Pesticide Residues in Coastal Tropical Ecosystems: Distribution, fate and effects - Chapter 4 pot

importation, exportation, manufacture, and distribution of products used for thecontrol of pests, and of the organic function of pesticides on plants and animals.Pest Control Product was

is controlled by movement of the intertropical convergence zone (ITCZ), whoseinfluence is then modified by the altitudinal differences that give rise to Kenya’svaried climatic regimes (NEAP, 1994) The country’s equatorial location and itsposition adjacent to the Indian Ocean also influence the local climate Kenyansoils are grouped into various units (NEAP, 1994) based largely on their physicaland chemical properties These play a major role in explaining vegetation typesand their distribution patterns Kenya may be divided into four major agroecologicalzones (AEZ) namely the highlands, savannah, coastal, and arid and semi-arid lands(ASAL) (Figure 4.1) The zones have distinct humidity ranges, mean annualtemperatures, rainfall patterns, and altitudes that largely dictate their respectiveecological potentials Kenya’s population was estimated at 27.5 million in 1995and was growing at a rate of 2.9 percent per annum (NDP, 1997) Its economy ispredominantly agriculture and agroforestry-based, contributing 26 percent to thegross domestic product (GDP) in 1997 (NDP, 1997) Agricultural activities areconcentrated in the highlands (high potential), savannah, and coastal (mediumpotential) AEZs (NEAP, 1994).

P E S T I C I D E R E G U L AT I O N I N K E N YA

H i s t o r y o f pe s t i c i d e us a g e

Control of the general use and handling of pesticides in Kenya goes back to thecolonial era The earliest recorded legislation dates from 6 September 1921 whenthe Public Health Act, Cap 242, was passed by the colonial government Sixteenyears later, a second Act of Parliament dealing with Cattle Cleansing, Cap 358, waspassed on 27 April 1937 This Act prescribed various preparations for destroying

ticks These preparations are still retained in law though several amendments havemodified the original prescriptions.

At the height of Kenya’s struggle for independence, when the colonial ment declared emergency rules, it also adopted a Voluntary Precaution Schemefor the agricultural industry Compliance with the scheme was on a voluntarybasis This Scheme led to the proclamation of the Poisonous Substances Ordinance

govern-of 1954 The ordinance was based on the United Kingdom Act govern-of 1952, whichprovided for the protection of employees against risk of poisoning by certainsubstances used in agriculture and incidental and connected matters

On the eve of Kenyan independence, the Pharmacy and Poisons Act ofParliament was passed by Westminster on 1 May 1957 The aim of this Act was toincorporate provisions in the law to provide for the control of the profession ofpharmacy and the trade in drugs and poisons Included in this Act was the control

of veterinary drugs and poisons with additional rules on the selling and labeling

of poisons, including pesticides

The now independent Kenya Parliament passed an Act on 11 May 1965 forthe prevention of adulteration of food, drugs, chemical substances, and incidentaland connected matters In this, the Food, Drug and Chemical Substances Act,Figure 4.1 The agroecological zones of Kenya

Cap 254, pesticides were given particular attention, and the term ‘chemicalsubstances’ was defined to refer to any substance or mixture of substances prepared,sold, or represented for use as:

Other legislative laws passed by Parliament that have a bearing on pesticideuse, distribution, and control include the Agriculture Act, Cap 318; the Fertilizersand Animal Foodstuffs Act, Cap 345; the Forest Act, Cap 385; the Plant ProtectionAct, Cap 324; and the Water Act, Cap 389 Although in some of these Actspesticides are not specifically mentioned, it is clear that to fulfill the Act’s objectivesthe control of pesticides may be invoked

The practice in Kenya has been for Parliament to pass sectorial laws for theregulation and control of environmental matters There is no umbrella law coveringall aspects of environmental matters Such a bill is on the drawing board and it ishoped that when passed by Parliament it will go a long way toward regulatingenvironmental issues, including pesticides The major deficiency in the presentpatchwork of laws is their scattered aims and ineffective implementation Penaltiesprescribed for offenders have also been overtaken by economic realities Kenya,therefore, needs an environmental act that will assist it to better manage itsenvironment Recent attempts to better regulate the use of pesticides are described

in the next section

C u r r e n t p e s t i c i d e r e g u l a t i o n s

Except for the Poisonous Substances Ordinance, 1954, the rest of the Actsmentioned in the previous section are still in force A replacement ordinance, calledthe use of Poisonous Substances Ordinance, which will regulate the protection ofpeople against the risks from exposure to poisonous substances, has been draftedbut has not yet been presented to Parliament

