Preferred Host Stage Research Articles

Host stage preference and parasitism behaviour of Aenasius bambawalei an encyrtid parasitoid of Phenacoccus solenopsis

ABSTRACTIn Pakistan, the cotton mealybug, Phenacoccus solenopsis Tinsley (Sternorrhyncha (Homoptera): Pseudococcidae), is a serious pest of many cultivated plants. A parasitoid, Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae), is associated with P. solenopsis. In order to mass rear A. bambawalei for a biological control programme, it is important to investigate the parasitoid’s host stage preference and its parasitism behaviour for P. solenopsis in order to optimise production. The present study showed that under both choice and no-choice conditions, the parasitoid preferred third instar and pre-reproductive host stage mealybugs for parasitism. Parasitoid larva developing inside the host exhibited a greater longevity, shorter developmental period and longer body size in these preferred host stages. Our study also confirmed that A. bambawalei showed no attraction to male mealybugs and no host feeding on any host stage was recorded. The ability of the parasitoid to effectively discriminate between suitable and non-suitable stages means that it is feasible to rear it on a mixed population.

Evaluation of Montandoniola confusa Streito and Matocq sp. nov. and Orius insidiosus Say (Heteroptera: Anthocoridae), for control of Gynaikothrips uzeli Zimmerman (Thysanoptera: Phlaeothripidae) on Ficus benjamina

Since its discovery in Florida in 2003, the weeping fig thrips, Gynaikothrips uzeli Zimmerman has spread rapidly throughout the southeastern United States in shipments of ornamental Ficus benjamina L. Concurrently, there have been reports of an invasive anthocorid, Montandoniola confusa (= moraguesi) Streito and Matocq sp. nov., widely associated with G. uzeli populations in landscape plantings of ornamental Ficus spp. We evaluated M. confusa and a commercially available anthocorid, Orius insidiosus Say, as biological control agents of G. uzeli. Prey preference studies revealed that eggs were the numerically preferred host stage for both predator species (representing 92% and 94% of all prey taken in ‘no choice’ and ‘choice’ tests, respectively). Females of both predator species consumed significantly more eggs than males (83–91 versus 25–35 per 48 h period, respectively), and (in the absence of eggs) also more larvae (4.1–5.5 versus 2.1–2.5). Fecundity of M. confusa was significantly higher than for O. insidious, 10.6 ± 1.5 eggs per 48 h versus 5.0 ± 1.4, respectively. Greenhouse tests on heavily infested F. benjamina revealed that M. confusa was a highly effective predator of G. uzeli. Evaluations with three F. benjamina cultivars showed that M. confusa reproduced throughout the year and reduced thrips populations ⩾95% and leaf galls by up to 77% within 5 weeks. By contrast O. insidiosus did not establish or significantly reduce populations of G. uzeli inside leaf galls. Methods to monitor and protect M. confusa in urban landscapes are discussed.

Preferred host stages, clutch size, and sex allocation by Cirrospilus coachellae (Hymenoptera: Eulophidae), a parasitoid of the citrus peelminer Marmara gulosa (Lepidoptera: Gracillariidae) with a view to its rearing and release as a biological control agent

Abstract Cirrospilus coachellae Gates (Hymenoptera: Eulophidae) is the principal parasitoid of larvae of the citrus peelminer, Marmara gulosa Guillen and Davis (Lepidoptera: Gracillariidae), in the desert grapefruit region of southern California and Arizona. M. gulosa or possibly a congener has recently been introduced into the San Joaquin Valley of central California, but without the parasitoid. Efforts have been underway to rear and release C. coachellae from southern California, so far without any success, and now Mexico. It is a synovigenic, facultatively gregarious, ectoparasitic idiobiont, whose clutch size depends on the size of its host. C. coachellae prefers the larger, sapfeeding instars (⩾0.35 mm) to which it allocates one to ten offspring per host larva (x = 2.5/host) infesting grapefruit both in the laboratory and the field. The sex ratio of C. coachellae offspring allocated to a M. gulosa larva is female biased both in the laboratory and the field and consisted mostly of a single male offspring coupled with a clutch of several female offspring or, less frequently, two male offspring associated with clutches of several female offspring. However, the pattern of sex allocation was more female biased for parasitoid clutches allocated to hosts parasitized in the laboratory than in the field and similarly sized clutches were more likely to be all female and they were allocated to larger hosts in the laboratory rearings than in the field parasitized hosts.

