Moving on hairy surfaces: modifications of Gratiana spadicea larval legs to attach on its host plant Solanum sisymbriifolium

Both larvae and adults of Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae: Cassidinae) feed exclusively on leaves of Solanum sisymbriifolium Lamarck (Solanaceae), which have simple and stellate trichomes. The simple trichomes can be non-glandular or glandular. The stellate trichomes present a long central ray that secretes a viscous exudate when broken. Trichome effects on movement of G. spadicea larvae were evaluated in the laboratory. Larval speed on intact petioles of S. sisymbriifolium was compared to those where the exudates and/or stellate trichomes were removed. Exudates had no effect on larval speed. Stellate trichomes mechanically slowed down first instar movement. Gratiana spadicea larval legs have a modified distal portion, the tarsungulus, whose rounded aperture shape matches that of the cylindrical pointed rays of S. sisymbriifolium stellate trichomes. The first three instars anchor the tarsungulus to the trichome rays, and get both attachment to the leaf surface and support to body impulsion. Morphological comparisons showed that the legs in the first larval instars are shorter than the central ray of the stellate trichome, so larvae have to walk above them. Fifth instar larvae have longer legs and walk by inserting the sharp tip of their tarsungulus directly into the leaf epidermis. The dimensions of the tarsungulus aperture vary in such a way that it can clasp every thickness of trichome ray for any larval instar. Contrary to other tarsungulus portions and larval body features, where growth is allometric, growth of the tarsungulus aperture is isometric throughout the larval stage. Thus, it is suggested that this G. spadicea leg structure is adapted for moving on hairy leaf surface of S. sisymbriifolium.     

美洲斑潜蝇的寄主植物种类、适合度及其为害性的评价

在山西省调查结果,美洲斑潜蝇的寄生有２９种栽培植物,１１种野生植物,它们分属１６个科,其中以葫芦科,茄科和豆科的种类居多。应用选择系数法和适合性指数法定量测定了１６种常见寄生对美洲斑潜蝇的适合度,建立了选择强度与适合度估测模。根据适合度将美洲斑潜蝇的寄生植物划分为３个类型,即适宜寄主、较适宜寄主和次要寄主,在上述研究的基础上,测定了该在不同寄主上的虫道面积和蛹的重量,明确了不同寄主植物对害虫发育的     

Parasitism,host feeding and immature development of Encarsia formosa reared from Trialeurodes vaporariorum and Bemisia tabaci on Trialeurodes ricini

Encarsia formosa Gahan (Hymenoptera: Aphelinidae), a thelytokous parasitoid, is an important biological control agent of whiteflies because of its outstanding reproduction and host‐feeding ability. In this study, we evaluated the parasitism, host feeding and developmental time of E. formosa populations reared on Trialeurodes vaporariorum (Westwood) (EFT) or on Bemisia tabaci (Gennadius) (EFB) when different nymphal instars of the castor whitefly, Trialeurodes ricini (Misra), were offered as hosts, with an aim to understand the preference of the parasitoid on nymphal instars of T. ricini. Experiments were conducted on castor bean plants at 26 ± 2°C, 50–60% RH and 16 : 8 (L : D) photoperiod. The results showed that E. formosa successfully oviposited and fed on all nymphal instars of T. ricini. However, numbers of the first instars fed on by the E. formosa populations reared on T. vaporariorum (EFT) and B. tabaci (EFB) were significantly greater (45.9 and 31.3, respectively) than those of the second (EFT: 30.4 and EFB: 15.8), the third (EFT: 22.4 and EFB: 13.2) and the fourth nymphal instars (EFT: 6.0 and EFB: 3.8). The number of T. ricini nymphs parasitized by E. formosa varied significantly among different instars, and the parasitism rates on the first instar (EFT: 15.2; EFB: 7.7) and fourth instar (EFT: 19.3; EFB: 4.9) were greater than those on the second and third instars. Encarsia formosa reared on T. vaporariorum had a significantly higher host feeding and ovipositing potential on T. ricini than EFB. When parasitizing the fourth instar nymphs, E. formosa completed development in a significantly shorter time (12.9 day) than when ovipositing in other instars (17.8–19.1 day). These results showed that EFT had a better host adaption than EFB. The information from this study should be useful for us to better understand the performance and nymphal preference of E. formosa from T. vaporariorum and B. tabaci when they parasitized and fed on T. ricini, and the interactions of parasitoids with different host whitefly species.     

