Green Horizon Newsletter - Volume 1

A Newsletter of the Kenyan Forest Health Centre, Forest Department, Ministry of Environment and Natural Resources, Nairobi, Kenya

Control of cypress aphid imminent

In 1991, the National Aphid Project, working closely with the International Institute for Biological Control (IIBC) Nairobi, and other national forestry programmes in southern and eastern Africa, began looking into ways of controlling the spread of a forest pest, cypress aphid, Cinara cupressi, by  natural means.  This method is technically referred to as biological control.  Classical biological control, the preferred method for exotic pests such as the cypress aphid, involves the identification and introduction of a living organism known to be a natural enemy of the pest.   The organism may be an insect, bacteria, fungus or virus which attacks the pest in its area of origin.

The cypress aphid is not native to Africa and was first reported on the continent in Malawi in 1986.   It rapidly spread to Kenya where it was initially reported in Ngong Division, Kajiado district in the Rift Valley Province in March 1990.  Within one year, it had covered the entire country.  Other eastern African countries such as Burundi and Tanzania also reported the presence of the cypress aphid.  Emergency control measurer were  actioned and involved spraying attacked trees with pesticides but, a more environmental friendly method was advised.  Biological control came out as the favoured method.

Natural Enemy.  In the course of surveys in Europe and the U.S.A., various insects were identified.  One emerged as a particularly effective natural enemy of Cinara cupressi.  This is a wasp, Pauesia juniperorum.  Adults are about 10mm long, with a black head, brown-black thorax, yellow legs and a yellowish abdomen which becomes darker in older insects.  Pauesia juniperorum lays its eggs in live aphids (one egg per aphid).  The eggs then hatch into larvae which start feeding on the aphid, killing it in the process.  The dead aphid hardens to form a tough cocoon usually referred to as a "mummy".  The pupa is formed inside the remains of the dead aphid.  The pupal state lasts six days at the end of which the adult emerges.

Vital Quarantine Measures.  Following approval by the Kenya Standing technical Committee for Imports and Exports (KSTCIE), Pauesia juniperorum was imported to Kenya in 1993 with the objective of rearing it and carrying out studies to further determine its suitability as a parasitoid for Cinara cupressi.  The following were the quarantine measures specified by the KSTCIE and which have, according to Mr. Roger Day, an entomologist at the International Institute for Biological Control (IIBC), been fulfilled to book.

1. The parasitoid would be reared on Cinara cupressi in the IIBC UK laboratories for several generations. 
2. The parasitoid would be transported to the IIBC Kenya station by air.
3. Prior to shipment, Parasitoid mummies were to be screened to ensure they were free of fungal pathogens.
4. No plant material would be shipped.
5. On arrival, parasitoid mummies would be taken to the IIBC quarantine laboratory where they would be held at 22^o C.  Emerging adults would be collected and used to establish cultures.  This parasitoid would be reared through one generation in quarantine.
6. During laboratory studies, the wasp would be tested to confirm that it does not attack other beneficial insects, particularly the lady bird beetles and predatory mites and its host range confirmed as exclusive to cypress aphids (i.e. other local aphids of conifers would be untouched).
7. After quarantine, permission would be required from the KSTCIE for the parasitoid to be released into the IIBC insectary for rearing in readiness for filed releases.

Life History.  Adults begin parasitising aphids soon after they emerge from the pupal cocoon.  Average adult longevity is about seven days at a temperature of 22^oC. when provided with a honey solution as food.  This rises to about 40 days at 15^oC.  On emergence, the female has an average egg complement of 34.  More eggs are formed throughout life.  Fertilised eggs develop into females while unfertilised eggs develop into males.  Eggs hatch into larvae which go through several instars (developmental stages) in about eight days and then turn into pupae.  Egg to adult development is approximately 14 days at 22⁰C.  This period does not include incubation.  This is the time between when eggs are laid and when they hatch which could be one or two days.  Laboratory tests carried in the UK have shown that Pauesia juniperorum attacks and develops normally in African Cinara cupressi.

Host specificity.  Pauesia juniperorum is a primary parasitoid and will not attack other parasitoid species but only aphids in the sub-family Lachninae which are restricted to conifers.  The parasitoid therefore has a very narrow host range and, consequently, is habitat-restricted.  Such habitat and host restriction is  a common feature of most aphid parasitoids.  On the basis of the fact that Pauesia juniperorum has a narrow host range,  it is concluded that in Africa, it will only attack Cinara cupressi and other aphids in the sub-family Lachninae.  Only one other aphid from this sub-family has been recorded from trees in southern and eastern Africa.  This is Cinara tujafilina, also introduced but a minor pest of the cypress.

Host location and selection.  Using various plant cues, including host plant odors, the female parasitoid searches for and reaches the habitat where host plants and hosts can be found.  Then, using more specific cues associated with the aphids, such as waste products, suitable hosts are identified and parasitised.  These behavioral patterns are very important in determining host specificity.  In France and South Africa, Pauesia species introduces to control aphids similar to the cypress aphid established and began exerting control of aphid populations within two years, during which time they also dispersed over large regions.  Studies by IIBC (unpublished data) have shown that in the laboratory, Pauesia juniperorum can cause substantial mortality of Cinara cupressi (over 65% on Kenyan Cinara cupressi).   Keeping in mind that it is also recommended as a possible biological control agent following past successes in Europe, it is likely that this parasitoid will have a major impact on the aphid when releases.

