A Review of Contributions of Moi University Towards the Control of Cypress Aphid

J. Mwangi - Department of Wood Science and Technology, Moi University, P.O. Box 1125, Eldoret, Kenya

Abstract

A large resource of cypress was infested with cypress aphid in East-Africa in 1990. Infestation levels varied between mild and sever. The damaged trees needed to be salvaged to avid total loss. There was limited information on aspects of utilisation of aphid infested cypress such as mechanical, physical, chemical and anatomical properties. Research was carried out at Moi University, Department of Wood Science and Technology to seek this information.

The incidence of fungal attack on wood from aphid killed trees and its susceptibility to fungal deterioration was also investigated. Results showed evidence of moulds and sapstain colonisation in wood from the trees examined. There was no evidence of more susceptibility to fungal deterioration for affected wood.

On the decay rates of wood from infected and uninfected trees, the results showed no significant difference between the two categories of wood which can be used under the same environmental conditions. The specific gravity, mechanical properties, moisture and lignin contents, showed no significant difference between affected and unaffected trees. The study also showed that cypress aphid attack did not affect the anatomical properties and seed quality of trees, nor did it change paper properties provided the attacked and dead trees are harvested prior to being attacked by borers, fungi and other wood biodeteriogens.

The dimensional stability of wood from aphid killed cypress trees was found to be generally low with higher seasoning defects than healthy trees. The seasoning defects were higher in infected trees from older stands (30 years) and after 12 months of attack. However, the attack by aphid did not significantly affect the creosote penetration and retention.

The cause of death in cypress trees infested by cypress aphid was also studied. It was found that the death is caused by desaping which interferes with mobilisations of nutrients.

Four local predators of cypress aphid were studied. Betasyrphus adligatus wied was found to have the highest mean daily consumption rate. Two types of insecticides, Bestox (Cypermethrin) Insecticidal soap and Marshal (Carbosulfan), were tested against cypress aphid, syrphid fly larvae and lady bird beetle. All the compounds were found to be effective on the aphid with soap solution having the highest control effectiveness.

Introduction

The cypress aphid Cinara cupressi was first detected in Africa in 1986 in Malawi where it was found causing damage to its host trees belonging to the family Cupressacea. Among this family the most susceptible species is Cupressus lusitanica which, incidentally, forms the bulk of the industrial forestry plantation in Kenya. Cypress constitutes about half of the industrial forestry plantations which account for over 80% of the country’s industrial wood supply (GOK, 1995). In addition to the cypress, another member of the family, Juniperus procera (African Pencil Cedar), which is also attacked by the aphid, forms the major vegetation cover of the country’s water catchment areas where it is found naturally growing and in established plantations. Cypress is also an important tree widely grown in rural farmlands as hedges, woodlots for the provision of fuelwood, timber, poles and as ornamentals.

The pest was detected in Kenya in February 1990 in Ngong division of Kajiado district from where it quickly spread to other areas of the country. The pest threatened to devastate over 80,000 hectares of cypress plantations, about 200,000 hectares of natural and plantation cedar, and an estimated 30,000 hectares of woodlots and hedges in rural farmlands. The potential loss as a result of the aphid damage was estimated at US$2 billion (GOK, 1995). The imminent danger of destruction of this forest resource was bound to have other far reaching environmental and socio-cultural impacts hence the government moved fast and addressed the pest menace. With the assistance of the donor community, the government launched the National aphid Project involving the Ministry of Environment Natural Resources and the Ministry of Research Technical Training and Technology as implementors. Moi University was identified as one of the project’s collaborators which included also the International Centre of Insect Physiology and Ecology (ICIPE), the National Museums of Kenya, the International Institute of Biological Control (IIBC) and the Nature Conservation Society of Africa (NCSA).

The main objective of the National Aphid Project was to develop sustainable management and control measures of cypress aphid pest through an Integrated Pest Management (IPM) strategy which is environmentally friendly, technically efficacious, economically feasible and socially acceptable.

The specific objectives of the project were to:

1. Conduct research on the biology, population dynamics, host interaction, impacts and methods of control including chemical, biological, silvicultural and genetic methods of the cypress aphid in order to provide a firm knowledge base from which to develop an IPM programme;
2. Contain the spread of the cypress aphid;
3. Strengthen the capability of agencies in the Government of Kenya in relevant NGO’s to manage forest pests.

