| Bemisia tabaci(Gennadius)(Hemiptera, Aleyrodidae),(Middle East-Asia Minor 1, MEAM1), also called “B-biotype”, is one of the most important invasive pests in China. Since its invasion in the mid-90 s, MEAM1 have been rapidly established and economic loss continues to increase. Encarsia sophia(Girault and Dodd)(Hymenoptera: Aphelinidae) a heteronomous hyperparasitoid and Eretmocerus hayati(Zolnerowich and Rose)(Hymenoptera: Aphelinidae) a solitary parasitoid, proved to suppress MEAM1 and they are regarded as good bio-control candidates. However, the utilization of these parasitoids for augmentative releases yet to be explored. With the aim of examining efficient way of utilizing these parasitoids which can enhance their efficiency and understanding of the effect of cold storage of the parasitoids, field and laboratory experiments were carried out to evaluate their control efficiency against MEAM1. The main objective of this thesis was to investigate banker plants on mass-rearing of En. sophia and Er. hayati for control of MEAM1 and to evaluate the effect of cold storage on these two parasitoids.First, the potential of En. sophia and Er. hayati to control MEAM1 using banker plant system was evaluated. Field study was conducted in 2013 and 2014 in Langfang Experimental Station, Hebei province, China, using melon plant, Cucumis melo L.(Cucurbitaceae) and castor, Ricinus communis L.(Euphorbiaceae), as a banker plant. Both banker plants supported rearing of these parasitoids and their emergence rate enhanced by 20% compared to pupa-card release. Release of parasitoids through the banker plant(C. melo) method was higher than adult release for both parasitoids with significant difference during 2013. However, no significant difference of parasitism was observed during 2014 between banker plant(R. communis) and pupa-card release. Moreover, the combined release of the parasitoids highlighted the effectiveness of these parasitoids when they are released together. Despite of the parasitism of all treatments, the population of the whiteflies was not reduced during the 2013 season. However, during the 2014 season, the population of the whiteflies were significantly less in all treatments during the 4, 5 and 6th week(from August 15 to 29) of the study period.Second, storage at low temperature is a valuable method for parasitoids that are to be used in biological control programmes. However, storage of parasitoids at low temperature is associated with major fitness costs. To investigate the influence of constant low temperature storage during pupal stages of these parasitoids, on the performance of adult wasps were assessed. The effect of storage at three temperatures(4, 8 and 12 ± 1oC, RH = 65 – 75% in full darkness), for three time durations(1, 2 and 3 weeks) and two pupal stages(10 and 12 days old) was studied. The result revealed that decrease in emergence, longevity and parasitism rate of En. sophia after low temperature storage with increasing storage time. The emergence rate was not affected at 12 oC for both pupal stages kept for a week. However, at lower temperature treatments(8 and 4oC) it reduced 67– 87.5% after two week storage time. The longevity of the emerged adults was not affected at 12 and 8oC for both pupal stages after one week storage, but it highly reduced with increasing storage time. Parasitism rate of the parasitoid was decreased significantly for both pupal stages at all temperature treatments regardless of storage time. For Er. hayati, the pupal survival was negatively affected at all treatments. Adult emergence was shorter for both pupal stages regardless of sex except males emerged from 12-d old pupa kept at 4oC. Adult survival was negatively affected at all storage treatments irrespective of pupal stage and sex. The result suggested that 12-d old pupa of En. sophia can be kept at 12 oC for up to 7 days with minimum negative effect due to cold storage.Third, the use of fluctuating temperature by a return to an optimum temperature for short period of time during cold storage has been known to reduce the injury caused by chilling damage. In this study the feasibility of storing the pupal stages of En. sophia and Er. hayati under fluctuating cold storage of the pupal stages were assessed. Two pupal stages, 10 and 12 day old for En. sophia and 12 and 15 day old for Er. hayati, were kept at 4, 6, 8, 10 and 12 ± 1oC, 60 ± 70% RH in full darkness. At each storage temperature, parasitoids were transferred daily every 22 hrs into 26 ? 1oC for 2hrs. Generally the late pupal stage for both parasitoids gave better result than earlier pupal stages. Pupae of both parasitoids kept above 10 oC showed minimum negative effect over the once kept below 10 oC. Storage of late pupal stages 12-6oC did not affect the rate of emergence after a week and longevity after 1 and 2 week storage period for both parasitoids. The rate of parasitism was comparable to control after a week storage time at 12 and 10 oC. This suggested that the late pupal stages are more cold tolerant than the earlier pupal stages for short storage time for both parasitoids.In conclusion, this study suggested C. melo and R. communis could be used as banker plants for augmenting these parasitoids. Hence these banker plants improved the emergence rate of the parasitoids compared to pupa-card release which is the common practice. For the purpose of cold storage, the optimum temperature is 12 oC for one week storage time under fluctuating temperature. The late pupal stage is the best stage for storage of these parasitoids. This has an implication for cold storage as it is very important to determine the least sensitive developmental stage, storage temperature and storage time for effective production of parasitoids. |
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