Impact of Males on the Numerical Response of Diaeretiella rapae (M'Intosh) (Hym., Aphidiidae), a Parasitoid of Lipaphis erysimi Kalt. (Hem., Aphididae)

Abstract

The number of emerging offspring was affected by the density of the female parasitoid and the co‐presence of males along with the females. Parasitisation rates were evaluated in 5 × 1.7 cm petri dishes at parasitoid densities 1, 2, 4, and 8 females only and males mixed with same numbers of females. The mean number of parasitoid progeny with 1, 2, 4, and 8 female densities were 41.0, 48.6, 61.6, and 75.0 while with the introduction of equal number of males it decreased to 26.8, 37.0, 50.6, and 64.6, respectively. Two mechanisms apparently contributed to this effect: decreased offspring of the females and alteration of egg distribution pattern. The number of progeny produced per female parasitoid was inversely proportional to the parasitoid number which explicates the intraspecific competition amongst the parasitoid.

Reproduction of Diaeretiella rapae on Russian wheat aphid hosts at different temperatures

“…We observed that the offspring sex ratio in D. rapae decreased with age, and hence ovipositional activity, despite the continuous presence of males. This result supports the assertion that the sperm supply of females is not replenished, and is in accordance with the observations of other authors (King, 1987;Abidi et al, 1990). Other factors known to influence the offspring sex ratio in aphidiids (e.g., the number of previous matings by the male, beginning of oviposition [i.e.…”

“…data) found that females of a D. rapae population from Iran, when offered honey and water in the absence of hosts, lived 23:8 0:8 and 6:0 0:4 days at 10.0 and 21.1 C, respectively; males lived 17:8 1:1and 4:9 0:5 days at the same temperatures, respectively. The mean longevity of D. rapae at the temperatures studied here are comparable in some cases, but not in others, to those previously reported by other authors (Hafez, 1961;Sedlag, 1964;Sethumadhavan & Dharmadhikari, 1969;Fukui & Takada, 1988;Abidi et al, 1990;Hayakawa et al, 1990;Reed et al, 1992) for different populations of this parasite under various sets of experimental conditions. The preoviposition period in female aphidiids is influenced by the prevailing environmental conditions, including temperature (Stáry, 1970).…”

“…) and their reproductive life is relatively short, particularly at moderate to high temperatures (see Figure 2b, c). Some authors reported developmental time values for different populations of D. rapae similar to the T c values observed in this study (Hayakawa et al, 1990;, while others reported considerably different values (Hafez, 1961;Sedlag, 1964;Campbell et al, 1974;Abidi et al, 1990).…”

“…On the other hand, fecundity was not significantly affected by ambient temperatures. Similar to the case for longevity, reports on the fecundity of D. rapae also are highly variable (Hafez, 1961;Hughes, 1963;Sedlag, 1964;Sethumadhavan & Dharmadhikari, 1969;Wilson & Lambdin, 1987;Fukui & Takada, 1988;Abidi et al, 1990;Hayakawa et al, 1990;Reed et al, 1992).…”

Foraging Behavior ofPraon volucre(Hymenoptera: Braconidae) a Parasitoid ofSitobion avenae(Hemiptera: Aphididae) on Wheat

“…This negative value shows an inverse relationship between parasitoid density and per capita searching efficiency. The negative relationship between per capita searching efficiency and parasitoid density was also documented in D. rapae on B. brassicae [29], and Lipaphis erysimi (Kaltenbach) [48,49]. This reaction refers to intraspecific competition in the parasitoids.…”