The most comprehensive law regulating pesticides is the Pest Control ProductsAct, which came into law on 19 May 1983 It was established to regulate the

importation, exportation, manufacture, and distribution of products used for thecontrol of pests, and of the organic function of pesticides on plants and animals.Pest Control Product was defined as ‘a device, product, organism, substance, or athing that is manufactured for directly or indirectly controlling, preventing,destroying, attracting, or repelling any pest’ The Act established a Pest ControlProducts Board (PCPB), which became operational in October 1984 PCPB’smandate as contained in the Act is described below under the respective categories:

R e g u l a t o r y

1 To register and approve for use all pest control products

2 To regulate the sale and distribution of pest control products through licensing

of imports and exports

3 To inspect and license all facilities used for the manufacture, storage, anddistribution of pesticides

4 To analyze any pesticides for efficiency before recommending for use

Te c h n i c a l

1 To receive and evaluate data from manufacturers and importers on the merits

of pest control products

2 To undertake, as appropriate, short and long term research to evaluate theimpact of pesticides on the environment

3 To collect information from international organizations such as FAO, WHO,EPA, UNEP, etc that are relevant to pesticide use and regulation

Tr a i n i n g a n d i n f o r m a t i o n

1 To educate and inform users and the general public on matters concerningthe safety and danger of using pesticides Other functions that fall under theTraining and Information category are advising relevant authorities on aspects

of pesticide management, training government extension agents and otherinterested personnel on pesticide management, and advising the government

on the status of approved pesticides Since its inception in 1986, the Boardhas also banned or restricted the use of a number of pesticides (Table 4.1)

P E S T I C I D E U S E A N D D I S T R I B U T I O N

Pa s t a n d c u r r e n t u s a g e p a t t e r n s

Agriculture has been the mainstay of Kenya’s economy This dependence onagricultural production has led to widespread pesticide use during the last fourdecades Lindane was introduced in Kenya in 1949, toxaphene in 1950, DDT in

1956, and dieldrin in 1961 (Kaine, 1976) Other compounds in use during the

1950s included dinitrocresol (DNC) and the OP compounds, TEPP (tetraethylpyrophosphate) and schradan (Keating, 1983).

The livestock industry has been adversely affected by diseases such as EastCoast fever or theileriasis (an acute disease of cattle transmitted by ticks and caused

by Theileria parva Theiler) and anaplasmosis (a peracute to chronic infectious disease

of ruminants frequently caused by blood-feeding insects such as ticks) Acaricidessuch as chlorfenvinphos have been used to combat the disease vectors DDT hasbeen instrumental in reducing the incidence of malaria, with the consequence of

many lives saved, by controlling malaria’s vector, the Anopheles mosquito.

Foxall (1983) reported that K Sh400 million worth of pesticides was being usedannually in Kenya These consisted of 50 percent fungicides, 20 percent insecticides,

20 percent herbicides, and 10 percent acaricides, rodenticides, molluscides, andnematicides, combined Currently about K Sh2.5 billion worth of pesticides isused in Kenya annually (Mwaisaka, 1999) In 1987, PCPB reported an increase inimports between 1984 and 1986 from K Sh350 million (1984) to K Sh410 million(1985) and then to K Sh580.2 million (1986) Between 1985 and 1987, pesticidesworth K Sh1,732.3 million were imported (Mwanthi and Kimani, 1993), while forthe period 1987 through 1990 a total of 31,234 T (PCPB, 1994) was importedinto the country The bulk of imported pesticides was consumed locally with lessthan 3 percent exported to neighboring countries About 20 percent were imported

Table 4.1 Pesticides banned or in restricted use in Kenya (from the Pest Control Products Board)

