A Study Of The Pine Woolly Aphid, Pineus Pini (l) (homoptera: Adelgidae),in East Africa
Odera, Jeff Adhaya
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The pine woolly aphid, Pineus (L) (Homoptera: Adelgidae), was first known as a pest in the northern temperate zones of holartica and in the northern orient. Heavy infestation by the pine woolly aphid was first discovered in the estates of the East African Agriculture and Forestry Research Organization (EAAFRO) at Muguga in January, 1969, where it was established on pines. The taxonomic status of the pine woolly aphid is briefly reviewed and it is concluded that only one species is present in Kenya. The history of the introduction of pines is discussed in relation to the occurrence of P. pini in East Africa, and it is concluded that the pine woolly aphid was introduced from Australia on pine scions, about six years ago. Subsequent spread has since occurred in all Two isolated outbreaks have been reported from seed orchard plots in West Kilimanjaro and in the southern highlands of Sao Hill of Tanzania. The development of the pine woolly aphid in Europe according to Marchal (1913) is reviewed. The life history at Muguga presented The larvae are mobile for about three days, then insert The eggs are laid on the bark. their stylets into the bark and become sessileo They become adults after four moults. Each apterous female may lay from 12 to 104 eggs. The virginoparae are less prolific than the apterous exsules, and one insect lays from 1 to 4 eggs. The habits and behaviour of the pine woolly aphid are discussed and evidence for dispersal of wineless crawlers and eegs by wind is demonstrated. Flight behaviours of the alatae indicate a possibility of migration. A method for the routine quantitative estimation of the pine woolly aphid population trends and their relationship with the physical and plant environment are outlined. Development occurs continuously throughout the year, and about four to five and a half generations of apterous parthenogenetic females are recorded. Winged insects which are also parthenogenetic occur in smaller f .El!!i has been reported on 35 specio.s of pines. Pinus massoniana Lambo, f.o elliottie Engelme, E- contorta Dougl. ex Loud. and Po radiata Do Don. were the most favored host while Po patula Schl. and Charno was less readily attacked. The majority of trees in a st and where the infestation is well established often develop heavy infestation, but a few trees remain abs91~tQly untouchedo. ayacahuite Ehrenb. and Po strobus var. chiapcnsis Martinez. were ~g~~letely resistant to attacko P. ~ feeds in the bark of all parts of the tree from the crown to the stem. The feeding method of the aphid is described, and it is shown that the injury and damage to the plant tissues is mainly due to the effect of salivary secretions which the insect injects into the plant when feeding. Death of the tree is gradual and usually progresses' from the top to the base, and from the outside to the centre of the crowne Damage is most severe on unhealthy trees. In a final discussion, it is argued that the pine woolly aphid is a primary pest, capable of killing healthy trees unless its population is regulated within endemic proportions. Complete eradication is unlikelyo Lmpor c ant factors in the control of the pine woolly aphid include predaition by Syrphid larvae and various Coccinelllds, and starvation in the first instar during dispersal. Preventive practices that are designed to.reduce the rate of spread of the pest are recommended. Biological control by introduced predatory insects is suggested. It is suggested that some of the extensive pine mono-cultures should be selectively replaced by mixed crops, consisting of soft and hard-wood trees.
University of Nairobi,