Fourth-instar Hosts Research Articles

Seasonal abundance and mutual interference of <i>Diaeretiella rapae</i> (McIntosh) on <i>Brevicoryne brassicae</i>

Brevicoryne brassicae (Hemiptera: Aphididae), known as cabbage aphid, is cosmopolitan in distribution that infests cruciferous crops such as broccoli, cabbage, cauliflower, and mustard. Brevicoryne brassicae is suppressed by various species of natural enemies, the most important and abundant being Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae). The present study was carried out at Dr. Y. S. Parmar University of Horticulture and Forestry, Nauni Solan, Himachal Pradesh, on the seasonal abundance and mutual interference of the parasitoid, D. rapae during the years 2020-2021. The study showed the peak population of both host (221.36 aphids/plant) and parasitoid (27.28 mummified aphids/plant) with 12.32 per cent parasitization on the 10th Standard Meteorological Week (SMW). On the 14th SMW of 2021, the aphid population was lowest (2.72 aphids/plant) and parasitization by D. rapae was highest (47.05%). The D. rapae when foraged at densities of 2, 4, 6 and 8 parasitoids per 30 and 50 constant host nymphs, the third-instar host nymphs had a higher mutual interference coefficient than fourth instar host nymphs. Therefore, D. rapae can be utilized as an important biocontrol agent in the management programme of a cabbage aphid (B. brassicae).

BIOLOGY AND LIFE HISTORY OF COTESIA RUFICRUS (HYMENOPTERA:BRACONIDAE) A POTENTIAL PARASITOID OF HYPOSIDRA TALAC (LEPIDOPTERA: GEOMETRIDAE) LARVAE, A MAJOR TEA PEST

ABSTRACT The black inch looper, Hyposidra talaca is considered as a major pest in tea in northern part of West Bengal and North East India. Among the natural enemy reported, Cotesia ruficrus is considered as one of the most gregarious endo-parasitoid wasps. In order to assess the potential of this natural enemy, a study on the biological parameters of C. ruficrus was evaluated on the different developmental stages (second, third and fourth instars) of the host larvae, H. talaca. The results indicated that, the mean duration of larval development was 12.0 ± 0.32, 11.0 ± 0.45 and 9.2±0.37 days in second, third and fourth instar host larvae respectively. The pupal period of C. ruficrus was found to be significantly different among the different larval stages of H. talaca. The successful parasitism of C. ruficrus and the number of cocoon formation of the parasitic wasp was reliant on the stage, body size and the physiological conditions of host larvae that it parasitizes. A maximum of 65.2±1.85 cocoons were formed when the fourth instar host larvae parasitized, followed by 27.2±3.04 in the third instar and 4.6±0.68 in the second instar host larvae. The number of females and males hatched out from each clutch was compared to the different host stages. .

Unsuccessful Host Stinging by Aphelinus asychis (Hymenoptera: Aphelinidae) Impacts Population Parameters of the Pea Aphid (Hemiptera: Aphididae).

The biocontrol values of natural enemies are strongly correlated to their ability to regulate the density of their host/prey. For parasitoids, apart from parasitism and host feeding, unsuccessful host stinging (i.e., stings that were aborted, abandoned, or discontinued without oviposition or host feeding) can also negatively affect their hosts and host populations. Although several studies have reported unsuccessful host stinging and its impacts on hosts, the effects of this type of attack on host life table parameters are still unclear. In the present study, we used the parasitoid Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and its host Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) to investigate the influence of unsuccessful host stinging on host populations under laboratory conditions at. Biological parameters of A. pisum were analyzed using an age stage, two-sex life table. The results of this study showed that unsuccessful host stinging was prevalent under laboratory conditions, and the frequency of this type of attack on third- and fourth-instar hosts was higher than the frequencies of parasitism and host feeding. Unsuccessful host stinging adversely impacted aphid populations, by decreasing aphid survival and reproduction, and impacts were greatest in hosts attacked at the first and fourth instars. These results indicate that unsuccessful host stinging enhances the biological control impact of A. asychis attacking A. pisum, and its effect on host populations should also be considered when selecting and mass rearing of parasitoids for biological control.