Effects of a host plant,Brassica juncea, on calling behaviour and egg maturation in the diamondback moth,Plutella xylostella

The influence of the presence of seedlings of a host plant, Oriental mustard,Brassica juncea (L.) Coss., on the calling behaviour and egg maturation in the diamondback moth,Plutella xylostella (L.), was investigated. In the presence of plants, females began calling at a younger age, began calling earlier in the night, and spent more time calling. Females which were kept with plants until after their first night of calling and then were isolated from plants, subsequently called less, at a level not significantly different from females which had never been exposed to plants. Of all females, both with and without plants, which were dissected at the end of the first night of calling (n=150), 93% contained mature eggs. Heavier females were significantly more likely to have mature eggs at adult emergence, to begin calling at a younger age and to spend more time calling on their first night of calling. The number of developed eggs in calling females was not significantly different in the presence or absence of host plants on the first night of calling. However, by the second night, females in the presence of plants contained significantly more eggs, indicating that the presence of plants accelerated egg maturation, both before and after the onset of calling.     

Host preference and suitability in the endoparasitoid Campoletis chlorideae is associated with its ability to suppress host immune responses

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Changes in host acceptance and host suitability as an effect of rearing Trichogramma maidis on a factitious host

Host acceptance and suitability of Ostrinia nubilalis Hbn. for Trichogramma maidis Pint. et Voeg. (Hymenoptera: Trichogrammatidae) were studied, after rearing the parasitoids on O. nubilalis or Ephestia kuehniella Oliv. (Lepidoptera: Pyralidae) for various numbers of generations. In cages, containing two maize plants with in total 30 egg masses of the natural host (O. nubilalis), wasps continuously reared on either E. kuehniella or O. nubilalis found egg masses in equal proportions. The former however, did not parasitize the eggs successfully, due to either low degree of host acceptance or insufficient host suitability or both. Subsequently, host acceptance behaviour of individual females from different strains was studied by means of direct observations after releasing them into a small arena containing eggs of O. nubilalis or E. kuehniella. Wasps continuously reared on O. nubilalis or 1–3 generations on E. kuehniella accepted egg masses of the natural host better than wasps continuously reared on E. kuehniella. Acceptance of O. nubilalis by the wasps gradually decreased with increasing numbers of generations reared on E. kuehniella. By rearing T. maidis, previously cultured on E. kuehniella, for five generations on O. nubilalis, acceptance of egg masses of this host species did not change. Host suitability of O. nubilalis appears to correspond with host acceptance of the strains. Contrary to the observations on O. nubilalis, acceptance and suitability of E. kuehniella were not influenced by the host on which T. maidis was reared. Results of this study show that host acceptance and suitability of the natural host are important quality factors for T. maidis when mass produced on a factitious host.

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Zusammenfassung Wirtsakzeptanz und Wirtseignung von Ostrinia nubilalis Hbn. für den Eiparasitoiden, Trichogramma maidis Pint. et. Voeg., wurden untersucht nach der Zucht auf dem natürlichen Wirt, O. nubilalis, oder auf dem Ersatzwirt, der Mehlmotte, Ephestia kühniella Zell.. Versuche mit Käfigen, in denen je zwei Maispflanzen mit insgesamt 30 Eigelegen von O. nubilalis und 40 Weibchen von T. maidis eingesperrt waren, zeigten, dass Weibchen, die seit über 150 Generationen auf O. nubilalis bzw. E. kühniella gezüchtet worden waren, die Eigelege gleich gut fanden. Während die auf O. nubilalis gezüchteten Parasitoide die Eigelege zu 80% parasitierten, war die Parasitierungsrate der auf E. kühniella gezüchteten Parasitoide gleich Null. Die Ursachen dieses Phänomens wurden in weiteren Versuchen durch direkte Beobachtungen über Wirtsakzeptanz und Wirtseignung untersucht. Einzelne Weibchen von Stämmen, die nur auf O. nubilalis oder während einer zunehmenden Generationenzahl auf E. kühniella gezüchtet worden waren, untersuchte man während 15 Minuten unter der Stereoskoplupe in einer kleinen Arena, die ein Eigelege des Maiszünslers oder Eier der Mehlmotte enthielt. Dabei zeigte sich, dass Wespen, die ausschliesslich auf Maiszünslereiern oder nur 1–3 Generationen auf Mehlmotteneiern gezüchtet worden waren, die Eigelege von O. nubilalis besser akzeptierten als solche, die seit vielen Generationen auf E. kühniella vermehrt worden waren. Die Wirtsakzeptanz verschlechterte sich mit zunehmender Generationenzahl auf E. kühniella. Wenn T. maidis nach 23 Generationen auf E. kühniella wieder während 5 Generationen auf O. nubilalis gezüchtet wurde, verbesserte sich die Akzeptanz der Eigelege von O. nubilalis nicht. Die Wirtseignung der Eigelege von O. nubilalis, stimmt überein mit der Wirtsakzeptanz der verschiedenen Stämme. Dies ergaben Versuche mit 15 Minuten Direktbeobachtung und bei 24 Stunden Expositionszeit. Im Gegensatz zu den Beobachtungen auf Eigelegen von O. nubilalis wurde die Akzeptanz und Eignung der Eier von E. kühniella durch die Zucht auf verschiedenen Wirten nicht beeinflusst. Das Ergebnis dieser Untersuchung zeigt, dass Akzeptanz und Eignung des natürlichen Wirtes wichtige Qualitätsfaktoren für T. maidis in der Massenzucht auf Ersatzwirten sind.

