A pinboard by
Vivian Mendez

Research Fellow, Macquarie University


Domestication effects on the life-history of Bactrocera tryoni, the Queensland Fruit Fly

Queensland fruit fly is the most economically damaging insect pest of Australia’s $9 billion pa horticultural sector, presenting a very significant barrier to domestic and international trade. Traditional insecticide-based control measures lead to environmental contamination and can leave hazardous residues on produce. My research supports the development of the Sterile Insect Technique (SIT), a chemical-free technique used for sustainable and environmentally safe management of the Queensland fruit fly. SIT entails the release of millions of sterile male flies that induce reproductive failure in females of pest populations, causing those populations to crash. SIT can take Australia a long way toward sustainable production of safe food. Massive production of flies is required for SIT. Flies that have been collected from nature are ‘domesticated’ for artificial rearing and then bred in a factory. The South Australian government has recently constructed a factory that will produce up to 100 million sterile flies each week. Sterile male flies produced by the factory will be released by aircraft to protect crops and to combat outbreaks in towns in the field by mating with wild females, preventing them from producing fertile eggs. My project focuses on how the domestication of factory colonies affects their physiology and behaviour, and hence their compatibility with wild populations and their suitability for use in SIT programs. Domestication and factory rearing impose significant stresses on the wild flies used to start a colony. For example, females are forced to lay eggs in oviposition devices instead of fruits, as a result, only some of the females adapt to the factory conditions and pass their genes to the next generation. During this domestication process, some traits are favoured and become exaggerated while others are lost. Some of the lost traits might be critical for the survival and sexual performance of the males once they are released in the field to compete with the wild males for matings. This is my main interest, as we strive to develop the most effective possible processes to ensure sustainability and a high level of crop protection in the field. My work is helping to establish the best domestication and rearing practices in the Queensland fruit fly SIT factory.


Purification and functional characterization of lectin with phenoloxidase activity from the hemolymph of cockroach, Periplaneta americana.

Abstract: Lectins also identified as hemagglutinins are multivalent proteins and on account of their fine sugar-binding specificity play an important role in immune system of invertebrates. The present study was carried out on the hemolymph lectin of cockroach, Periplaneta americana with appropriate screening and purification to understand its molecular as well as functional nature. The lectin from the hemolymph was purified using ion-exchange chromatography. The approximate molecular weight of purified lectin was 340 kDa as determined by FPLC analysis. Rabbit erythrocytes were highly agglutinated with purified lectin from the hemolymph of P. americana. The hemagglutination activity (HA) of lectin was specifically inhibited by fucose. Glycoproteins also inhibited the HA activity of lectin. The amino acid sequences of the purified lectin revealed homology with amino acid sequences of allergen proteins from P. americana. Purified lectin showed the highest phenoloxidase activity against dopamine. The activators such as exogenous proteases and LPS from Escherichia coli and Salmonella minnesota significantly enhanced the PO activity of the purified lectin. Besides, the presence of copper and hemocyanin conserved domain in the purified lectin provided a new facet that insects belonging to the ancient clade such as cockroaches retained some traces of evolutionary resemblance in possessing lectin of ancient origin.

Pub.: 31 May '17, Pinned: 28 Nov '17

New activity of yamamarin, an insect pentapeptide, on immune system of mealworm, Tenebrio molitor.

Abstract: In insects, two types of the immune responses, cellular and humoral, constitute a defensive barrier against various parasites and pathogens. In response to pathogens, insects produce a wide range of immune agents that act on pathogens directly, such as cecropins or lysozyme, or indirectly by the stimulation of hemocyte migration or by increasing phenoloxidase (PO) activity. Recently, many new immunologically active substances from insects, such as peptides and polypeptides, have been identified. Nevertheless, in the most cases, their physiological functions are not fully known. One such substance is yamamarin - a pentapeptide isolated from the silk moth Antheraea yamamai. This yamamarin possesses strong antiproliferative properties and is probably involved in diapause regulation. Here, we examined the immunotropic activity of yamamarin by testing its impact on selected functions of the immune system in heterologous bioassays with the beetle Tenebrio molitor, commonly known as a stored grains pest. Our results indicate that the pentapeptide affects the activity of immune processes in the beetle. We show that yamamarin induces changes in both humoral and cellular responses. The yamamarin increases the activity of PO, as well as causes changes in the hemocyte cytoskeleton and stimulates phagocytic activity. We detected an increased number of apoptotic hemocytes, however after the yamamarin injection, no significant variations in the antibacterial activity in the hemolymph were observed. The obtained data suggest that yamamarin could be an important controller of the immune system in T. molitor.

