PRIMARY AND SECONDARY PARASITES OF AN ALFALFA-INFESTING APHID, THERIOAPHIS SP., IN MANITOBA

In 1984 and 1985 a total of 51 mummies of the genus Therioaphis sp. (Hornoptera: Aphididae) were collected on alfalfa, Medicago sativa L., in several localities in southern Manitoba: Glenlea, Oakbank, Rosenort, St. Adolphe, and Ste. Agathe [status of North American species of Therioaphis is uncertain; some workers regard Therioaphis on alfalfa and those on clover as different species, whereas others regard those found on alfalfa as merely strains of the species from clover (A.G. Robinson, personal comrnunication)]. The mummies were held in gelatin capsules at 20°C and a 16L:8D cycle, and 44 parasite adults that emerged were identified. Two primary parasites pecies. Praon exsolelurn (Nees) and Binodoxys sp. (Hymenoptera: Aphidiidae), were recorded (Table 1). Cocoons from which adults of P. exsoleturn emerged were formed between the mummy and the substratum, whereas cocoons of the two Binodoxys specimens were inside the mummies. The three secondary parasite species (Table 1) emerged only from the hosts with external cocoons and presumably had developed on P. exsoleturn. Each of the seven hosts from which no parasites emerged had an external cocoon which contained a decomposed parasite larva, either P. exsoletum or one of the secondary species.

The effect of superparasitism by Aphidius smithi (Hymenoptera: Aphidiidae) on the food budget of the pea aphid, Acyrthosiphon pisum (Homoptera: Aphididae)

The food budget of diet-fed, second-instar pea aphids when superparasitized by Aphidius smithi was similar to that of single-parasitized aphids. Aphids containing two parasite eggs or embryos consumed less diet and grew at a slower rate than did healthy controls. Feeding, assimilation, and growth increased significantly after the parasite larva(e) had hatched from the trophamnion. During the late stages of parasite larval development, host growth was increased by 133% and honeydew excretion by 146% over control values. During the same period, parasitized aphids converted ingested and digested food, respectively, with 66% and 86% greater efficiency than did controls. These increases were higher than in single-parasitized aphids, perhaps as a result of the larger number of teratocytes present in superparasitized hosts.

The effect of parasitism by Aphidius smithi (Hymenoptera: Aphidiidae) on the food budget of the pea aphid, Acyrthosiphon pisum (Homoptera: Aphididae)

Parasitism by Aphidius smithi affected the food budget of its host, Acyrthosiphon pisum, fed on a synthetic diet. During the embryonic stage of the parasite, the weight-specific rates of feeding, food assimilation, and growth were less in parasitized aphids than in controls. In the presence of a developing parasite larva, aphids ingested more food but assimilated it less efficiently; they achieved the same or a higher relative growth rate than nonparasitized aphids as a result of having either a higher feeding rate or a higher efficiency of incorporation of assimilated food, or both. Honeydew excretion was up to 129% higher in aphids containing a parasite larva. Parasitism by A. smithi did not obviate host feeding and capacity for growth until host size was sufficient for the successful development of the parasite larva.It is suggested that the nutritional requirements of the parasite larva differ from those of the aphid. Thus parasitism affects the homeostatic regulation of aphid feeding and food assimilation by causing an imbalance of nutrients in the host's haemolymph.

MICROCTONUS STELLERI (HYMENOPTERA: BRACONIDAE, EUPHORINAE), A NEW PARASITE OF THE ALFALFA WEEVIL INTRODUCED INTO THE UNITED STATES

Microctonus stelleri Loan is described as a new species. This euphorine braconid occurs in France, Germany, Sweden, and Russia. It is umvoltine and its only known host is the alfalfa weevil, Hypera postica (Gyllenhal). In the spring the mature parasite larva issues from the overwintered adult host and forms a white cocoon in the ground litter. In about 2 weeks the adult parasite emerges, mates, and oviposits in larva of the alfalfa weevil. The parasite egg hatches and the first-instar larva remains within the host until the following spring. In northern France M. stelleri was the dominant parasite in overwintering adults of H. postica. Parasitism ranged from 0 to 13% though it was usually less than 6%. Laboratory studies showed that M. stelleri females live longer, have a higher rate of oviposition, and parasitize more hosts than females of M. colesi Drea, a parasite of the weevil in the United Slates. A technique is described for the recovery of M. stelleri from adult alfalfa weevils. From 1966 to 1970, 4387 parasites were imported from France and released at 24 localities in the United States.