Banned pesticides in Kenya Common name Former use of the pesticide

Dibromochloropropane (DBCP) Soil fumigant

Ethylene dibromide (EDB) Soil fumigant

2,4,5-T phenoxy herbicide Herbicide

Parathion(methyl and ethyl) Insecticides

Restricted pesticides in Kenya

Aldrin; dieldrin Termites in building industry – no longer available

in Kenya DDT Public health only for control of mosquitoes in

mosquito breeding grounds – no longer available

in Kenya

in technical grade form and were formulated locally while the rest were imported

as ready to use formulated products For example, malathion (technical) is usedlocally for the formulation of 2 percent malathion dust and technical carbofuran(furadan) is used for the preparation of 3G, 5G, and 10G granular formulations.Examples of formulated products imported ready for use include furadan 350 STand marshal 250 FC (carbosulfan) Tables 4.2 to 4.5 show 1986 through 1995pesticide imports into Kenya in monetary, metric, and percentage terms By 1997,the Pest Control Products Board (PCPB) had registered 370 formulations, represent-ing 217 active ingredients for use in Kenya About 22 percent of the volumeimported were highly hazardous, 20 percent moderately hazardous, 45 percentslightly hazardous, and the remainder were unclassified (Ohayo-Mitoko, 1997)

A decline in the volume of imports is noticeable between 1988 and 1990 Thiswas probably due to the ban and restriction of some OC pesticides Munga (1985)reported that 70 T of DDT had been used annually for agricultural pest control

on maize and cotton while other OCs, e.g lindane, aldrin, and dieldrin, were usedfor seed dressings DDT was last imported into Kenya in 1985, aldrin and dieldrin

in 1992 (PCPB) OCs still in use in Kenya include endosulfan and lindane.Approximately 33 percent of Kenyan farmers, primarily large farm operators,use pesticides On most small farms, which are mostly subsistence-level farms,there is minimal use of pesticides Cash crops, such as coffee, use about 50 percent

of imported pesticides while horticultural crops require another ~25 percent(Kanja, 1988) Other important crops that require a significant quantity of pesticidesare cotton, sugarcane, maize, and tea Herbicides, as a substitute for mechanical

or hand weeding, are also used by coffee, maize, barley, wheat, sugarcane, and teafarmers

T h e p e s t i c i d e i n d u s t r y i n K e n y a

The Kenyan pesticide industry comprises companies that manufacture a.i.(s) used

in pesticide formulation, formulators contracted to manufacturers of a.i.(s) used

Table 4.2 Importation of different groups of pesticides into Kenya (1986–95) (value of cost and freight in M Kshs, adapted from the Pest Control Products Board)

Year Insecticides and acaricides Herbicides Others Fungicides Total

Table 4.3 Importation of different groups of pesticides into Kenya (1986–95) (adapted from Pest Control Products Board and quantity expressed in T finished product) Year Insecticides and Acaricides Herbicides Others Fungicides Total

Table 4.4 Importation of different groups of pesticides into Kenya (1986–95) (expressed

as a percentage of the total monetary value of imports)

Year Insecticides and acaricides Herbicides Fungicides Other Total

Table 4.5 Importation of some pesticides into Kenya (1986–92)

(technical) (T) (technical) (T) (technical) (L) (technical) (L)

in the formulation of agricultural chemicals and related products, and contractedrepresentatives of manufacturers of agricultural chemicals and related productsnot otherwise represented in Kenya Most firms are overseas-based companies,except for the Pyrethrum Board of Kenya (PBK), which extracts pyrethrins from

the pyrethrum plant Chrysanthemum cinerariaefolium Trev (Compositae) Kenya has

been the world’s largest producer of pyrethrum products, exporting ground flowersfor the mosquito coil market in addition to refined extract for inclusion in aerosols

To increase toxicity and consequently lower production costs of containing insecticides, it is combined with synergists, such as piperonyl butoxide,which in themselves are not toxic (Casida, 1973; Vickery and Vickery, 1979) Othercompanies and organizations are also involved in the distribution and use ofpesticides and related products They include locally formed companies andcooperative societies like the Kenya Farmers Association (KFA) Some manu-facturers do not have facilities in Kenya but market their pesticides through anappointed agent(s)

pyrethrum-Historically firms in the agrochemical industry have been responsible forpesticide distribution in Kenya The principal importers before 1963 includedPest Control Ltd (founded in England), Murphy Chemicals (a subsidiary of Mayand Baker), and Shell Chemical Industries (a subsidiary of Shell Oil) The primarypesticide distributors included the Kenya Farmers Association (KFA) and BEACorporation (owners of Mitchell Cotts and Simpson and Whitelaw Seed Merchants)(Rocco, 1999) The pesticides were used mostly on plantations, estates, and largefarms owned by companies or individuals After 1963 (post independence), most

of the large farms were subdivided, and consequently the distribution of pesticidesinvolved more farmers and became more complex, i.e through cooperativesocieties Representatives of overseas pesticide manufacturers are now involved inthe importation of pesticides Additionally they serve as the principal distributors,supplying pesticides directly to the large-scale and estate farmers and providingcontinuous supply to stockist shops throughout Kenya The government regulatesthis sector through the PCPB