Two Parasitoids of Diaphorina citri (Hemiptera: Liviidae) have Shared, Stage-Specific Preference for Host Nymphs that does not Impact Pest Mortality Rates

Assessing the oviposition preference and offspring performance of 2 parasitoid species being used to establish classical biological control of Diaphorina citri Kuwayama (Hemiptera: Liviidae) infesting citrus may provide important insight into their potential coexistence in California, USA. Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae), an ectoparasitoid, preferred fourth and fifth instar D. citri nymphs for oviposition in both choice and no-choice experiments. Larval development and adult longevity of T. radiata offspring were positively correlated to female oviposition preference. Oviposition preferences of T. radiata were unaffected by conspecific and heterospecific competitors. Diaphorencyrtus aligarhensis (Shafee, Alam & Agarwal) (Hymenoptera: Encyrtidae), an endoparasitoid, preferred third and fourth instar hosts in choice experiments and fourth instar hosts in nochoice experiments. Parasitoid larvae that developed in these instars performed better than larvae that developed in second and fifth instars. The oviposition preferences of D. aligarhensis were unaffected by competitors in choice arenas, but were affected in no-choice experiments. Populations of T. radiata and D. aligarhensis from Pakistan, where they exist in sympatry and used in the experiments reported here, demonstrated a shared preference for fourth instar D. citri nymphs, which has not been documented previously for populations of D. aligarhensis from other geographic regions. This shared preference did not affect D. citri mortality rates, but it may affect the ability of D. aligarhensis to establish in areas of California where T. radiata is currently present.

Reproductive biology of Holepyris sylvanidis (Hymenoptera: Bethylidae)

Holepyris sylvanidis (Hymenoptera: Bethylidae) is reported as a cosmopolitan parasitoid of coleopteran including a major pest of stored products, the confused flour beetle Tribolium confusum. The reproductive biology, and hence biocontrol potential of H. sylvanidis is relatively little known. Here we describe and evaluate aspects of egg size, immature development, adult mating behaviour, pre-oviposition time, fecundity, host attack and use, and adult longevity. Our key findings are that ≈72% of presented T. confusum immatures presented to females were attacked and ≈39% of these were fed on destructively with the remainder oviposited onto. First instar host larvae and host pupae were only utilized for feeding, second and third instar larvae were commonly used for either feeding or oviposition while fourth, fifth and sixth instar hosts were almost exclusively used for oviposition. Females usually laid single egg clutches and their average lifetime fecundity was ≈16.5 eggs. Females regularly provisioned with hosts often ceased laying eggs up to several weeks before their death but continued to kill and feed on hosts during this period. Adult longevity was greatly enhanced by the provision of hosts (females) or by non-host food sources (males). We conclude that the inoculative biocontrol potential of H. sylvanidis is likely to be limited by a low realized fecundity and the combination with other control methods in an IPM-approach is needed. Its ability to find and kill hosts may make it more suitable for inundative deployment.

Body size affects host defensive behavior and progeny fitness in a parasitoid wasp, Lysiphlebus fabarum

AbstractThis study tested effects of maternal body size on foraging behavior and progeny development in a thelytokous population of Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae). Small and large wasps were reared from first and second instar hosts [black bean aphid, Aphis fabae Scopoli (Hemiptera: Aphididae)], respectively, and each was provided with a patch (bean leaf disk) containing either 15 small (second instar) or 15 large (fourth instar) hosts for a 30‐min foraging period. Neither body size nor host size affected time allocation to various behaviors within a patch, but second instar aphids produced significantly more mummies than fourth instars. The preferred attack orientation was from the side of the aphid, suggesting wasps were sensitive to the risk of smearing with cornicle secretions. Few wasps developed in fourth instar hosts, suggesting later host instars were somewhat resistant to parasitism. Second instar hosts, the most suitable stage for L. fabarum development, relied more on defensive behavior, specifically kicking and secreting cornicle droplets. Large wasps were more likely to elicit a double cornicle secretion, indicating that aphids graded their response to the size of the attacker. Larger wasps were also more likely to be smeared with cornicle secretion, suggesting they were more vulnerable than small wasps. Although small wasps had smaller eggs than large wasps, there was no effect of maternal egg size on the size of progeny. However, daughters of small females emerged with larger egg loads than daughters of large mothers, and their eggs tended to be slightly smaller, although not significantly. Regression analysis revealed a positive correlation between maternal egg size and progeny developmental time for small and large wasps, and between maternal egg size and progeny egg load for small wasps. These results confirm maternal effects of body size in an aphid parasitoid, and reveal that vulnerability to host behavioral defenses is also body size dependent.

