Janet Irungu

Aflatoxin Contamination Detected in Nutrient and Anti-Oxidant Rich Edible Stink Bug Stored in Recycled Grain Containers.

Recently, there has been multi-agency promotion of entomophagy as an environmentally-friendly source of food for the ever increasing human population especially in the developing countries. However, food quality and safety concerns must first be addressed in this context. We addressed these concerns in the present study using the edible stink bug Encosternum delegorguei, which is widely consumed in southern Africa. We analysed for mycotoxins, and health beneficials including antioxidants, amino acids and essential fatty acids using liquid chromatography coupled to quadrupole time of flight mass spectrometry (LC-Qtof-MS) and coupled gas chromatography (GC)-MS. We also performed proximate analysis to determine nutritional components. We identified the human carcinogen mycotoxin (aflatoxin B1) at low levels in edible stink bugs that were stored in traditonally woven wooden dung smeared baskets and gunny bags previously used to store cereals. However, it was absent in insects stored in clean zip lock bags. On the other hand, we identified 10 fatty acids, of which 7 are considered essential fatty acids for human nutrition and health; 4 flavonoids and 12 amino acids of which two are considered the most limiting amino acids in cereal based diets. The edible stink bug also contained high crude protein and fats but was a poor source of minerals, except for phosphorus which was found in relatively high levels. Our results show that the edible stink bug is a nutrient- and antioxidant-rich source of food and health benefits for human consumption. As such, use of better handling and storage methods can help eliminate contamination of the edible stink bug with the carcinogen aflatoxin and ensure its safety as human food.

Effects of vector control on the population structure of tsetse (Glossina fuscipes fuscipes) in western Kenya

Displacement rates of tsetse affect performance of targets during vector control. Fly size, one of the indicators of population structure usually obtained from wing measurement, is among the determinants of displacement rates. Although recovery of tsetse in previous intervention areas has been widely reported, the population structure of tsetse that recover is rarely evaluated despite being associated with displacements rates. Previously, intervention trials had reduced tsetse densities by over 90% from >3 flies/trap/day to <1fly/trap/day on Big Chamaunga and Manga islands of Lake Victoria in western Kenya. In this study, we assessed the recovery in densities of Glossina fuscipes fuscipes on the two islands and evaluated the effects vector control might have on the population structure. A before and after intervention study was undertaken on four islands of Lake Victoria in western Kenya; Small and Big Chamaunga, Manga and Rusinga Islands, two of which tsetse control intervention had previously been undertaken. Three years after intervention average G. f. fuscipes catches in biconical traps were estimated on each island. Wing centroid size (CS) (a measurement of fly size) and shape, indicators of the population structure of flies from the four islands were compared using geometric morphometric analyses. CS and shape of available female but not male tsetse wings obtained before the intervention trial on Big and Small Chamaunga islands were compared with those from the same islands after the intervention trial. G. f. fuscipes apparent density on the previous intervention islands were>9 flies/trap/day. Irrespective of sex, wing shape did not isolate tsetse based on their islands of origin. The fly size from Big and Small Chamaunga did not differ significantly before intervention trials (P = 0.728). However, three years after the intervention flies from Big Chamaunga were significantly smaller than those from Small Chamaunga (P < 0.003). Further, there was an increase in the divergence of wing morphology between flies collected from Big Chamaunga and those from Small Chamaunga after tsetse control. In conclusion, even though populations are not isolated, vector control could influence the population structure of tsetse by exerting size and wing morphology differential selection pressures. Therefore, we recommend further studies to understand the mechanism behind this as it may guide future vector control strategies.