     

Differential selection of host plants by twoPieris species: the role of oviposition stimulants and deterrents

Oviposition responses ofPieris rapae L. andP. napi oleracea Harris to nine crucifers, one Capparidaceae and one Tropaeolaceae were directly compared under controlled conditions. Chemical fractions from these plants were also tested on both insects for the presence of oviposition stimulants or deterrents. The results showed that plant chemistry is a key factor in differential selection of potential hosts by thesePieris species. Some plant species were equally acceptable to bothPieris species. However,P. rapae preferred cabbage over most test plants whereasP. napi oleracea strongly preferred plant species that were avoided byP. rapae. The observed preferences were explained in most cases by the presence of stimulants and deterrents in extracts of the plants. The twoPieris species have apparently evolved differential sensitivities to the chemical stimuli that trigger or deter oviposition. The balance of positively and negatively interpreted sensory signals evoked by plant chemicals obviously plays an important role in acceptance or rejection of a plant by both species. The role of specific glucosinolates and differing structure-activity relationships is suggested.     

Performance on different host plants of an alien and an indigenous Bemisia tabaci from China

The capacity of the Middle East‐Asia Minor 1 putative species of the whitefly Bemisia tabaci (Gennadius) species complex, commonly referred to as the ‘B biotype’, to invade has often been linked to its presumed wider host range than the indigenous competitors. To determine whether this alien putative species and the indigenous Asia II 1 whitefly putative species, commonly referred to as the ‘ZHJ2 biotype’, differ in their ability to use different host plants, we compared their development, survival and reproduction on eight crop species/cultivars that are commonly cultivated in Zhejiang, China. Of the eight host plants tested, B performed substantially better than ZHJ2 on squash, tomato and tobacco, B and ZHJ2 preformed equally well on cotton and sweet potato, while ZHJ2 performed better than B on kidney bean and pepper. These results indicate that while B generally has a wider host range than many indigenous B. tabaci, an indigenous B. tabaci can perform as well as or better on some host plants. These results combined with the cropping patterns in Zhejiang suggested that the differential capacity to use various host plants between whitefly species is important in mediating the process of invasion by an alien whitefly species.     

Pollen beetle (Meligethes aeneus) oviposition and feeding preference on different host plant species

The oviposition and feeding preferences of the pollen beetle, Meligethes aeneus, were determined in choice and no-choice tests in field, semi-field and greenhouse trials. Plant species used were Brassica napus, B. campestris, B. juncea, B. nigra, B. carinata, Sinapis alba and Crambe abyssinica. With respect to number of eggs laid, S. alba and C. abyssinica were inferior to the other species. Pollen beetles laid fewer eggs on B. nigra than on the other Brassica spp. in no-choice tests, however this difference was partly due to fewer eggs laid per bud rather than fewer buds used for oviposition. Most eggs, for all plant species, were deposited in buds sized 2–3 mm. Feeding damage on all plant species was relatively similar. Pollen beetles seem to have a wider host range for feeding than for oviposition. There was good agreement in plant species ranking as oviposition hosts between the field, semi-field and greenhouse trials.     