Pub.: 13 Sep '17, Pinned: 28 Nov '17

The Value of a Comparative Approach to Understand the Complex Interplay between Microbiota and Host Immunity.

Abstract: The eukaryote immune system evolved and continues to evolve within a microbial world, and as such is critically shaped by-and in some cases even reliant upon-the presence of host-associated microbial species. There are clear examples of adaptations that allow the host to simultaneously tolerate and/or promote growth of symbiotic microbiota while protecting itself against pathogens, but the relationship between immunity and the microbiome reaches far beyond simple recognition and includes complex cross talk between host and microbe as well as direct microbiome-mediated protection against pathogens. Here, we present a broad but brief overview of how the microbiome is controlled by and interacts with diverse immune systems, with the goal of identifying questions that can be better addressed by taking a comparative approach across plants and animals and different types of immunity. As two key examples of such an approach, we focus on data examining the importance of early exposure on microbiome tolerance and immune system development and function, and the importance of transmission among hosts in shaping the potential coevolution between, and long-term stability of, host-microbiome associations. Then, by comparing existing evidence across short-lived plants, mouse model systems and humans, and insects, we highlight areas of microbiome research that are strong in some systems and absent in others with the hope of guiding future research that will allow for broad-scale comparisons moving forward. We argue that such an approach will not only help with identification of generalities in host-microbiome-immune interactions but also improve our understanding of the role of the microbiome in host health.

Pub.: 30 Sep '17, Pinned: 28 Nov '17

The more the merrier: Conspecific density improves performance of gregarious larvae and reduces susceptibility to a pupal parasitoid

Abstract: Aggregation can confer advantages in animal foraging, defense, and thermoregulation. There is a tight connection between the evolution of insect sociality and a highly effective immune system, presumably to inhibit rapid disease spread in a crowded environment. This connection is less evident for animals that spend only part of their life cycle in a social environment, such as noneusocial gregarious insects. Our aim was to elucidate the effects of group living by the gregarious larvae of the Glanville fritillary butterfly with respect to individual performance, immunity, and susceptibility to a parasitoid. We were also interested in the role of family relative to common postdiapause environment in shaping life-history traits. Larvae were reared at high or low density and then exposed to the pupal parasitoid wasp Pteromalus apum, either in presence or absence of a previous immune challenge that was used to measure the encapsulation immune response. Surviving adult butterflies were further tested for immunity. The wasp offspring from successfully parasitized butterfly pupae were counted and their brood sex ratios assessed. Larvae reared at high density grew larger and faster than those at low density. Despite high mortality due to parasitism, survival was greater among individuals with high pupal immunity in both density treatments. Moreover, butterfly pupae reared at high density were able to kill a larger fraction of individuals in the parasitoid broods, although this did not increase survival of the host. Finally, a larger proportion of variation observed in most of the traits was explained by butterfly family than by common postdiapause rearing environment, except for adult survival and immunity, for which this pattern was reversed. This gregarious butterfly clearly benefits from high conspecific density in terms of developmental performance and its ability to fight a parasitoid. These positive effects may be driven by cooperative interactions during feeding.

