|Romeis, J - BAYER AG, MONHEIM GERMANY|
|Madhuri, K. - UNIVERSITY OF HYDERUBAD|
Submitted to: Entomological Research Bulletin of
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 21, 2000
Publication Date: N/A
Interpretive Summary: Several species of Clavigralla attack pigeonpea in the semi- arid tropical regions of Africa and Asia. Two of the most important species in India were investigated in this study: C. gibbosa and C. scutellaris. Eggs of the two species are easily separated: C. gibbosa eggs are rough and sculptured and C. scutellaris eggs are smooth. This finding will allow substantially more accurate population and damage estimates to be made for these two species. Clavigralla scutellaris egg clusters are significantly larger than C. gibbose clusters (19.9 vs. 10.5 eggs per cluster) and this may partly explain the higher level of parasitism by Gryon clavigrallae, a scelionid egg parasitoid. Overall, the parasitoid killed 40% of C. gobbosa eggs and 58% of C. scutellaris eggs. Positive relationships were observed between egg cluster size and parasitism, and between egg cluster density and parasitism. This study has shown that Gryon clavigrallae is an important natural enemy of Clavigralla eggs in the field, and could perhaps be considered for use against other Clavigralla species or in other locations.
Technical Abstract: Two species of Clavigralla pod sucking bugs, C. gobbosa Spinola and C. scutellaris (Westwood), were collected from pigeonpea, Cajanus cajan, in South India. Eggs of the two species are easily separated by the surface structure and the condition of the eggs after eclosion. With an average of 19.9 eggs/cluster, C. scutellaris lays significantly larger egg clusters than C. gibbosa with an average of 10.5 eggs/cluster. The scelionid egg parasitoid Gryon clavigrallae Mineo was the only natural enemy observed in the field. The parasitoid was present as soon as the first Clavigralls spp. Egg clusters were found on the pigeonpea plants and parasitized between 8.3 and 82.8% of the egg clusters. Overall, G. clavigrallae killed 40.0 and 57.6% of C. gibbosa and C. scutellaris eggs, respectively. The percentage of egg clusters parasitized increased curvilinear with egg cluster density. But no correlation was found between egg cluster density and egg parasitism. The percentage of both egg clusters and eggs per cluster parasitized increased significantly with egg cluster size. The mortality of the developing parasitoids and nymphs was higher in eggs C. scutellaris as compared to eggs of C. gibbosa. The overall parasitoid sex ratio (proportion males) recorded from field-collected egg clusters was 0.26 but varied with egg cluster size and with the number of eggs parasitized per cluster. The maximum parasitoid sex ratio was recorded on egg clusters with two or three parasitized eggs and then declined with an increase in the number of eggs parasitized per cluster.