Following the outbreak of the cypress aphid, the Forest Department was at a loss on what to do with the infested wood material as sawmillers and other wood utilisers were hesitant at utilising such material. The sawmillers and other licensees were demanding lower royalty charges on the aphid infested material claiming that the attacked wood was of inferior quality compared to the wood from healthy trees. Other socio-cultural beliefs were associated with the aphid infested cypress. One of such beliefs is that the attacked cypress wood, when used as fuelwood, caused sterility in women. The Department of Wood Science and Technology at Moi University carried out research work between 1990 and 1995 to address various issues associated with the cypress aphid attack. This paper gives a summary of the studies undertaken by students in the Department of Forestry and Department of Wood Science and Technology.

Incidence of Fungal Attack on Wood from Aphid-Killed Trees

The objective of this study was to investigate whether wood from aphid killed cypress trees showed evidence of fungal attack whilst standing in the forest and whether such wood is mor susceptible to fungal attack than wood from unaffected cypress trees.

Samples of wood were collected from 3 aphid killed trees from different stands aged 12, 18 and 30 years; while samples of un-attacked cypress wood were collected from a tree in an 18-year-old stand for use as a control. The stands were from Nabkoi Forest Station in Uasin Gishu District.

The study showed evidence of bacteria, primary moulds and sapstain colonisation in wood from the trees examined (Mbiri and Venkatasamy, 1993). It further showed that there was no evidence that wood from the aphid-killed trees is more susceptible to attack than wood from the un-attacked tree. The study recommended that the aphid killed trees should be harvested immediately after death of trees to avoid loss through deterioration by fungi and other biodeteriogens. It also recommended that low cost and simple wood preservation methods be devised to preserve wood from aphid-killed trees.

The study suggested that further work be conducted to investigate the following:

1. The length of time for which the aphid-killed trees can be allowed to remain in the forest and still yield utilisable timber.
2. Detailed investigation on the fungal deterioration of aphid-killed stand cypress trees.

Comparative Studies of Decay Rates of Wood from Sound and Aphid-Killed Cypress Trees.

This study aimed at comparing the rates of wood decay for aphid-killed and unaffected cypress trees aged 10, 20 and 30 years and which had been left standing in the forest for 6, 12 and 18 months after the aphid attack. The study also tried to identify the types of decay and establish whether there is a certain pattern and make recommendations from the findings.

The study found that there was no difference in the decay rates between the two categories of wood both under terrestrial (ground contact) and aquatic environments (Mbuvi and Venkatasamy, 1995). Bacteria, sapstain and soft rot fungi were observed to attack and cause wood decay under ground contact conditions. Under aquatic situations, only bacteria and sapstain fungal attack were observed in both categories of wood. The affected wood from the attacked trees was found to have lower moisture contents than those of unaffected cypress trees.

The study concluded that untreated wood from aphid-killed cypress trees can be used under the same environmental conditions as wood from healthy cypress trees. It was recommended that further studies are necessary to investigate the consistently low moisture contents and decay rates in infected woods.

Mechanical Properties of Aphid-Attacked Cypress Wood

This study was carried out with the objective of comparing the mechanical strength properties between attacked and unattacked cypress wood. The mechanical properties tested included shear parallel to the grain, static bending and compression parallel to the grain. In this study wood from the attacked and unattacked cypress trees was subjected to the above tests. The trees were selected from a 30-year-old plantation in Elburgon Forest Station.

The study found that there is no significant difference in the mechanical strength properties between wood form the infected tree and that of the non-infected tree.

The study concluded that the timber from cypress attacked by aphid should be treated as normal timber from healthy cypress trees.

Incidence of Fungal and Insect Attack in Aphid-Killed Cypress Trees

The objective of this study was to assess microbiological and insect deterioration of wood from trees which had been attacked and killed by the cypress aphid and left standing in the forest for varying periods of time. The specific objectives were as follow:

• To assess the severity of bacterial and fungal damage caused within the inner layers of dead standing trees, from bark to pith
• To identify the patterns of fungal attack present, sapstain, soft rot, white rot and brown rot
• To assess damage and the intensity of such damage caused by insects colonising the dead trees.
• Make recommendations based on the findings.

The study concluded that both bacteria and sapstain fungi colonise and attack the wood of cypress trees killed by the cypress aphid which were left standing even for short periods of 6 months or more (Munguti and Venkatasay, 1992). The severity of attack increases with the period of time the trees are left standing in the forest. Soft rot fungi was found to start causing wood decay after 18 months and over. The aphid-killed trees we4re also found to be prone to attack by wood borer insects. Notable among these insects is Oemida gahani.

