Exeristes Comstockii Research Articles

Survival and Fecundity of Three Insects Reared on Four Varieties of Scotch Pine Christmas Trees

Three economically important pests-Zimmerman pine moth, Dioryctria zimmermani (Grote); European pine sawfly, Neodiprion sertifer (Geoffroy); and pine needle scale, Chionaspis pinifoliae (Fitch) -were reared on 4 varieties of Scotch pines. Survival and fecundity of each species were evaluated in 1994 and 1995 at Michigan State University’s Kellogg Experimental Forest (Kalamazoo County), Michigan. The varieties tested were Riga, Belgium. Land O’Pine, and Pike Lake Improved. Survival and fecundity of D. zimmermani did not differ significantly among varieties. Larval mortality ranged from 70 to 100%and was attributed to poor establishment on host trees, parasitism by Exeristes comstockii (Cresson) and Hyssopus rhyacioniae (Gahan), and infection by Hirsutella nodulosa (Petch). European pine sawflies reared on Riga trees had significantly lower survival, needle consumption, and pupal weight, and a longer development period than sawflies reared on the other varieties. The ichneumonid Pleolophus basizonus (Gravenhorst) parasitized 30% of the sawfly pupae in 1994. Abundance and fecundity of C. pinifoliae reared on Belgium and Land O’Pine were significantly lower than that of scales reared on varieties Riga and Pike Lake Improved. Results indicated that none of the varieties tested was resistant to all 3 pests.

Partial Life Tables for the Red Pine Shoot Moth, Dioryctria resinosella (Lepidoptera: Pyralidae), in Wisconsin Red-pine Plantations

Partial life tables were prepared for the red pine shoot moth, Dioryctria resinosella Mutuura, in three red-pine, Pinus resinosa Aiton, plantations in central Wisconsin during a period of shoot-moth population decline. Survivorship in the early instars ranged from 72–78% in 1982 and from 22–75% in 1983. In the fifth instar, survivorship ranged from 0–4% in 1982 and 0–31% in 1983. Pupal numbers were very low both years and survivorship was variable; it ranged from 0–100%. Phrynofrontina sp., Exeristes comstockii (Cresson), Bracon rhyacioniae (Muesebeck), Hyssopus rhyacioniae (Gahan), and Elachertus sp. were parasitoids present in high numbers. B. rhyacioniae caused the greatest impact on shoot-moth populations, particularly in the fifth instar. Heavy fifth-instar mortality appeared related to shoot-moth population declines. However, mortality in other life stages not included in the partial life tables, such as dispersing early instar larvae, possibly were involved.

The Effects of Flowers on the Longevity and Fecundity of Two Native Parasites 1 of the European Pine Shoot Moth 2 in Ontario 3

A study was made of the effects of feeding on various flowers on the longevity of Exeristes comstockii Cresson and the longevity and fecundity of Hyssopus thymus Girault. Both species are important native ectoparasites of Rhyacionia buoliana (Schiffermueller) at times, and their feeding on many species of flowers significantly increases the longevity of females over that of starved controls. The fecundity of H. thymus females fed on various flowers was at least comparable to that of honey-fed females in most cases, and in some was significantly greater. The implications of the presence of flowering plants within pine plantations and the success of parasites are discussed and the establishment and encouragement of flowering plants in plantations are recommended.

Influence of Host Fatty Acid Composition on That of Ichneumonoid and Chalcidoid Wasps

