Cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), obtained from cotton, Gossypium hirsutum L., fields in the Gorgan region of northern Iran, were colonized on 'Varamin' cotton plants in a growth chamber. The development, survivorship, and life table parameters of the cotton aphid were evaluated at 27.5 +/- 1 degrees C, 65 +/- 10% RH, and aphotoperiod of 14:10 (L:D) h of artificial light on five commonly growing cotton cultivars: Varamin, 'Sealand' (relatively resistant cultivar), 'Bakhtegan', 'Sahel' (both relatively susceptible cultivars), and 'Siokra' [resistant to Bemisia tabaci (Gennadius)]. The developmental times of immature stages ranged from 4.6 d on Bakhtegan and Varamin to 6.3 d on Sealand, whereas the immature survival was 97.5 to 65% on Sahel and Siokra, respectively. On average, there were 28.7, 28.3, 23.5, 20.1, and 16.8 nymphs produced per female on Sahel, Bakhtegan, Varamin, Sealand, and Siokra, respectively. The intrinsic rate of natural increase (r(m)) for cotton aphids on Sahel was the highest, whereas the values for r(m) varied from 0.284 (nymphs per female per d) on Siokra to 0.368 on Sahel. Jackknife estimates of generation times (T), net reproductive rate (R(0)), doubling time (DT), and finite rate of increase (lambda) on these cultivars were as follows: 9.79-10.84 d for T, 9.23-23.81 nymphs per female for R(0), 2.17-3.19 d for DT, and 1.28-1.38 nymphs per female per d for lambda. Cotton aphid performance was at its highest on Sahel and lowest on Siokra.

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Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae), an economically important biocontrol agent, was reared on almond pollen for 50 generations. We evaluated the effect of rearing predators on this pollen by comparing biological parameters at different generations (G1–G50). The shortest and longest development time occurred in G5 and G10, respectively. Females at the fifth and 50th generations laid eggs earlier than those of other generations. Females at G50 laid eggs over a longer period and produced more eggs than females of other generations, although females in the earlier generations had a higher gross reproductive rate and net reproductive rate than later generations. The intrinsic rate of increase, as well as the finite rate of increase of N. cucumeris in the fifth and 50th generations was significantly greater than those in other generations, while the first generation had the lowest values of these parameters. The dorsal shield length of both females and males and the width of females were found to be unaffected by their constant feeding on almond pollen. However, the number of rearing generations significantly affected the width of males. Long-term rearing of N. cucumeris for at least 50 generation on almond pollen did not substantially affect the predator's quality and this food source could be used for the mass production of this predator. Almond pollen should be assessed in rearing other phytoseiid mites that are important in biocontrol strategies.

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Functional response and mutual interference are the most important behavioural characteristics that reveal different aspects of host–parasitoid interactions. In this study, functional response and mutual interference of the parasitoid wasp, Diaeretiella rapae (M’Intosh) attacking the cabbage aphid, Brevicoryne brassicae (Linnaeus) were investigated. Logistic regression was used to distinguish the shape of the functional response (type II or III). Nonlinear least-square regression was used to estimate the attack rate (a) and handling time (Th). Nicholson’s model and linear regression were used to determine per capita searching efficiency and interference coefficient, respectively. Logistic regression suggested a type II response on B. brassicae nymphs. The per capita parasitism decreased significantly from 80.80 (67.33%) to 11.85 (9.88%) as parasitoid densities increased from 1 to 8 females. Consequently, the per capita searching efficiency decreased significantly from 1.173 to 0.205 as parasitoid densities increased from 1 to 8. The rate of parasitism increased as the host density increased from 2 to 50, and subsequently the parasitoid density decreased from 8 to 1. Therefore, different host–parasitoid ratios could affect the efficacy of D. rapae.

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