The preference of Trichopria drosophilae for pupae of Drosophila suzukii is independent of host size

Controlling the cosmopolitan pest Drosophila suzukii (spotted wing drosophila) is a challenge for fruit growers. A promising agent for biological control of that pest are parasitoid wasps. Especially the widespread pupal parasitoid Trichopria drosophilae had shown the ability to parasitise the pest fly. However, as a biocontrol agent, parasitoids can only be effective when they prefer the pest to other insects. Until now studies have been inconsistent concerning the preference of T. drosophilae for D. suzukii and whether the preference depends on pupal volume. To clarify this inconsistency, we used video recordings of parasitisation experiments with a set up to observe the direct host preference of the parasitoid. Additionally, the volume of each host pupa was measured. We found significant preference of T. drosophilae for D. suzukii pupae independent of the pupal size and of the host species the wasps were reared on. The article also discusses the sex ratio and the success of the parasitoid in the different pupae characteristics.

Some Biological and Behavioral Studies of the Tetrastichus sp. (Hymenoptera: Eulophidae), a Pupal Parasitoid of Brontispa longissima Gestro (Coleoptera: Chrysomelidae)

The Tetrastichus sp. was identified as a pupal parasitoid indigenous to the Philippines. The total development period of Tetrastichus sp. from egg to adult was 16 days under laboratory conditions. The average incubation, larval and pupal periods were 3.5, 4.8, and 7.4 days, respectively. The average adult longevity was 5.5 (male) and 6.4 (female). Upon emergence of an adult wasp from the host pupa, mating took place shortly and the female look for suitable host pupa of Brontispa longissima for oviposition. Tetrastichus sp. is an endogregarious parasitoid. From one parasitized pupa of Brontispa longissima, around 6 - 66 individual wasps emerged with a mean of 22.4 while parasitized pupae collected from the field yielded 4 - 21 individuals with a mean of 12.7. Majority of the wasps emerged in the morning (70%) while 30% emerged in the afternoon. Sex ratio of male and female was 1:5.4 in laboratory condition while 1:3.7 under field condition with females outnumbered the males. Tetrastichus sp. was observed in some cases to reproduce parthenogenetically. Longevity of Tetrastichus sp. can be enhanced to a mean of 7.3 and 6.0 days by feeding on sugar and honey, respectively while water and coconut pollen resulted in longevity of 3.3 and 2.4 days, respectively. Adults without food lived only one day. Parasitism efficiency ratio of 10 parasitoids: 10 host pupae resulted in 90% parasitism. One to two day old pupa of B. longissima was preferred by Tetrastichus sp. for oviposition with a mean of 86.7% parasitism. Percent pupal parasitism in the field ranged 25.7 - 42.3% with an average of 27.6% in selected areas in Mindanao. Tetrastichus sp. was found to effectively control B. longissima under field condition. The study indicated that Tetrastichus sp. is an effective control agent of B. longissima and could be used in the field to prevent economic damage of the palms by the pest.

Two different life-history strategies determine the competitive outcome betweenDirhinus giffardii(Chalcididae) andPachycrepoideus vindemmiae(Pteromalidae), ectoparasitoids of cyclorrhaphous Diptera

Dirhinus giffardiiSilvestri andPachycrepoideus vindemmiaeRondani are solitary parasitoids attacking puparia of many cyclorrhaphous flies. They are not typical ectoparasitoids, as they feed on host pupae within puparia that develop from the exoskeleton of host larvae.Dirhinus giffardiidid not kill its host until the parasitoid egg developed into a larva, whileP. vindemmiaepermanently paralysed its host at the time of oviposition. As a result, ovipositing into a young host puparium (< 1 day old) in which the host pupa has not yet fully formed resulted in complete death of offspring inP. vindemmiae, butD. giffardii, although suffering higher mortality than in older host puparia, still showed a level of successful development. In a choice experiment, both parasitoids preferred to attack 2- to 3-day-old puparia in which the host pupae had fully formed, rather than 1-day-old host puparia.Pachycrepoideus vindemmiaealways prevailed in competition because it injected venom that not only paralysed the host, but also caused the death ofD. giffardiilarvae in multi-parasitized hosts.Dirhinus giffardiipreferred to attack unparasitized hosts rather than hosts previously parasitized byP. vindemmiae, whileP. vindemmiaedid not show a preference between unparasitized hosts and hosts previously parasitized byD. giffardii.