No danger recorded.  Pauesia juniperorum poses no danger to man, crops, livestock or the environment in general.  The parasitoid will only attack aphids.  Other beneficial insects are safe.  Furthermore, there is no likelihood of it causing any indirect environmental damage or pollution nor can any conflict of interest be envisaged arising from the successful biological control of Cinara cupressi.

The IIBC wrote to the Kenya Standing Technical Committee on Import and Exports for permission to release the parasitoid.  Permission was granted in a letter dated March 25th 1994 and trial releases are soon to commence.  These are advisable not for fear of something wrong but for purposes of observance.  The parasitoid has been reared in the laboratory and it is up to the scientist to determine  whether it will do as well in the field as it has in the laboratory.

Pauesia juniperorum has several attributes that make it a good biological control agent.  Being host and habitat specific, it is safe for both humans and the environment.  It has a high fecundity, short development time and attacks the host in all its developmental stages.   The potential efficacy of Pauesia juniperorum as a biological control agent has been demonstrated by rearing it on Kenyan Cinara cupressi for over ten generations.  It also attacks the winged aphids which are attributed with rapid dispersal.  With all these and in view of the successes achieved elsewhere, it is widely believed that Pauesia juniperorum will establish and have a significant control on Cinara cupressi.

Leucaena psyllid reported to have spread all over Kenya

The leucaena psyllid, Heteropsylla cubana or the "jumping plant lice," is reported to have spread all over Kenya after an initial report two years ago where it was found in Kilifi area.  This insect originates from Central and South America which is also the native range of Leucaena leucocephala.  The adult psyllid is about 2mm long and yellow in colour.   It is common on the young growth of leucaena trees together with the young wingless forms; nymphs, and clusters of orange eggs.  The pest has been recorded in nearly all leucaena growing areas of Kenya and is now widespread throughout Africa.

Leucaena psyllid adults and nymphs inflict injury to leucaena plants by de-sapping young shoots, leaves and flowering structures.  This results in complete defoliation of susceptible leucaena varieties.  In severe cases the plants do not recover.

Leucaena is a multi-purpose plant species with a variety of uses. It inevitably requires different approaches to the management and control of the psyllid.

Caterpillar causing heavy mortality on mangroves

Mangrove forests growing in coastal areas around the world and on the Kenya Coast have a number of unique values.  They provide rich habitat for fish and other aquatic fauna.  In mangroves south of Mombasa, artificial beds have been established for the propagation of oysters.. The complex root systems of trees which occur in mangrove ecosystems help maintain the stability of estuaries and coastlines.  At a recent assessment of the extent and condition of Kenya's mangroves by staff from the Forest Department and the Forest Health Management Centre, widespread dieback and mortality of Sonneratia alba, one of the area's principle mangrove trees was detected.  This is a pioneer tree which invades newly formed deposits on the outermost edges of coastlines and estuaries.  The dieback is caused by a large and yet unidentified stem boring caterpillar.  Another insect identified as a moth was also found causing damage.

Foresters are concerned that the heavy mortality of Sonneratia alba could affect the stability of coastal zones.

Reports on woodborers attacking Casuarina and Grevillea Robusta trees in Nyandarua District confirmed

On the 30th March 1994, a team travelled to Nyandarua District to investigate reports from farmers concerning wood borers.  The team was made up of two foresters from FHM, two scientists from KEFRI and another three from IIBC.

On arrival there, the presence of a wood borer was confirmed.  Casuarina were under attack and so was Grevillea Robusta.  Specimens of the wood borers were collected for purposes of identification.  The group then traveled to Menengai in the Rift Valley to check out other reports of dying eucalyptus.  They found the trees yellowing and others with brown leaves.  The same was confirmed in Londiani with reported similar conditions on a tree of different species.  Eucalyptus trees at Kedowa were also under attack.

Preliminary observations on a dieback and decline of cedar, Juniperus procera, in Kenya

Dieback and mortality in natural forests of Juniperus procera in portions of Kenya have been reported.  Symptoms include presence of small witches brooms and resinous lesions on all sides of branches.  Dieback begins in the upper crown and the tree eventually dies.  The condition covers extensive areas of cedar forests in the Mokogondo forest in Laikipia District and the Maralal forest in the Samburu District.  Reports of extensive damage have also been received from the Narok District in southwestern Kenya.  In the Mokogondo Forest, heavy dieback and morality comprising up to 80-90% of the cedar component of the stands was observed.  In the Maralal Forest, which is at a somewhat higher elevation, heavy dieback and mortality was on the whole of the drier western half of the Leroghi ranges where cedar dominance is recorded. Frequent forest fires are reported as well as serious overgrazing.  In mixed stands of Juniperus procera, Podocarpus sp., Olea spp. and other species, dieback and mortality is at significantly lower levels.  Juniperus procera is the only species currently affected.  There are indications that the condition has been present in these forests since the early 80's.

The cypress aphid, Cinara cupressi, which is causing severe damage to Cupressus lusitanica and other members of the family.  Cupressaceae is not a major cause of the dieback and mortality.  14 different factors were identified by Dr. Anderson, a pathologist from the USDA Forest Service, affecting the cedar.  Dr. Anderson was on a one-month mission to the FHM Centre as a consultant, courtesy of the United States Department of Agriculture - Forest Service in August 1994.   Dr. Anderson's visit is partly a result of the agreement signed by the Permanent Secretary in the Ministry of Environment Mr. Justus Sabari and Mr. Jack Ward Thomas, Chief of Forest Service, USDA.