| Phenotypic plasticity is an adaptive mechanism for insects to produce different phenotypes in response to different environmental conditions.The phenotypic plasticity(such as the length/short or absence/present of wings)of Thysanoptera has long been a problem for thrips descriptive taxonomists in classification and identification.Therefore,the adaptation mechanism of thrips morphological characters to the environment has gradually become an important direction for the classification and biological research of taxa within this insect by studying its phenotypic plasticity.Most species of fungus-feeding thrips belong to the Phlaeothripidae,and is widely distributed in tropic and subtropic regions.They mainly live in the leaves and topsoil of the forest,and feed on fungal spores.These groups are sensitive to environmental changes and are indicators of the health of forest ecosystems.In order to understand the influence of environmental conditions on the phenotypic plasticity of fungus-feeding thrips,in this study,the effects of temperature and crowding degree on wing polymorphism and biological characteristics of fungus-feeding species Holurothrips morikawai Kurosawa were studied under laboratory conditions,The main research results are as follows:1.The biological characteristics of H.morikawaiThere is an obvious sexual dimorphism in H.morikawai,and the male is smaller than the female,which may be related to the behavior of protect their own egg masses of the female.The femoral wings are mainly macropterae,brachypterae and intermediates,while the males are mostly brachypterae and have no macropterae.The body colour is mostly dark brown.The larva is the gregarious type,but adult is the scattered type.The dew and fungal mycelium either small fungal spores were taken from the litter leaves of the Ficus altissima Blume.It has the ability to avoid light and is mostly inside or at the bottom of the blade.Both males and females may mate several times,and females lay eggs once or twice.The abdomen of the female lay eggs is red,egg is oval shape and block arrangement.When the female lays her eggs,there is an egg protecting activity,from laying eggs to egg hatching.H.morikawai have five immature stages,the larval stage is active and lively,the feeding behaviour is vigorous,the body color becomes deeper and the body size increases with the increase of the food intake.After entering the pupa stage,the operation begins to be slow,not feeding and excreting,and the development of the wing buds begins at the prepupa stage.The new emergence adult’s limbs,antennae,wings and head are all pellucid.After being disturbed by outside stimulation,the abdomen rises up,the tail tube secretes a yellowish-brown liquid,and then quickly climbs away.2.The effect of temperature on the biological characteristics of H.morikawaiIn this paper,the influence of temperature on development of H.morikawai were studied under laboratory conditions using temperatures of 18°C,24°C and 30°C.The results indicated that,the lower developmental threshold temperature was 18 °C and 64.37 degree-days,but the percentage survival of immature stages was highest.The development period of immature stages decline form 18°C to 30°C and average of 40-44 degree-days.Survival declined to 21% at 30°C.The highest survival was 91% at 24°C,the highest total fecundity occurred at 24°C with 77.31 eggs per female and the reproduction periods also longest at 24°C.Thus,the optimum temperature for the development and reproduction of the H.morikawai is 24°C.The temperature effect on the nymphaea’s growth and development,female’s longevity and reproduction,and the influence of temperature on growth of thrips mostly in larva stage,adults with a strong tolerance to temperature changes.In addition,there was no significant difference in the fecundity of the female and the brachypterae female,but the macropterae female was slightly longer than the female.3.Effects of temperature on the H.morikawai wing dimorphismIn this paper,the influence of temperature on wing form of determination of H.morikawai were studied under laboratory conditions using temperatures of 18°C,24°C and 30°C.On the basis of the ratio of fore wing length to head width(RWL)of adult thrips we defined individuals with RWL above 4 as macropterous forms,those with RWL below 2 as brachypterous forms,others with RWL between 2 and 4 as intermediats form.Our results showed that the wing form of female is mainly macropterous forms and brachypterous forms,and the intermediats form is low.Percentages of macropterous individuals among females were 45% at 18°C,and the percentages of macropterous individuals were declined to 17% at 30°C.And the percentages of brachypterous were increased with temperature increased.The male has not seen the macropterous,mainly with the brachypterous.The percentages of brachypterous were 94.1% at 24°C.The percentages of brachypterous were no significant difference between 18°C and 30°C.The results show that the high temperature producing brachypterous and the low temperature can lead an increase in the differentiation of the macropterous.4.The effect of crowding on the H.morikawai wing dimorphismInitial numbers of the H.morikawai larvae per cage were 1,3,10,20 and 30 individuals at 24°C.The results showed that H.morikawai wing was mainly divided into brachypterous at low density,with macropterous in high density.In addition,with the increase of population crowding,the head width of adult decreased and the individual showed miniaturation tendency.The results show that the density of the larvae is one of the key factors to determine the wing differentiation,and it is one of the strategies for H.morikawai to escape the crowded population. |
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