Ichneumon promissorius (Erichson) (Hymenoptera: Ichneumonidae): Factors Affecting Fecundity, Oviposition, and Longevity

Ichneumon (=Pterocormus) promissorius (Erichson) (Hymenoptera: Ichneumomidae), a native of Australia, is a pupal parasitoid which searches the soil surface for host pupation sites, burrows into a pupal gallery, and oviposits in the host pupa. Fecundity and rate of oviposition were influenced by the mating status of females, the host from which females developed, and the frequency in which females were exposed to hosts. Virgin females continued laying eggs many days after mated females had stopped. A preoviposition period of 17 d in mated females did not affect the oviposition curve or the number of eggs laid, suggesting that the oogenesis is arrested until female wasps are exposed to host pupae. Female wasps exposed to pupae for 24 h every fifth day lived longer than female wasps continuously exposed to pupae. However, females that were continuously exposed to pupae laid more eggs. Virgin females reared on Spodoptera exigua (Hübner) pupae laid fewer eggs than virgin females reared on Helicoverpa zea (Boddie) pupae. These data will be important in evaluating the potential of I. promissorius as a biological control agent for pest species in the United States and will be useful in developing laboratory rearing procedures for I. promissorius.

SEASONAL DEVELOPMENT, BEHAVIOR, AND HOST SYNCHRONY OF DACNUSA DRYAS (NIXON) (HYMENOPTERA: BRACONIDAE) PARASITIZING THE ALFALFA BLOTCH LEAFMINER, AGROMYZA FRONTELLA (RONDANI) (DIPTERA: AGROMYZIDAE)

Studies in eastern Ontario showed that the exotic parasite Dacnusa dryas (Nixon) typically has three generations a year that correspond seasonally to those of its host, the alfalfa blotch leafminer, Agromyza frontella (Rondani). The mature larvae of the third generation enter diapause in September and resume development in the spring. The egg – first instar interval, which occurs within the actively feeding leafminer, developed at rates similar to those of the host larva. The remaining two instars and the pupa, which occur within the host puparium, developed at rates similar to those of the host pupa; in the two non-diapausing generations, the durations of these stages decreased with rise in temperature from 13 to 23 °C. Coincidence of wasp flight and hatch of leafminer eggs was high in all three generations. This host–parasite synchrony results mainly from a sequence of three events during their life cycles: lack of development of the parasite beyond the first instar within the host larva, a temperature-dependent rate of development of the subsequent stages which is similar to that of the host pupa, and different overwintering strategies which result in the parasite emerging later than its host to sustain the relationship. Behavior of the parasite is described in relation to host detection, egg deposition, and reproduction.

Aspects of the biology and behavior of Nesolynx sp. (Hymenoptera, Eulophidae)

This research was carried out to study some aspects of the biology and behavior of Nesolynx sp. (Hymenoptera, Eulophidae), a pupal parasite of Psorocampa denticulata (Lepidoptera, Notodontidae) a defoliating caterpillar of Eucalyptus spp. in Brazil. The adults emerge from the host pupa through a circular hole on Its dorsal region. Mating occurs righ after the emergence and the longevity of adults was two days for the males and four days for the females. Regarding to the host species Diatraea saccharalis showed a number of adults significantly greater than Galleria mellonella and the increasing temperature from 21±1 °C to 26±1°C caused a significative increasing in the number of emerged adults in both host species. The emergence of adults increased proportionally to the period of exposition to the host up to 3.50 days; after that, a considerable decrease in the emergence was observed. The parasitoid showed parthenogenetic reproduction therefore the average number of emerged males was significantly greater than the number of females. The sex ratio was similar for the insects emerged from virgin or mated females (0,96) and the life cycle lenght was around 18.34 days for both conditions.

