Baldwyn Torto

Aggregation pheromone system of adult gregarious desert locust schistocerca gregaria (forskal)

Hexanal, octanal, nonanal, decanal, hexanoic acid, octanoic acid, nonanoic acid, and decanoic acid were identified in the volatile emissions from fifth instars ofSchistocerca gregaria by coupled gas chromatography-electroantennography (GC-EAD) detection and coupled GC-mass spectrometry (MS). In laboratory assays, synthetic blends of the eight compounds, with acids and aldehydes tested separately, evoked strong aggregation responses from fifth instars, similar to responses evoked by a crude volatile extract of the nymphs. A nymphal fecal volatile phenolic blend of guaiacol and phenol, which we have previously shown to evoke an aggregative response from different stages of the insect, significantly synergized the activity of the blend of eight compounds, suggesting mutually augmentative roles for nymphal and fecal volatiles in evoking aggregation. These results indicate that the aggregation behavior of gregarious second to fifth instars is modulated by three sets of pheromonal compounds: aldehydes and acids emitted by the nymphs themselves and phenols associated with their feces.

Evidence for mediation of two releaser pheromones in the aggregation behavior of the gregarious desert locust, Schistocerca gregaria (Forskal) (Orthoptera: Acrididae)

The response of nymphal and adult gregarious phase desert locust,Schistocerca gregaria, to a choice of two columns of air, one permeated with airborne volatiles emanating from nymphs or adults and the other untreated, was investigated in a single-chamber bioassay arena. The nymphs, whether released individually or in groups, preferred to be within the precinct of the air column treated with airborne volatiles of the nymphs but were indifferent to volatiles of the adults. Conversely, older adults responded only to their own volatiles but not to those of the nymphs or young adults. The young adults were responsive only to volatiles of the older adults. Charcoal-trapped volatiles from the nymphs and the adults reproduced the effect of living locusts. These results indicate that there are two different aggregation pheromones inS. gregaria: a juvenile pheromone produced by nymphs and an adult pheromone specific to adults.

Odorants that Induce Hygienic Behavior in Honeybees: Identification of Volatile Compounds in Chalkbrood-Infected Honeybee Larvae

Social insects that live in large colonies are vulnerable to disease transmission due to relatively high genetic relatedness among individuals and high rates of contact within and across generations. While individual insects rely on innate immune responses, groups of individuals also have evolved social immunity. Hygienic behavior, in which individual honeybees detect chemical stimuli from diseased larvae and subsequently remove the diseased brood from the nest, is one type of social immunity that reduces pathogen transmission. Three volatile compounds, collected from larvae infected with the fungal pathogen Ascosphaera apis and detected by adult honey bees, were identified by coupled gas chromatography-electroantennographic detection and gas chromatography-mass spectrometry. These three compounds, phenethyl acetate, 2-phenylethanol, and benzyl alcohol, were present in volatile collections from infected larvae but were absent from collections from healthy larvae. Two field bioassays revealed that one of the compounds, phenethyl acetate is a key compound associated with Ascosphaera apis-infected larvae that induces hygienic behavior.

Multitrophic interaction facilitates parasite–host relationship between an invasive beetle and the honey bee

Colony defense by honey bees, Apis mellifera, is associated with stinging and mass attack, fueled by the release of alarm pheromones. Thus, alarm pheromones are critically important to survival of honey bee colonies. Here we report that in the parasitic relationship between the European honey bee and the small hive beetle, Aethina tumida, the honey bees alarm pheromones serve a negative function because they are potent attractants for the beetle. Furthermore, we discovered that the beetles from both Africa and the United States vector a strain of Kodamaea ohmeri yeast, which produces these same honey bee alarm pheromones when grown on pollen in hives. The beetle is not a pest of African honey bees because African bees have evolved effective methods to mitigate beetle infestation. However, European honey bees, faced with disease and pest management stresses different from those experienced by African bees, are unable to effectively inhibit beetle infestation. Therefore, the environment of the European honey bee colony provides optimal conditions to promote the unique bee–beetle–yeast–pollen multitrophic interaction that facilitates effective infestation of hives at the expense of the European honey bee.

