Candidate Attractants for Bactrocera invadens (Diptera: Tephritidae) Male Flies from Gynandropsis gynandra (Capparidaceae)

These investigations aimed at evaluating the attractiveness of Gynandropsis gynandra a plant that attracted male Bactrocera invadens, which is an invasive pest known to cause devastating losses in mangoes, citrus, guava and banana among other fruits. B. invadens male flies were attracted to G. gynandra beginning from 0630 to 1230 hrs in the field.  The highest mean number of flies attracted were 65.26 ± 1.06/plant/day, showing a strong positive correlation during the day (r2 = 0.9423). Using GC-EAD and GC-MS two compounds namely, 4-methyl-3-penten-2-one, and 4-hydroxy-4-methyl-2-pentanone were identified to elicit antennae response of the male B. invadens. These two compounds were identified from both G. gynandra and male B. invadens gut extracts of field collected flies. However only 4-hydroxy-4-methyl-2-pentanone was identified from gut extract of laboratory reared B. invadens.  Results from this study has provided an insight into the interactions between a non-host plant and an invasive pest, and opened up the prospects for further investigation on the possibility of future use of 4-hydroxy-4-methyl-2-pentanone and 4-methyl-3-penten-2-one in control strategies aimed at B. invadens. Key words: Bactrocera invadens, parapheromones, olfactometer, GC-EA

Cellular and molecular targets of waterbuck repellent blend odors in antennae of glossina fuscipes fuscipes newstead, 1910

Insects that transmit many of the world’s deadliest animal diseases, for instance trypanosomosis, find their suitable hosts and avoid non-preferred hosts mostly through olfactory cues. The waterbuck repellent blend (WRB) comprising geranylacetone, guaiacol, pentanoic acid, and d-octalactone derived from waterbuck skin odor is a repellent to some savannah-adapted tsetse flies and reduces trap catches of riverine species. However, the cellular and molecular mechanisms associated with detection and coding of the repellent odors remain to be elucidated. Here, we demonstrated that WRB inhibited blood feeding in both Glossina pallidipes Austen, 1903 and Glossina fuscipes fuscipes Newstead, 1910. Using the DREAM (Deorphanization of Receptors based on Expression Alterations in odorant receptor mRNA levels) technique, combined with ortholog comparison and molecular docking, we predicted the putative odorant receptors (ORs) for the WRB in G. f. fuscipes, a non-model insect

Responses of Bactrocera invadens (Diptera:Tephritidae) to Volatile Emissions of Fruits from Three Hosts

Bactrocera invadens is an invasive fruit fly species of Asian origin that was first detected in Kenya in 2003 and now has been reported in many parts of the African continent. The responses of B. invadens towards odour blends emitted from three host fruits, namely mango (Mangifera indica), marula (Sclerocarya birrea), and Indian almond (Terminalia catappa) growing in Nguruman and Embu in Kenya, were monitored in a dual choice olfactometer. Three mango varieties were tested (sensation, apple and kent), each at immature, mature unripe and ripe stages. Marula and Indian almond fruits were tested when mature, both when unripe and ripe. Results showed that, both male and female B. invadens were attracted equally to mature unripe and ripe mango fruits. However, in all cases attraction to immature fruits was significantly lower (P < 0.05). Two-way comparisons showed no significant difference between sensation and apple, but both attracted significantly more flies than kent. There were no significant different in attraction when M. indica, T. catappa and S. birrea were compared between each other. The results indicate that mature host fruits emit volatile constituents that are attractive to the fruit flies and if characterized may be useful in monitoring and managing B. invadens. Keywords: Bactrocera invadens, fruit hosts, attraction, 2-choice wind tunne

Overview of antimicrobial compounds from African edible insects and their associated microbiota

This review discusses advances in the identification and bioactivity analysis of insect antimicrobial peptides (AMP) compounds, with a focus on small molecules associated with the microbiota of selected African edible insects. These molecules could be used as templates for developing next-generation drugs to combat multidrug-resistant pathogens. Previous research indicates that each insect species produces a distinct antimicrobial peptide that acts against specific microorganisms. The article analyzes several likely AMP-producing insects and their compounds. Edible insect-produced AMPs/small molecules’ chemistry receives little attention as researchers have concentrated on the discovery of antibacterial and antifungal peptides/polypeptides in plants

Spiroacetals in the Colonization Behaviour of the Coffee Berry Borer: A 'Push-Pull' System

