Esther N. Kioko

Forest Habitat Conservation in Africa Using Commercially Important Insects

African forests, which host some of the worlds richest biodiversity, are rapidly diminishing. The loss of flora and fauna includes economically and socially important insects. Honey bees and silk moths, grouped under commercial insects, are the source for insect-based enterprises that provide income to forest-edge communities to manage the ecosystem. However, to date, research output does not adequately quantify the impact of such enterprises on buffering forest ecosystems and communities from climate change effects. Although diseases/pests of honey bees and silk moths in Africa have risen to epidemic levels, there is a dearth of practical research that can be utilized in developing effective control mechanisms that support the proliferation of these commercial insects as pollinators of agricultural and forest ecosystems. This review highlights the critical role of commercial insects within the environmental complexity of African forest ecosystems, in modern agroindustry, and with respect to its potential contribution to poverty alleviation and pollination services. It identifies significant research gaps that exist in understanding how insects can be utilized as ecosystem health indicators and nurtured as integral tools for important socioeconomic and industrial gains.

Semi-captive rearing of the African wild silkmoth Gonometa postica (Lepidoptera: Lasiocampidae) on an indigenous and a non-indigenous host plant in Kenya.

The life cycle of the African wild silkmoth Gonometa postica Walker was studied between September 2000 and September 2001 in the Uasin Gishu District of western Kenya with Acacia mearnsii de Wild and Acacia hockii de Wild as host plants. The initial population of G. postica was set up from healthy live pupae in cocoons collected from host plants in the study area. Oviposition was carried out in net sleeves and small plastic cages. Moth emergence and oviposition were bimodal, occurring between September and October 2000 and between March and April 2001, respectively. Larvae were reared in semi-captivity by using net sleeves on the branches of the two host plants. Larvae passed through six developmental instars. The pupal stage lasted from December to February during the short rains and from June to September during the long rains. Moth fecundity in the net sleeves was higher than that of those kept in plastic cages and fewer eggs hatched in the plastic cages compared with the net sleeves. Larvae reared on A. mearnsii had a shorter developmental period compared with those reared on A. hockii. Male larvae spun cocoons earlier than females but moths of both sexes emerged simultaneously. Sexual dimorphism was exhibited in both pupal and adult stages, females being larger and heavier than males. The importance of the semi-captive rearing technique for sustainable utilization of wild silkmoths for mass production of cocoons is discussed.

Use of Sleeve Nets to Improve Survival of the Boisduval Silkworm, Anaphe panda, in the Kakamega Forest of Western Kenya

Abstract Prospects for development of a wild silk industry in Africa would be improved if silkworm survival during mass production could be improved. A study on the survival of the Boisduval silkworm, Anaphe panda (Boisduval) (Lepidoptera: Thaumetopoeidae) was conducted with and without protection by net sleeves in two different forest habitats (natural and modified) in the Kakamega forest of western Kenya. Overall, cohort survival was significantly higher (P < 0.001) in the natural than in the modified forest, but larval survival was improved over three-fold by protection with net sleeves in both habitat types. In the modified forest, only 16.8% of unprotected larvae survived to the pupal stage and formed cocoons, whereas 62.3% survived in the same environment when they were protected with net sleeves. In the natural forest, 20.4% of unprotected larvae survived, whereas 67.7% survived in net sleeves. There was also a significant effect of season; cohorts of larvae that eclosed in the wet season had significantly lower survival than those eclosing in the dry season (P = 0.02). Sources of mortality appeared to be natural enemies (parasites, predators and diseases) and climatic factors.

Monitoring wild silkmoth, Gonometa postica Walker, abundance, host plant diversity and distribution in Imba and Mumoni woodlands in Mwingi, Kenya

A survey of the abundance of larvae and pupae of Gonometa postica Walker and their host plants was undertaken in the long rainy season in 2006 at six sites in the Imba and Mumoni forests of Mwingi, eastern Kenya. One hundred trees of the primary host species of G. postica were sampled at each site, in addition to minor host species with G. postica pupae. The density of each tree species was calculated and the height, canopy, diameter and number of branches were measured. In order of decreasing abundance, the host plants in Imba forest were Acacia tortilis, A. elatior and A. nilotica, and in Mumoni forest, A. tortilis, A. nilotica, A. mellifera and A. brevispica. A. elatior had significantly more larvae than the other host plants in Imba. In Mumoni, A tortilis and A. mellifera had significantly more larvae, followed by A. nilotica and A. brevispica. The minor host plants harbour significantly more pupae than the major host plants in the two forests. In general, Imba had a significantly higher abundance of larvae and pupae than Mumoni. Host plant species richness did not differ between the two forests, but their evenness was significantly higher in Imba than in Mumoni.

Spatial distribution of cocoon nests and egg clusters of the silkmoth Anaphe panda (Lepidoptera: Thaumetopoeidae) and its host plant Bridelia micrantha (Euphorbiaceae) in the Kakamega Forest of western Kenya

A study on the spatial distribution of the silkmoth Anaphe panda (Boisduval) cocoon nests, egg clusters and the host plant Bridelia micrantha (Hochst) Baill. was conducted in two different habitats of the Kakamega Forest of western Kenya: Ikuywa (indigenous forest) and Isecheno (mixed indigenous forest). Fhe mean densities of cocoon nests, egg clusters and B. micrantha were significantly different in the two blocks and were not semi-randomly distributed in the two habitats. The host plants were underdispersed in the indigenous forest, whereas they were overdispersed in the mixed indigenous forest. The cocoon nests were overdispersed and the silkmoth egg clusters were underdispersed in the two blocks of forest. This study reveals that A. panda tends to distribute its egg clusters uniformly over the lower and middle crown of B. micrantha with a preference to eastern localization and confirms the insufficient presence of populations of this silkmoth in a mixed indigenous forest compared with an indigenous forest. Consequently, indigenous forests should be managed in a sustainable way and more indigenous tree species should be used in reforestation campaigns.