It was recommended that aphid-killed trees be salvaged and utilised soon after death to avoid loss of wood by biodeteriogens. Other infested plantations outside the study area need to be investigated, especially those in high potential areas where the activities of the biodeteriogens are expected to be higher. Studies to investigate changes in permeability and mechanical properties of wood from aphid-killed trees left standing for more than 12 months were also recommended.

Utilisation of Aphid-Killed Cypress Trees in Kenya

An industrial survey was carried out to determine the attitude of forest product industries and other timber users towards utilisation of aphid-killed cypress trees as their raw materials. The survey was carried out among leading companies that utilise cypress trees as their raw materials in Kenya. Notable among these companies are Timasales which owns Sokoro Plywood fibreboard and sawmills; Railply dealing with plywood, floor tiles, sawmilling and furniture- making; Elgeyo sawmills dealing with sawmilling, plywood, blockboards and tea chests; Kabiyet sawmills dealing with sawn timber; and other small scale sawmills and furniture-making enterprises. The Kenya Wildlife Service which has a national fencing project in game reserves and parks, private ranches and farms were also included in the survey.

For the construction industry which is mainly concerned with the mechanical strength properties, a study done earlier found that there is no significant difference in mechanical wood properties between the timber from cypress aphid-killed and healthy trees if the aphid -killed trees are harvested soon after death before other wood biodeteriogens set in.

In the panel boards industry, it was observed that initially people had a negative attitude towards the utilisation of wood from aphid infested trees. However, it was later found that these fears were unfounded as it was proved that there is no significant difference in the panel board properties between aphid-killed and healthy trees as long as the wood has not been attacked by wood borers, fungi and other biodeteriogens.

In the pulp and paper industry, the results showed that cypress aphid attack did not affect the paper quality if the attacked and dead trees are harvested prior to attack by borers, fungi and other wood biodeteriogens.

As concerns fencing posts, cypress was found to be unpopular as a fencing material. However, cedar posts were found to be preferred to cypress and other species. Black wattle tree (Acacia mearnsii) was found to be the main alternative to cedar posts following the government ban on exploitation of cedar. The other species used were noted to be Eucalyptus and several indigenous species. The cypress aphid attack on natural and plantation cedar forests was observed to have no affect on the demand for cedar posts for use in fencing. The study recommended that infested or aphid-killed cedar trees be utilised as fencing material.

The survey also found that some farmers in rural areas had cut and used their infected trees for fuelwood without any problem. The survey recommended that cypress trees of lesser top diameters, which has been killed by aphid and which cannot be utilised otherwise, be exploited for firewood and charcoal production. The same should apply to heavily biodegraded trees of utilisable diameter.

The survey concluded that aphid-killed cypress wood is good for various uses if the trees are harvested and processed within a period of two years after death (Okeyo and Mwangi, 1993).

Dimensional Changes and Seasoning Defects in Aphid-Killed and Healthy Cypress Trees

The main objective of this study was to determine whether there are any significant differences between the dimensional stability and seasoning characteristic of sawn wood from aphid-attacked and non-attacked cypress trees. The study further evaluated differences in dimensional changes in wood from aphid-attacked cypress trees of varying ages which have been subjected to different periods of attack ranging from 6, 12 and 18 months.

Samples for the study were collected from stands aged 20, 25 and 30 years from different plantations in different geographical locations namely Elgyo, Kipkabus, Kerita, Shamanek, North Marmanet and Hombe Forest Stations.

The study concluded that cypress aphid-attacked trees generally have lower moisture contents than healthy trees. The moisture content was lowest in the older trees in both categories (Imala and Venkatasmy, 1995). Wood from trees killed by cypress aphid had higher dimensional changes and seasoning defects compared to wood from healthy trees. The seasoning defects were found to be generally higher in aphid-attacked trees from older stands of 30 years or more and highest after 12 months of aphid attack.

The study recommended air drying method for material from aphid-killed trees as this technique does not seem to cause severe seasoning defects and dimensional changes in sawn wood as compared to kiln and oven drying.

Studies to investigate the mechanical properties, anatomical changes and modifications of the chemistry of wood from aphid-attacked trees were recommended.