Preliminary studies on the biology of Orasema assectator Kerrich (Hym., Eucharitidae), parasitic on Pheidole and causing damage to leaves of tea in Assam

The so-called ‘sewing blight ’ of tea in Assam is an effect of oviposition in the young leaves by two species of Eucharitid, Orasema initiator Kerrich and O. assectator Kerrich. The affected leaves develop brown spots round the oviposition punctures, wither prematurely and adversely affect the quality of the made tea. Normally only a small proportion of bushes is affected and these are associated with the presence of nests of an undetermined species of Pheidole.An account is given of the life-history of O. assectator, and the developmental stages are briefly described. The eggs are laid singly in incisions made by the ovipositor on the underside of the leaf in parallel rows arranged lengthwise. The newly hatched larvae exist as free-living planidia on the leaf surface, whence they are carried by unknown means into the ants' nests in the soil beneath the tea bushes. Here the planidium transfers to the last-instar larva of the ant and penetrates its body. There it remains inactive until its host reaches the prepupal stage, whereupon endoparasitic feeding and development start. After the host pupa has formed, the parasite larva emerges, establishes itself below the thorax of its host, and remains there, feeding ectoparasitically, through two further instars, completely consuming the contents of its host. The mature larvae remain scattered in the ant's nest and pupate a few days later; both larvae and pupae are cared for by the worker ants.

Observations on Carcelia evolans (Wied.) (Diptera, Tachinidae), a parasite of Diparopsis watersi (Roths.) (Lepidoptera, Noctuidae), in Northern Nigeria

SummaryCarcelia evolans (Wied.) is a common parasite of Diparopsis watersi (Roths.) in Northern Nigeria. The egg and early larval stages have not been observed, but the latter are thought to be passed in the larva of the host. The fully grown parasite larva appears to leave its host after the latter has entered the soil and formed its pupal cell, and either immediately before, or after, the host pupates. The parasite puparium is thus formed inside the pupal cell of D. watersi, but outside the host. Before forming its puparium, the parasite larva excavates a pit in the wall of the cell, thus facilitating the subsequent exit of the adult fly, which can push through the weakened cell at this point.The life-cycle of C. evolans is closely adapted to that of its host, with short-term generations during the cotton season alternating with a long-term, or diapause, generation during the dry season. It is believed that C. evolans goes into diapause as a minute first-stage larva, but the factors that induce diapause are unknown.The short-term pupal period of C. evolans (12–14 days) was less variable than that of D. watersi (11–31 days) at 27±5°C. In dry conditions, inside and outside the laboratory, the mean duration of diapause for C. euolans (27·3–38·8 weeks) was longer than that of D. watersi (22·9–36·2 weeks). In pupation troughs, approximating to field conditions, the mean duration of diapause in D. watersi (43·2 weeks) was greater than that of its parasite (36·1 weeks). The spreadover of emergence of the parasite from pupation troughs was more regular than that of moths, with no peak in October.Earlier estimates of the incidence of parasitism at Samaru are probably inaccurate because adult flies have now been shown to be capable of escaping through the apertures of the perforated zinc of the cages then in use. Estimates of the rate of parasitism, made in southern Katsina, showed that 23·1 per cent, of pupal cells obtained at Daudawa between 13th November and 24th December 1959 from cotton that had earlier been treated with insecticidal sprays were parasitised, compared with 30·7 per cent. of those obtained in the same period from unsprayed cotton four miles away. The rate of parasitism was particularly low (16 per cent.) amongst the larvae collected at Daudawa in November, due possibly to the insecticide applications that had been made earlier in the season.These results imply that the parasite is easier to kill than its host, and an increasing use of insecticides on cotton in Northern Nigeria may therefore adversely affect the degree of control achieved by the parasite.

