Abstract
Syrphid (<em>Diptera: Syrphidae</em>) larvae and pupae (149) were collected from an organically grown cabbage field maintained by Department of Agricultural Biology, Faculty of Agriculture, University of Peradeniya. Out of them 15 adults of syrphids emerged and were identified as <em>Allograpta javania</em> and <em>Episyrphus viridaureus</em> (Wiedemann). Most larvae died during rearing. Out of the remaining, 66.7% were parasitized. A significant correlation coefficient (0.83) between the mean number of cabbage aphids and syrphid larvae was noticed. Three species of hoverfly parasitoids, <em>Diplazon orientalis</em> (Cameron) and <em>Diplazon laetatorius</em> (F.) (Ichneumonidae) and <em>Syrphophagus </em>sp. (Encyrtidae) were reared. The <em>Diplazon laetatorius</em> is found to be a new record from Sri lanka. The most frequently found parasitoid was <em>Diplazon laetatorius</em> and the per cent parasitism was 50. The per cent parasitism of <em>Diplazon orientalis</em> and <em>Syrphophagus</em> sp. was 42.3 and 6.3 respectively. Morphological details of each parasitoid species is presented. A significant correlation coefficient (0.91) between total hoverfly larvae and the parasitized hoverfly larvae was noticed. At the beginning of observations, the number of the parasitized larvae was small. As the number of syrphid larvae feeding in cabbage aphid colonies was increasing, the percentage of parasitized larvae increased. During observations in a conventional cabbage field at Paingamuwa area in the Kandy District, 40 syrphid larvae and pupae were collected. Out of them, thirteen adults of syrphids emerged and were identified as <em>Allograpta javania</em> and <em>Episyrphus viridaureus</em>. Most larvae died during rearing. Out of the remaining 10.37% were parasitized. Total number of hoverfly larvae in the insecticide free vegetable field was more than four times higher than the conventionally managed field. Predators of aphids other than syrphids were found at the two sites in low numbers. <br /><br />DOI: <a href="http://dx.doi.org/10.4038/tar.v21i1.2591">http://dx.doi.org/10.4038/tar.v21i1.2591</a><br /><br /><em>Tropical Agricultural Research</em> Vol. 21(1): 99-109 (2009)
Highlights
The family Syrphidae comprises three subfamilies, 180 genera, and about 6,000 described species (Vockeroth and Thompson, 1987)
Observations on cabbage aphids were taken at an insecticide free farm maintained by Department of Agricultural Biology, Faculty of Agriculture, University of Peradeniya and at conventional cabbage field at Paingamuwa area in the Kandy District
Total number of hoverfly larvae in the insecticide free vegetable field was more than four times higher than the conventionally managed field
Summary
The family Syrphidae comprises three subfamilies, 180 genera, and about 6,000 described species (Vockeroth and Thompson, 1987). The larvae of the subfamily Syrphinae commonly known as hoverfly larvae are considered as specialized aphidophagous predators distributed worldwide (Chambers et al, 1986; Vockeroth and Thompson, 1987). Hoverflies along with other aphidophagous insects play a very important role in the reduction of aphid populations (Sobota and Twardowski, 2004). Occurrence of syrphids is one of the most important factors decreasing the number of cabbage aphids, a main pest of cabbage vegetables (Wnuk, 1971; Wnuk and Fusch, 1977; Wnuk and Wojciechowicz, 1993)
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