

The hemlock woolly adelgid (Hemiptera: Adelgidae: Adelges tsugae Annand) is an invasive insect, introduced from Japan to eastern North America, where it causes decline and death of hemlock trees. There is a closely related lineage of A. tsugae native to western North America. To inform classical biological control of A. tsugae in the eastern USA, the density and phenology of three native western adelgid specialist predators, Leucopis argenticollis (Zetterstedt), Le. piniperda (Malloch) (Diptera: Chamaemyiidae), and Laricobius nigrinus Fender (Coleoptera: Derodontidae), were quantified in the Pacific Northwest. Infested branches were collected from western hemlock (Pinaceae: Tsuga heterophylla (Raf.) Sarg.) at four sites around the Puget Sound, Washington and three sites in Oregon. Immature Leucopis were identified to species using DNA barcodes. Leucopis argenticollis was roughly twice as abundant as Le. piniperda. Laricobius nigrinus larvae were more abundant than the two species of Leucopis during the egg stage of the first adelgid generation, but Leucopis were present as feeding larvae during the second adelgid generation when La. nigrinus was aestivating in the soil, resulting in Leucopis being more abundant than La. nigrinus across the entire sampling period. Adelges tsugae and La. nigrinus densities were not correlated, while A. tsugae and Leucopis spp. densities were positively correlated. Leucopis spp. and La. nigrinus densities were negatively correlated. These results support the complementary use of La. nigrinus and the two Leucopis species for biological control of A. tsugae in the eastern USA, and point to the need for further investigation of spatial and temporal niche partitioning among the three predator species.

THE POPULATION OF WHITE-BELLIED PLANTHOPPERS AND THEIR NATURAL ENEMIES: THE NEW PEST OF CORN IN LAMPUNG

The Population of White-Bellied Planthoppers and their Natural Enemies: the New Pest of Corn in Lampung. The white-bellied planthoppers (Stenocranus pasificus), hereinafter referred to as WBP, as new exotic pests in Lampung have the poten-tial to reduce corn production and threaten national food sovereignty. Therefore, population of the pest needs to be managed to prevent the outbreaks. However, there is still limited information on the bio-ecology of WBP. Thus, this research was conducted to: 1) study the population growth pattern of WBP on various corn cultivars and 2) document the natural enemies of WBP. This research was carried out from May to December 2017with a survey method on several corn fields in South Lampung and planting trial on an experimental field of Faculty of Agriculture, Universitas Lampung planted with 3 corn cultivars, i.e. Madura, P-27 and NK which were arranged in randomized complete block design with three replications. The results of the research showed: 1) there were two peaks of population density observed during plant growth. The peak of adult stage of macroptera population density occurred at 17 and 53 days after planting (dap), the highest number of leaves with oviposition mass was observed at 24 and 65 dap, while the peak of population density of nymph stage and adult stage of brachiptera occurred at 31 and 75 dap; 2) Natural enemies of WBP included 9 orders, classified as specialist predators of mirid bugs (Cyrtorhynus) and rove beetles (Paederus), and generalist predators of spiders (Araneae) and lady beetles (Coccinellidae). The population of specialist predators was fluctuated depending on WBP population, while the population of generalist predators was varied.