Effect of fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) strain and diet on oviposition and development of the parasitoid Euplectrus platyhypenae (Hymenoptera: Eulophidae)

Oviposition tendency and subsequent development of the parasitoid wasp Euplectrus platyhypenae Howard was compared using the corn and rice host strains of Spodoptera frugiperda (J. E. Smith) fed corn (Zea mays, ‘Truckers Favorite’) or stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis, ‘Florona’). In no-choice and two-choice experiments using newly molted fourth instar hosts, female wasps preferred to oviposit on corn strain larvae fed corn plants. Rice strain larvae were parasitized when fed corn plants, but only after the host had reached an optimal size. This preference might be due to differences in size between host strains at a given stage. No oviposition preference for corn or rice strain larvae fed grass was observed. When female wasps were given a choice between corn and rice strain larvae, they always produced more female offspring on the corn strain than the rice strain larvae, irrespective of the host plant the larvae fed upon. Among rice strain hosts, those fed corn hosted more female offspring than those fed grass. The data also show that host quality had a direct effect on parasitoid size, since larger parasitoid offspring resulted from the largest host fed corn plants, and smaller offspring resulted from the smallest hosts, rice strain larvae fed stargrass. Furthermore, E. platyhypenae larval mortality occurred in hosts of both strains fed stargrass, which may indicate that stargrass allelochemicals are not appropriate for this parasitoid. Implications of these results for biological control methods are discussed.

Everyone's a Loser: Parasitism of Late Instar Whiteflies byEncarsia inaronhas Negative Consequences for Both Parasitoid and Host

AbstractDespite strong evolutionary pressure for an ovipositing parasitoid to use only hosts with high suitability, there are examples of parasitoid attacks that fail. Here we document one such instance, in which a parasitoid does not discriminate against an inappropriate host life stage, resulting in negative consequences for both the parasitoid and host. The solitary koinobiont parasitoid Encarsia inaron (Walker) was originally imported to North America to control the ash whitefly, Siphoninus phillyreae (Haliday), but readily parasitizes and completes development in other whitefly hosts, including Bemisia tabaci (Gennadius) and Trialeurodes abutiloneus (Haldeman). For both B. tabaci and T. abutiloneus, when younger host instars were parasitized, parasitism was successful and adult wasps emerged. In fourth instar hosts, however, adult parasitoids rarely emerged; rather, adult whiteflies were produced. Dissections over time showed that the wasp larvae continued to develop within these adult whiteflies, but did not successfully complete development. Furthermore, the adult whiteflies suffered reduced fecundity compared with nonparasitized adults and ultimately died as a result of parasitism. Our results suggest that E. inaron may be incapable of arresting the development of hosts parasitized as fourth instars, instead engaging in a developmental race that results either in a win for the parasitoid, or a loss for both the parasitoid and the host.

The effect of host developmental stage at parasitism on sex‐related size differentiation in a larval endoparasitoid

Abstract. For their larval development, parasitoids depend on the quality and quantity of resources provided by a single host. Therefore, a close relationship is predicted between the size of the host at parasitism and the size of the emerging adult wasp. This relationship is less clear for koinobiont than for idiobiont parasitoids. As size differentiation in host species exhibiting sexual size dimorphism (SSD) is likely to occur already during larval development, in koinobiont larval endoparasitoids the size of the emerging adult may also be constrained based on the sex of the host caterpillar. Sex‐specific growth trajectories were compared in unparasitised Plutella xylostella caterpillars and in second and fourth instar hosts that were parasitised by the solitary larval koinobiont endoparasitoid Diadegma semiclausum. Both species exhibit SSD, where females are significantly larger than males. Healthy female P. xylostella caterpillars developed significantly faster than their male conspecifics. Host regulation induced by D. semiclausum parasitism depended on the instar attacked. Parasitism in second‐instar caterpillars reduced growth compared to healthy unparasitised caterpillars, whereas parasitism in fourth‐instar caterpillars arrested development. The reduction in growth was most pronounced in hosts producing male D. semiclausum. Parasitism itself had the largest impact on host growth. SSD in the parasitoid is mainly the result of differences in growth rate of the parasitoid–host complex producing male and female wasps and differences in exploitation of the host resources. Female wasps converted host biomass more efficiently into adult biomass than males.

