Importance of Host Feeding in the Biological Control of Insect Pests: Case Study of Egg Parasitoid Species (Hymenoptera: Chalcidoidea: Trichogrammatidae)

Abstract

Over recent decades, intraguild predation (IGP) has attracted special attention, both from the theoretical and practical standpoints. The present paper addresses the interference competition between two Trichogramma species (egg parasitoids)-on the one hand, the extrinsic interactions (i.e., the indirect competition between female T. achaeae and T. brassicae), and on the other, the intrinsic interactions between the larvae of both species. Furthermore, T. achaeae is a better competitor than T. brassicae due to a dual mechanism-the former acts as a facultative hyperparasitoid of the latter, exclusively considering parasitism relationships as well as presenting predation activity by host feeding, which gives preference to eggs previously parasitized by T. brassicae over non-parasitized eggs. Both mechanisms are dependent on the prey density, which is demonstrated by a change in the functional response (i.e., the relationship between the numbers of prey attacked at different prey densities) of T. achaeae adult female-it changes from type II (i.e., initial phase in which the number of attacked targets increases hyperbolically and then reaches an asymptote, reflecting the handling capacity of the predator), in the absence of competition (an instantaneous search rate of a' = 9.996 ± 4.973 days^-1 and a handling time of T_h = 0.018 ± 0.001 days), to type I (i.e., linear increase in parasitism rate as host densities rise, until reaching a maximum parasitism rate, and an instantaneous search rate of a' = 0.879 ± 0.072 days^-1 and a handling time of T_h ≈ 0) when interference competition is present. These results show that there is a greater mortality potential of this species, T. achaeae, in conditions of competition with other species, T. brassicae in this case. Based on this, their implications in relation to the biological control of pests by parasitoid species are discussed.

Keywords: Trichogramma achaeae; Trichogramma brassicae; facultative hyperparasitoid; functional response; intraguild predation; synovigeny.

Figure 7

Comparison of intraguild predation (IGP) trophic webs: (a) predator–predator IGP (Coenosia attenuata–Nesidiocoris tenuis–Bemisia tabaci) (Ref. [63] and author’s own elaboration), compared to (b) parasitoid–parasitoid IGP (Trichogramma achaeae–T. brassicae–host).

Figure 1

Diagram showing the treatments carried out with Trichogramma achaeae (T.a.) and T. brassicae (T.b.): (A) female T.a. parasitizing unparasitized hosts, (B) female T.b. parasitizing unparasitized hosts, (C) female T.b. parasitizes eggs previously parasitized by T.a., and (D) female T.a. parasitizes eggs previously parasitized by T.b.

Figure 2

Dead E. kuehniella egg percentage (±SE) resulting from the activity of the T. achaeae and T. brassicae females (parasitism or host feeding) in competition with the other species, under laboratory conditions (25 ± 1 °C, 60–80% RH, and 16:8 h L:D cycle) (bars followed by different letters indicate significant differences at P = 0.05).

Figure 3

Percentage (±SE) of parasitoid adult emergency from E. kuehniella host eggs parasitized by T. achaeae and T. brassicae female adult, in competition with other species, under lab conditions (25 ± 1 °C, 60–80% RH, and 16:8 h L:D cycles).

Figure 4

Mean (±SE) number of dead E. kuehniella eggs (parasitism + host feeding) resulting from the parasitic activity of T. achaeae or T. brassicae female adult, and the predicted values according to the functional response at different density levels under lab conditions (25 ± 1 °C, 60–80% RH, and 16:8 h L:D cycles).

Figure 5

Mean (±SE) number of dead E. kuehniella eggs (parasitism + host feeding) resulting from the parasitic activity of T. achaeae and T. brassicae female adults, along with the predicted values according to the functional response at different host density levels, in competition with the other species, under laboratory conditions (25 ± 1 °C, 60–80% RH, and 16:8 h L:D cycles).

Figure 6

Relative percentage (±SE) of E. kuehniella eggs killed by host feeding alone, resulting from the activity of T. achaeae and T. brassicae adult female, according to the host density and whether they had previously been parasitized by the other species, under laboratory conditions (25 ± 1 °C, 60–80% RH, and a 16:8 h L:D cycle).