Assessment of life history parameters of Aspidiotus nerii (Hemiptera: Diaspididae) to improve the mass rearing of Aphytis melinus (Hymenoptera: Aphelinidae)

The biological control of Aonidiella aurantii (Maskell) on citrus can be achieved with periodic releases of the parasitoid Aphytis melinus DeBach. A. melinus is normally reared on parthenogenetic strains of the scale Aspidiotus nerii Bouche. The developmental rate, crawler production and survival of A. nerii were studied at two temperatures (25 +/- 1 and 30 +/- 1 degrees C) and two levels of relative humidity (RH; 55 +/- 5 and 85 +/- 5%) on squash. Temperature had an important effect on developmental rate, but RH did not. At 30 degrees C, no growth was observed and no crawlers were produced. At 25 degrees C, development of the L1, L2 and young females' stages required 24.4 +/- 0.7, 11.1 +/- 0.8 and 13.2 +/- 0.3 days, respectively. At 25 degrees C, times until the appearance of mature females, the start of crawler production and the peak of crawler production were 48.7 +/- 0.1, 50.1 +/- 0.7 and 63.3 +/- 1.0 days, respectively. Crawler production lasted 42.6 +/- 1.9 days, and the 50% production level was reached on day 13. Initially, crawler survival was higher at 30 degrees C (65.9 +/- 2.8%) than at 25 degrees C (51.7 +/- 4.8%), but by the end of development survival was much higher at 25 than 30 degrees C (88.0 +/- 2.1 vs. 22.9 +/- 2.7%). RH had no effect on either initial or final survival. Average progeny production was of 28.0 +/- 2.8 crawlers per female at 25 degrees C. The relationship between the weight of groups of crawlers and their number was: Number = 1031 + 835,500 x weight of group (g) (R-2 = 0.826), which can assist in colony management. The importance of selecting the correct strain of A. nerii is emphasised.