The fatty acid composition of parasitic wasps from various families of the Ichneumonoidea and Chalcidoidea appears to be influenced to varying degrees by the composition of their hosts or diets. Qualitatively, each parasite is identical to its host. Quantitatively, the representatives studied from the family Ichneumonidae appear to be influenced to the greatest extent. The latter duplicate the fatty acid patterns of their hosts, and retain no characteristics that could be considered their own. A great deal of data are now compiled concerning the fatty acid composition of insects (Fast, 1970; Gilbert, 1967). Certain characteristics of these compositions are taxonomic in nature (Barlow, 1964) and persist regardless of dietary fatty acid composition (Barlow, 1966; Thompson and Barlow, 1971a). Most free-living Hymenoptera have a typical fatty acid pattern characteristic of a great many insects and vertebrate tissue in which palmitate and oleate comprise about 85% of the fatty acids. In contrast, the ichneumonid parasites, Itoplectis conquisitor and Exeristes comstockii, reared on hosts with widely different patterns, have patterns very similar to their hosts and retain no characteristics that can be conReceived for publication 25 January 1972. sidered their own (Bracken and Barlow, 1967; Thompson and Barlow, 1970b). Several studies have since been carried out to evaluate the mechanism of this phenomenon (Barlow and Bracken, 1971; Thompson and Barlow, 1971b). Although these parasites duplicate the fatty acid patterns of their host, they do have a distinct fatty acid metabolism of their own with respect to synthesis and turnover, but appear to lack the mechanism of pool size regulation present in other insects. The definitive study of the duplication phenomenon by rearing parasites on alternate hosts is very difficult and perhaps impossible in the case of the highly advanced chalcidoids. However, a comparison of the fatty acid composition of a parasite and its host suggests if TABLE I. The fatty acid composition of ichneumonoid and chalcidoid wasps and their corresponding hosts. Percentage of total fatty acids recovered from column* Parasite and host 12 14:0 16:0 16:1 18:0 18:1 18:2 18:3 MSDt MSDRt Superfamily Ichneumonoidea Family Aphidiidae 1. Aphidius smithi 1 10 15 4 9 24 32 6 384.58 4.29 Acyrthosiphon pisum (Hom.) 2 51 4 3 7 10 14 8 Family Braconidae 1. Aphaereta pallipes 4 16 17 6 24 34 135.72 0.71 Agria affinis (Dip.) 2 19 29 4 32 13 2. Microplitis croceipes Tr 1 12 4 9 29 29 17 102.96 0.75 Heliothis zea (Lep.) Tr 16 Tr 7 23 48 6 3. Macrocentrus ancylivorus 1 28 6 15 34 8 9 39.14 2.60 Gnorimoschema operculella (Lep.) Tr 32 14 3 34 8 8 Family Ichneumonidae 1. Itoplectis conquisitor 1 21 42 1 26 10 3.86 0.01 Ostrinia nubilalis (Lep.) 1 23 44 1 23 10 45.25 0.06 2. Itoplectis conquisitor Tr Tr 38 1 1 44 11 4 45.25 0.06 Galleria mellonella (Lep.) Tr Tr 30 3 1 52 14 1 3. Exeristes comstockii 1 16 1 8 37 38 7.8 0.02 Galleria mellonella (Lep.) Tr 19 2 8 32 38 4. Exeristes comstockii 1 24 17 2 47 9 20.38 0.04 Lucilia sericata (Dip.) 2 29 20 3 40 7

Synthesis of fatty acids by the parasite Exeristes comstockii (Hymenop.) and two hosts, Galleria mellonella (Lep.) and Lucilia sericata (Dip.)

In contrast with many other insects, whose characteristic fatty acid compositions are influenced to a limited extent by dietary fatty acid composition, the fatty acid composition of the total lipid of the ichneumonid parasite Exeristes comstockii is very similar to that of its diet, that is, the host on which it is reared. When the parasite was reared on two hosts, Lucilia sericata and Galleria mellonella, with very different fatty acid patterns, it retained no characteristic fatty acid composition of its own.Radioisotope studies demonstrated that Exeristes comstockii, Galleria mellonella and Lucilia sericata incorporate 14C from 14C-1-acetate into fatty acids with radioactivity distributions consistent with de novo, elongation, and desaturation synthetic mechanisms.Exeristes comstockii was found to incorporate 14C-1-acetate into fatty acids at higher rates than either host. It appears, therefore, that the parasite has a fatty acid metabolism of its own, with respect to synthesis and turnover, although the fatty acids are qualitatively and quantitatively very similar to those in the host. The origin of the fatty acids of E. comstockii is partially explained by synthesis of fatty acids at different rates than its host, and direct incorporation of host fat, but the parasite appears to lack to great extent the control over pool size normally present in other insects.

DIORYCTRIA BANKSIELLA (LEPIDOPTERA: PYRALIDAE) IN THE WESTERN GALL RUST, ENDOCRONARTUM HARKNESSII (BASIDIOMYCETES: UREDINALES)

AbstractThe seasonal occurrence and larval habits of Dioryctria banksiella Mutuura, Munroe, and Ross in the western gall rust Endocronartium harknessii (J. P. Moore) Y. Hiratsuka of jack pine, Pinus banksiana Lamb., were studied in Manitoba and Saskatchewan. The early instars score the gall tissue below the bark, and the later instars mine the gall tissue and heartwood. The insect overwinters in the larval stage. The last-instar larvae pupate partly exposed and not entirely within the rust gall from June to July and adults emerge from July to August. The six species of parasites recovered from D. banksiella were Bracon lutus Provancher, Bracon sp., Microchelonus sp., Agathis binominata Muesebeck, Exeristes comstockii (Cresson), and Stiboscopus n. sp. Morphological characters used in separating the last-instar larvae and pupae of D. banksiella from those of other known species of Dioryctria are given.

Incorporation of Na-1- 14 C-acetate into the fatty acids of two insect parasites (Hymenoptera) reared on different hosts.