Pygostolus falcatus (Nees) (Hymenoptera, Braconidae), a parasite of Sitona species (Coleoptera, Curculionidae).

Pygostolus falcatus (Nees), an endoparasitic Braconid of the subfamily Blacinae, was reared from Sitona lineatus (L.), S. hispidulus (F.) and S. humeralis Steph. of Swedish origin. The life-history and immature stages of P. falcatus were studied in the laboratory at 74°F. and in field cages preparatory to its liberation in Canada as a control agent of the sweetclover weevil, S. cylindricollis Fhs.The immature stages develop in the haemocoele of the weevil. After deposition, the egg increases in volume to a maximum of 335 times. At eclosion, the cells of the trophamnion dissociate and increase in volume in relation to the growth of the larva. Supernumerary larvae are eliminated soon after eclosion, and one larva only develops in a host weevil. At 74°F., the final-instar larva emerges from the host weevil 15–16 days after deposition of the egg. Development of many first-instar larvae in a wide range of Sitona species was arrested by diapause. Five larval instars are described and illustrated. Oviposition is prevented in weevils in the summer of their development and eliminated in overwintered weevils by the parasite egg and first-instar larva. The weevil dies within hours of emergence of the parasite larva.Reproduction is parthenogenetic and thely tokous. The maximum number of eggs laid by a female was 46; the number of eggs laid per day per female varied from 0 to 11. Oviposition takes place both in light and in complete darkness and a preference among species of Sitona was not evident. The maximum number of weevils parasitised by a female in a field cage was 39; the number parasitised per day varied from 0 to 8.The species overwinters as a first-instar larva in weevils which became adult in the previous summer. There were two discrete parasite generations in 1958 in Swedish weevils, both of which developed in early and mid-summer within overwintered weevils. The maximum rate of parasitism of S. lineatus by larvae of the mid-summer parasite generation in 1958 was 73·3 per cent.The value of P. falcatus as a control agent of Sitona populations is limited by low parasitism of the new weevil generation of the current year and diapause of the first-instar larva.

Notes on Pseudendaphis maculans Barnes, a Cecidomyid Endoparasite of Aphids in Trinidad, B. W. I.

An account is given of the life-history of Pseudendaphis maculans Barnes, a common and widely distributed endoparsite of Aphids, especially of Toxoptera aurantii (Boy.), in Trinidad. Alates are parasitised to a much smaller extent than apterae : it is thought that this is due to the parasite larva inhibiting wing development. Nymphs appear to be attacked usually during the first stadium; the parasite larva is fully fed after 6 to 7 days. Shortly before the larve leaves its host the latter assumes a characteristic spotty appearance, due to numerous granules of dark matter that are readily visible through the integument, which has become paler and more transparent than normal. Pupation takes place in the soil: 9–10 days after leaving the host the adult emerges, invaribaly during the early afternoon.

THE LIFE CYCLE OF APANTELES CARPATUS (SAY) (HYMENOPTERA: BRACONIDAE), A PARASITE OF THE WEBBING CLOTHES MOTH, TINEOLA BISSELLIELLA HUM.

This parasite has been reared from larvae of the webbing clothes moth obtained from different localities as well as experimentally. All parasites obtained by natural and experimental infections were females. Oviposition occurred and parasites developed in host larvae weighing 1.6 to 6.8 mg. The parasites oviposited more readily in a host enclosed in a case, especially if the case contained fecal pellets of the host. Eggs were deposited in various parts of the host. A single parasite developed to maturity even though several eggs may have been deposited in the host, each by a separate "thrust" of the ovipositor. Morphological features of the larvae are illustrated. The rate of development varied even at constant temperature. The average length of the life cycle at 27 °C. was 26 days but at 20 °C. it required several months. Experiments were carried out to determine the factors responsible for the variation in the rate of development. The parasite larva, upon emerging from the host, usually spins a white, silken cocoon, although metamorphosis was sometimes completed even though no cocoon was produced.