J. M. Kabaru

Study on the microstructure of African wild silk cocoon shells and fibers

Silk fibers and cocoon shells from four African wild silkmoths Gonometa postica, Anaphe panda, Argema mimosae and Epiphora bauhiniae-were studied to gain insight into the structure-property-function relations and potential commercial application. The surface and cross-section of cocoon shells and fibers revealed the presence of prominent structural variations. Cocoon shells were multilayered and porous structures constructed from highly cross-linked fibers that are densely packed within the sericin/gum. Fibers had fibrillar sub-structures running along the fiber axis and with greater number and size of voids. The ecological significance and implication of these structures for further application are discussed.

Biology of the Coconut Bug, Pseudotheraptus wayi, on French Beans

Abstract The coconut bug, Pseudotheraptus wayi Brown (Heteroptera: Coreidae), is a major pest of a wide range of economically important crops in Eastern and Southern Africa. The suitability of French beans, Phaseolus vulgaris L. (Fabales: Fabaceae) as an alternative food for mass rearing of P. wayi was determined by elucidating its development, survival, and reproduction on French bean pods in the laboratory. Development and survival of immatures on French beans was comparable to what is reported with two hosts previously used for rearing this species, namely coconut and cashew. Adults survived thrice longer and laid almost twice more eggs on the French beans than was reported for the two hosts above. These findings suggest that French beans are more suitable for mass rearing of this species than coconut and cashew, which have been used previously but can be scarce and too costly.

Potential for Melia volkensii fruit extract in the control of locusts

Summary Fruits from the East African tree, Melia volkensii (Gurke) contain terpenoid compounds with well-establishcd insecticidal activity. At high doses a concentrated M. volkensii extract (Mv) causes death or lack of physical fitness in locusts by irreversible paralysis of the locust skeletal muscles, without affecting the malpighian tubules or the pulsation of the dorsal heart. This effect is temperature related, with lower doses becoming more effective as the temperature increases. This action favours Mv toxicity against locusts in hot desert areas. Mammalian toxicological studies showed that Mv does not present any acute or chronic toxicity effects when orally administered to laboratory mice. It was thus not possible to establish an oral LD50 for the product in mice. Mv production in bulk and shelf-life are discussed with a view to demonstrating its advantages as a possible locust control product.

Structure, Composition, and Properties of Silk from the African Wild Silkmoth, Anaphe panda (Boisduval) (Lepidoptera: Thaumetopoeidae)

Silk cocoon nests, as well as the fiber structure, compositions, and properties of the African wild silkmoth, Anaphe panda, collected from Kakamega tropical rainforest (western Kenya) were studied using scanning electron microscopy, high-pressureliquid chromatography, tensile tests, and thermogravmetric analysis, and they were compared with the industrial standard, Bombyx mori. Cocoon nests are complex structures made up of inner, middle, and outer layers. The inner hard parchment was found to protect a mass of (20–200) individual soft flossy cocoons that enclose the pupae. The outer surface of the cocoon nests was covered with a mass of hair-like bristles. Fibers contained crescent-shaped and globular cross-sections with nods at regular intervals. Alanine (34%) and glycine (28%) were the dominant fibroin amino acids observed. Total weight loss after degumming the cocoon nest was 25.6%. Degummed fibers showed higher moisture regain of 9% when compared with cocoon nests (8%). The fibers had 0.4 GPa breaking stress and 15.4% breaking strain. Total weight loss values after thermogravimetric analysis were 86% and 90% for degummed fibers and cocoon shells, respectively.

Description of pre-adult stages of the coconut bug, Pseudotheraptus wayi

Abstract The coconut bug, Pseudotheraptus wayi Brown (Hemiptera: Heteroptera: Coreidae), is a serious pest of a number of crops in Eastern and Southern Africa. Both adults and nymphal stages are destructive because they suck sap from their hosts. The identity of the pest is currently based exclusively on the description of adults. This paper describes eggs and instars of P. wayi, with the goal to enhance identification of all stages for effective monitoring and management of the pest. Morphological illustrations are presented, and differences among the instars, as well as their relationship with the adult stage, are discussed.

Cashew Volatiles Mediate Short-Range Location Responses in Pseudotheraptus wayi (Heteroptera: Coreidae)

ABSTRACT Pseudotheraptus wayi Brown (Heteroptera: Coreidae) is a major pest of cashew in East Africa, but little is known about its chemical ecology. Here, we show by using behavioral assays and chemical analysis that some components of cashew leaf volatiles are attractants for male P. wayi. By using a petri dish arena-EthoVision video-tracking assay, males oriented closer to crude cashew leaf odor than females. In coupled gas chromatography-electroantennographic detection analysis, we found that four components of cashew leaf volatiles that were identified by coupled gas chromatography-mass spectrometry and confirmed with authentic standards as (E)- and (Z)-&bgr;-ocimene, alloocimene, and (Z)-3-hexenyl butyrate appeared to elicit stronger and more consistent responses in male than female antennae. We recorded electroantennograms from antennae of either sex, which confirmed that antennal responses of males to synthetic components of the cashew leaf odor were stronger than those of females. In the petri dish arena-Etho Vision video-tracking assay, males oriented closer to the synthetic cashew leaf monoterpenes than females. Our results suggest that specific monoterpenes in cashew leaf volatiles may serve as candidate kairomones for males.

Effect of Post-Treatment Temperature on the Insecticidal Activity of Neem, Azadirachta Indica A. Juss. Seed extract on Schistocerca Gregaria (Forskal): A preliminary Report

The influence of post-treatment temperature on the insecticidal activity of Azadirachta indica (A. Juss) seed extract against the desert locust, Schistocerca gregaria (Forskål) is reported. In tests on adults, the toxicity of crude A. indica seed extract increased by about 10-fold when the post-treatment temperature was raised from 22°C to 40°C. This temperature-dependent toxicity was observed in insects treated either topically or via injection. This phenomenon could partly explain the wide variability in efficacy of neem extracts reported by different investigators.RésuméL’article expose l’influence des températures après traitement, sur l’activité insecticide des extraits de graines du nime, Azadirachta indica (A. Juss), utilisés dans la lutte contre le criquet du désert, Schistocerca gregaria Forskål. Au cours des essais sur les adultes, les extraits bruts obtenus des graines de A. indica ont accru leur activité par 10 fois, quand la température après traitement passait de 20°C à 40°C. Cette interdépendance de la toxicité et la température fut observée chez les insectes traités par application externe ou par injection. Ce phénomène pourrait expliquer en partie, la grande variabilité d’efficacité des extraits de nime rapportée par plusieurs chercheurs.