Identification of kairomones of second instar nymphs of the variegated coffee bug Antestiopsis thunbergii (Heteroptera: Pentatomidae)

The variegated coffee bug Antestiopsis thunbergii Gmelin is a key pest of Coffea arabica in East Africa. Although the bug feeds on various parts of the coffee plant, it has a strong preference for mature green berries which are essential for the bug to complete its life cycle, reproduce and enhance its longevity. To locate mature green coffee berries, we hypothesized that second instar nymphs, which are the most mobile and active feeding immature stage of the bug, must rely on key volatile compounds emitted by the host for recognition. We tested this hypothesis using behavioral and electrophysiological assays and chemical analysis. In olfactometer assays, the second instar nymphs were strongly attracted to volatiles emitted from mature green berries but avoided those from ripe coffee berries of C. arabica. Coupled gas chromatography–electroantennographic detection (GC/EAD) isolated five antenally active components from mature green berries volatiles, four of which were identified by coupled GC–mass spectrometry as toluene, anisole, methyl 3-ethyl-4-methylpentanoate and (5S,7S)-conophthorin. In concentration assays, in which second instar nymphs did not respond to toluene, they were strongly attracted to anisole, methyl 3-ethyl-4-methylpentanoate and (5S,7S)-conophthorin, and a blend from the three compounds at concentrations lower or equivalent to the natural volatile extract. Our results suggest that the blend from these three compounds allows host recognition in second instar nymphs of the variegated coffee bug and is a candidate kairomone for monitoring the pest in coffee plantations.

Sticky small target: an effective sampling tool for tsetse fly Glossina fuscipes fuscipes Newstead, 1910

BackgroundSmall targets comprising panels of blue and insecticide-treated black netting material each 0.25 × 0.25 m have been shown to attract and kill Glossina fuscipes fuscipes Newstead, 1910 (Diptera: Glossinidae) thereby reducing its population density by over 90% in field trials. However, their attractive ability has not been fully exploited for sampling purposes. Therefore, in this study we assessed the effectiveness of using sticky small targets as sampling tools for G. f. fuscipes in western Kenya. We also determined the influence of colour on the landing response of female and male flies on sticky small targets.MethodsUsing a series of randomised block experiments, the numbers of tsetse flies caught with sticky small targets were compared with those caught with biconical traps. A negative binomial regression was used to model fly catches. Odds ratios as measures of association between the landing response on the blue or black panel of the sticky small target and the sex of flies were obtained from a multiple logistic regression.ResultsThe results showed that sticky small targets caught 13.5 and 3.6 times more female and male tsetse flies than biconical traps (Z = 9.551, P < 0.0001 and Z = 5.978, P < 0.0001, respectively). Females had a 1.7 times likelihood of landing on the black panel than males (Z = 2.25, P = 0.025).ConclusionThis study suggests that sticky small targets are an effective sampling tool for G. f. fuscipes. Therefore, we recommend the use of sticky small targets as an alternative to biconical traps for observational and experimental investigations of G. f. fuscipes.

Ripe coffee berry volatiles repel second instar nymphs of Antestia bugs (Heteroptera: Pentatomidae: Antestiopsis thunbergii )

Understanding the roles of volatile organic compounds (VOCs) in insect–plant interactions is a key component towards the development of safe pest management strategies and sustainable agriculture. Kairomones in unripe berries of Coffea arabica mediate host recognition of second instar nymphs of Antestia bugs, Antestiopsis thunbergii Gmelin, and are good candidates for the pest management. In the current study, we investigated the VOCs that contribute to deterring the pest from ripe berries. Behavioral assays showed that headspace volatiles collected from ripe berries were significantly avoided by second instar nymphs. A mixture of the ripe berry volatiles and unripe berries (known preferred diet) was also significantly avoided when tested against blank or unripe berries, thereby confirming that VOCs from ripe berries had altered the host recognition process and had an odor masking effect. Coupled gas chromatography/mass spectrometric (GC/MS) analysis of the headspace volatiles revealed a blend of chemicals of which ten elicited electrophysiological activity in antennae of second instar nymphs. Five of these compounds including; 3-hydroxy-2-butanone, 2-heptanone, 2-isopropyl-3-methoxypyrazine [IPMP], 2-isobutyl-3-methoxypyrazine [IBMP] and (E)-β-caryophyllene were identified as unique to the volatiles of ripe berries and they elicited avoidance behavior in second instar nymphs when tested singly and in a blend. In addition, their blend also inhibited responses of nymphs to a synthetic attractant blend (kairomone). Our results suggest that the blend of the five compounds can be exploited as repellents in the management of A. thunbergii by pushing the pest away from coffee plantations or interfering with the pest–host recognition process through masking of suitable host odors.