THE DIFFERENTIAL EFFECT OF ENVIRONMENTAL FACTORS UPON MICROBRACON HEBETOR SAY (HYMENOPTERA: BRACONIDAE) AND ITS HOST, EPHESTIA KÜHNIELLA ZELLER (LEPIDOPTERA: PYRALIDAE)

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Abstract
1. Larwe of Ephestia kükniella Zeller, when stung by the parasite Microbracon hebetor Say, become soft, flaccid and motionless. 2. Associated with the flaccidity of the stung larvae is a greatly lowered respiratory rate through the temperature range used, namely 10° C. to 32° C. 3. Not only does the Microbracon sting lower the respiratory rate but it decreases the sensitivity of Ephestia larvæ to change in temperature to such an extent that between all temperature intervals used the Q10 of larvæ stung by Microbracon was less than that of normal larvæ. Between 10° C. and 15° C., the Q10 was 1. 4. Orthodichlorbenzene in a median paralytic dosage (just sufficient to cause a reversible paralysis in half the larvæ) produced stiffness and rigidity in Ephestia larvæ. Associated with this stiffness was a marked increase in respiration rate beyond that of untreated larvæ except at 32° C. where it fell below that of normal larvæ. 5. Ether in a median paralytic dosage produced flaccidity in Ephestia larvæ. Associated with this flaccidity was a marked decrease in respiratory rate, but at no temperature was the decrease produced by ether of the same magnitude as that produced by the Microbracon sting. 6. Unlike the respiratory rate, the respiratory quotient was not affected by the parasite sting nor by either of the two chemical agents used. 7. Rise in temperature to the point at which the rate of development of Ephestia decreases, namely 32° C., was associated with a drop in respiratory rate and a decrease in respiratory quotient from the range indicating carbohydrate metabolism to that indicating protein. Not only normal larvæ, but also those treated with ether or orthodichlorbenzene or stung by the parasite, showed a decrease both in rate and quotient at 32° C.

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