Sustentabilidad

Prologue

‘The world is a scene of risk’, wrote John Dewey, ‘it is uncertain, unsta-ble, uncannily unstable. Its dangers are irregular, inconstant, not to be counted upon as to their times and seasons … plague, famine, failure of crops, disease … are always just around the corner’ (1929: 41). But Dewey, an empirical rationalist, also emphasized the positive aspects of life – abundance, joy, ideals, ceremonies and song. People in Malawi therefore not only have to contend with the ravages of insect pests in rela-tion to agricultural crops, but also find that insects invade their homes and granaries, and at irregular intervals, swarms of locusts descend upon their fields. In this chapter I want to focus on these two categories of insect pests – those that relate to domestic households; and, from a historical perspective, the impact of the larger grasshoppers on the agricultural economy. These represent the inconstant risks of the subsistence farmers in Malawi. As a kind of interlude, I shall also briefly discuss the forest pests of Malawi.

Household Pests

Discussions I had with local people in the Domasi Valley, north of Zomba, and in the village adjacent to Kapalasa Farm, suggest that many different kinds of insects are seen as troublesome (bvuta) in varying degrees. But here we may discuss the five key species that have particu-lar salience for Malawians.

Cockroach, Mpemvu (Periplaneta americana) (Order: Blattoidea) The term ‘cockroach’ comes from the Spanish cucaracha, and it is esti-mated that these insects have inhabited the world for more than 250 million years, as the earliest fossil cockroaches look very much like contemporary species. They are indeed tough, resilient creatures that have amazing endurance and are able to live in extreme conditions. They appear to live everywhere that humans live. In one apartment in Austin,

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Texas, around one hundred thousand cockroaches were found, for they are adept scavengers, and are highly omnivorous, feeding on almost anything (H. E. Evans 1970: 48–61).

Several species of cockroach are found in Malawi, and the large American cockroach is perhaps the commonest, although as Skaife suggests, its name may be somewhat misleading, for it is probable that most of the domestic cockroaches originally came from Africa (1979:

46). The cockroach is ubiquitous in rural areas, and found in most huts and houses, and it is mainly nocturnal. It tends to like warm, damp condi-tions. Some huts I have slept in have been literally swarming with cock-roaches, and they can disturb one’s sleep, although they are quite harmless. Given their oval, flattened shape and greasy appearance they are loathed by Europeans; but Malawians tend to tolerate them, even though they find them troublesome and often attempt to eradicate them.

As they are seen as defecating a good deal (nyatsa kwambiri) and as moving among the relish stores, cockroaches are thought by some people to cause diarrhoea (segula m’mimba, ‘open stomach’). Evans indeed confirms that, although cockroaches are basically clean animals, they do in fact carry bacteria that can cause intestinal disorder (H. E. Evans 1970:

49; Service 1996: 219; but cf. Lauck 1998: 83). The suggestion that the cockroach is edible always meets with a negative response, and, like the black rat, which also frequents houses, it is never eaten. People also see the cockroach as destroying (onongeka) things, and use the insecticide Doom (Dumu), bought at local stores to clear their houses of the pest.

Termites, Chiswe (Order: Isoptera)

Termites are seen principally as agricultural pests, particularly on maize, beans and pigeon pea; but they also cause a great deal of damage to houses, especially the traditional ‘wattle and daub’ huts. As their diet consists essentially of plant material of a woody nature, the termites are apt to cause much damage to the wooden structures of a house – doors, beams, posts, and often their presence is undetected until the structures collapse. During the colonial period considerable damage was caused to houses even within urban areas, and directives were issued regarding measures to be taken in the building of brick houses. This entailed the construction of a termite-proof thick layer of cement, at least an inch (26 mm) thick, and treating the woodwork with creosol or a solution of mercuric chloride. Alternatively, sheets of metal were recommended as foundations to the house (MNA/51/359/31). Brick houses with a ‘tin’

(malata) roof are now generally favoured in rural areas, not only because they give more protection from termites, but also because timber and thatching grass are becoming increasingly scarce, given the widespread

deforestation. Apart from the occasional digging-out and destroying of the queen from a termite colony that may be close to a house, or using Sevin as a pesticide, local people rarely practise control measures against termites. These insects also cause considerable damage to forestry plan-tations and to exotic trees, especially blue gums (Eucalyptus spp.). Often tree seedlings are completely lost to termites, specifically through the ring-barking of the base of the plant (Meke 1995).