Biological assessment of Macrocentrus linearis and Apanteles polychrosidis (Hymenoptera: Braconidae) as parasitoids of the obliquebanded leafroller, Choristoneura rosaceana (Lepidoptera: Tortricidae)

The biologies of two endoparasitoids of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) from organically managed apple orchards in the southern interior of British Columbia, Canada were studied in the laboratory. Macrocentrus linearis (Nees) (Hymenoptera: Braconidae) oviposited into first through fourth instar obliquebanded leafrollers. A sympatric leafroller species found in this area of British Columbia, the three-lined leafroller, Pandemis limitata (Robinson) (Lepidoptera: Tortricidae) was not accepted as an alternate host species by M. linearis. When provided with honey-water and held under fall and summer orchard temperatures, M. linearis females survived significantly longer under fall than summer temperatures (=28.3±2.4 and 20.2±2.5 days, respectively) but parasitized a similar number of obliquebanded leafroller larvae (=12.2±5.0 and 24.4±9.2 larvae, respectively). A mean of 20.6±4.9 larvae emerged per parasitized obliquebanded leafroller in the host's fifth or sixth instar. Obliquebanded leafroller larvae parasitized by M. linearis consumed significantly more diet than unparasitized hosts from fifth instar to pupation, suggesting that M. linearis may not reduce host feeding damage to fruit except through the ultimate reduction of host populations. Apanteles polychrosidis Viereck (Hymenoptera: Braconidae) parasitized the first through third instars of both the obliquebanded and three-lined leafrollers. When provided with honey-water and held at temperatures typical of either fall or summer in orchards, A. polychrosidis females survived significantly longer (=46.6±3.1 and 26.4±2.5 days, respectively) and parasitized significantly more obliquebanded leafrollers under fall than summer temperatures (=61.5±7.2 and 18.4±5.3 total larvae, respectively). A single A. polychrosidis larva emerges from a third or fourth instar leafroller host. Consequently, parasitized obliquebanded leafroller larvae consumed significantly less diet than unparasitized larvae from fourth instar to pupation. Attributes of both parasitoids are compared with those of another common obliquebanded leafroller parasitoid, Apophua simplicipes (Cresson) (Hymenoptera: Ichneumonidae).

Influence of host size on the clutch size and developmental success of the gregarious ectoparasitoid Eulophus pennicornis (Nees)(Hymenoptera: Braconidae) attacking larvae of the tomato moth Lacanobia oleracea (L.) (Lepidoptera: Noctuidae)

The relationship between clutch size, host size and progeny survival in the gregarious ectoparasitoid Eulophus pennicornis was investigated in a number of scenarios. When naive parasitoids were exposed singly to Lacanobia oleracea hosts, clutch size was strongly correlated with the size of the host. However, survival of parasitoid offspring was negatively affected by the size of the host such that, in larger hosts, greater wasp larval and pupal mortality was recorded. As a result, no gain in realised fecundity was achieved through parasitizing L. oleracea larvae of mass >0.4 g over hosts of mass between 0.2-0.3 g. When exposed to populations of mixed stadium hosts (larvae in the fourth, fifth and sixth instars) during the entire lifespan of the wasp, host size and clutch size were correlated in early ovipositions (first three ovipositions). However, as the wasps aged, the relationship was much less apparent. When the parasitoid was restricted to foraging upon populations of sixth instar hosts only, no relationship between host size and clutch size was apparent. Exposure of the parasitoid to mixed and fixed stadium host populations showed that final (sixth) stadium hosts were the most frequently parasitized (ca. 96% of parasitized hosts) and that the average numbers of eggs laid per wasp, and the number of hosts parasitized, was significantly lower when the parasitoid was provided with fourth or fifth instar hosts only. The results indicate that the reproductive success of E. pennicornis does not increase with increasing host size or greater resource availability above a certain threshold, and that the physiological status of the host at the time of parasitism is the governing factor determining oviposition decisions and parasitoid survival. We conclude that E. pennicornis has been selected to preferentially utilize those hosts that maximize progeny survival and to adapt clutch size to the size of such hosts. We hypothesize that the major driver leading to the evolution of this strategy is the ability of the parasitoid to physiologically regulate the host.