Sodium-1-14C-acetate was injected into larvae of the parasite, Exeristes comstockii, reared on Galleria mellonella or on Lucilia sericata. The concentration and specific activities of the fatty acids in the larvae were measured 24 h later. The concentration of palmitoleic acid was 10 times greater in C. comstockii when it grew on L. sericata but the specific activity of this fatty acid was the same on either host. It is concluded that the level of palmitoleic acid and probably other fatty acids in the parasite is controlled predominantly by changes in metabolic rates which are regulated by the concentration of the fatty acid in the parasite's diet, that is, host tissue. Direct deposition of dietary fat would not accomplish this result.Another parasite, Itoplectus conquisitor, reared on G. mellonella was also examined.

Parasites of Rhyacionia buoliana and Their Occurrence at Different Crown Levels of Red Pine in Wisconsin1

The native parasite complex associated with the introduced European pine shoot moth, Rhyacionia buoliana Schiffermüller), at Two Rivers, Wisconsin, includes 2 dipterous and 18 hymenopterous species. Data are presented on the percent parasitization effected by the parasite complex, the activity of each of the species involved, and the portion of the tree crown from which hosts parasitized by these species were collected. These data are used to define the area of crown-level activity in which host finding and subsequent parasitism occur. The commonest parasites reared were the primaries Hyssopusthymus Girault and Exeristes comstockii (Cresson), and the secondaries Eurytoma pini Bugbee and Habrocytus thyridopterigis Howard. Average parasitization from 1961 to 1963 was 8.34%. Based on the expected number of parasitized hosts per 1000 infested buds, Hyssopus thymus appears to be the most important parasite. It shows about equal preference for hosts in middle and lower crown levels. Effectiveness of Exeristes comstockii is limited because it is heavily hyperparasitized, requires an alternate host, and is a solitary form. Exeristes comstockii is most active in the middle crown. Eurytoma pini is the most active secondary parasite; it is equally active in the middle and lower crown levels.

Stimulation of Yolk Deposition in an Ichneumonid Parasitoid by feeding Synthetic Juvenile Hormone

SOME ichneumonid parasitoids need to feed on their hosts for egg maturation. Leius1 found significant differences in fecundity of the parasitoid Scambus buolianae (Htg.) when it was fed various species of lepidopterous hosts, and he has attributed these to variations in the chemical composition of the haemolymph of the different hosts. Exeristes comstockii (Cresson) is another example of an ichneumonid in which full maturation of ovaries occurs only when fed on a host or a synthetic diet2. Ovarian development in a number of insects is regulated by endocrine activity of the corpus allatum3, and compounds like farnesol can mimic the activity of the corpus allatum hormone in promoting yolk deposition when applied topically to decapitated Rhodnius4 and allatectomized Periplaneta americana5. The following experiments were conducted to determine (1) whether feeding E. comstockii sugar solution containing farnesol or its derivative farnesyl methyl ether, as well as topical application of the latter, would promote maturation of the ovaries, and (2) whether farnesyl methyl ether added to a synthetic diet would increase egg deposition.

Distribution of the European Pine Shoot Moth, Its Parasites, and Associated Insects in Red Pine Trees and Stands

Twenty species of parasites and associated insects were reared from shoots of red pine, Pinus resinosa Ait., infested with the European pine shoot moth, Rhyacionia buoliana (Schiffermuller), at Oakland, Md. In trees 7 ft tall, Hyssopus thymus Girault was more abundant than Exeristes comstockii Cresson, but the reverse was true in trees half that height. Total parasitism and parasitism by H. thymus and Eurytoma pini Bugbee were greater in the lowest ⅓ than in the topmost ⅓ of the tree; E. comstockii and associated insects of uncertain status—lepidopterans, coleopterans, and the dipteran Oscinella conicola (Green)—were most abundant in the topmost ⅓. Of Itoplectis conquisitor (Say) only males were reared. Usually only 1 shoot moth larva was found per shoot, but occasionally there were as many as 5; more than 1 larva per shoot occurred more often in the topmost than in the lowest ⅓ of the trees. Trees 3½ ft tall had a higher infestation rate than those 7 ft tall. Lammas shoots were infested at the same rate as normal shoots. In 3½-ft trees, 23% of the shoots were in the lowest ⅓ and 24% in the topmost ⅓ of the tree; in 7-ft trees, 50% and 10%, respectively.

Life Histories and Immature Stages of Four Ichneumonid Parasites of the European Pine Shoot Moth Rhyacionia buoliana (Schiff.) in Ontario

AbstractFour indigenous parasites of R. buoliana are discussed: Exeristes comstockii (Cress.), Scambus hispae (Harr.), Scambus tecumseh Vier. and Itoplectis conquisitor (Say). The first three are external larval parasites and the fourth an internal pupal parasite. Observations are given on the hosts, life histories, and habits under laboratory conditions. The immature stages are described.