Bed Bugs, Nsikidzi (Cimex hemipterus) (Family: Cimicidae) This ‘hideous pest’, as the bed bug has been described (Johnston 1897:

239), probably belongs to a group of parasitic insects that primarily evolved in relation to bats, but later switched to humans. It has a distinc-tive odour, which some people can detect in an infested bedroom. This acts as a deterrent to birds, bats and other potential predators (H. E. Evans 1970: 171–3).

Having been bitten by bed bugs while sleeping in both local huts and in rest houses, I can personally vouch that these are troublesome pests.

They are small tick-like insects, dark reddish-brown (HB 6 mm) and are wingless, flattened and oval in shape. They are parasitic and feed on the blood of humans, and live by day in the cracks and crevices and in other sheltered places in houses, coming out at night to feed on humans (Sweeney 1970: 40). They have the ability to live for long periods without food, and become particularly evident when a person goes to sleep in an old disused hut. They are very difficult to eradicate. People vary in their reactions to the bites of the bed bug. Some hardly notice the effects, while others may become quite ill. I developed lumps on my back, and the bitten areas were both achy and itchy. For local people it is considered troublesome in that they are not able to sleep well (samagona bwino), and their main protection against the bedbug is to plaster the floor and walls of a house in a careful manner so as to eradicate any cracks where the bedbug may take shelter. Others use Sevin as a pesticide, pouring (thira) it around the walls.

Maize Weevil, Nankafumbwe (Sitophilus zeamays) (Family:

Curculionidae)

For local people this is the best-known of the weevils that feed on maize in the granaries (nkhokwe) or in maize stores. Indeed, with increasing thefts of maize in rural areas, and the difficulty of obtaining bamboo and timber to construct granaries, more and more people are storing maize in bags inside the house, which makes the maize harvest even more suscep-tible to losses from the maize weevil. This insect is a tiny snouted beetle, dark brown, and 3 mm long, which feeds on the grain of maize and other

cereals. It is a strong flier, has a cosmopolitan distribution, and is believed to have originated in India (Sweeney 1962: 20). It inflicts an enormous amount of damage, and losses are incalculable. I have seen bags of maize that were literally riddled with the maize weevil, and losses are said to be bigger with the increasing use of hybrid maize, which has a softer husk than the local maize (chimanga chamakolo). Also, maize stored in gran-aries tended to have fewer maize weevils, as air circulates continuously between the maize cobs. Everyone suggested to me that in the past the nankafumbwe affected the maize far less, though rodents were often a problem. It has been estimated that in the past losses caused by the maize weevil were generally low – less than 5 per cent in traditional storage systems – where farmers cultivated local varieties of maize (Schulten 1969; Robertson 1997).

If people discover that maize is infested with weevil, women will put the maize on a reed mat (mphasa), in the sun to dry (yanika), and then again winnow (peta) the maize. An infusion of tobacco is also said to be a control measure, but most people use Actellic, obtained from a market vendor at around 10MK per packet, as the main pesticide. Other people have suggested to me the use of ashes from groundnut husks (makako anthedza) as a deterrent to overcome (gonjetsa) this troublesome insect.

Although the maize weevil is the primary pest of maize, very often this weevil breaks into the grain, and is then followed by the flour beetle (Tribolium spp.) (Family: Tenbrionidae), which often destroys much of what is left. Though not as common as the maize weevil, it is nonetheless common in all stored products, especially maize and groundnut flour.

Two other small beetles are common pests of stored maize. Both are also described as nankafumbwe, and belong to the family Bostrychidae, which is composed of wood-boring beetles. The first is the lesser grain borer, Rhizopertha dominica. This is a tiny, dark brown beetle, 3 mm long, its body covered with small tubercles. It is a common pest of stored products, including maize.

The other is the now well-known larger grain borer (Prostephanus truncatus). Originally a pest from tropical America, this is a tiny, cylin-drical, dark brown beetle, 3–4 mm long, with rather rectangular elytra. It is a strong flier, and was initially detected in Tanzania in 1981, and has since spread throughout eastern Africa, as well as to Ghana, Nigeria and other parts of West Africa. It was first recorded in Malawi in 1991 in the Karonga and Chitipa districts, and in the past decade it has multiplied, and is now found throughout the country. It is thus now described as a

‘permanent resident’ of Malawi, and causes severe damage to maize cobs and dried cassava. The loss of grain can be as high as 30 per cent, and in the Lower Shire valley in 1999 farmers reported losses as high as 70 per

cent. In spite of widespread damage and losses, farmers in Malawi are still unfamiliar with the larger grain borer – frequently dubbed LGB, and so development agencies, such as the Malawian–German Plant Protection Project, funded by GTZ, have been conducting an ‘awareness campaign’

to help farmers and extension workers to appreciate the damage that this pest is causing to stored maize. Recommended control measures have included the use of such insecticides as the organophosphates and pyrethroids, usually in combination (Actellic). But given the high cost of such pesticides, research has been conducted involving a predator beetle, Teretriosoma nigrescens, as a potential biological control agent to reduce the population of the larger grain borers (IPM Newsletter 6/2002; for a pioneering study of the insect pests of stored products in Malawi see Sweeney 1962).

