LIFE-HISTORY OF APHIS-GOSSYPII ON CUCUMBER - INFLUENCE OF TEMPERATURE, HOST-PLANT AND PARASITISM

Life table data for Aphis gossypii Glover (Homoptera: Aphididae), an i mportant pest in glasshouse cucumber crops, were studied at 20, 25 and 30 degrees C on two cucumber cultivars (Cucumis sativus L.) in contro lled climate cabinets. The development time on the cucumber cv. 'Sporu ' ranged from 4.8 days at 20 degrees C to 3.2 days at 30 degrees C. Im mature mortality was approximately 20% and did not differ between temp eratures. Most mortality occurred during the first instar. Reproductio n periods did not differ among temperatures, but at 25 and 30 degrees C more nymphs were produced (65.9 and 69.8 nymphs/female, respectively ) than at 20 degrees C (59,9 nymphs/female) because of a higher daily reproduction. Intrinsic rate of increase was greatest at 25 degrees C (r(m)=0.556 day(-1)). At 20 and 30 degrees C the intrinsic rate of inc rease was 0.426 and 0.510, respectively. On cv. 'Aramon', the developm ent time of A. gossypii was approximately 20% longer at all temperatur es. Immature mortality did not differ between the two cultivars. The i ntrinsic rate of increase on cv. 'Aramon' was 15% smaller than on cv. 'Sporu'. The use of cucumber cultivars partially resistant to aphids i s discussed in relation to biological control of cotton aphid in glass houses. Development time and immature mortality on leaves of the middl e and upper leaf layer of glasshouse grown cucumber plants (cv. 'Aramo n') were comparable to development in the controlled climate cabinets. On the lower leaves immature mortality was much higher (approximately 82%) than on leaves of the middle (24.0%) and upper leaf layer (24.5% ). Reproduction was less on the lower leaf layer (45.9, 70.5 and 70.1 nymphs/female on leaves of the lower, middle and upper leaf layer, res pectively). Aphids, successfully parasitized by Aphidius colemani Vier eck (Hymenoptera: Braconidae) only reproduced when they were parasitiz ed after the third instar. Fecundity was 0.1 to 0.9 and 10.5 to 13.3 n ymphs/female for aphids parasitized in the fourth instar or as adults, respectively. Reproduction of aphids that were stung but survived the attack was lower than for aphids not stung. Average longevity of thes e aphids was equal to the longevity of aphids not stung by A. colemani .