Coffee berries are known to release several volatile organic compounds, among which is the spiroacetal, conophthorin, an attractant for the coffee berry borer Hypothenemus hampei. Elucidating the effects of other spiroacetals released by coffee berries is critical to understanding their chemo-ecological roles in the host discrimination and colonization process of the coffee berry borer, and also for their potential use in the management of this pest. Here, we show that the coffee berry spiroacetals frontalin and 1,6-dioxaspiro [4.5] decane (referred thereafter as brocain), are also used as semiochemicals by the coffee berry borer for host colonization. Bioassays and chemical analyses showed that crowding coffee berry borers from 2 to 6 females per berry, reduced borer fecundity, which appeared to correlate with a decrease in the emission rates of conophthorin and frontalin over time. In contrast, the level of brocain did not vary significantly between borer-uninfested and infested berries. Brocain was attractive at lower doses, but repellent at higher doses while frontalin alone or in a blend was critical for avoidance. Field assays with a commercial attractant comprising a mixture of ethanol and methanol (1:1), combined with frontalin, confirmed the repellent effect of this compound by disrupting capture rates of H. hampei females by 77% in a coffee plantation. Overall, our results suggest that the levels of frontalin and conophthorin released by coffee berries determine the host colonization behaviour of H. hampei, possibly through a 'push-pull' system, whereby frontalin acts as the 'push' (repellent) and conophthorin acting as the 'pull' (attractant). Furthermore, our results reveal the potential use of frontalin as a repellent for management of this coffee pest.DF

Analysing chemical attraction of gravid Anopheles gambiae sensu stricto with modified BG-Sentinel traps.

BACKGROUND: Cues that guide gravid Anopheles gambiae sensu lato to oviposition sites can be manipulated to create new strategies for monitoring and controlling malaria vectors. However, progress towards identifying such cues is slow in part due to the lack of appropriate tools for investigating long-range attraction to putative oviposition substrates. This study aimed to develop a relatively easy-to-use bioassay system that can effectively analyse chemical attraction of gravid Anopheles gambiae sensu stricto. METHODS: BG-Sentinel™ mosquito traps that use fans to dispense odourants were modified to contain aqueous substrates. Choice tests with two identical traps set in an 80 m(2) screened semi-field system were used to analyse the catch efficacy of the traps and the effectiveness of the bioassay. A different batch of 200 gravid An. gambiae s.s. was released on every experimental night. Choices tested were (1) distilled versus distilled water (baseline) and (2) distilled water versus soil infusion. Further, comparisons were made of distilled water and soil infusions both containing 150 g/l of Sodium Chloride (NaCl). Sodium Chloride is known to affect the release rate of volatiles from organic substrates. RESULTS: When both traps contained distilled water, 45% (95 confidence interval (CI) 33-57%) of all released mosquitoes were trapped. The proportion increased to 84% (95 CI 73-91%) when traps contained soil infusions. In choice tests, a gravid female was twice as likely to be trapped in the test trap with soil infusion as in the trap with distilled water (odds ratio (OR) 1.8, 95% CI 1.3-2.6). Furthermore, the attraction of gravid females towards the test trap with infusion more than tripled (OR 3.4, 95% CI 2.4-4.8) when salt was added to the substrates. CONCLUSION: Minor modifications of the BG-Sentinel™ mosquito trap turned it into a powerful bioassay tool for evaluating the orientation of gravid mosquitoes to putative oviposition substrates using olfaction. This study describes a useful tool for investigating olfactory attraction of gravid An. gambiae s.s. and provides additional evidence that gravid mosquitoes of this species are attracted to and can be baited with attractive substrates such as organic infusions over a distance of several metres

Mass spectral determination of phenylacetonitrile (PAN) levels in body tissues of adult desert locust, Schistocerca gregaria

Wings and legs of the gregarious desert locust, Schistocerca gregaria have been shown to be release sites of phenylacetonitrile (PAN), the major adult male-produced pheromone. However, there is limited information on the distribution of PAN within the locust. Here we show, using gas chromatography–mass spectrometry (GC–MS), that PAN occurs in nearly all body parts of both adult males and females of the locust in varying amounts. PAN was 20-fold more concentrated in males than in females. In females, PAN was concentrated more in the tarsal segments. The greatest amounts of PAN were in 2- and 3-week old female and male body parts, respectively. No trace of PAN was found in similar ages and sexes of the solitarious phase desert locust. Our results show that PAN is distributed in the body matrix of both sexes of gregarious phase locusts and suggest that no specific tissue is responsible for biosynthesis of the pheromone.http://www.elsevier.com/locate/jinsphysab201

Afrotropical sand fly-host plant relationships in a leishmaniasis endemic area, Kenya

