Study Of Interspecific Interactions Of Bactrocera Dorsalis Hendel And Bactrocera Correcta Bezzi (Diptera: Tephritidae)

Interspecific interactions between exotic species and the similar niche of indigenous species, which could be an important decisive factor of invasion success for exotic species. In history, a number of examples of indigenous species were replaced by exotic species among insects. The oriental fruit fly Bactrocera dorsalis Hendel and the guava fruit fly Bactrocera correcta Bezzi attach to Bactrocera in Tephritidae of Diptera, which are quarantine pests of economic importance. The former is our country’s number one fruit fly pests, wide distribution and severe damage. Although the latter only distributes in a handful of areas in our country at present, but it has great harmfulness and the potential of further diffusion. Two fruit flies have a wide niche overlap, interspecific competition will become their main ecology relationship if they distribute in the sympatric area, and which will be the important challenge of further expansion for B. correcta. This study revealed competitive mode, intensity of competition, and competition hierarchy of B. dorsalis and B. correcta by two major competition ways of resource exploitative competition and behavioral interference competition. To foresight the possibility of expansion success of B. correcta, and enrich interspecific competition mechanism of the family Tephritidae and invasion biology theory research.The specific research results are as follows:(1) Research on adult oviposition preference and offspring performance of B. dorsalis and B. correcta on 6 kinds of host fruits, namely guava, banana, papaya, orange, tomato and carambola. Adult oviposition preference was tested by providing intact host fruit exposed directly to adult and sliced fruit placed in egg collector, respectively. Offspring performance test was assayed by investigating development and survive of larvae on the feeding host. The results showed that oviposition preferences were significantly different with the two ways of host fruits provided. Host fruits to be more selected by odor-lured oviposition were more suitable for the development of offspring. This result was inconformity with the reports from some literatures. Furthermore, the oviposition preference and offspring performance between B. dorsalis and B. correcta were not only parallel but also discrepant, which indicated that host ecological niches of the two fruit flies were both overlapping and differentiating to a certain degree.(2) Resource exploitative competition. Research showed the higher the population density, intraspecific competition was more intense. Through consulting the two parameters of weight of pupa and survival rate, most appropriate density of B. dorsalis and B. correcta was 5 ~ 20 heads /10 g artificial feed. When their population density exceeded most appropriate density, intraspecific competition would be distinct. Specific performances were with the increase of density, percentage of pupation and eclosion rate decreased continuously, development duration of larvae shortened and development duration of pupa prolonged little by little, weight of pupa lightened gradually. In fact, changing of these growth parameters had close correlation. B. dorsalis and B. correcta had effect of undercrowding, its main features were longer developmental duration, lighter pupa, lower survival rate. B. dorsalis and B. correcta had similar density effect, so their population regulation mechanism was consistent, but the B. correcta larvae had variable abilities to resist crowd.(3) Interspecific interactions on the stage of egg and pupa. It didn’t find interspecific competition phenomenon that eggs of B. dorsalis and B. correcta mixed by equal numbers with same egg age, who had no effect on egg duration and hatchability of eggs for each other. However, pupae of two fruit flies mixed in different proportion and different pupa age, when their pupae were fresh, and mixed with the other pupae of older one day, eclosion rate of the later pupae were respectively 87.67±3.61% and 84.33±2.56% for B. dorsalis and B. correcta, which were significantly less than the respective controls. This outcome implied that the later pupae were inhibition of growth by the former pupae.(4) Oviposition competition. The results of the study about oviposition competition of B. dorsalis and B. correcta showed that interference behavior of two fruit flies in the process of oviposition didn’t play a major role in interspecific competition, which could be ignored. When two fruit flies laid eggs on the same host competition in a short duration, B. dorsalis managed to faster and more occupy space on the host as far as possible by increasing the number of oviposition apertures. When two fruit flies laid eggs on the same host competition in a long duration, no matter in the face of what kind of host, coexisting with B. correcta, under more circumstances B. dorsalis was promoted to produce more eggs. But for B. correcta, in most cases the number of emergence adults from the co-infested hosts were suppressed. It was similar with identification ability to the infested hosts for B. dorsalis and B. correcta. The recognition ability to fresh eggs was poor, less females oviposited on the host with at least 600 eggs, and two fruit flies could hardly discriminate the congener eggs and heterogeneous eggs. When the eggs on hosts basically hatched and has become larvae, which had a significant inhibitory effect to subsequent ovipositing behavior of fruit flies. The existence of the fruit fly larvae on the hosts was the fundamental cause of subsequent ovipositing behavior of fruit flies. When a variety of hosts coexisted, B. dorsalis occupy preferentially their favourite host guava, but most of B. correcta had to be going for less to choose the second favourite host carambola.(5) Mating intervention. Mating rhythm of B. dorsalis and B. correcta highly overlapped, concentrating at dusk, and mating rhythm of asymmetric mating of male B. correcta and female B. dorsalis was just the same. Asymmetric mating of two fruit flies was universal and objective, but it hadn’t specialized property. When male B. correcta and female B. dorsalis mixed no matter how population density, and the ways of combination, and mating experience, asymmetric mating would definitely happen. Hybrid ratio was usually more than 20%. Furthermore, adult day age of two fruit flies were less than three weeks or more than six weeks, hybrid ratio would be more, it could even reach the quantity of selfing. Mating duration of selfing of two fruit flies was very similar, for example, for three-week-old of adults, on average, it lasted more than four hours, mating duration of asymmetric mating lasted only more than one hours. The most important thing was that asymmetric mating did not produce offspring. Mated adults whether selfing or hybridization mated again no time interval, mating pairs were less than without mating experience adults. Two fruit flies mixed half-and-half raised in a cage, it made no difference on the longevity of the adults, but it decreased the amount of eggs at initial stage for two species females, namely delayed the pre-oviposition duration for each other. In a word asymmetric mating of two fruit flies had some negative effect to reproduction of both species.(6) We made more explicit research on the modes and strength of interspecific competition between Ceratitis capitata Wiedemann and two Bactrocera species(B. dorsalis and B. correcta) by experiments on behavioral interference of adult fruit fly. The results testified no mating interference between C. capitata and two Bactrocera species; but in oviposition competition, two Bactrocera species showed a distinct advantage, suppressing observably population numbers of C. capitata. Despite all this, the strength of competition was not enough to defend against invasion of C. capitata. Moreover B. dorsalis showed more remarkable inhibitory effect to C. capitata on interspecific competition than B. correcta.In conclusion, B. dorsalis had the strongest competitive power among three fruit flies, as long as both species competed under their suitable conditions, B. dorsalis indeed had a strong competitive advantage. However, B. dorsalis competed with whether B. correcta or C. capitata, intensity of competition not enough to suppress the occurrence of the other party. In fact, under more appropriate condition for B. correcta or C. capitata but inappropriate to B. dorsalis, B. dorsalis will be at a disadvantage position. In short, it stands a good chance that B. correcta invade into the occurrence area of B. dorsalis, and could coexist with B. dorsalis, but under normal conditions, population of B. correcta was difficult to go beyond B. dorsalis.