DIADEGMA INSULARIS (HYMENOPTERA: ICHNEUMONIDAE) PARASITISM OF THE DIAMONDBACK MOTH (LEPIDOPTERA: PLUTELLIDAE) IN SOUTHWEST VIRGINIA

Parasitization rates of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), by Diadegma insularis (Meus.) (Hymenoptera: Ichneumonidae) were determined in a pesticide-free cabbage planting in Southwest Virginia. Diadegma insularis, which parasitizes later instars of the host larvae but emerges from the host pupa, was responsible for 46% and 69% of the mortality in 1983 and 1984, respectively. Higher parasitization rates were found in pupae collected from the Abbott and Cobb #5 cabbage variety, even though infestations of diamondback moths were higher on other varieties. Although most pupation of the diamondback moth occurred on the lower cabbage leaf surfaces, the proportion of parasitized hosts found on upper versus lower leaf surfaces did not differ significantly.

ARTIFICIAL DIETS FOR THE ADULT PARASITOID ITOPLECTIS CONQUISITOR (HYMENOPTERA: ICHNEUMONIDAE)

Two artificial diets — one liquid, the other candied — developed for adult Itoplectis conquisitor, an ichneumonid parasitoid, proved equal in performance for fecundity to a natural food regimen involving blood of host pupa, Galleria mellonella. Feeding on the liquid diet resulted in a parasitoid emergence rate from host pupae of 42.9 ± 8.6%; on the candy diet, 52.2 ± 15.8%; and on the natural regimen, 54.4 ± 4.0%. Therefore, host material was not needed to feed the adults. Other advantages of these artificial diets include convenience, economy, efficacy, and manageability for proper insect husbandry.

Notes on the distribution and biology of Pediobius furvus (Gah.) (Hym., Eulophidae), a parasite of graminaceous stem-borers

Pediobius furvus (Gah.) (Eulophidae) is a parasite of the pupae of Pyralid and Noctuid stem-borers on graminaceous crops in Africa between 17°N and 17°S. It co-exists with the other pupal parasites Dentichasmias busseolae Heinr. and Procerochasmias nigromaculatus (Cam.) (Ichneumonidae) and Hyperchalcidia soudanensis Steffan (Chalcididae), but it is more abundant below 4000 ft where P. nigromaculatus does not occur. Mating follows a courtship dance, and oviposition occurs in any part of the host pupa. The life-cycle is completed in 18–20 days at 30°C, and up to several hundred adults may emerge from a single host pupa, the most suitable pupae being 2–3 days old at the time of oviposition. Longevity was improved when sucrose was provided as food. Host pupae outside the stem were parasitised, but puparia of Diptera and cocoons of Apanteles sesamiae Cam. (Braconidae) were not parasitised in the laboratory. Pupae formed inside cocoons were not attacked. Pediobius furvus has become established in Madagascar on Sesamia calamistis Hmps, and is considered promising for biological control of graminaceous stem-borers in other countries.

ECOLOGICAL OBSERVATIONS ON CHRYSOCHARIS LARICINELLAE (HYMENOPTERA: EULOPHIDAE), A PARASITE OF THE LARCH CASEBEARER (COLEOPHORA LARICELLA)

An account is given of host acceptance, the influence of temperature on fecundity and longevity, and searching capacity of Chrysocharis laricinellae (Raczeburg), a parasite of the larch casebearer, Coleophora laricella (Hübner).Fourth-instar case-bearing larvae were the preferred stages for attack. The size of the parasite progeny varied directly with the size of the host. Fecundity of progeny reared from small hosts was significantly less than that of progeny reared from large hosts. Not all parasite adults could successfully oviposit through the tough skin of the host pupa. C. laricinellae showed poor searching capacity. Superparasitism was common at low host densities of the casebearer and resulted in either one parasite emerging or in total parasite mortality. A sex ratio where females predominated resulted when sufficient numbers of preferred stages of the host were presented to mated C. laricinellae. The temperature threshold for attacking hosts was 55°F, and for development of the parasite 40°F. At 50°F the adults lived 4 months on the average.Therefore C. laricinellae is able to survive in the field without alternate hosts and at very low host densities. The parasite seems to depend on a continuing supply of suitable instars of host species in sufficient numbers to be effective. If C. laricella is the only available host species in the ecosystem the biological control value of this chalcid must be rated as poor.