Other important groups include the Agrochemicals Association of Kenya (AAK),the Kenya Safe Use Project and the Kenya Environment Secretariat The AAKwas established in 1958 as the Pesticide Chemicals Association of East Africa andwas formed when the participants saw the need for a joint approach followingdiscussions with the Ministry of Agriculture At that time, the government wastrying to establish certain standards for local formulations, particularly dustingpowders After the demise of the East African Community in 1977, the name waschanged to the Pesticide Chemicals Association of Kenya (Rocco, 1999) Then in

1997, to reflect the broadening interests of its members, the name was changedagain to the Agrochemicals Association of Kenya In 1987, the Association started

a training program on the safe use of pesticides This encouraged the InternationalGroup of National Associations of Agrochemical Manufacturers (GIFAP) to startthe Kenya Safe Use Project in 1991 (Rocco, 1999)

In the public health sector, pesticides have offered control of vector-bornediseases such as malaria, African sleeping sickness, bilharziasis (an infection by

parasitic flukes of the genus Schistosoma Sambon), and fascioliasis (an infection caused by liver flukes of the genus Fasciola L.) through pesticide spray programs

aimed at controlling the vectors including mosquitoes, tsetse flies, and water snails.WHO programs to eradicate these pests in areas like Mwea Tabere settlementscheme (an area set aside for rice growing and human settlement), Kano Plain,and Lambwe Valley have rendered them habitable Historically dieldrin, DDT,and endosulfan were used for the control of mosquitoes and tsetse flies, but due totheir detrimental effects on non-target organisms, the less persistent OP, carbamate,and pyrethroid insecticides are now used Pirimiphos methyl is currently beingused to control adult mosquitoes outdoors and permethrin is used for householdresidual sprays and for treating bed mosquito nets, curtains, and fabrics forprotection against mosquitoes and other biting insects Cyhalothrin-λ is also used

in public health for control of houseflies, mosquitoes, and cockroaches Niclosamideand trifenmorph have been used at Mwea Tabere to control the water snail

Biomphalaria pfeifferi Krauss (Gastropoda: Planorbidae), which is a vector of

bilharz-iasis Household pests such as flies, cockroaches, fleas, rats, and mice have beencontrolled using various products (see Table 4.6)

S t o r a g e p e s t s

Problems associated with storage insect pests on maize in Kenya have existed eversince the crop was first introduced This is because the high temperatures andrelative humidity in most regions of the country strongly favor the growth anddevelopment of these pests (Asman, 1966) The infestation trend of harvestedcrops can be broken into three phases depending on the species attacking the cropand the storage environment The first phase occurs when the grain is maturing in

the field and is characterized by infestations by primary pests, e.g Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) and Sitotroga cereallela Olivier (Lepidoptera: Gelechiidae) (Floyd, 1971; Ayertey, 1978), which attack whole grain Ephesta cautella

Walker (Lepidoptera: Pyrilidae) is absent from the grain during this phase Once

grain is shelled and placed in the warehouse, E cautella becomes important in close association with other secondary pests, particularly Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), Corcyra cephalonica Stainton (Lepidoptera: Galeriidae), and Oryzeaphilus surinamensis L (Coleoptera: Silvinidae) (Delima, 1973) Secondary

pests are those that feed on grain already damaged by primary pests and also on

fragments of grain The third phase, in which E cautella is less important, occurs

when control operations are less than optimal and comprises infestations by

Rhizopertha dominica Fabricius (Coleoptera: Bostrichidae), Cryptolestes spp (Coleoptera: Cucujidae), and Tenebroides mauritanicus L (Coleoptera: Trogositidae) (Graham,

1970a) Attempts to control the pests have relied heavily on the use of pesticidesincluding DDT, γ-BHC, pyrethrins, and malathion, but they have achieved limited

success (McFarlane, 1969) Presently bromophos, dichlorvos, pirimiphos-methyl,and permethrin are the primary insecticides used, although control is incompleteand the pests still cause significant losses Pests attacking grain stored on the farmare controlled by residual chemical sprays on storage structures and insecticidaldusting of cob maize (Anonymous, 1974) In contrast, the primary methodemployed at centralized storage facilities has been fumigation (McFarlane and

Table 4.6 Some pesticides used in Kenya (adapted from the Pest Control Products Board) Pesticide common name Type: use

λ-Cyhalothrin Insecticide: for use on cotton, horticulture,

ornamentals.