Pub.: 07 Nov '17, Pinned: 28 Nov '17

Optimising irradiation dose in mass-produced Queensland fruit fly, Bactrocera tryoni, for sterile insect release: the incorporation of residual effects on F1 progeny

Abstract: The sterile insect technique (SIT) is a potential tool for the management and eradication of incursions of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). Mass-produced B. tryoni are irradiated during the pupal stage to induce reproductive sterility. As increasing irradiation dosage results in declining fly quality, determining the lowest possible dosage that induces sufficient reproductive sterility is of particular interest. However, in calculating reproductive sterility, previous research has not considered carryover irradiation effects to F1 progeny. To test for these effects, B. tryoni pupae were exposed to one of five target dose ranges: 0, 20–25, 40–45, 60–65, or 70–75 Gy. Upon adult eclosure, fly quality was assessed using standard quality control (QC) measures: adult eclosure rates, flight ability, sex ratio, and longevity under nutritional stress. No effect of irradiation dose on any of the QC measures was found. Residual fertility was assessed by measuring larval eclosure failure for all doses. For the 0–45 Gy doses, mortality was measured during development of F1 progeny and larval eclosure rates were measured in F2 progeny. For irradiated females, irradiation dose significantly affected egg production, as well as increasing mortality during pupation of F1 progeny. For irradiated males, irradiation dose strongly affected larval eclosure of F1 progeny and, similar to females, mortality increased during pupation with higher doses. Our results suggest that residual effects of irradiation dose decreases F1 progeny viability and current estimates of residual fertility for B. tryoni underestimate the actual residual fertility. We conclude by synthesising our results with the previous findings and we propose that the target irradiation dose for B. tryoni may be lowered to 55–60 Gy.

Pub.: 21 Jan '17, Pinned: 20 Oct '17

Raspberry ketone supplements promotes early sexual maturation in male Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae).

Abstract: Raspberry ketone (RK) is highly attractive to sexually mature, but not immature, males of many Bactrocera species, including Queensland fruit fly ('Qfly', Bactrocera tryoni), and acts as a metabolic enhancer in a wide diversity of animals. We considered the possibility that, as a metabolic enhancer, RK in adult diet might accelerate sexual maturation of male Qflies.Recently emerged adult Qfly males (0-24 hrs old) were exposed to RK-treated food for 48 hours and were then provided only sugar and water. Four doses of RK (1.25, 2.5, 3.75 and 5 %) along with 0% control were tested with two types of food: sugar alone and sugar mixed with yeast hydrolysate (3:1). For flies tested when 4 - 10 days old, all RK doses increased mating probability of flies fed sugar mixed with yeast hydrolysate but did not show any effect in mating probability of flies fed only sugar. No effects of RK were found for flies tested when 10 - 30 days old for either diet group. There was no evidence that RK affected longevity at any of the doses tested.Feeding of RK together with yeast hydrolysate to immature Qfly increases mating propensity at young ages and accordingly shows significant potential as a pre-release supplement that might increase the proportion of released flies that attain sexual maturation in Sterile Insect Technique programs.

Pub.: 01 Feb '17, Pinned: 20 Oct '17

Evolutionary genomics of grape (Vitis vinifera ssp. vinifera) domestication.

Abstract: We gathered genomic data from grapes (Vitis vinifera ssp. vinifera), a clonally propagated perennial crop, to address three ongoing mysteries about plant domestication. The first is the duration of domestication; archaeological evidence suggests that domestication occurs over millennia, but genetic evidence indicates that it can occur rapidly. We estimated that our wild and cultivated grape samples diverged ∼22,000 years ago and that the cultivated lineage experienced a steady decline in population size (Ne ) thereafter. The long decline may reflect low-intensity management by humans before domestication. The second mystery is the identification of genes that contribute to domestication phenotypes. In cultivated grapes, we identified candidate-selected genes that function in sugar metabolism, flower development, and stress responses. In contrast, candidate-selected genes in the wild sample were limited to abiotic and biotic stress responses. A genomic region of high divergence corresponded to the sex determination region and included a candidate male sterility factor and additional genes with sex-specific expression. The third mystery concerns the cost of domestication. Annual crops accumulate putatively deleterious variants, in part due to strong domestication bottlenecks. The domestication of perennial crops differs from that of annuals in several ways, including the intensity of bottlenecks, and it is not yet clear if they accumulate deleterious variants. We found that grape accessions contained 5.2% more deleterious variants than wild individuals, and these were more often in a heterozygous state. Using forward simulations, we confirm that clonal propagation leads to the accumulation of recessive deleterious mutations but without decreasing fitness.

Pub.: 19 Oct '17, Pinned: 20 Oct '17