<I>Aphidius ervi</I> (Hymenoptera: Braconidae) Increases Its Adult Size by Disrupting Host Wing Development

The parasitoid wasp Aphidius ervi (Haliday) disrupts formation of wings by its host, the pea aphid, Acyrthosiphon pisum (Harris). Because apterous aphids are larger than alates, we hypothesized that blocking wing formation leads to larger parasitoids emerging from apterous hosts. In an initial experiment, we found that parasitoid larvae could not always prevent host wing formation when the parasitoid began development in fourth instar hosts, allowing us to experimentally test the hypothesis. Both male and female parasitoids emerging from hosts that did not develop wings were heavier than those emerging from alate hosts. Parasitoids emerging from apterous mummies also had significantly longer thoraxes. For insect parasitoids, increasing size has been positively correlated with several measures of fitness. Thus, A. ervi likely gains a fitness advantage by disrupting host wing development.

A biological assessment of Apophua simplicipes (Hymenoptera: Ichneumonidae) as a parasitoid of the oblique banded leafroller, Choristoneura rosaceana (Lepidoptera: Tortricidae)

Apophua simplicipes (Cresson) (Hymenoptera: Ichneumonidae) is a common parasitoid of the oblique banded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) in organically managed apple orchards in the southern interior of British Columbia, Canada. The biological characteristics of a laboratory colony of A. simplicipes were studied. When held at 15 and 25°C and provided with honey water, individual females survived an average of 60.6±6.1 and 29.8±4.7 days, oviposited 196.7±50.7 and 326.6±51.3 eggs and parasitized a total of 163.4±40.4 and 229.4±35.8 hosts, respectively. Females oviposited into first through fourth instar oblique banded leafrollers, with significantly more parasitism occurring in the first two instars compared to the third and fourth instars. No parasitoid larvae survived past the first larval stage in parasitized fourth instar hosts. Apophua simplicipes did not parasitize larvae of three-lined leafroller, Pandemis limitata (Robinson) (Lepidoptera: Tortricidae) which is sympatric with oblique banded leafrollers in orchards in the southern interior of British Columbia. Female predation and host feeding from wounds on early instars of both leafroller species was observed under laboratory conditions. In addition, early instar hosts exited diet feeding sites in response to the probing activity of the ovipositing wasps. A similar escape reaction in the orchard may cause a leafroller larva to move away from its feeding site, making it more vulnerable to predation or movement off the tree. Apophua simplicipes larvae emerged from fifth and sixth instar hosts. Parasitized oblique banded leafroller hosts consumed significantly less meridic diet than unparasitized female larvae from fifth instar through to parasitoid emergence or leafroller pupation. Our laboratory results suggest that A. simplicipes may reduce field populations of oblique banded leafroller and decrease pest feeding damage.

Responses of Lipolexis oregmae (Hymenoptera: Aphidiidae) to different instars of Toxoptera citricida (Homoptera: Aphididae).

The effects of host instar of Toxoptera citricida Kirkaldy (Homoptera: Aphididae) on the performance of the parasitoid Lipolexis oregmae (Gahan) (Hymenoptera: Aphidiidae), originally Lipolexis scutellaris Mackauer, were evaluated in an effort to increase basic knowledge of this host-parasitoid association, improve field sampling methods, and potentially predict the success of parasitism in the field. L. oregmae was able to oviposit and develop in all four instars of T. citricida; however, there are differences in the quality of different host instars. Although second-instar hosts produce more L. oregmae progeny and a higher female-biased sex ratio, fourth-instar hosts produce L. oregmae progeny that are larger and have a higher realized fecundity. However, fourth-instar hosts require a longer handling time and expose the parasitoid female to more aphid behavioral defenses than do second-instar hosts. Additionally, results suggest that fourth-instar hosts may elicit a physiological immune response to parasitism; when aphids were observed being stung once, the number of L. oregmae larvae present on dissection after 4 d and the number of eclosed adults was lower in fourth- than in second-instar hosts. Pupal mortality of L. oregmae was also higher in fourth-instar hosts compared with second-instar hosts. The results of this study confirm that L. oregmae has a high reproductive rate and low incidence of incomplete parasitization on this host and is one of only a few natural enemies able to complete development in all instars of the brown citrus aphid in Florida.