Carbosulfan (carbofuran or furadan) Insecticide: control of maize stalkborer, coffee

berry borer, cotton pests, aphids, thrips, lister scale, soil pests (e.g termite grubs and nematodes) in coffee nurseries Seed dressing in beans and maize for the control of soil borne and early foliar pests.

Cypemethrin Insecticide: for use on cotton, vegetables, citrus,

and other fruits and army worm and locust control.

Chlorpyrifos Insecticide: for use on cotton, locust and army

worm control, soil pests and larvicide for public health.

Carbofuran Systemic insecticide/nematicide: soil pests,

nematodes, early foliar feeding pests on coffee, bananas, pineapples, pyrethrum, nurseries, maize Applied with mechanical granular applicators.

Glyphosate Herbicide: post-emergence systemic control of

weeds in coffee, tea plantations, sugarcane, pasture destruction, reduced tillage.

Copper hydroxide or 50% Fungicide: for the control of Coffee Berry metallic copper Disease (CBD), leaf rust, bacterial blight on

coffee, and horticultural crops.

Chlorfenvinphos Acaricide: for the control of all species of ticks

found in East Africa (vectors of East Coast fever), also fleas, lice on cattle, goats, sheep Amitraz (N-methylbis Acaricide: for veterinary use to control ticks and (2,4-xylylimino-methyl)amine) other ectoparasites on cattle – 0.025% aqueous

dispersion applied as dip or spray at 7 d intervals Coumatetralyl Rodenticide: for the control of rats and mice Bacillus thuringiensis Berliner Biological insecticide: for control of

var kurstaki 16 lepidopterous larvae and other pests on

vegetables; for the control of giant looper, green looper, leaf skeletonizers, and jelly grub in coffee.

Pyrethrin/permethrin/ Insecticide: aerosol for the control of crawling piperonyl butoxide/ dichlorvos and flying insects, cockroaches, ants, flies,

mosquitoes.

Sylvester, 1969) For immediate control of pest outbreaks or surface infestations,pesticides are sprayed directly on the grain surface and on storage fabrics, thereafterproviding residual protection (McFarlane and Sylvester, 1969).

Lalah and Wandiga (1996) found that after 51 weeks of storage, 34 to 60 percent

of the initial radiolabelled malathion dust remained on stored beans Phaseolus vulgaris and maize Zea mays irrespective of the storage method used, i.e the open basket

storage model or the modern wooden box model Half-life of the pesticide rangedfrom 194 to 261 d for maize and 259 to 405 d for beans in open baskets or closedboxes, respectively

A c a r i c i d e s

Ticks cause the greatest loss of livestock and are the most important vectors ofdisease agents in domestic animals (Kaine, 1976; Keating, 1983) Several differentacaricides with varying application rates, residual action periods, stripping rates,stability, and safety have been used to combat them (Keating, 1983) The use ofacaricides in Kenya has been orchestrated to avoid resistance development byrestricting the number of available acaricides Sodium arsenite was the onlyacaricide in use in Kenya between 1912 and 1949 for vector control of seriouslivestock diseases such as East Coast fever (Keating, 1983) The first resistance to

arsenic was reported in the blue tick Boophilus decolaratus (Acari: Ixodidae) in 1953.

Lindane (benzene hexachloride, BHC or hexachlorocyclohexane, and HCH) was

introduced in 1949 and resistance to BHC was first noted in 1954 in B decolaratus

(Keating, 1983) The development of tick strains resistant to arsenic and HCH led

to the increased use of toxaphene, a chlorinated camphene, which was introduced

in 1950 (Keating, 1983) By 1956, toxaphene was the major acaricide in use, due

to its stability in dip washes and its prolonged residue effect Other OCs, i.e DDTand dieldrin, were introduced in 1956 and 1961, respectively, but because tickresistance developed, the OC acaricides were banned in 1976 (Keating, 1983) Afurther disadvantage of OC acaricides was that they accumulated in body fat andwere secreted in milk from dairy animals

OP compounds, such as dioxathion and coumaphos were introduced in 1959(Keating, 1983) In 1961, resistance to toxaphene was noted in two strains of the

red-legged tick (Rhipicephalus evertsi (Acari: Ixodidae)) (Anonymous, 1961) and in B decolaratus in 1962 (Anonymous, 1962) leading to increased use of OP compounds.

