The Biology of Ceranisus Menes (Walker) (Hym., Eulophidae), a Parasitoid of the Bean Flower Thrips Megalurothrips Sjostedti (Trybom) (Thys., Thripidae): a Comparison Between African and Asian Populations

Abstract

During the first series of tests, it was found that the one and two days old larvae were slightly faster to handle, and also significantly less resistant, and more likely to be accepted by all strains of C. menes. Thus larvae from these two age groups were used to maximize parasitization success in the subsequent second and third tests. The results of this investigation indicated that there were in feet biological differences between the four strains of C. menes, on M sjostedti host. There were significant differences between strains in the sub-components of the host handling time, but no difference in the overall host handling time. The average host handling time for the Malaysian, the two Indian strains, and the local strains were respectively 27.4, 29.0, 25.8, and 31.6 seconds. It was also found that the four strains of C. menes were slightly different in their ability to overcome the resistance of M. sjostedti larvae. The results showed that 40.6 and 46.4 percent of larvae encountered by the Malaysian and local strains respectively, were resistant to the parasitoid. With the two Indian strains they were 53.2, and 53.5 percent. The analysis indicated no difference between the Malaysian and local strains; or between the two Indian strains. The first two strains were however slightly better to overcome M. sjostedti host resistance, than the two Indian strains. The acceptance of M. sjostedti was definitely more successful with the local than with the exotic strains. More than twenty five percent (25.5%) of the non resistant larvae were accepted by the local strains for oviposition. Acceptance of this thrips species decreased significantly in the order: the two Indian strains (4.7 and 3.3 percent), Malaysian strain (0.4 %). Thus, at the host selection phase of the parasitization process, the behaviour of the local strain was found to be the most compatible for a successful parasitization o f M. sjostedti. However, in the physiological test, the suitability of M. sjostedti was found to be very poor for the local strain, as well as for the second Indian strain (Indian2). Their survival rates (proportion of eggs that survive up to adult stage) in this species of thrips was estimated at 0.06 for both strains. Unexpectedly, it was significantly higher (0.36) for the first Indian strain (Indianl).The possibility that M .sjostedti could have co-evolved with the Asian population of C. menes in the past was discussed. The results of the life history notes in the last test confirmed those of the first and second tests. The Indian2 strain was not able to reproduce in M. sjostedti, in contrast to the local and Indianl strain. The sex ratio of the offspring population was 0 for the local, as compared to 0.67 for the Indianl strain. On the other hand, the total fecundity of the Indianl strain was very low, as compared to that of the local strains: Ten (10) female wasps of Indianl strain produced an average of two (2) offspring, whereas the same number of females of the local strain produced an average of up to 867 offspring. As a consequence, the population growth parameters Ro and rm were null for all the 3 strains of C. menes. The mean developmental time of the Indianl and local strains were respectively 23.0 and 21.0 days for males. In fact, each of the 4 populations of C. menes was unique in the biological features it exhibited when M. sjostedti was offered as host. This can be seen as the onset of bio types differentiation among the 4 populations of this species of parasitoid. The difference on the two Indian strains, both originating from the same geographical area are discussed. When comparing the local strain on M. sjostedti against the Asian strains on their respective check hosts F. schultzei and M usitatus, the results of the first test showed that the host handling time by the local strain (31.6 seconds) was not significantly different from those of the two Indian strains (24.1, and 30.0 seconds). Host resistance against the local strain (40.6%) was also not significantly different from that against the Malaysian (47.2%). Host acceptance by the local strain (25.5%) was also not significantly different from that of the Malaysian strain (27.9%). However there were significant differences in the suitability of their respective check hosts, suggesting that physiological incompatibility must have been the only reason why the local strain could not perform as well on M. sjostedti as the Asian strains were doing on their check hosts. The survival rate of the local strain (0.06) was significantly lower than that of the first and second Indian strains, which were 0.20 and 0.46 respectively. The mean developmental time for males of the local strain (2 1 .0 days) was higher than that of the Indian2 strain (18.7 days), but it was lower than that of the Indianl strain (22.5 days). The possible explanations for the lack of suitability of M. sjostedti to the local strain of C. menes are also discussed. In conclusion, this study has brought some insight into the biological diversity among the different geographical populations of C. menes. It has demonstrated that none of the 4 selected strains of C. menes from Southeast Asia and Africa would be able to parasitize successfully M. sjostedti. Each of them was hampered by behavioural and/or physiological incompatibility with this thrips species. The possibility of manipulating the Asian population to obtain better success with M sjostedti is discussed The validity of the model and the critiques of the methodology used for the behaviour study are also discussed.

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Thesis (PhD) - University of Ghana, 1999

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