The bioecology of phlebotomine sand flies is intimately linked to the utilization of environmental resources including plant feeding. However, plant feeding behavior of sand flies remains largely understudied for Afrotropical species. Here, using a combination of biochemical, molecular, and chemical approaches, we decipher specific plant-feeding associations in field-collected sand flies from a dry ecology endemic for leishmaniasis in Kenya. Cold-anthrone test indicative of recent plant feeding showed that fructose positivity rates were similar in both sand fly sexes and between those sampled indoors and outdoors. Analysis of derived sequences of the ribulose-1,5-bisphosphate carboxylase large subunit gene (rbcL) from fructose-positive specimens implicated mainly Acacia plants in the family Fabaceae (73%) as those readily foraged on by both sexes of Phlebotomus and Sergentomyia. Chemical analysis by high performance liquid chromatography detected fructose as the most common sugar in sand flies and leaves of selected plant species in the Fabaceae family. Analysis of similarities (ANOSIM) of the headspace volatile profiles of selected Fabaceae plants identified benzyl alcohol, (Z)-linalool oxide, (E)-β-ocimene, p-cymene, p-cresol, and m-cresol, as discriminating compounds between the plant volatiles. These results indicate selective sand fly plant feeding and suggest that the discriminating volatile organic compounds could be exploited in attractive toxic sugar- and odor- bait technologies control strategies.German Academic Exchange Service (DAAD) In-Region Postgraduate Scholarship; Combatting Arthropod Pests for better Health, Food and Climate Resilience funded by Norwegian Agency for Development Cooperation (Norad); UK’s Foreign, Commonwealth & Development Office (FCDO); Swedish International Development Cooperation Agency (Sida); Swiss Agency for Development and Cooperation (SDC); Federal Democratic Republic of Ethiopia and the Ministry of Higher Education, Science and Technology, Kenya.https://journals.plos.org/plosntdspm2022Zoology and Entomolog

Effect of larval density and substrate quality on the wing geometry of Stomoxys calcitrans L. (Diptera: Muscidae)

BACKGROUND : In insects, oviposition decisions may lead to egg deposition in substrates with different larval density and nutritional levels. Individuals developing in such substrates may present plasticity in their phenotype. Here, we investigated the effect of two factors related to oviposition decisions, namely larval density and substrate quality, on the wing size and wing shape of the stable fly, Stomoxys calcitrans L. (Diptera: Muscidae). METHODS : We reared S. calcitrans larvae at different densities (5, 15 and 25) and on different substrates (camel, cow, donkey and sheep dung). For each fly that emerged, we recorded body weight, and detached, slide-mounted and photographed the right wing. Next, we collected 15 landmarks on each photographed wing, and applied geometric morphometric analysis to assess variation in wing size and wing shape of S. calcitrans across the different larval densities and substrate types. RESULTS : We observed that wing size and wing shape of S. calcitrans were affected by larval density and the nature of the developmental substrate. Flies reared in a group of 5 had larger wing centroid size, wing length, wing width, wing area and wing loading compared with those reared in a group of 25. Also, flies developed in donkey and sheep dung had larger wing centroid size, wing length, wing width, wing area and wing loading in comparison with those grown in camel and cow dung. Canonical variate analysis followed by discriminant analysis revealed significant wing shape variation in S. calcitrans across the different densities and substrates. Wing size had a significant but weak positive effect on wing shape. CONCLUSIONS : This study demonstrates the high sensitivity of S. calcitrans wings to variation in larval density and developmental substrate, and that use of landmark-based geometric morphometric analysis could improve our understanding of how flies of veterinary importance respond to environmental variability.We thank Deutscher Akademischer Austauschdienst (DAAD) for providing SBSB with a doctoral scholarship through the ARPPIS-DAAD scholarship programme. This work was supported by the IBCARP camel, grant no. DCI-FOOD/2014/ 346-739 - mainly by the European Union and Max Planck Institute for chemical ecology - icipe partner group to MNG. We also gratefully acknowledge the financial support for this research by the following organizations and agencies: Swedish International Development Cooperation Agency (Sida); UK Department for International Development (DFID); the Swiss Agency for Development and Cooperation (SDC); and the Kenyan Government.http://www.parasitesandvectors.comam2019Zoology and Entomolog

Biological traits of wild-caught populations of Aedes aegypti in dengue endemic and non-endemic regions of Kenya

Variation in vector traits can modulate local scale differences in pathogen transmission. Here, we compared seasonal variation in the wing length (proxy for body size) and energy reserves of adult wild-caught Aedes aegypti populations from a dengue endemic (Kilifi) and non-endemic (Isiolo) area of Kenya. Vector sampling in the dengue endemic site was conducted during the dry and wet seasons. In the non-endemic area, it was limited to the dry season which characterizes this ecology where sporadic or no rainfall is commonplace during the year. We found variation by site in the body size of both sexes, with an overall smaller size of Ae. aegypti populations collected from Isiolo than those from Kilifi. Our results show that although total carbohydrates and lipids levels were highest in both sexes during the dry season, they were two-fold higher in males than females. However, we found weak correlations between body size and energy reserves for both sexes, with body size being more sensitive in identifying differences at a population level. These results provide insights into the determinants of the vectoring potential of Ae. aegypti populations in dengue endemic and non-endemic ecologies in Kenya.UK’s Foreign, Commonwealth & Development Office (FCDO), the Swedish International Development Cooperation Agency (SIDA), the Swiss Agency for Development and Cooperation (SDC), the Federal Democratic Republic of Ethiopia, and the Government of the Republic of Kenya.https://bioone.org/journals/journal-of-vector-ecologyhj2022Zoology and Entomolog