It is a well established fact that the families Lygaeidae and Coreidae feed on the seeds of a number of plant families both in the tropics and temperate zones. Some of the species are recorded as pests of economic crops (Singh and Taylor 1978, Appert 1956). Their association with the seeds of forest trees has however not been documented. The species Anoplocnemis phasiana (Coreidae) was noted by Maxwell-Lefroy (1909) as being associated with trees of the genus Erythrina in India. For the Lygaeidae he had no clear evidence to offer with regard to their feeding habits. In more recent times there has been a considerable advance in the study of the biology and feeding habits of both of these families and a number of the species indigenous to temperate zones have been studied in detail (Sweet 1959, Puchkov 1956, Southgate and Woodroffe 1953).
The Coreidae in particular have been shown to be closely associated with the Leguminosae (Dolling 1977, Schaefer 1980, Singh and Singh 1978 and Solomon and Froeschner 1981) albeit only with low growing species such as crops of grain legumes. It is known that the species Anoplocnemis curvipes, a pest of cowpeas, takes refuge in trees when disturbed and it is possible that feeding on unripe pods on trees acting as shelter could also take place.
Slater (pers. comm.) suggests that the larger species of Coreidae, rather than the smaller Lygaeidae, are most likely to feed on Acacia due to the hardness of the seed. Recently nymphs of Nemausus sp. (Coreidae) have been recorded feeding in the nearly mature fruits of Acacia tortilis ssp. raddiana from the Hogger Plateau in South Eastern Algeria. The extent of the damage on the pods and seeds was not however assessed but their very presence on these fruits is of interest as Prof. Slater (pers. comm.) had previously recorded this species on the seed pods of Acacia caffra in Pretoria, South Africa (see also Schaefer 1980).
The plant bugs have modified mouthparts in that they form a tube or rostrum (Fig. 5) which gives the insect the appearance of having a trunk. Within this tube move the stylets - sharp needle-like structures with which the insect pierces the plant tissue. The effect of feeding by adults of A. curvipes is severe distortion of cowpea pods with considerable loss of yield. The method of feeding by plant bugs as a whole is to inject saliva into the plant tissue which assists in its breakdown thereby making this tissue easier to assimilate. Besides assisting the insect to obtain its food requirements, the saliva acts as an irritant and causes the cells surrounding the point of feeding to grow disproportionately or, if feeding is severe, to shrivel completely.
As no data is available of species being involved with most of the Acacia sp. with which this project is concerned, it is impossible to give details of the length of the cycle from egg to adult. The Coreid Clavigralla tomentosicollis (previously known as Acanthomia tomentosicollis) studied by Egwuatu and Taylor (1977) as a pest of cowpeas in Nigeria had a developmental period in the field of 17 days. Cowpeas are a seasonal crop and no record has been made of alternative hosts which would enable the species to survive in their absence. It is possible that a number of these larger Hemiptera feed on Acacia sp. although there is no recorded evidence.
Fig. 5 - Mouthparts of Hemiptera - rostrum marked with arrow