Post-egression host tissue feeding is another strategy of host regulation by the Koinobiont wasp, Toxoneuron nigriceps

Progeny fitness determines the performance of the parasitoid Therophilus javanus, a prospective biocontrol agent against the legume pod borer

Therophilus javanus (Bhat & Gupta) is an exotic larval endoparasitoid newly imported from Asia into Africa as a classical biological control agent against the pod borer Maruca vitrata (Fabricius). The parasitoid preference for the five larval instars of M. vitrata and their influence on progeny sex ratio were assessed together with the impact of larval host age at the time of oviposition on development time, mother longevity and offspring production. In a choice situation, female parasitoids preferred to oviposit in the first three larval instars. The development of immature stages of the parasitoid was observed inside three-day-old hosts, whereby the first two larval instars of T. javanus completed their development as endoparasites and the third larval instar as ectoparasite. The development time was faster when first larval instars (two- and three-day-old) of the host caterpillars were parasitized compared to second larval instar (four-day-old). The highest proportion of daughters (0.51) was observed when females were provided with four-day-old hosts. The lowest intrinsic rate of increase (r) (0.21 ± 0.01), the lowest rate of increase (λ) (1.23 ± 0.01), and the lowest net reproductive rate (Ro) (35.93 ± 6.51) were recorded on four-day-old hosts. These results are discussed in the light of optimizing mass rearing and release strategies.

Cotesia ruficrus (Hymenoptera: Braconidae) Parasitizing Cnaphalocrocis medinalis (Lepidoptera: Pyralidae): Developmental Interactions and Food Utilization Efficiency of Hosts

Cotesia ruficrus (Haliday), a gregarious larval endoparasitoid, is an important biological control agent of various pest species. The developmental interactions between the host rice leaf folder, Cnaphalocrocis medinalis (Guenée), and its koinobiont parasitoid, C. ruficrus, were investigated for the first time under laboratory conditions. The effects of host instar at parasitization on the development time, clutch size, and survival of C. ruficrus were determined. The results showed that the parasitoids starting parasitism in the fourth-instar larvae had the shortest development duration and highest fecundity. Meanwhile, the growth of the host parasitized by C. ruficrus in various instars was also observed. The results indicated that the growth of the parasitized larvae was significantly inhibited, compared with unparasitized ones, irrespective of the host instar at oviposition. In addition, the effect of parasitism on food consumption and utilization of the fourth-instar larvae was determined, suggesting that the nutritional physiology of the host was affected by parasitism. Wet or dry weight gain, food consumption, and fecal matter were all significantly reduced in the parasitized larvae in contrast with the unparasitized larvae. Parasitization by C. ruficrus could significantly increase the approximate digestibility of the host.

Postegression Feeding Enhances Growth, Survival, and Nutrient Acquisition in the Endoparasitoid Toxoneuron nigriceps (Hymenoptera: Braconidae)

Toxoneuron nigriceps Viereck (Hymenoptera: Braconidae), a koinobiont endoparasitoid of the tobacco budworm, Heliothis virescens F. (Lepidoptera: Noctuidae), derives nutrition from the host hemolymph during the internal portion of its larval development but feeds destructively on host tissues externally after egression. To investigate the importance of this tissue-feeding phase, and to evaluate the behaviors associated with postegression feeding, T. nigriceps larvae were subjected to one of four treatments: 1) allowed to carry out normal tissue feeding, 2) deprived of tissue feeding, 3) presented with tissues scraped away from the host remains, and 4) fed tissues scraped from an unparasitized H. virescens larva. Additionally, total carbohydrates, lipids, and proteins were quantified from pre and posttissue feeding T. nigriceps larvae to examine the effect of postegression feeding on parasitoid nutritional physiology. Parasitoids that received no tissues after egression, or that received tissue from an unparasitized H. virescens larva, had significantly smaller body masses at all stages than those allowed to feed naturally or fed tissues scraped from a parasitized host. Parasitoids that underwent normal host feeding after egression also reached larger masses then those fed scraped host tissue. Parasitoids that received no tissue after egression survived to adulthood significantly less often than those that were presented with any H. virescens tissue. This suggests that postegression tissue feeding is a vital developmental step for T. nigriceps, and that T. nigriceps will not only feed when normal postegression behavior is disrupted, but will also feed on unparasitized tissue. The quantification of macronutrients in the tissues of pre and posttissue feeding T. nigriceps larvae showed significantly elevated proportions of proteins, lipids, and carbohydrates in the tissues of larvae that had completed feeding, with the greatest difference being in total lipids.

The parasitoid, Cotesia flavipes (Cameron) (Hymenoptera: Braconidae), influences food consumption and utilization by larval Diatraea saccharalis (F.) (Lepidoptera: Crambidae)

Parasitoids exploit host insects for food and other resources; they alter host development and physiology to optimize conditions to favor parasitoid development. Parasitoids influence their hosts by injecting eggs, along with a variety of substances, including venoms, polydnaviruses, ovarian fluids, and other maternal factors, into hosts. These factors induce profound changes in hosts, such as behavior, metabolism, endocrine events, and immune defense. Because endoparasitoids develop and consume tissues from within their hosts, it is reasonable to suggest that internal parasitization would also influence host food consumption and metabolism. We report on the effects of parasitism by Cotesia flavipes on the food consumption and utilization of its host, Diatraea saccharalis. Cotesia flavipes reduces the host food consumption, but parasitized larvae considered a unit with their parasitoid's attained the same final weight as the nonparasitized larvae. Nutritional indices, midgut activities of carbohydrases, and trypsin of parasitized and nonparasitized D. saccharalis were assessed. Parasitized larvae had reduced relative food consumption, metabolic and growth rates, coupled with higher efficiency for conversion of the digested, but not ingested, food into body mass. Parasitism also affected food flux through the gut and protein contents in the midgut of parasitized larvae. The activity of α-amylase and trehalase in parasitized host was enhanced in the first day after parasitism relative to control larvae. Saccharase activity remained unchanged during larval development. Trypsin activity was reduced from the fifth to ninth day after parasitism. We argue on the mechanisms involved in host food processing after parasitism.