Cascading effects of host size and host plant species on parasitoid resource allocation

Abstract

1. The bottom-up factors that determine parasitoid host use are an important area of research in insect ecology. Host size is likely to be a primary cue for foraging parasitoids due to its potential influence on offspring development time, the risk of multiparasitism, and host immunocompetence. Host size is mediated in part by host-plant traits that influence herbivore growth and potentially affect a herbivore's quality as a host for parasitoids.2. Here, we tested how caterpillar host size and host plant species influence adult fly parasitoid size and whether host size influences wasp parasitoid sex allocation. We measured the hind tibia lengths and determined the sex of wasp and fly parasitoids reared from 11 common host species of polyphagous caterpillars (Limacodidae) that were in turn reared on foliage of seven different host plant species.3. We also tested how host caterpillar species, host caterpillar size, and host and parasitoid phenology affect how the parasitoid community partitions host resources. We found evidence that parasitoids primarily partition their shared hosts based on size, but not by host species or phenology. One index of specialisation (d ) supports our observation that these parasitoids are quite generalised within the Limacodidae. In general, wasps were reared from caterpillars collected in early instars, while flies were reared from caterpillars collected in late instars. Furthermore, for at least one species of solitary wasp, host size influenced sex allocation of offspring by ovipositing females.4. Host-plant quality indirectly affected the size attained by a tachinid fly parasitoid through its direct effects on the size and performance of the caterpillar host. The host plants that resulted in the highest caterpillar host performance in the absence of enemies also yielded the largest parasitoid flies, which suggests that host plant quality can cascade up to influence the third trophic level.

Trade-offs in host choice of an herbivorous insect based on parasitism and larval performance

“…The size or developmental stage of host larvae (Stoepler et al 2011), host immune function (Schmid-Hempel 2005), host density (Lessells 1985), light environment (Stoepler and Lill 2013) and volatile cues released by herbivore-damaged plants Fig. 4 The relationship between mean pupal mass (mg) and percent parasitism among field-collected fall webworms over the course of the study (R 2 = 0.38, n = 16, p < 0.02).…”

Effects of climate warming on host–parasitoid interactions

“…As atmospheric CO 2 concentrations increase, plant nitrogen content will in general be reduced, making plants of lower nutritional quality for herbivores (Bezemer & Jones, 1998). If lower plant quality reduces host size, parasitoids developing on smaller hosts may themselves be smaller on emergence (Lampson et al ., 1996;Stoepler et al ., 2011; but see Kouamé & Mackauer, 1991). Smaller adult parasitoids have lower fecundity and dispersal ability, reducing their fitness (Godfray, 1994).…”

“…Smaller adult parasitoids have lower fecundity and dispersal ability, reducing their fitness (Godfray, 1994). Furthermore, as many parasitoids lay fertilised, female eggs in better-quality hosts (Charnov, 1982), altered host plant quality could potentially alter parasitoid sex ratios via its impact on host insect size (Stoepler et al ., 2011). As only female parasitoids kill hosts, male-biased sex ratios could reduce parasitism rates in the short term, resulting in reduced efficacy of biological control and ultimately lower crop yields.…”

Refrigerated Eggs of Riptortus pedestris (Hemiptera: Alydidae) Added to Aggregation Pheromone Traps Increase Field Parasitism in Soybean

“…The higher parasitism by T. acacioi, T. annulata, T. brasiliensis, T. bruni, T. pretiosum, and T. soaresi on eggs of A. kuehniella stored for longer periods may be related to factors such as these species having: 1) stronger ovipositors than the other parasitoids tested, 2) the ability to recognize chemical signals more efficiently, and/or 3) higher tolerance to changes in physical stimuli such as color, size and shape of chilled eggs (Stoepler et al 2011). Except T. soaresi, the above species also showed high adult emergence from host stored for longer periods.…”

“…Longer storage times may result in decreased nutritional quality for this parasitoid's embryos by deterioration of the yolk (Pratissoli et al 2003). Parasitoid females can reject eggs with altered chemical and physical stimuli (Soares et al 2009;Goubault et al 2011;Penaflor et al 2011;Stoepler et al 2011) such as eggs that contain cryoprotectants (glycerol, alanine) to resist cooling (Rivers et al 2000). Storage can also modify the egg shape and affect the host recognition by the parasitoids (Conti et al 1996).…”