Functional response of Diaeretiella rapae (McIntosh) (Hym., Aphidiidae) to Diuraphis noxia (Mordwilko) (Hom., Aphididae) hosts

Abstract

Functional‐response experiments involving the parasitoid Diaeretiella rapae (McIntosh) (Hym., Aphidiidae) and Diuraphis noxia (Mordwilko) (Homo., Aphididae) hosts were conducted. The host densities used were 10, 20, 40, 80, and 160 hosts per arena per day. Searching bouts lasted 24 h, and female parasitoids were allowed to search over two consecutive days. New hosts were offered to parasitoids after the first 24 h. Temperature was maintained at ca. 21°C, photoperiod was set at 14L:10D, and humidity ranged from 50 to 70 % RH. In general, the offspring sex ratio did not appear to vary significantly with a host density of up to 80 hosts per female per day. However, the proportion of female offspring increased when female parasites were offered 160 hosts per day. In addition, the overall proportion of female offspring produced across all host densities offered decreased on day 2 (0.582 ± 0.037) relative to day 1 (0.661 ± 0.023). Diaeretiella rapae displayed a Type 2 functional response to D. noxia hosts during the first 24 h. The functional response displayed during the second 24 h was unlike any response commonly reported in the literature, with an initial rise followed by a sharp decline in numbers of mummies produced when more than 40 hosts were offered. This was presumably due to the greater depletion of the female parasitoid's egg complement after 24‐h exposures to high host densities (80 and 160 hosts), rather than to lower host densities (10, 20 and 40 hosts). The functional response parameters for day 1 were à =1.341 arenas per day and Th = 0.017 days per mummy. The maximum attack rate per 24‐h period (i.e. 1/Th) was 59.5 mummies.

Development and Parasitism byAphelinus certus(Hymenoptera: Aphelinidae), a Parasitoid ofAphis glycines(Hemiptera: Aphididae)

“…Aphidiinae braconids exhibit a type II age-speciÞc realized fecundity pattern, characterized by increasing egg deposition over the Þrst few days of adult life followed by a rapid decline (Jervis et al 2008). This pattern is similar to that found for D. rapae, which at high host densities exhausted its egg supply, resulting in reduced parasitism the following day (Bernal et al 1994). Aphelinidae display type III or IV fecundity patterns, characterized by a prolonged low egg deposition rate (Jervis et al 2008).…”

“…For example, D. rapae can theoretically parasitize a maximum of 23.5Ð59.5 aphids per day (Bernal et al 1994, whereas Binodoxys communis can parasitize 15.7 aphids in 4 h . However, the functional response and related values (i.e., theoretical maximum parasitism) can change over time (Bernal et al 1994), and thus a functional response determined from a parasitoidÕs Þrst encounter with a host cannot be extrapolated over its entire life. Jervis et al (2008) identiÞed four agespeciÞc realized fecundity patterns in parasitoids, which may be useful to predict the change in functional response over time.…”

Parasitismo de Aphidius colemani Viereck (Hymenoptera: Aphidiidae) em diferentes densidades de Myzus persicae (Sulzer) (Hemiptera: Aphididae)

“…A maior proporção de fêmeas é importante para o controle biológico com parasitóides da família Aphidiidae, já que a fêmea necessita acasalar apenas uma vez e um macho pode acasalar com várias fêmeas (Hagvar & Hofsvang 1991) além da manutenção e aumento da população dos inimigos naturais dependerem do número de fêmeas geradas (Brooijmans & Lenteren 1997). Bernal et al (1994), testando a razão sexual de Diaeretiella rapae (McIntosh) sobre o pulgão Diuraphis noxia (Mordvilko), não encontraram diferença significativa até a densidade de 80 hospedeiros, porém para a densidade 160 hospedeiros o número de fêmeas geradas foi maior. Sinha & Singh (1979), trabalhando com o parasitóide Trioxys indicus Subba Rao & Sharma e o hospedeiro Aphis craccivora Koch, encontraram maior número de fêmeas com o aumento da densidade do hospedeiro.…”

Host instar preference and functional response of Aphidius transcaspicus, a parasitoid of mealy aphids (Hyalopterus species)

“…In contrast to the shape of the functional response, the level of the upper asymptote of the response, which represents the maximum daily number of aphids parasitized, may be more indicative of the biological control potential of these aphid parasitoids. In this context, the upper asymptote of 64.3 aphids day -1 for A. transcaspicus places this species among those with the greatest daily parasitism potential (58-70 aphids day -1 ) as found for Aphidius colemani (Jones et al 2003;Byeon et al 2011), Diaeretiella rapae (Bernal et al 1994), Ephedrus cerasicola (Hofsvang and Hagvar 1983), Lysiphlebus testaceipes (Hughes et al 1992;Jones et al 2003), and Lysiphlebia mirzai (Tripathi and Singh 1991). Most other Aphidius species that have been studied have lower upper asymptotes from seven to 30 aphids day -1 (Hughes et al 1992;Zamani et al 2006;Tahriri et al 2007), and from five to 46 aphids day -1 for Trioxys and Aphelinus species, and Lysiphlebus fabarum (Collins et al 1981;Hughes et al 1992;Rakhshani et al 2004;Mahmoudi et al 2010).…”