Conocephalus populations were highest in the Guinea savanna zone (E.A. Heinrichs and C. Williams, WARDA, 1995, unpubl. data). The status of this pest in the Sudanian savanna has not been reported. Conocephalus spp. prefer the more moist habitats of the continuum toposequence. Extremely low populations were observed in the upland sites (E.A. Heinrichs, 1992, WARDA, unpubl. data). Populations were higher in the hydromorphic and lowland sites, with the highest incidence in the latter (Fig. 67). Incidence was similar in both the weeded and nonweeded plots. Plant damage and ecology. Although the host range of Conocephalus spp. has not been reported, grasshoppers, in general, have a wide range of hosts and it is likely that this also holds true for Conocephalus spp. This grasshopper was the most abundant orthopteran occurring in the monthly planting test on the WARDA Farm. Conocephalus spp., at WARDA, occurred in lowland rice throughout the crop growth period. Peak populations were recorded at 8 WAT in 1994–95 (Fig. 68). Conocephalus are present throughout the year at WARDA, but populations vary greatly within the year (Fig. 69). Peak populations were observed in the plots transplanted in October and November and lowest numbers were collected in the January transplanted plots. Little research has been done on the feeding damage in rice caused by the various Conocephalus spp. in Africa. Conocephalus longipennis has been reported to damage rice plants (Grist and Lever 1969). In Asia, C. longipennis feeds on rice, but it is also a predator of the rice seed bug, stem borer eggs, and the nymphs of
Number of adults 2,000 sweeps–1 25
20
Weeded Nonweeded
15
10
5
0
Upland 1
Upland 2 Hydro 1 Hydro 2 Lowland Toposequence site
Fig. 67. Number of adult Conocephalus spp. collected by sweep net in weeded and nonweeded rice plots at five toposequence sites on the continuum (E.A. Heinrichs, WARDA, M’bé, 1992, unpubl. data).
Number of adults 1,800 sweeps–1 250
200
150
100
50
0 2
4
6 8 10 Weeks after transplanting
12
Fig. 68. Number of adult Conocephalus spp. collected by sweep net at the indicated weeks after transplanting of lowland rice (variety Bouaké 189) plots. Numbers represent 12 monthly transplanting dates throughout 1 yr, May 1994–April 1995 (E.A. Heinrichs, WARDA, M’bé, 1995, unpubl. data).
Number of adults 900 sweeps–1 200
150
100
50
0 May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr 1994 1995
Fig. 69. Number of adult Conocephalus spp. collected by sweep net in lowland rice (variety Bouaké 189) plots transplanted at monthly intervals throughout 1 yr, May 1994–April 1995. Numbers represent total adults collected at biweekly intervals from 2 to 12 WAT over six sample dates (E.A. Heinrichs, WARDA, M’bé, 1995, unpubl. data).
leafhoppers and planthoppers (Barrion and Litsinger 1987). On rice, this species feeds on both the foliage and rice panicles (Rothschild 1971, Barrion and Litsinger 1987). It eats the highly nutritive rice anthers by cutting through the lemma or palea, thus, damaging the rice spikelets. Conocephalus damage is distinguished from bird, rat, or rice bug damage by the small holes eaten in each spikelet. Birds and rats strip off many spikelets and bugs feeding on the seeds do not make observable holes. Feeding holes on damaged 1-d-old spikelets are observed to turn from white to brown by 73