The OPs were often used during this period in combination with arsenic, HCH,and toxaphene (as toxaphene still effectively controlled one of the most important

species of ticks R appendiculatus Neumann (Acari: Ixodidae), the vector of East Coast Fever (ECF)) R appendiculatus eventually developed resistance to toxaphene

leading to its ban (Kenya, 1976) Then in 1976, two OPs, dioxathion and quintiofos,and a carbamate, carbaryl, were gazetted and recommended for use Acaricidesthat are still in use in Kenya include carbaryl, quintiofos, chlorfenvinphos,coumaphos, and several formamidines However, amitraz is the most widely used.Synthetic pyrethroids are currently undergoing efficacy tests and some, e.g

cypermethrin, have been recommended for use Most farmers treat their cattle incattle dips because this is more economical and they find it easy to maintain thecorrect chemical concentration in the dip.

(1966) found that after fumigation with methyl bromide, the E cautella population

attained its third generation peak in 140 days During this period, about 3,000adults were caught in flight traps each day Thereafter, the moth population declined

to a level of one to 10 moths per day because of pressure from the predatory mite

Blattisocius tarsalis Berlese (Acari: Ascidae), a destructive feeder of E cautella eggs.

He noted that in the absence of B tarsalis and chemical sprays, E cautella populations were high and often occurred in combination with another pest T castaneum Muhihu

(1996) observed that although pesticides are considered effective, in that theysubstantially reduce pest numbers, complete eradication is not possible Graham(1970b) postulated that where an insecticide combined with mite control wasnecessary, some pesticides appeared to be more toxic to the mite than to the moth

and that the continued use of the insecticide led to increased importance of E cautella as a pest in maize stores Incomplete eradication by malathion of E cautella has been observed in other countries (Graham, 1970b) and other pests, e.g T casteneum, have also developed resistance to malathion (Champ and Dyte 1976).

Biological control has been an important component of pest control in Kenya

The common coffee mealybug (CCM) Planococcus (Pseudococcus) kenyae Le Pelley

(Hemiptera: Pseudocóccidae) was imported into Kenya from Uganda The firstepidemic occurred in 1923 and continued until 1951 when it was reduced to aminor pest (Hill, 1975; Abasa, 1981) Because insecticides had proven ineffective,

parasites were used to fight the CCM These included Anagyrus kivuensis Compere (Hymenoptera: Encyrtidae) and Anagyrus beneficians Compere (Hymenoptera:

Encyrtidae) (Hill, 1975) The parasites attack the CCM on coffee and indigenousplants However, the coffee tree has to be kept free from unwanted sucker growth(upright shoots growing low on the trunk of the tree) because these suckers are

attacked by the green scale Coccus alpinus De Lotto (Hemiptera: Coccidae) and A kuviensis is less effective in the presence of green scale Ants, Pheidole punctulata Mayr

(Hymenoptera: Formicidae), also aid the flourishing of the CCM by attacking itsparasites (Abasa, 1981) To prevent this, trees were sprayed with a band of dieldrin(100 ml of 18 percent dieldrin in 20 ml water) mixed with methylene blue for

identification of banded trees This prevented ants from reaching the parasites.Only badly infested trees were sprayed to runoff with 60 percent diazinon Anumber of coccid pests of coffee were controlled with this integrated pest control

method This included the white waxy scale Gascardia brevicauda Hall (Hemiptera: Coccidae), the green scale (C alpinus), the star scale or yellow-fringed scale Asterolecanium coffeae Newstead (Hemiptera: Asterolecaniidae), and the root mealybug Planococcus citri Risso (Homoptera: Pseudococcidae) (Abasa, 1981) However, dieldrin

has now been banned for use in Kenya and ethion is currently used to control thescales and mealy bugs in coffee and the ants that attend to them

The cassava mealybug Phenacoccus manihoti Metile-Ferrero (Homoptera: coccidae) is a major pest of cassava Manihoti esculenta Crantz (Euphorbiaceae), a major source of carbohydrates in Kenya A parasitic wasp Epidinocarsis lopezi De

Pseudo-Santis (Hymenoptera: Encytidae) was released and has been shown to control

populations of the cassava mealybug (Kariuki et al., 1991a) Another pest of cassava, the cassava green mite Mononychellus tanajoa Bodar (Acari: Tetranychdae), has been found to be affected by exotic phytoseeids Neoseiulus ideaus Denmark and Muma (Acari: Phytoseiidae) (Kariuki et al., 1993) A newly introduced phytoseeid Typhlondromalus aripo De Leons (Acari: Phytoseeidae) was released in 1995 and 1996

and has established itself in the western and coastal regions of Kenya (Kariuki

et al., 1998) Populations of N ideaus were found to have established themselves

33 months after their initial release (Mambiri et al., 1994).