Effect of Seasons and Larval Food Plants on the Quality of Gonometa Postica Cocoons

The effect of food plants [Acacia elatior Brenan, A. tortilis (Forssk.) and A. nilotica (L.) Del.] on the development time of Gonometa postica Walker (Lepidoptera: Lasiocampidae) larvae and the quality of their cocoons was studied in the Imba and Mumoni forests of Mwingi, Eastern Kenya, during the long (March-May) and short (October-December) rainy seasons of 2006 and 2007. Larvae were reared in semi-captivity in net sleeves attached to branches of the plants. The period between hatching of eggs and spinning of cocoons, as well as their weight, as determinants of cocoon quality were recorded. In addition, collections of cocoons from the wild were done in the two forests from the same host plants for assessment of their quality. In the cage experiment, larval development period and quality of cocoons differed according to food plants, seasons and sites, whereas quality of cocoons sampled from the wild habitat was similar for all food plants and seasons but varied according to site. Generally, there was a positive correlation between weight of cocoon, its length and width for the two seasons for both the semi-captive population and those from the wild. Larvae reared on A. elatior had a shorter development period and higher cocoon quality than those raised on A. tortilis and A. nilotica. Generally, temperature and relative humidity significantly influenced larval development time and the effect was both positive and negative. Rainfall was generally higher in Mumoni than in Imba. The implications of the above findings for the semi-captive rearing of G. postica to increase the quality of cocoons are discussed.

Parasitoids of the African wild silkmoth, Gonometa postica (Lepidoptera: Lasiocampidae) in the Mwingi forests, Kenya

Gonometa postica Walker produces silk of high quality, but it is affected by parasitoids attack. A study on the parasitism of G. postica larvae and pupae on host and non‐host plants were undertaken for the first and second generations, corresponding to the long (March–May) and short (October–December) rainy seasons in 2006 at six field sites, three each in the Imba and Mumoni forests of Mwingi, eastern Kenya. All freshly spun cocoons of G. postica were sampled at each site from a total of 100 trees of host plants and other non‐host plants where they have migrated before pupation. The cocoons were kept individually in fine net‐sealed plastic vials to determine percentage parasitism. Two dipterans and four hymenopteran larval–pupal parasitoids were identified from the two forests. The most common parasitoids were Palexorista sp. (Diptera: Tachinidae) and Goryphus sp. (Hymenoptera: Ichneumonidae) with parasitism ranging from 1.8 to 32.7% and 2.2 to 7.5%, respectively. Parasitism varied significantly according to host or non‐host plants, seasons and sites. This study indicates that, of the six parasitoid species recovered, only two had a significant impact in reducing the quality of the cocoons.

Extraction of Natural Silk Fibre from Cocoons of Argema mimosae (Lepidoptera: Saturniidae)

In recent years, numerous actions for sustainable exploitation of forest resources have been undertaken, but few deal with commercialization of forest insects. Several tree based insect products, like wild silk, can be linked with forest conservation activities to provide livelihood services of different economic scales to forest dependent people. African wild silkmoth, Argema mimosae Boisduval, is one of the forest insects, a moth in the family of Saturniidae producing wild silk, but there is need for definite procedures for extracting silk fibre from its cocoons. This study evaluated physical characteristics of the A. mimosae cocoons and outlined a procedure to extract viable silk fibre for use in silk industry. Cocoons of the A. mimosae were collected from natural forest of Arabuko-Sokoke, Kenya (3°20′ S, 39°55′ E), and others obtained by semi-captive rearing of the silkmoth larvae. The cocoons of A. mimosae were described to be silvery in colour, tough and thick with distinctive perforations on the surface and a prominent valve-like opening with loose filaments at one end. The study recorded 120 min as the optimum boiling time for the cocoons to yield silvery brown silk floss using sodium carbonate (Na2CO3) as the degumming agent. Cocoons boiled in distilled water could not be deflossed into floss, but remained hard and intact, as compared with those of the control, Bombyx mori. This reveals that A. mimosae cocoons can be processed for natural silk fibre production and offer communities adjacent to forests an excellent opportunity to engage in production of natural wild silk.

Oviposition Preferences of the African Wild Silkmoth, Gonometa postica Walker (Lepidoptera: Lasiocampidae) on Different Substrates

Gonometa postica Walker (Lepidoptera: Lasiocampidae) is currently being utilised for commercial wild silk production in Eastern Kenya. The oviposition preferences of female G. postica on four substrates in a net-sleeved cage was studied in the laboratory in the long and short rainy seasons in 2007 for two generations, i.e. early (late March to April) and late flights (late September to October) of the moth. The first generation moths laid the highest number of eggs on net sleeves followed by plastic pot, twigs and wooden plank, whereas the second generation moths preferred wooden plank and net sleeves over the plastic pot and twigs. The mean number of eggs, egg clusters laid and percentage egg viability were significantly higher, and the oviposition period was longer for the first than the second generation moths. The mean weight of cocoons was significantly heavier for the first than the second generation. A highly significant positive linear relationship existed between the total number of eggs laid and the cocoon weight. The slopes of the two regression lines for the number of eggs laid against the weight of cocoons were significantly different between the two generations. This information serves to optimise the production of eggs in net sleeved cages in an indoor environment for the semi-captive rearing of the larvae.