Behavioural responses in three ichneumonid pollen beetle parasitoids to volatiles emitted from different phenological stages of oilseed rape

AbstractPollen beetles (Meligethes spp.; Coleoptera: Nitiduliae) are a major pest of oilseed rape, Brassica napus L. (Brassicaceae) in northern Europe. Phradis interstitialis Thomson, P. morionellus Holmgr., and Tersilochus heterocerus Thomson (Hymenoptera: Ichneumonidae) are among the most frequent pollen beetle parasitoids. These three species differ in temporal occurrence, as well as in preferred host stage. The behavioural responses of female parasitoids to odours from oilseed rape at bud and flowering stage were evaluated in two‐choice experiments. The role of visual stimuli was examined by combining green and yellow colours with odour stimuli. All three species were attracted to odours from the bud stage of oilseed rape. Tersilochus heterocerus was attracted to odours of flowering rape, but the two Phradis species avoided the flower odours. However, when the odours of flowering rape were combined with yellow, and odours of the bud stage were combined with green, P. interstitialis was equally attracted to both stimuli, and T. heterocerus showed an increased preference for flower odours, while no effect of colours could be found in P. morionellus. The observed differences in responses between the parasitoids may reflect differences in their biology and may be involved in the niche segregation of these often coexisting species. The volatile blends released from the two phenological stages were identified and compared. Clearly, odours can be reliable cues for differentiating between oilseed rape in the bud and flowering stage. Of 20 identified compounds, 18 were released at a significantly higher rate from flowering plants. The terpenes sabinene, myrcene, limonene, and (E,E)‐α‐farnesene were the dominant volatiles in the bud and flower headspace. A group of aromatic compounds including benzaldehyde, methyl benzoate, and phenyl acetaldehyde were mainly released from flowering rape.

Temporal Synchrony BetweenMacrocentrus cingulum(Hymenoptera: Braconidae) with Its Preferred Host,Ostrinia nubilalis(Lepidoptera: Crambidae)

The seasonal occurrences of Macrocentrus cingulum Brischke and its host, Ostrinia nubilalis Hubner, were studied. Overwintering fifth-instar O. nubilalis were collected from the field in 1997, 1998, 2001, and 2002 and reared under controlled laboratory conditions to determine pupation and adult eclosion periods for M. cingulum and O. nubilalis. In addition, pheromone and yellow sticky traps were established in the field in 2001 and 2002 to monitor adult activity of O. nubilalis and M. cingulum. Mathematical equations were constructed based on the laboratory and field data. The equations confirmed the temporal co-occurrence of M. cingulum and O. nubilalis adults. However, third- and fourth-instar O. nubilalis, the preferred host stages of M. cingulum, occur later in the growing season. The timing of M. cingulum adult life expectancy and the occurrences of its preferred host stages in the field were predicted using the equations, published degree-day requirements for O. nubilalis and information from the literature on adult M. cingulum longevity. When the predicted period of M. cingulum adult activity was compared with the predicted timing of third- and fourth-instar O. nubilalis, M. cingulum adult presence was synchronized with preferred host stages.

Parasitoid Complex of the Mealybug Oracella acuta (Lobdell) (Hemiptera: Pseudococcidae), in Georgia, USA

The parasitoid complex of the mealybug Oracella acuta (Lobdell) was examined in two field populations in Georgia in 1995–96. Allotropa n. sp. and Zarhopalus debarri Sun were the primary endoparasitoids emerging from O. acuta. Adult abundance varied seasonally, with Allotropa n. sp. numbers peaking in June and Z. debarri in September. Parasitism rates of female O. acuta exceeded 60% at one site and ranged from 24 to 29% at the other site. The adult female was the preferred host stage for parasitism (76%), though Allotropa n. sp. and the endoparasitoid Acerophagus coccois E. Smith occasionally utilized second and third instar females as hosts. These two species exhibited gregarious parasitism, with up to 5 Allotropa n. sp. or 4 A. coccois emerging from a single host. Adult longevity of female and male Z. debarri averaged 6.4 and 5.3 days, respectively, and access to a food source usually increased adult lifespan. Female Z. debarri contained an average of 119 eggs, compared to 74 eggs per female for Allotropa n. sp.

Impact of the parasitoid Lathrolestes ensator (Hym., Ichneumonidae, Ctenopelmatinae) as antagonist of apple sawfly Hoplocampa testudinea (Hym., Tenthredinidae)

Abstract: Lathrolestes ensator (Brauns) was the only parasitoid species reared from larvae of apple sawfly Hoplocampa testudinea (Klug) collected in Dutch orchards. The life history parameters of apple sawfly and its parasitoid L. ensator were investigated in field and semi‐field experiments. Usually, the adult parasitoids emerge in synchrony with the preferred host stage, the second instar sawfly larvae. Parasitoid females carried 120–175 eggs, but never laid more than half this number. The mortality of sawfly eggs and larvae varied from 75 and 99%. The eggs and mining larvae are most vulnerable, as the older larvae survive for 90% on average. Three factors at least determine how many of the descending larvae become adult sawfly or parasitoid next spring. The failure of descending larvae to construct a cocoon varied from 7 to 31% and was highest in clay soil. Probably a similar mechanical hindrance prohibited more emerging adults, of both sawfly and L. ensator, from attaining the surface in heavier soils next spring. Relatively more sawfly prepupae than parasitoids died in the cocoon stage, from fungus disease or other causes, but more parasitoids than hosts stayed in prolonged diapause. Mainly due to this last factor, the overall result was a decrease of the parasitoid : host ratio during the first season underground. A life table based on survival rates during various life stages yields a net reproductive rate of up to 2.4 daughters per female sawfly. It indicates that 60% of the sawfly larvae need to be parasitized to stop population growth, or correspondingly less when more than 75% of the host eggs and young larvae are killed by predators or other causes.

