[ The effect of larval and imaginal feeding on fertility in syrphids ]

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A Kh Saidov (1969)
[ The effect of larval and imaginal feeding on fertility in syrphids ]
in Sbornik Nauchnye Trudy Tashkentskii gos. Univ im VI Lenin

“Ecology and biology of animals in Uzbekhistan” UDK 595.7-15

translated by Brian Cooper
In biological methods of pest control, the fertility of enotmophages is of primary importance as one of the factors responsible for suppressing the pest population. In this paper, results of studies of fertility with respect to larval and imaginal nutrition are presented for three syrphid species feeding on cotton aphids in Bukhara province. These species are Scaeva albomaculata, Sphaerophoria scripta and Syrphus corollae.

The conditions of life and nature of syrphid larvae are very varied. They live in [...]

The quantity and quanlity of food eaten in the larval and imaginal stages affects considerably their fertility. According to the literature, in laboratory conditions, Syrphus corollae lays its maximum number of eggs when feeding on Aphis fabae, Myzus persicae and species of Macrosiphum (Bombosch 1962). Our laboratory experiments with these three species confirm that larval nutrition to some extent affects the fertility of the imago and the survival of larvae (Table 1).
Table 1: Fertility with respect to larval nutrition in May 1964. Figures in brackets are the averages per female. Flies were reared identically until dissection.
Species Date of Aphid Eggs in one female

dissection range mean

Scaeva albomaculata 13 Aphis craccivora 108-192 176.2

20 Aphis gossypii 88-173 121.5

26 Myzus persicae 117-186 148.3
Sphaerophoria scripta 14 Aphis craccivora 113-169 149.1

22 Aphis gossypii 89-141 106.1

27 Myzus persicae 92-146 113.5
Syrphus corollae 15 Aphis craccivora 97-152 134.5

25 Aphis gossypii 94-131 119.5

28 Myzus persicae 103-142 122.3
In all three syrphid species, when fed on Aphis craccivora nymphs, the potential fertility was then at a maximum, and lowest when fed on Aphis gossypii.
The imaginal nutrition of syrphids affects their fertility to a greater extent (Table 2). In each of the cages a pair of flies was placed, and flowers and twigs heavily infested with aphids were placed in jars with water. When the imagos were reared on flowers of Lepidium latifolium [Cruciferae], their fertility was almost 1.5 times higher than when fed on sugar syrup. In order to develop eggs, syrphids need additional nutrition. With inadequate nutrition, fertility fell markedly, and therefore in nature with seasonal changes in flower availability, the fertility of flies also varies.

Species Date Aphid Eggs laid per female

range mean
Scaeva albomaculata 9-10.vii Lepidium latifolium 320-282 297.8

22-29.iv Lepidium repens 221-169 193

24-25.vi Allium sativum 272-221 242

29-30.vi Petroselinum crispum 261-209 231.2

2-3.vii Sugar syrup 89-141 188.6
Sphaerophoria scripta 9-10.vii Lepidium latifolium 231-189 218

22-29.iv Lepidium repens 171-136 154

24-25.vi Allium sativum 212-177 190.4

29-30.vi Petroselinum crispum 219-181 194

2-3.vii Sugar syrup 166-112 151.8

Syrphus corollae 9-10.vii Lepidium latifolium 247-201 224.6

22-29.iv Lepidium repens 198-161 172.2

24-25.vi Allium sativum 211-176 198

29-30.vi Petroselinum crispum 231-186 206.4

2-3.vii Sugar syrup 171-143 162.4

In Bukhara the maximum fertility of all three coincided with the period of flowering of Lepidium latifolium and other umbelliferous [?] species. At this time, the seed plants of onion, carrot and dill were beginning to flower. The minimum fertility was observed in early spring and late autumn, when few flowering and nectariferous plants were present; this corresponds to the 1st, 2nd and late generations. The aromatic white and dense flowers of Lepidium were particularly attractive to the flies, so that in cotton fields where this plant grows the number of syrphids is always high. Apart from Lepidium, syrphids are attracted by flowers of seed onions, carrot, dill, parsley and coriander, which can be sown on small plots near cotton fields.

In natural conditions, flies only lay on plants infested with aphids, scattered among colonies, or slightly higher above them. Females glue them vertically with the narrow end uppermost. The process of oviposition lasts 1-2 days. From 5-6 to several dozen can be laid all at one time.

Other factors besides larval and imaginal nutrition can affect oviposition and fertility. Volk (1964) ... [...]
According to our observation, oviposition is stimulated by honeydew. Thus in the absence of infested plants, oviposition does not occur, but as soon as we placed branches of white acacia [Alhagi camelorum] or licorice species, or peach, with aphids, the flies began to lay at once. In Volk’s lab experiments, flies laid even on filter paper when this was sprayed artificially with a solution of honeydew.
Francis Gilbert


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