On the bionomics and ecology of Heteronychus licas (Klug) (Coleoptera, Dynastinae), a new pest of sugar-cane in Nigeria

Extract

Late in 1962, Heteronychus licas (Klug) was recorded causing damage to sugar-cane for the first time in Nigeria. It had previously been known there only as an inhabitant of grassland and a negligible pest of yams (Dioscorea spp.). The damage to sugar-cane, which was first noted at an early stage in the development of a large commercial sugar-growing estate (the first in the country) in Nothern Nigeria, resmbles that caused by Lepidopterous stem borers; the young shoots and tillers are eaten away around soil level by the larvae and adults and are eventually killed (‘deadhearts’). The adults sometimes tunnel in the pith of older canes, but seldom kill them. Surveys on the estate in 1963–64 showed that damage by the beetle was becoming increasingly important. In anticipation that this might happen, field and laboratory investigations into the habits and life-historv of H. licas were carried out in the same two years, and the initial results are reported.

There is one generation a year. Oviposition took place in moist soil near the bases of cane plants from late October to December. In the laboratory, the average female laid 60–75 eggs over a period of 1–3 weeks, hatching occurred after 9–16 days and the three instars lasted successively 14–19, 15–24 and 20–25 days. Larvae were found in the field from November to March, but occured in large numbers only during January and early February, mostly within a depth of 1 ft. in the soil; only those in the second and third instars fed on the canes. Puation took place in a cell 112–3 ft. below the surface; the prepupal and pupal stages together lasted 23–31 days in the laboratory. In the field, pupae were most numerous in February and March and adults, which began to emerge early in March, reached their greatest numbers between then and May.

Evening catches at a light-source showed that H. licas had two flight seasons each year, a subsidiary (post-teneral) one in April-June and a main (pre-reproductive) one in October-November, separated by a period of inactivity. Egg laying follows the second, and the adults die. Factors influencing the behaviour of the adults are discussed.

There were marked seasonal fluctuations in the incidence of ‘deadhearts’ caused by H. licas; it was highest in March-June each year, lowest during the period of adult inactivity, and again high during October-November.

Larvae kept together in the laboratory inflicted mutual injuries, mostly ending in death, but the extent to which this occured in nature could not be determined. Five Carabid species were found preying on the larvae in the field, and one on the adults as well. The importance of these and other possible predators and of parasites for the control of H. licas is discussed.

Measures that could be adopted for control are reviewed the literature.