Effects of Creosote Retention and Penetration in Wood from Cupressus lusitanica Attacked and Killed by Aphids

The objectives of this study were to investigate the retention and penetration of creosote in wood from cypress trees killed by the cypress aphid and to investigate the correlations between the treatability of wood from dead and healthy cypress trees. Samples used in the study were obtained from healthy and aphid-attacked cypress trees from 12-, 14- and 15-year-old cypress plantations in Kaptagat Forest Station in Uasin Gishu district.

The study found that there is no significant difference between the aphid-attacked cypress trees in creosote retention and penetration (Rotich and Venkatasamy, 1992). Consequently, the aphid attack has no affect on the treatability of wood from healthy and aphid-killed cypress trees.

The study recommended that further research be undertaken to investigate the treatability of aphid-killed cypress wood using other wood preservatives and other treatment methods.

Properties of Cupressus lusitanica Attacked by the Cypress Aphid

This study investigated whether the cypress aphid attack had any affect on the moisture content, specific gravity and lignin content of cypress trees. The study was carried out using material from healthy cypress trees and cypress trees which had been attacked by the cypress aphid. The samples used in the study were obtained from a 15-year-old cypress plantation in Kaptagat Forest Station in Uasin Gishu district.

The study showed that there is no significant difference between healthy and aphid attacked cypress trees for the three properties studied (Mbithi and Mwangi, 1992).

The study recommended that further investigation be undertaken on the three properties using materials from different geographical locations.

Affect of Aphid Attack on Anatomical Characteristics of Cypress lusitanica Stem

The objective of this study was to investigate whether cypress aphid attack has any affect on the anatomical characteristics of cypress wood. The study was conducted using wood obtained from healthy and aphid attacked cypress trees obtained from the Chepkoilel Campus of Moi University.

Microscopic observation of individual cell types from sections obtained from the sample stems showed that there is no significant difference in the anatomical characteristics between the healthy cypress trees and the aphid attacked trees (Gacheru and Ringo, 1992). The study, which was conducted on trees which had been attacked by the aphid for a period of 1-2 years, concluded that the aphid attack has no affect on the anatomical characteristics of the cypress wood.

The study recommended the carrying out of detailed studies on the anatomical characteristics using cypress trees infected for longer periods.

Affect of Cypress Aphid Attack on the Quality of Seeds

This study was carried out to determine whether the cypress aphid attack had any affect on the quality of cypress seeds. The study was done using seeds from healthy cypress trees and seed from infested trees. The seed quality test parameters were a germination test, a cutting test, a tetrazollium chloride test, seed moisture content and seed weight. The seeds for the study were obtained from South Kinangop Forest Station.

The study found that, except for seed weight, there is no significant difference in seed quality between the healthy cypress trees and the aphid attacked trees. As for the seed weight, it was found that the more severe the attack on the mother trees, the less the weight of the seeds. However, seeds from healthy cypress trees had the highest quality seeds compared to those from the attacked trees.

This study disproved the belief that seeds obtained from aphid infested cypress trees were of inferior quality and not viable.

Death Causative Mechanism in Cypress Trees Infested by Cypress Aphid

The objective of this study was to establish how death of trees occurred during aphid infestation. It was found that death was caused by desaping which interferes with the mobilisation of nutrients. Deterioration of the host quality leads to the flight of the aphids. Trees which may be wholly brown may recover after being deserted by the aphids. It was recommended that further work be undertaken to determine if aphid attack has any affect on conduction and permeability.

Contribution Towards the Control of the Devastating Cypress Aphid Cinara cupressi Buckton Infestation in Africa

Mwangi and Kariuki (1996) carried out a study at Moi University to evaluate the impact of four local predators of the cypress aphid Cinara cupressi Buckton and to assess their status based on voracity and preference. Of the four species Betasyrphus adligatus Wied was found to have the highest mean daily consumption rate followed by Cheilomenes lunata F (larvae), then Chrysopa sp (larvae), and finally Cheilomenes lunata F (adult).

A preference test conducted by offering a known number of cabbage aphids Brevicoryne brassicae L. and cypress aphid Cinara cupressi Buckton showed that B. adligatus and C. lunata larvae had special preference to the cypress aphid while the Chrysopa sp and C. lunata (adult) showed no preference to the cypress aphids. The most commonly encountered predator in the field was the adult Cheilomenes sp.