Another biological control program, which has registered success, is that for

the larger grain borer (LGB) Prostephanus truncatus Horn (Coleoptera: Bostrichidae).

This is a pest causing serious losses of stored maize and cassava that is spreading

widely in East and West Africa (Nang’ayo et al., 1994) Releases of its natural predator Teretriosoma nigrescens (Coleoptera: Bostrichidae) resulted in a strong negative pressure on LGB populations (Nang’ayo et al., 1994) Irish potato Solanum plantanim

L (Solanaceae), another important source of carbohydrates in Kenya, has been

attacked by the potato tuber moth Pthorimaea opercullela Zeller (Lepidoptera: Pyrilladae) However, releases of the parasitoid Copidosoma koehleri Blanchard

(Hymenoptera: Encyrtidae), which parasitizes eggs of PTM, did not bring it under

control (Mambiri et al., 1993).

Biological control methods have been used to fight weeds Salvinia molesta Mitchell

(Salviniceae) is a free floating aquatic fern native to South America, which wasintroduced into Kenya as an ornamental It is a fast-growing weed and was reported

to double in weight every 4.5 days in Lake Naivasha, a closed basin, freshwater

lake on the floor of the Rift Valley (Kariuki et al., 1991b) It forms dense mats, thus

interfering with fishing activities and water pumping (for both domestic and

irrigation purposes), among other activities The weevil Cyrtobagous salviniae Calder

and Sands (Coleoptera: Curculionidae) was released in 1991 It established itself

and brought the weed under control (Kariuki et al., 1991b; Oduor et al., 1995) However, the water hyacinth Eichhornia crassipes Solms (Pontederiaceae) is quickly taking over as the major aquatic weed (Oduor et al., 1995) Trials with the bruchids Neochetina bruchi Hustache (Coleoptera: Curculionidae) and Neochetina eichhorniae

Warner (Coleoptera: Curculionidae) have shown that they are establishing

them-selves (Oduor et al., 1995) and may bring this aquatic weed under control.

Pe s t r e s i s t a n c e t o i n s e c t i c i d e s

Armstrong and Smith (1958) studied the effects of commonly used OC insecticides

on the mosquito vector for malaria and found it was susceptible to DDT, λ-BHC,and dieldrin In Kenya, rice is grown under irrigation in two main areas: Ahero, inNyanza Province near Kisumu, and Mwea Tabere, in Eastern Province near Embu

(Okedi, 1988) Mosha and Subra (1982) found Anopheles gambiae Giles (Diptera:

Culicidae) was the most common malaria vector in these areas Fields are sprayedregularly with insecticides for control of agricultural pests and applied chemicalsinclude fenitrothion, carbofuran, and, previously, DDT These spraying activities

result in pesticides being present in A gambiae breeding sites in rice paddies where

its larvae are found in large numbers Chapin and Wasserstrom (1981) suggestedthat direct exposure of mosquitoes to agricultural insecticides may exert a selectionpressure leading to the development of resistance to those insecticides present and

those with similar modes of action Okedi (1988) found that there were A gambiae

larvae, which showed high resistance to fenitrothion and DDT, at Ahero and Mwea.However, little or no resistance existed for pesticides not used for pest control, e.g.dieldrin and malathion The development of resistance to insecticides by malariavectors has been one of the causes of the resurgence of malaria in the region(Okedi, 1988)