Behavioural response of the malaria vector Anopheles gambiae to host plant volatiles and synthetic blends

BackgroundSugar feeding is critical for survival of malaria vectors and, although discriminative plant feeding previously has been shown to occur in Anopheles gambiae s.s., little is known about the cues mediating attraction to these plants. In this study, we investigated the role of olfaction in An. gambiae discriminative feeding behaviour.MethodsDual choice olfactometer assays were used to study odour discrimination by An. gambiae to three suspected host plants: Parthenium hysterophorus (Asteraceae), Bidens pilosa (Asteraceae) and Ricinus communis (Euphorbiaceae). Sugar content of the three plant species was determined by analysis of their trimethylsilyl derivatives by coupled gas chromatography–mass spectrometry (GC-MS) and confirmed with authentic standards. Volatiles from intact plants of the three species were collected on Super Q and analyzed by coupled GC-electroantennographic detection (GC-EAD) and GC-MS to identify electrophysiologically-active components whose identities were also confirmed with authentic standards. Active compounds and blends were formulated using dose–response olfactory bioassays. Responses of females were converted into preference indices and analyzed by chi-square tests. The amounts of common behaviourally-active components released by the three host plants were compared with one-way ANOVA.ResultsOverall, the sugar contents were similar in the two Asteraceae plants, P. hysterophorus and B. pilosa, but richer in R. communis. Odours released by P. hysterophorus were the most attractive, with those from B. pilosa being the least attractive to females in the olfactometer assays. Six EAD-active components identified were consistently detected by the antennae of adult females. The amounts of common antennally-active components released varied with the host plant, with the highest amounts released by P. hysterophorus. In dose–response assays, single compounds and blends of these components were attractive to females but to varying levels, with one of the blends recording a significantly attractive response from females when compared to volatiles released by either the most preferred plant, P. hysterophorus (χ2 = 5.23, df = 1, P < 0.05) or as a synthetic blend mimicking that released by P. hysterophorus.ConclusionsOur results demonstrate that (a) a specific group of plant odours attract female An. gambiae (b) females use both qualitative and quantitative differences in volatile composition to associate and discriminate between different host plants, and (c) altering concentrations of individual EAD-active components in a blend provides a practical direction for developing effective plant-based lures for malaria vector management.

Evaluation of the Distribution and Impacts of Parasites, Pathogens, and Pesticides on Honey Bee (Apis mellifera) Populations in East Africa

In East Africa, honey bees (Apis mellifera) provide critical pollination services and income for small-holder farmers and rural families. While honey bee populations in North America and Europe are in decline, little is known about the status of honey bee populations in Africa. We initiated a nationwide survey encompassing 24 locations across Kenya in 2010 to evaluate the numbers and sizes of honey bee colonies, assess the presence of parasites (Varroa mites and Nosema microsporidia) and viruses, identify and quantify pesticide contaminants in hives, and assay for levels of hygienic behavior. Varroa mites were present throughout Kenya, except in the remote north. Levels of Varroa were positively correlated with elevation, suggesting that environmental factors may play a role in honey bee host-parasite interactions. Levels of Varroa were negatively correlated with levels of hygienic behavior: however, while Varroa infestation dramatically reduces honey bee colony survival in the US and Europe, in Kenya Varroa presence alone does not appear to impact colony size. Nosema apis was found at three sites along the coast and one interior site. Only a small number of pesticides at low concentrations were found. Of the seven common US/European honey bee viruses, only three were identified but, like Varroa, were absent from northern Kenya. The number of viruses present was positively correlated with Varroa levels, but was not correlated with colony size or hygienic behavior. Our results suggest that Varroa, the three viruses, and Nosema have been relatively recently introduced into Kenya, but these factors do not yet appear to be impacting Kenyan bee populations. Thus chemical control for Varroa and Nosema are not necessary for Kenyan bees at this time. This study provides baseline data for future analyses of the possible mechanisms underlying resistance to and the long-term impacts of these factors on African bee populations.

Effects of shifting to crowded or solitary conditions on pheromone release and morphometrics of the desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae)

