The maxillary palps of Tephritidae are selectively tuned to food volatiles and diverge with ecology

The maxillary palp is an auxiliary olfactory organ in insects, which, different from the antennae, is equipped with only a few olfactory sensory neuron (OSN) types. We postulated that these derived mouthpart structures, positioned at the base of the proboscis, may be particularly important in mediating feeding behaviors. As feeding is spatio-temporally segregated from oviposition in most Tephritidae, this taxonomic group appears quite suitable to parse out sensory breadth and potential functional divergence of palps and antennae. Scanning electron microscopy and anterograde staining underlined the limited palpal olfactory circuit in Tephritidae: only three morphological subtypes of basiconic sensilla were found, each with two neurons, and project to a total of six antennal lobe glomeruli in Bactrocera dorsalis. Accordingly, the palps detected only few volatiles from the headspace of food (fermentation and protein lures) and fruit (guava and mango) compared to the antennae (17 over 77, using gas-chromatography coupled electrophysiology). Interestingly, functionally the antennae were more tuned to fruit volatiles, detecting eight times more fruit than food volatiles (63 over 8), whereas the number of fruit and food volatile detection was more comparable in the palps (14 over 8). As tephritids diverge in oviposition preferences, but converge on food substrates, we postulated that the receptive ranges of palpal circuits would be more conserved compared to the antennae. However, palpal responses of three tephritid species that differed in phylogenetic relatedness and ecologically niche, diverged across ecological rather than phylogenetic rifts. Two species with strongly overlapping ecology, B. dorsalis and Ceratitis capitata, showed inseparable response profiles, whereas the cucurbit specialist Zeugodacus cucurbitae strongly diverged. As Z. cucurbitae is phylogenetically placed between B. dorsalis and C. capitata, the results indicate that ecology overrides phylogeny in the evolution of palpal tuning, in spite of being predisposed to detecting food volatiles.

Heavy metal pollution in leachates and its impacts on the quality of groundwater resources around Iringa municipal solid waste dumpsite

Heavy metal pollution in groundwater due to leachates leaking from the Iringa municipal dumpsite was investigated. The pollution was studied by analyzing pH, electrical conductivity (EC), total dissolved solids (TDS), and heavy metals (Fe, Pb, Cr, Cd, Cu, Ni, Mn, and Zn) in leachates collected within the dumpsite and groundwater samples from residential wells close to the dumpsite. The pH of the leachate samples varied from 7.40 to 9.10, implying alkaline behavior and the methanogenic phase of solid waste deposits. The levels of EC, TDS, and heavy metals (Fe, Pb, Cr, Cu, Ni, Mn, and Zn) in leachates were above the national and/or international standards. On other hand, groundwater samples presented pH values ranging from 7.15 to 7.60 which were within the World Health Organization acceptable limit. The concentrations of EC, TDS, Fe, Pb, Ni, Mn, and Zn in most groundwater samples exceeded the national and/or international permissible limits for drinking water. In addition, the water quality indices (WQI) of groundwater samples ranged between 8.30 and 17.90, which implied the excellent quality of groundwater sources. However, the presence of high levels of heavy metals above the permissible limits in both leachate and groundwater samples signified potential risks to the environment and public health. Therefore, the present study calls for proper management of municipal solid waste to reduce the potential risks of further contamination on the groundwater resources and environment around the Iringa municipal dumpsite.

Diverging olfactory sensitivities to yeast volatiles reflect resource partitioning of tephritids and drosophilids

As pests of fruits and vegetables, ovipositing tephritid fruit flies are infamous for their frugivory. Yet, adult tephritids have remained saprophytic in their feeding behavior, as they require decomposing, protein rich media for sexual maturation and oogenesis. Drosophilid fruit flies, in contrast, are saprophytic both during oviposition and feeding. Here we compared the sensory and behavioral responses of two tephritid (Bactrocera dorsalis and Ceratitis capitata) and two drosophilid species (Drosophila melanogaster and Drosophila suzukii) to differentially aged cultures of the yeast Saccharomyces cerevisiae. We assessed convergence and divergence in the detection of and behavioral response to these attractive substrates, and how these might be linked to the roles of the substrates for the different taxa. The headspace shifted substantially as broth cultures transitioned from active (1-day) to inactive (8- and 15-days). Interestingly, Drosophila flies were significantly attracted to actively fermenting 1-day old yeast cultures, whereas the preference shifted to older cultures for the tephritids. Bactrocera dorsalis flies preferred inactive, lysing cultures (8- and 15-days old). We identified compounds from the 1- to 8-days old broth cultures that elicited antennal responses in each species. Synthetic blends composed of antennally active compounds evoked similar behavioral responses as broth cultures. Similarly, the attractiveness of less attractive broth cultures (1- and 8-days old for drosophilids and tephritids, respectively) could be augmented by adding volatiles of the more attractive cultures. The results show that the volatile profiles of fermenting substrates evolve quantitatively and qualitatively, and that fly species key into volatile blends that indicate suitability of the substrates for their purposes. For drosophilids early arrival at fermenting substrates confers a competitive advantage to offspring. In contrast, for tephritid the concentration and availability of protein is facilitated by older, lysed yeast cultures. The data from this comparative study are also instrumental in the development of novel lures for these pests.

Translating olfactomes into attractants: shared volatiles provide attractive bridges for polyphagy in fruit flies

Tephritid flies are serious fruit pests. Despite clear niche differences, many species show considerable overlap in fruit preferences, of which we here analysed the olfactory correlate. Using the volatiles of four unrelated fruit species, antennal responses were quantified to construct a fruit-odour response database for four tephritid species. Although responses were distinct with a significant niche-correlated bias, the analyses show that the probability of detection of a volatile strongly increased with its sharedness across fruits. This also held for the unrelated fruit fly Drosophila melanogaster (DoOR repository-based analyses). We conjectured that shared volatiles signify 'host' to the fly 'nose' and induce attraction. Indeed, blends of volatiles shared by fruit and detected by all four species were very attractive for tephritid species, more than fruits. Quantitative whole antennal recordings en lieu of, or complementing bottom-up molecular neurogenetic approaches, enables comparative olfactomics in non-model species, and facilitate interpretation of olfaction in evolutionary, ecological, and applied contexts.

Anticonvulsant activity of extracts of Diospyros fischeri stem bark

Evaluation of extracts of Diospyros fischeri Gurke (Ebenaceae), which is used traditionally for the treatment of epilepsy shows that the aqueous extract of the tem bark has no effect against picrotoxin induced convulsions in mice. However, an 80% ethanol extract of the bark caused dose-dependent suppression of convulsions induced by 10 mg/kg body wt picrotoxin, at doses between 100-3200 mg/kg body wt. Petroleum ether, 1:1 dichloromethane:methanol, and methanol extracts also suppressed picrotoxin-induced convulsions, but had a slightly lower inhibitory effect. The petroleum ether extract was the most active, but all were less active than the ethanol extract. Unlike phenobarbitone, which at 50 mg/kg body wt completely suppressed convulsions induced by 10 mg/kg body wt picrotoxin, none of the plant extracts completely suppressed convulsions in the mice. These results support the traditional uses of D.fischeri for the treatment of epilepsy. Given the seemingly innocuous nature of the extracts more work is suggested to ascertain their clinical application.