Response Of Grapholita Molesta(Busck) To Short-term High Temperature And The Molecular Mechanisms

The oriental fruit moth, Grapholita molesta (Busck), is one of the most important insectpests damaging stone and pome fruits, such as apple, peach and pear, and causing severeeconomic loss of fruit productivity. At present, G. molesta mainly distributes in the temperatezone of Europe, America, Asia, Australia and Africa. Their occurrence lasts from spring tolate autumn, in which the summer temperature is often higher than30°C，even than40°C. Ithas been documented that the optimum developmental temperature for G. molesta is from23to29°C. Under the goblal warming, extreme-high temperature is expected to increase infrequency and intensity, therefore, how can G. molesta adapt the temperature stress is crucialto their existence and development, but research on this aspect is rare now. Here, we devotedto investigating the thermal tolerance of G. molesta and their response to high temperature,and to exploring the the expression profiles of heat shock protein on heat resistant of G.molesta under the short-term high temperature treatment, in order to indicate the influence ofhigh temperature on this insect pest and the molecular mechanism on thermal adaptability,meanwhile provide a reasonable measure for prevention and control.Main results of this study are as follows.1．The thermal tolerance of G. molesta was strong, and varied between differentdevelopmental stages. The results showed that there was little effect on their survival whenthe temperature was below38°C. It indicated that G. molesta had a relative high thermaltolerance, but it was lethal for G. molesta at46°C for1h. The survivals of eggs, pupae andadults decreased with the increase of temperature and the prolongation of heating duration.When the temperature was below44°C, the thermal tolerance was pupae> adults> eggs.Short-term high temperature hardening, such as38or40°C, could improve the survival rateof adult when they encountered high temperature stress again, which indicates that it has theplastic response to adapt high temperature. However, no evidence showed the heat tolerancecould be enhanced in egg or pupa after heat hardening. The longevity of G. molesta adultsincreased with the temperature rising, whereas, these was no significant difference betweenfemale and male adult in the same temperature. Adults were heat shocked after41°C for1h,then the number of eggs laid decreased after recovery. Further studies showed that high temperature affected male adults greatly, but no evidence showed the reproduction of femaleswas influenced. To some extent, female adult was more thermal tolerance than male. Egghatchability was not affected by their parents after thermal stress, compared to control.2．Two heat shock protein genes were cloned. We cloned two heat shock protein genes,named Gmhsp90(GenBank accession number: JX678980) and Gmhsp70(GenBankaccession number: JX678981). The deduced amino acid sequence from Gmhsp90contains5typical motifs of the hsp90family and Gmhsp70contains3typical motifs of hsp70family.They show high similarity to other insect species.3．Three housekeeping genes were cloned. We cloned three housekeeping genes,which were α-tubulin, β-tubulin and GAPDH. They were named GmtuA (GenBank accessionnumber: JX970946), GmtuB (GenBank accession number: KJ027658) and GmGAPDH(GenBank accession number: KJ094948), and their deduced amino acid sequences containtypical motifs of their family, respectively, and show high similarity to other insect species.The expression stabilities of housekeeping genes obtained under high temperature stressshowed that GmtuA，GmtuB had the good stability, which could be taken as the referencegene for real time quantitative PCR of G. molesta, but GmGAPDH was unsuitable.4．The expression patterns of Gmhsp90and Gmhsp70under high temperatures wereinvestigated in our studies. The results showed that Gmhsp90and Gmhsp70could beinduced by high temperature, and their expression increased with the temperature rising. Itindicates they play an important role on the resistance of thermal stress. The inducedexpressions of Gmhsp90and Gmhsp70in female were at a lower temperature and earlier timethan in male, which showed that female was more sensitive to high temperature than male. Atthe time of24h after heat hardening, expressions of Gmhsp90and Gmhsp70could decreaseto the level before heat hardening, which indicated that heat shock proteins could be degraded.Gmhsp90and Gmhsp70would be induced earlier in the heated hardening adults than theunheated hardening ones when encountered high temperature again, which indicated that heathardening could enhance the response speed of heat shock protein in G. molesta.Our studies imply that G. molesta has the great thermal tolerance, which may be themain reason for the existence in wide range and occurrence on hot summer days.