We have studied the effect of shifting the desert locust, Schistocerca gregaria (Forskal) from crowded to solitary conditions, or vice versa on the emission of the adult aggregation pheromone (as measured by released phenylacetonitrile) and compared this with changes in morphometrics. Adult males of the F0 generation resulting from shifting crowd-reared (gregarious) hoppers, fledglings or mature adults (aged 20–22 days after the final moult) to solitary conditions did not produce phenylacetonitrile, similar to solitary-reared adults. Conversely, adults of the F0 generation resulting from shifting solitary-reared (solitarious) hoppers, fledglings or mature adults to crowded conditions produced pheromone at levels which were not significantly different from those of control adults from the crowd-reared colony. The levels of pheromone increased in the F1 generation but decreased and leveled off in the F2 and F3 generations. Extreme sensitivity to crowding was demonstrated by the fact that even pairing of one solitarious hopper with another produced F0 adult males that produced phenylacetonitrile, although in significantly lesser amounts than by males reared at a density of four per cage or by crowd-reared control males. In contrast, morphometrics changes were slow and required several generations. The FC ratio (hind-femur length to head capsule width) was more sensitive to treatment effects than the EF ratio (fore-wing to hind-femur length), in agreement with previous findings. We conclude that pheromone titres are a more sensitive measure than morphometrics to determine the onset of phase change in the desert locust.

Chemical Ecology of Animal and Human Pathogen Vectors in a Changing Global Climate

Infectious diseases affecting livestock and human health that involve vector-borne pathogens are a global problem, unrestricted by borders or boundaries, which may be exacerbated by changing global climate. Thus, the availability of effective tools for control of pathogen vectors is of the utmost importance. The aim of this article is to review, selectively, current knowledge of the chemical ecology of pathogen vectors that affect livestock and human health in the developed and developing world, based on key note lectures presented in a symposium on “The Chemical Ecology of Disease Vectors” at the 25th Annual ISCE meeting in Neuchatel, Switzerland. The focus is on the deployment of semiochemicals for monitoring and control strategies, and discusses briefly future directions that such research should proceed along, bearing in mind the environmental challenges associated with climate change that we will face during the 21st century.

Studies on the maturation-accelerating pheromone of the desert locustSchistocerca gregaria (Orthoptera: Acrididae)

SummaryThe accelerating effect of mature males of the desert locust,Schistocerca gregaria, on the maturation of immature male and female conspecifics was confirmed. The onset of sexual activity was found to correlate with yellowing of the male insects. Using the colour as an indicator of maturation, the maturation-hastening effect of an hexane extract from mature males was also confirmed. Likewise, volatiles from mature males placed in the upper storey of a two-chamber bioassay system (no visual or tactile contact possible) and charcoal-trapped volatiles from the mature males also induced accelerated maturation in recipient males placed in the lower storey. GC and GC-MS analysis of volatiles collected from 4-week-old mature males showed the presence of anisole, benzaldehyde, veratrole, phenylacetonitrile and 4-vinylveratrole, roughly at the ratio 4.8:7.0:3.3:79.8:5.0. In addition, guaiacol, phenol, benzoylnitrile, benzyl alcohol and 2-benzoyloxyphenylacetonitrile were present in smaller amounts. These compounds were either absent or found only in trace amounts in the female volatiles. Earlier, we had shown that essentially the same blend collected from younger males (10–20 d old, not yet demonstrating signs of maturation) induced strong aggregation of both sexes of adult desert locusts, suggesting a parsimonious role for the pheromone system: as an adult aggregation signal and as a maturation accelerant in young adults.

A scientific note on Varroa destructor found in East Africa; threat or opportunity?

In many areas of the world where it is managed, the honeybee, Apis mellifera, has been plagued by diseases, pests and parasites. Of these, the parasitic mite, Varroa destructor Anderson and Truman (Acari:Varroidae), is considered by many as the most devastating. We found this mite in honeybee colonies throughout Kenya and in Tanzania for the first time in early 2009. Beekeepers surveyed were neither aware of the mite’s presence nor had they observed any negative impact on the survival and/or productivity of their bees. In March of 2009, we sampled 38 honeybee colonies (likely A. m. scutellata, and possibly A. m. scutellata hybrids) in seven locations in Central and Eastern Kenya. We employed a common sampling technique to determine mite presence/absence that utilizes powdered sugar to dislodge mites from adult bees (Macedo et al., 2002). An average of 717 ± 43 bees per colony were sampled and Varroa mites were found in all 38 colonies examined with numbers ranging from 3–108 per sample and averaging 26.3 ± 25.9 per colony. In a further similar survey (April–May, 2009) of 125 additional colonies located in the eastern, western and coastal regions of Kenya (69 colonies in 18 locations), coastal Tanzania (18 colonies in 4 locations) including Ugunja and Pemba Islands, collectively referred to as Zanzibar (likely A.m. litorea), and Western Uganda (14 colonies in 4 locations), 87% of the