|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: June 1, 2000
Citation: Romeis, J., Shanower, T.G., Madhuri, K. 2000. Biology and field performance of Gryon clavigrallae (Hymenoptera: Scelionidae), an egg parasitoid of Clavigralla spp. (Hemiptera: Coreidae) in India. Entomological Research Bulletin of. 90(3): 253-263 DOI: 10.1017/S0007485300000377. 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: The biology and impact of Gryon clavigrallae Mineo, an egg parasitoid of Clavigralla scutellaris Spinola and C. gibbosa (Westwood), was investigated. The calculated developmental threshold temperatures for females and males were 15.6°C and 15.8°C, respectively. Emergence exceeded 94% at temperatures between 22 and 30°C. Adult females lived on average 28–96 days when fed with honey. Without food, adults lived < 6 days. Mean fecundity was 56.4 eggs per female. A significant trend of lower fecundity after longer periods of host deprivation was observed. Gryon clavigrallae females successfully oviposited in host eggs of all ages though eggs < 4 days old were preferred. Total host handling times were significantly longer on C. gibbosa eggs (23.5 min) than on C. scutellariseggs (12.0 min). Females readily distinguished parasitized from non-parasitized host eggs. Superparasitism was observed when few or no unparasitized eggs were available. Eggs of the two Clavigralla species can be separated by surface structure and condition after eclosion. Clavigralla scutellaris laid significantly larger egg clusters than C. gibbosa (19.9 versus 10.5 eggs per cluster). Gryon clavigrallae was present as soon as the first Clavigralla spp. egg clusters were found on pigeonpea. The percentage of egg clusters parasitized increased early in the season with egg cluster density and remained high (up to 83%) despite fluctuations in host density. Overall, G. clavigrallae parasitized 40 and 58% of C. gibbosa and C. scutellaris eggs. The percentage of egg clusters parasitized and the number of eggs parasitized per cluster increased significantly with egg cluster size. The overall parasitoid sex ratio was highly female biased but varied with the number of eggs parasitized per cluster.