Effects of Glyptapanteles liparidis (Hym.: Braconidae) parasitism, polydnavirus, and venom on development of microsporidia-infected and uninfected Lymantria dispar (Lep.: Lymantriidae) larvae.

Effects of parasitism, polydnavirus, and venom of the endoparasitoid Glyptapanteles liparidis on Lymantria dispar larvae infected with the microsporidium Vairimorpha sp. and uninfected hosts were studied. We tested the impact on growth and development of hosts, as well as on microsporidian infection. Both parasitism and polydnavirus/venom treatment alone caused a slight increase in growth rate and relative growth rate in uninfected fourth instar hosts. This effect was more pronounced with the addition of Vairimorpha infection. With no parasitism, however, infection reduced host growth markedly. Microsporidiosis delayed larval molts of L. dispar, and additional polydnavirus/venom treatment or parasitization induced significantly earlier molting. Polydnavirus/venom treatment of uninfected L. dispar resulted in prolonged larval development due to supernumerary molts and in higher pupal mortality. Infected larvae treated with polydnavirus/venom died earlier than infected larvae that were not treated and produced more Vairimorpha spores per unit fresh mass of the host.

Possible bases of pseudoparasitism in Spodoptera littoralis larvae stung by Microplitis rufiventris

The effects of host age and parasitoid female age on the occurrence of ‘Pseudoparasitism’, using the Spodoptera littoralis– Microplitis rufiventris host–parasitoid system were investigated. The first four larval instars of the host are not equally suitable for parasitoid development. The proportion of pseudoparasitized hosts significantly increases when: (1) the age of the female parasitoid increases; (2) oviposition occurs mostly in fourth instar larvae; (3) a later age of the host instar is used; (4) the mandibles of the newly hatched parasitoid larvae mistakenly attack host interior organs (e.g. Malpighian tubules); and (5) an imperfect growth pattern of teratocytes occurs. The reluctance of female wasps to parasitize fourth instar host larvae is not due to the thickness of host cuticle but possibly due to the unfavourable physiological state of the host larvae. The age of host larvae at the time of parasitization may influence the adverse effects of parasitoid factors (e.g. polydnavirus, venom and teratocytes) on the growth of host larvae. It is suggested that females of M. rufiventris are able to determine the suitability of a potential host instar for the development of their offspring. The cell diameter of M. rufiventris teratocytes increases with increasing age of host larvae at the time of oviposition. The association within the host of living parasitoid larvae and functional teratocytes may be important for the survival of each other and consequently for successful parasitism.

Cotesia orobenae (Hymenoptera: Braconidae), a Gregarious Endoparasitoid of Evergestis rimosalis (Lepidoptera: Pyralidae), and Hyperparasitoids in Virginia Brassica Crops

Abstract Cotesia orobenae Forbes (Hymenoptera: Braconidae) is a gregarious endoparasitoid of the cross-striped cabbageworm (Evergestis rimosalis Guenee) (Lepidoptera: Pyralidae), a minor pest of Brassica crops in Virginia. Cocoons of C. orobenae were collected, weekly, from field plots of broccoli and cabbage crops in Whitethorne, Montgomery County (VA) during 1989 and 1990. Counts were also made of the eggs and larvae of E. rimosalis to determine the pest′s seasonality. In January 1991, C. orobenae cocoons were collected from the held plots to see if C. orobenae overwinters within cocoons. In May 1993, trap plants bearing E. rimosalis larvae were placed among the field plants weekly to determine if C. orobenae adults are present and ovipositing early in the season. Field counts of E. rimosalis eggs and larvae in 1990 indicated the occurrence of three generations off. rimosalis from June to October, but parasitism of larvae on trap plants by C. orobenae in May 1993 suggested that the parasitoid is present in mid-May. C. orobenae oviposits in first through third instar E. rimosalis and the resulting larvae feed internally on the developing host, exit the fourth (last) instar host, and spin cocoons in a loose mass. Mean brood size of 118 C. orobenae field-collected cocoon masses was 9.2 ± 4.4 cocoons per mass. Out of 1085 cocoons, adult C. orobenae emerged from 77%, hyperparasitoids emerged from 7%, and nothing emerged from 16%. Females accounted for 73% of the emerging C. orobenae adults. Data from field-collected cocoons suggest that C. orobenae enter diapause in late September and overwinter in cocoons. Six pupal hyperparasitoids were recovered: Isdromas lycaenae (Howard) (Ichneumonidae); Conura (=Spilochalcis) torvina (Cresson) and Conura (=Spilochalcis) albifrons (Walsh) (Chalcididae); Hypopteromalus tabacum (Fitch), Catolaccus cyanoideus Burks, and Trichomalopsis viridescens (Walsh) (Pteromalidae).