Synthetic attractants for the bark beetle parasitoid Coeloides bostrichorum Giraud (Hymenoptera: Braconidae).

Coeloides bostrichorum Giraud parasitoids (Hymenoptera: Braconidae) attack late larval stages of various bark beetle species breeding in spruce. Volatile compounds collected from Norway spruce (Picea abies) infested by Ips typographus L. (Coleoptera: Scolytidae) were analysed by coupled gas chromatography-mass spectrometry (GC-MS) and GC-electroantennographic detection (GC-EAD). Monoterpene hydrocarbons are the predominant volatile compounds of fresh Norway spruce, while the presence of oxygenated monoterpenes indicates damaged trees. Between one and eight EAD-active oxygenated monoterpenes were used, in amounts reflecting their natural abundance in spruce trees containing bark beetle larvae, to prepare five synthetic baits which were tested in wind tunnel bioassays. Odour samples collected from spruce logs containing the preferred host stage were attractive, while similar samples from uninfested logs failed to elicit any flight activity. However, when a four- or an eight-component synthetic bait was added to volatiles collected from uninfested spruce logs, this combination was as attractive as volatiles collected from infested spruce logs.

VIPOSITIONAL BEHAVIOR OF THE PARASITOID PALEXORISTA LAXA (DIPTERA: TACHINIDAE) ON HELIOTHIS ZEA (LEPIDOPTERA: NOCTUIDAE) LARVAE

The distribution and number of eggs deposited by the tachinid parasitoid Palexorista laxa (Curran) on instars of Heliothis zea (Boddie) were studied. Significantly more eggs were deposited on the thoracic segments of instars 2–5 than on the head or abdominal segments. This may be an adaptation by the parasitoid to avoid removal of the eggs by the host's mandibles. This selectivity of egg placement was not observed on first instars or prepupae. Significantly more eggs were deposited on fourth instars than on any other host developmental stage, suggesting that this may be the preferred host stage for parasitization.

Air-assisted electrostatic application of permethrin to glasshouse tomatoes: Droplet distribution and its effect upon whiteflies ( Trialeurodes vaporariorum) in the presence of Encarsia formosa

An air-assisted electrostatic sprayer, producing 18 μm VMD droplets, applied permethrin to the apical foliage of a glasshouse tomato crop. The deposit on abaxial surfaces provided efficient control of first-instar whitefly larvae, Trialeurodes vaporariorum, while minimizing direct contamination of developing fruit and foliage where larval stages preferred for parasitization by Encarsia formosa occur. Coverage of the inner leaves was less than on peripheral foliage, but the efficiency of droplet distribution was better, indicating approximately equal effectiveness. Parasitization was greater on untreated rows, which had a higher density of preferred host stages than the sprayed plants. Sooty mould completely spoiled the fruits picked from unsprayed rows during August, compared with 30–40% clean fruit on the treated rows. Total yield did not differ between rows.

Studies in Ovipositional Behaviour and Control of Sex in Aphytis Melinus Debach, a Parasite of California Red Scale, Aonidiella Aurantii (Mask.).

The growing adult female red scale was the most preferred stage for A. melinus, followed by the second growing instar and lastly the male prepupa. The numbers of scale parasitized, the total of eggs laid, the number of eggs per scale, sex ratio and size of the parasites produced were all ranked in the same order. The mean size of parasites produced within the third instar decreased as the number of parasites per host increased. In the absence of the preferred host stages, female A. melinus laid readily in the unpreferred stages. In both A. melinus and A, chrysomphali it was noted that in multi- parasitism pupation, pupal development and adult emergence of all parasites in one host were synchronized. In A. melinus the sex and number of eggs laid per host are influenced by the host's size and quality. When A. melinus laid more than one egg in one host, it laid female eggs first and male eggs later; apparently the spermatheca goes through a period of fatigue, and is incapable of delivering sperm to the eggs descending the oviduct. Sex ratio decreases with increase in number of parasites per host and density of parasite population relative to hosts. The deposition of parasite eggs in a host by one female was observed during a short cycle of oviposition. A. melinus laid its eggs both 'above' and 'below' the body of the scale, whereas A. chrysomphali did so exclusively 'below'. In young mated A. melinus, eggs laid above the body of the scale were females and those below were males, but in old mated females all eggs, wherever laid, were male. Host development stops as soon as a parasite egg is laid. A. melinus avoids laying eggs in already parasitized hosts. The stages of red scale were ranked according to the percentage of mutilated individuals as: first moult (most mutilated), second instar, first instar, third instar, male prepupa and male pupa; second-moult females, egg-maturation stage and crawler-producing stage were unmutilated. A. melinus sometimes partitions her clutch of eggs into two hosts, particularly when host density is high. Partitioning in A. melinus may substitute for the generally accepted practice of super- parasitism, which would not be appropriate because the parasite is able to distinguish between parasitized and unparasitized hosts, is able to sense host density and to distribute her progeny on available hosts. Partitioning is advantageous for biological control. Behaviour of oviposition, mutilation and mutilation feeding in A. melinus are described in detail.