It is of interest that in his Reminiscences of Livingstonia Robert Laws mentions that in the past ship’s biscuits were heavily infested with weevils. Before eating a biscuit, a seaman would therefore break it and tap it on the table to dislodge any weevils before putting the biscuit in his mouth (1934: 239).

Itch Mite, Chinyakanyaka (Sarcoptes scabiei, Order: Acarpina) The mites are not insects, but are arthropods allied to the ticks. They are tiny creatures, greyish-white, 0.4 mm long, and barely visible. They are parasitic on mammals, including humans. The itch mite infests humans, burrowing under the skin, and can cause intense itching or scabies.

People describe it as taking hold of you (gwira), but say that, at a distance, you do not see it (samaona), even though it bites you (luma). As a control measure people pound the leaves of the cassava plant in water and then sprinkle (waza) the infusion near the floor of the house to get rid of them. Alternatively, people use ashes as a deterrent. People suggest that when the itch mites are around there is never any peace (mtendere).

There are many other domestic pests that are troublesome to people in Malawi, and these include the human louse (nsabwe, Pediculus humanus), the common house fly (ntcheche, Musca domestica), the tumbu fly (mphutsi, Cordylobia anthrophaga), fleas (utitili, Cteno-cephalides sp.), the common cricket (kalijosolo, Gryllus bimaculatus) and several species of ants that enter houses, particularly in the search for sugar. Two species are particularly involved: the sugar ant (chimalasuga, Camponotus maculatus) and the brown house ant (Pheodole mega-cephala).

From discussions I had with around seventy people in the villages adja-cent to Kapalasa Farm where I enquired as to the most troublesome pest of the household (nyumba), data contained in Table 5.1 were obtained.

Other pests mentioned were the common house fly, the maize weevil, termites, common crickets and tumbu fly. People recognize that certain insects like the house fly (ntchenche) are troublesome in that they defe-cate (nyera) in food, and spread diseases such as diarrhoea, although one person thought that the fly was a carrier of malaria (malungo).

The mosquito (udzudzu) was also frequently discussed as a household pest, and considered troublesome (bvuta is the common expression), and is associated with malaria – but this is the subject of the next chapter.

Forest Pests

Although efforts have been made to establish community-based forest areas, the majority of woodlands and forestry plantation in Malawi – mainly of pines and eucalyptus – fall under the auspices of the forestry department or private estates. Around 97 per cent of Malawi’s forests consist of indigenous woodlands, mostly dominated by Julbernardia and Brachystegia spp. (miombo) trees, and around 38 per cent of this consists of protected forest reserves (781,360 ha) (NRI 1996: 31). Blue gum (Eucalyptus) plantations are widespread, and there are extensive forestry plantations on the mountains of Mlanje, Zomba, Dedza and the Viphya, mostly under various pines. In 1966 a forest entomology section of the Forest Reserve Institute (FRIM) was established in Zomba, and much research has been undertaken on the forest insects of Malawi (R. F. Lee 1971; Esbjerg 1976). Forest insect pests are of little interest or concern to ordinary people in Malawi, but four pests are worth discussing here for their wider interest and public concern.

Table 5.1 Numbers of People Considering Specific Insects their most Troublesome Household Pests (of a Total of 70

Interviewees from Villages around Kapalasa Farm)

Pest Local Name Number of Persons

Ants Nyerere Chimalasuga 16

Cockroach Mphemvu 15

Bedbug Nsikidzi 9

Itch mite Chinyakanyaka 8

Mosquito Udzudzu 6

Fleas Utitili 4

Human louse Nsabwe 4

Eucalyptus Wood Borer (Phoracatha semipunctata) (Family:

Cerambycidae)

This longicorn beetle is an exotic species, a native of Australia, and seems to have followed the eucalyptus trees in spreading throughout the world.