DIAPAUSE INITIATION AND PUPATION SITE SELECTION OF THE BRACONID PARASITOID MICROPLITIS MEDIATOR (HALIDAY): A CASE OF MANIPULATION OF HOST BEHAVIOUR

AbstractMicroplitis mediator (Haliday), a braconid parasitoid reared on the bertha armyworm, Mamestra configurata (Walker), entered diapause at 16 °C and a 12L:12D (100%) or 14L:10D photoperiod (99%) but not at 16 °C or 21 °C under a 16L:8D photoperiod or at 21 °C and a 12L:12D photoperiod. Diapause development was accelerated by cold treatment; adults emerged from diapause more rapidly with increasing duration of cold exposure at least up to 120 days. The main pupation site was found to be on senescent canola leaves which formed a leaf litter on or near the plants. Nearly all unparasitized fourth-instar hosts (98–100%) were found on host plants, whether the conditions induced diapause or not. Only 16–23 and 0% of parasitoids pupated on host plants under conditions of non-diapause or diapause induction, respectively. Because the pupation site of the parasitoid depends on movement of the host, these results suggest that mature parasitoid larvae modify movement of their host.

Covariance of adult size and development time in the parasitoid waspAphidius ervi in relation to the size of its host,Acyrthosiphon pisum

Adult size (in terms of dry weight; DW) and development time (Tp) of the solitary parasitoidAphidius ervi varied when reared in different nymphal instars of its host, apterous virginoparae of the pea aphid (Acyrthosiphon pisum). Parasitoid DW increased with an increase in the DW of the host at parasitization, from the first to the third aphid instar. Female wasps gained 1.1 times more in DW than their male counterparts in all four host classes, butTp did not significantly differ between the sexes. Parasitoid DW was consistently more variable thanTp. The two traits covaried positively with an increase in host size from the first to the third instar, but they varied independently in parasitoids from fourth-instar hosts. The host size (and stage) at the time of parasitization imposes constraints on the growth and development of immatureA. ervi that are reflected in the pattern of covariation between DW andTp. When growing in aphids below a certain size threshold, parasitoids can maximize fitness by a trade-off between DW andTp. Consequently, the assumption implicit in host-size models of parasitoid oviposition decisions — that females incur a relatively greater reduction in size (used as an index of fecundity) than males when developing in poor quality hosts — can be falsified.

Seasonal cycles of Myiopharus aberrans and M. doryphorae (Diptera: Tachinidae) parasitizing Colorado potato beetles in upstate New York

Abstract Leptinotarsa decemlineata larvae in potato fields were parasitized by two species of Myiopharus: M. aberrans and M. doryphorae . In both species, males eclosed about 1 day earlier than females, and adult flies were active in July, August, and early September. M. doryphorae appeared to parasitize second-, third-, and fourth-instar larvae, and the parasitoid adults emerged from dead fourth-instar hosts. There were two or more generations per year; however, most parasitism occurred late in the season after a large proportion of the host population had entered diapause and dug into the soil. M. doryphorae's overwintering stage is unknown; this is a significant handicap in using this species in biological control. Unlike M. doryphorae , M. aberrans ' females parasitized only fourth-instar larvae, and its developmental time was approximately 2 days longer than that of M. doryphorae . M. aberrans ' life cycle also appeared to follow closely that of its host. Maggots that were larviposited early in July completed development and adults eclosed from fourth-instar hosts after they dug into the soil. Those that were larviposited late in the season entered an estival-autumnal-hibernal diapause, overwintered, and emerged from the adult beetles during the following spring. Moist soil conditions increased the incidence of successful emergence of M. aberrans from these beetles. Field populations of M. aberrans could be conserved and enhanced by habitat manipulation during spring and summer.