L o c a t i o n o f p e s t i c i d e u s e w i t h r e s p e c t t o t h e

m a r i n e e n v i r o n m e n t

Figure 4.2 is a map of Tana River basin showing the irrigation schemes, includingthe Hola irrigation scheme In the 1960s and 1970s, DDT was extensively used inthe Hola irrigation scheme as the primary insecticide for cotton, maize, and horti-cultural crops For cotton pests, it was applied as a 5 percent dust at 5.5 to 11.0 kg

ha–1 The quantity of DDT used during this period was estimated at 12 T annuallywith at least 80 percent being used for the control of cotton pests (Munga, 1985).Monocrotophos was also used in the early stages of the scheme for cotton pests(Munga, 1985) As a combination spray mixture, monocrotophos/DDT (10percent/40 percent) was applied with ultra low volume (ULV) equipment at 2.5 to3.0 L ha–1 Spraying of cotton at Hola was initiated using an EIL to justify theneed for pesticide application and this threshold value was the appearance of pests

on >5 percent of cotton plants (Munga, 1985) The 1983 cotton season requiredseven aerial applications of endosulfan 25 percent (ULV of 6 to 12 g a.i ha–1),deltamethrin 0.5 percent (ULV of 12.5 g a.i ha–1), and hostathion 25 percent(ULV) over the period June to September In addition to aerial spraying, handspraying continued for small areas affected by pests until December, although nospecific schedule was followed (Munga, 1985)

Starting in 1980, synthetic pyrethroids and endosulfan (as thiodan) began toreplace DDT for control of cotton pests (Munga, 1985) During the 1980–81 cottongrowing season, an estimated 350 kg of cypermethrin was used and, during the

1982 to 1984 cotton growing seasons, an estimated 3.9 T of endosulfan and 76 kg

of deltamethrin were used per season (Munga, 1985) Endosulfan has also beenwidely used as an alternative to DDT and dieldrin for tsetse fly and cotton pestcontrol in Kenya and other tropical and subtropical countries of Africa (Munga,1985) Table 4.7 lists some important pests, the crops susceptible to attack, and thecontrol measures used in the Tana River District (1992 to 1993) (Pest ControlProducts Board of Kenya)

Aerial spraying is the pesticide application technique that is most prone to spraydrift This can result in pesticide falling onto non-target areas, especially freshwaterbodies located in the irrigation scheme Soil erosion also contributes to movingpesticide residues into water bodies Athi River (see Figure 4.3) was found to contain

a number of pesticide residues arising from the extensive use of agriculturalpesticides in the Kiambu District (UNEP, 1982)

Approximately 97 percent of Kenya’s rice crop is produced under irrigationschemes covering 9000 ha (Anonymous, 1985) Notable among these are the Ahero

Figure 4.2 Map of the Tana River basin showing irrigation schemes and other

developments (from Tana and Athi Rivers Development Authority, Nairobi, Kenya)

Table 4.7 Important pests and control measures taken in Tana River district (1992 and 1993)

Maize stalk borer Maize, sorghum, millet Cypemethrin, trichlorfon,

carbofuran American bollworm Cowpeas, green grams, Cypermethrin, carbosulfan,

tomatoes profenofos/cypermethrin

beans Stainer pink bollworm, Cotton Cypermethrin, carbonsulfan,

Army worms Cereals, pastures Cypermethrin 2.5% ULVa

Scales Citrus, robusta coffee Carbosulfan, chlorpyrifos,

omethoate

Note:

a ULV indicates that pesticide was applied with ultra low volume application technology.

Rice Research Station in western Kenya and the Mwea Irrigation Scheme in theupper reaches of the Tana River Lalah (1993) reported that carbofuran (as 5percent technical furadan granules) is applied in the seed furrow at the rate of0.54 kg a.i ha–1 to control soil-dwelling or foliar-feeding insects and mites Lalah(1993) found that carbofuran dissipated faster from flooded soil than from non-flooded soil, with levels approaching 40 percent in less than 25 days and fallingbelow 20 percent after 111 days Carbofuran is highly soluble in water, and thustends to move into the water column above flooded soil While most of the pesticidewas found in the top 10 cm layer of soil, its movement into the water column poses

a risk of contamination of nearby streams and canals These waters flow into theNyando River and, ultimately into Lake Victoria, the world’s largest freshwaterlake (Figure 4.3) The potential for contamination of freshwater streams and lakeswas highest in the first three weeks following pesticide application

P E S T I C I D E C O N TA M I N AT I O N O F T H E

E N V I R O N M E N T

S e d i m e n t s

Everaarts et al (1997) examined pesticide residues in sediments and

macro-invertebrate organisms along the Kenyan coast They found PCBs and pesticideresidues in sediment samples from two shallow coastal stations at the mouth ofSabaki River (Figure 4.3) PCB congeners 28, 52, 101, 153, and 138 were detected

at the two sites in a concentration range of 7.1 to 62.2 ng g–1 of organic carbon