It is now found in South America, the Middle East, the Mediterranean region and most of Africa, and was first recorded in Malawi at Blantyre Sawmill in 1969. A decade later it had spread to virtually all the blue gum plantations in Malawi. It is a typical longicorn beetle: dark brown, with yellowish bands across the elytra (HB 40 mm) and a very long antenna (50 mm long). The beetle favours dead or dying trees, and in Zambia, in drought-stressed areas, up to 90 per cent of the blue gum trees have been reported killed because of infestation. The damage is inflicted by the pale yellowish larvae, which tunnel under the bark, and when infestation is severe, can form a dense network of overlapping galleries, and even ring-bark the tree. In attempts to control the beetle it was deemed advisable to peel the bark off all felled trees soon after logging, and before transplan-tation, and to remove all dead or dying blue gum trees. The beetle still has a presence throughout the country (Esbjerg 1976: 45; Majawa 1981).

Pine grasshopper (Plagiotriptus pinivorus) (Family:

Eumasticidae)

For many decades the exotic pine plantations of Malawi seemed to be relatively free of insect pests. Then in the late 1960s there was a serious outbreak of this grasshopper on Chambe plateau, Mulanje, for in July 1969 this species caused severe defoliation of the Pinus patula trees. This necessitated aerial spraying with the insecticide gamma-BHC. The grasshopper is plump, wingless, green and relatively small, 20–30 mm long. Originally it fed on indigenous trees of the Euphorbiaceae family, such as msopa (Bridelia micrantha) and mpefu (Macaranga capensis);

but it seems to have successfully changed its feeding habits, moving on to the pines. It subsequently became a pest on Zomba plateau, and seems to prefer Pinus patula, although it also feeds on Cupressus lindley (R. F.

Lee, 1972).

The outbreak of this grasshopper on Chambe plateau was recorded as the ‘most serious insect infestation’ that the Forestry Department had so far experienced, but was nonetheless noted as the ‘only real pest of Pinus patula in this country’ (Esjberg 1976: 18; Powell 1977). Less than a decade later there was a serious infestation of aphids on the pines.

Although of less economic importance, the allied species Malawia leei (family: Lentulidae) is also a pest on Pinus patula. A small, wingless, pale reddish-brown grasshopper (HB 20 mm) it feeds on the needles of the pines, and has been recorded on Chambe plateau.

Pine Woolly Aphid (Pineus pini) (Family: Adelgidae)

In 1976 Esjberg wrote that fortunately ‘woolly aphids have not yet been recorded from the Malawian forests’ (1976: 24). Only eight years later (1984) this exotic pest was recorded in the Chongoni forest, Dedza, where an estimated 1,500 ha of Pinus kesiya were severely infested with the aphid. Since then it has been recorded in all parts of the country, and is a great concern, as some 90 per cent of the country’s forestry plantations are under pine (62,454 ha), and the aphid, when infestation is severe, can cause losses of up to 30 per cent of the annual growth of the trees.

The pine woolly aphids are tiny and barely visible to the eye, but are usually detected by the presence of small tufts of whitish ‘wool’ that they leave at the base of pine needles. They feed on the juices of the needles, and on young bark, and whole twigs may become covered with woolly mats. This can cause die-back of the stems, and yellowing of the pine needles, and, where infestation is high, the slow demise of the trees.

The allied pine needle aphid (Eulachnus rileyi) (family Lachnidae) is also a common pest on pine trees, on both Pinus kesiya and Pinus patula.

Also an exotic, it was first recorded in 1979, having spread through south-ern Africa in the preceding decade. These are tiny insects, grey to reddish, 1–2 mm long, with wax-covered bodies. They are extremely mobile, and feed on the pine needles, causing yellowish mottling. When infestation is severe, they can inflict much damage, and up to 30 per cent loss in annual tree growth. In 1990 it was estimated that in Malawi, coupled with the pine woolly aphid, this insect caused damage worth US$5.2 million.

Neither insecticides not biological controls have yet proved to be effec-tive in controlling the pine aphid (Atuahene 1992; Chilima 1997).

Cypress aphid (Cinara cuppressivora) (Family: Lachnidae) This exotic aphid was first recorded in Malawi in 1986 in a cypress hedge on the Viphya plateau, and has since spread throughout Malawi. It feeds mainly on cypress and cedar trees, and does not appear to attack pines, and is chiefly associated with such trees as the cypress Cuppressus lusi-tanica and the Mulanje cedar, Widdringtonia whytei. The aphids feed on the slender stems of the trees, rather than on the foliage, and cause

Cypress aphid (Cinara cuppressivora) (Family: Lachnidae) This exotic aphid was first recorded in Malawi in 1986 in a cypress hedge on the Viphya plateau, and has since spread throughout Malawi. It feeds mainly on cypress and cedar trees, and does not appear to attack pines, and is chiefly associated with such trees as the cypress Cuppressus lusi-tanica and the Mulanje cedar, Widdringtonia whytei. The aphids feed on the slender stems of the trees, rather than on the foliage, and cause