Thermoregulation Ability Of Locusta Migratoria Manilensis And Its Relationship With Pathogenesis Of Metarhizium Anisopliae

In the aspect of using microorganism to control locusts,we frequently met with the problem that the effect in the lab was good but not ideal in the field.The problems included the velocity to death was slow,the death rate was low and control effect was bad or unstable to some kinds of locusts.In the recent years,the researchers found that one of the primary reason was thermoregulation fever of locusts. As the body temperature raised,the immunity ability of insect enhanced and the conidia germination and growth was restricted.In order to clarify the action of thermoregulation in the course of mutual effect between Locusta migratoria manilensis and Metarhizium anisopliae,and provide a base for L. migratoria manilensis biological control,we studied the biological character of Metarhizium anisopliae LA isolate under different temperature,thermoregulation ability of L.migratoria manilensis and effect of thermoregulation to infected L.migratoria manilensis.The main results were summarized as follows.The germination velocity of LA isolate and lethal velocity to L.migratoria manilensis were fastest at 30℃.Cultivated at 38℃,spore germination rate began to be restricted.At 40℃,spore germination rate was closed to zero.High temperature had some influences on spore germination,dealing LA spore at 48℃with different times,germination velocity and germination rate were both reduced.Transferred to 30℃and cultivated 24h,there were only 10.6%-20.9%spore which could germinate.Protease activities reached to the highest after being cultivated 6 days and when the temperature was 37℃. Chitinase activities reached to the highest after being cultivated 5 days and when the temperature was 50℃.L.migratoria manilensis had rather strong resistance to high temperature.When Ta was 44℃,the highest LT₅₀ and LT₉₀ respectively were 112.5h and 326.4h.When Ta was 50℃,the highest LT₅₀ and LT₉₀ respectively were 11.4h and 20.6h.Without radiant heat,when Ta＜32℃,Tb＞Ta and Ta＞32℃, Tb＜Ta.When Ta raised at the velocity of 0.5℃/min,1.0℃/min,1.5℃/min and 2.0℃/min,Tb raised with Ta and temperature wave appeared.The death time of adult locusts was higher than nymphs and its ability of high temperature resistance was better.With radiant heat,locusts were inclined to choose higher temperature which would not damage their body.Transferred from shadow to illumination then to shadow,the velocity of temperature raise and descent were adult＞fifth instar＞fourth instar＞third instar nymph.At the same radiant heat resource,Tb raised fastest at straight irradiation.When the angle of radiant enlarged,the velocity of raising Tb was slow down.Wind influenced Tb at the condition of with radiant heat.Without radiant heat,the effect of wind to Tb was small.Thermoregulation influenced the death time,mortality,behavior of temperature chosen and fecundity.Given radiant heat at the right day after inoculation and the third day,the differences of LT₅₀ and LT₉₀ reached 3.6d and 7.1d.Given 9h and 3h radiant heat per day,the differences of LT₅₀ and LT₉₀ reached 3.5d and 6.6d.Compared with health locusts,infected locusts were inclined to choose the position of high temperature.After infection,the mature velocity of female adult locust was faster than ck,the egg pods of infected locusts was higher than ck at prophase and lower at anaphase.Hatch rate of infected locusts was obviously lower than ck..Inoculated with the same dose of LA spore,the death time of with thermoregulation was obviously longer than without thermoregulation.The climax of Beidagang in Tianjin was suitable for L.migratoria manilensis.The average Tb difference of third nymph to fifth nymph and adult in sunny and cloudy weather were respectively 2.7℃, 3.7℃,4.8℃and 4.2℃.There were no obvious effect of cage folding in the field to thermoregulation. After sprayed with oil solution,suspended emulsion and bait of Metarhizium anisopliae,Tb were all higher than ck in the three periods of daily measurement and the daily mean Tb were adult＞fifth instar＞fifth instar＞third instar.Thermoregulation influenced cell immunity and humour immunity.The hemocyte concentration of infected locusts without thermoregulation descent to 2.2×10⁷/ml,the infected locust with thermoregulation ascended to 8.1×10⁷/ml.Without injection,the phagocytic activity of with thermoregulation was more higher than without thermoregulation after injection of silica beads 4h and 24h,but the difference disappeared at 72h.There were no obvious difference of free beads between INT, IT,CNT and CT after 24h injection of LA,but after 96h of injection of LA,the phagocytic activity descent obviously and free beads come to 89.0%.10 days after injection of LA,there was no survival of INT,but the phagocytic activity of IT was higher than ck.PO activity of CT and CNT was stable.PO activity of IT and INT was a course of increase by degrees to degression.The increase of PO activity at IT was obvious and raised to the highest at the seventh day.Nine days after injection,there was no survival of INT and PO activity of IT began to descend.