Pesticidal Screening of Various Insecticides on Cypress Aphid (Cinara cupressi, Buckton)

Single applications of 0.00016%, 0.0008%, 0.04%, 0.2% and 1% active ingredient (a.i.) of Bestox (Cypermethrin), Insecticidal Soap (fatty acids), and Marshal (Carbosulfan) were tested against cypress aphid, syrphid fly larvae and lady bird beetle in a semi-field condition (Mwangi and Otieno, 1996). All the compounds were found to be efficacious on the aphid with soap solution having the highest affect. The LD50 (lethal dose that kills 50% of the insects by body weight) for Cypermethrin, fatty acids, and Carbosulfan was found to be 184.27, 53.73 and 637.00 respectively. Cypermethrin and fatty acids were found to be selective on non-target organisms. Fatty acids showed a higher residual control on foliage than the other test compounds. Acute dermal, oral and inhalation toxicities of the test compounds were generally found to be low if precautions for safe use are strictly adhered to.

Conclusion

This work has shown that wood from infested plantations is good for use even after 2 years of infestation. It has, therefore, saved the Government of Kenya from losing about US$18 million worth of aphid-infested plantations. The work has also shown that infested wood can be treated with preservatives to add value to it. Lastly, affordable methods of controlling cypress aphid using soapy solution and locally available natural enemies have been demonstrated.

Recommendations

It is recommended that the Department of Wood Science and Technology (WST) in collaboration with the Forest Health Management Centre at Karura, continue to monitor the lever of biodegradation arising from the cypress aphid attack in all Kenyan Forest plantations. Additionally, the Department of WST should be facilitated to initiate work that can lead to production of treatment schedules for infested and non-infested cypress thinnings which are currently going to waste.

The Department of Forestry at Moi University should initiate work on pathogen studies for pathogenic control of the cypress aphid.

References

Gacheru, D.M. and W.N. Ringo. 1992. Effect of aphid attack on anatomical characteristics of Cupressus lusitanica. BSc. (WSc. & Tech) Special Project Report. Dept. of WST, Moi University.

Imala, A.V. and R. Venkatasamy. 1994. A study of dimensional changes and seasoning defects in timber from aphid-killed cypress trees. BSc. (WSc. & Tech) Special Project Report. Dept. of WST, Moi University.

Maranga, W.J. and J. Mwangi. 1993. Death causative mechanism in cypress trees infested by cypress aphid. BSc. (WSc. & Tech) special Project Report. Dept. of WST, Moi University.

GOK. 1995. Master Plan. Forest Department Head Quarters, Karura, Nairobi.

Mbiri, J.K. and R. Venkatasamy. 1993. The incidence of fungal attack on wood from aphid-killed trees and short-term susceptibility of such wood to fungal deterioration. BSc. (WSc. & Tech) Special Project Report. Dept. of WST, Mio University.

Mbithi, S.K., and J. Mwangi. 1992. Properties of Cupressus lusitanica attacked by the cypress aphid (Cinara cupressi). BSc. (WSc. & Tech) Special Project Report. Dept. of WST, Moi University.

Mbuvi, M.J. land R. Venkatasamy. 1995. Comparative studies of decay rates of wood from sound and aphid-killed cypress. BSc. (WSc. & Tech) Special Project Report. Dept. of WST, Moi University.

Muema, M.M. and J. Mwangi. 1993. Effect of a cypress aphid attack on the quality of cypress seeds. BSc. (WSc. & Tech) Special Project Report. Dept. of WST, Moi University.

Munguti, S.M. and R. Venkatasamy. 1995. Incidence of fungal and insect attack in aphid-killed cypress trees. Bsc. (WSc. & Tech) Special Project Report. Dept. of WST, Moi University.

Mwangi, J. and M. Kariuki. 1996. A contribution towards the control of the devastating cypress aphid Cinara cupressi infestation in Africa - Submitted to African Crop Science Journal in 1996.

Mwani, J. and T.O. Otieno. 1996. Pesticide screening of various insecticides on cypress aphid -submitted to Commonwealth Forestry Association in 1996.

Okeyo, O. and J. Mwangi. 1993. Mechanical properties of aphid-attacked Kenya cypress - Paper presented to the cypress aphid Technical Taskforce Committee.

Rotich, R.K. and R. Venkatasay. 1992. Effects of creosote retention penetration in wood from Cupressus lusitanica attacked and killed by cypress aphid. BSc. (WSc. & Tech) Special Project Report. Dept. of WST, Moi University.