扶桑绵粉蚧若虫对不同蔬菜寄主的选择性与适生性

测定了扶桑绵粉蚧2龄若虫对11科24种蔬菜的取食选择性。结果显示,在8种绿叶类蔬菜中,扶桑绵粉蚧对旋花科的空心菜具有较强的取食选择性;在8种果实类蔬菜中,扶桑绵粉蚧喜欢取食葫芦科的南瓜;在8种根茎类蔬菜中,扶桑绵粉蚧喜欢取食茄科的马铃薯和天南星科的芋艿。在11科蔬菜中,扶桑绵粉蚧比较嗜好茄科、葫芦科、旋花科、菊科、天南星科等科的蔬菜。24种蔬菜上,扶桑绵粉蚧的瞬时增长率ri均大于0,表明24种蔬菜均能满足扶桑绵粉蚧生长发育和种群增长的需要。综合比较扶桑绵粉蚧对寄主的选择性、种群建立率和瞬时增长率,认为扶桑绵粉蚧在马铃薯、南瓜、空心菜、生菜、芋艿、苋菜等蔬菜上的适生性较高,在大豆、豇豆、木耳菜等蔬菜上的适生性较低。     

The effect of herbivore density on host plant mediated interactions between two insects

Recent work suggests that foliar- and root-feeding insects can interact in a novel plus-minus fashion. However, the effects of herbivores may be different at different densities. This paper describes two laboratory experiments investigating the effect of increasing insect density on plant performance and the host-plant mediated interaction between a leaf-mining fly and root-feeding chafer larvae. Above- and below-ground insect herbivory decreased plant performance. The effects of the root feeder were, for some parameters, different between the two densities of chafer larvae. Leaf mining significantly decreased the performance of the chafer larvae, while root herbivory was found to increase the pupal weight (related to fecundity) of the leaf miner. The effects of root herbivory suggest that the relationships between herbivore density and plant performance may be curved as the greater chafer density had no significant increased effect on the plants or foliar-feeding insects.     

Influence of host species and age on host preference of Trissolcus semistriatus

Trissolcus semistriatus(Hymenoptera: Scelionidae) has a high potentialfor being an effective biological control agentfor the sunn pest, Eurygaster integriceps.This study was conducted to determine thepreferences of T. semistriatus in termsof host species and age of variousheteropteran host eggs (E. integriceps,Dolycoris baccarum, Graphosoma lineatum,Eurydema ornatum, Holcostethus vernalis). Theresults indicated that a small portion ofparasitism of E. ornatum eggs wasobtained (28.5%), although high parasitismrates were found in other host eggs(90.0–80.0%). A high percentage of adultemergence was also recorded. When tested for its ability toparasitize host eggs of different ages,T. semistriatus was found to preferyounger hosts: it showed parasitism ratesgreater than 50% with up to 3 daysold E. integriceps and D.baccarum, and with up to 4 days old G. lineatum and H. vernalis. However, theparasitism rates in all the ages of E. ornatum eggs were much lower than for other hostspecies. The developmental times in all hostspecies at different ages was extended withincreased host age. It was concluded that G. lineatum and D. baccarum could beused for mass production of egg parasitoids.     

8种寄主植物对朝鲜球坚蚧(Didesmococcus koreanus Broch)的适合度及自然种群增长的影响

在室外对8种寄主植物上朝鲜球坚蚧的刺吸、产卵以及种群动态进行了系统调查,并运用选择性指数(SI)、嗜食性指数(PI)、危害指数(DI)和种群趋势指数(I)等4种指数系统定量评价了8种寄主对朝鲜球坚蚧的适合度以及自然种群增长等的影响.结果表明,好、中、弱3种生长势的寄主对朝鲜球坚蚧的适合度由高至低的顺序均是桃、梅、李、杏、苹果、梨、樱和山楂;在一个生长季节内,8种寄主适合度总体变化均表现为正态分布形,呈弱-强-弱态势,都以6月份的8种寄主适合度表现最高,且以生长势好的寄主最高,中等的次之,弱的最差.朝鲜球坚蚧更趋向于梅、桃、李和杏寄主上刺吸取食和产卵,且若蚧存活率、卵的孵化率以及羽化率均较高,自然种群增长最快,4种指数均较大(SI>0.875、PI>5.469、I>5.75、DI>1.049).桃、梅、李和杏寄主是该蚧的最适宜类寄主;苹果、梨和樱寄主植物是适宜类寄主;山楂为次适宜类寄主.PI与DI间回归方程为:PI=0.3389 DI(r0.01=0.937).8种寄主表皮毛密度、长度、皮层厚度和枝条直径等物理结构与适合度的强弱均呈负相关(r0.01=-0.976),其对该蚧刺吸取食和产卵等行为起到抑制作用.山楂表皮毛密度、长度、皮层厚度和枝条直径分别是最适宜类寄主枝条4种物理结构指标平均值的2.73、3.27、2.77倍和3.47倍.这些对抗蚧育种、预测测报以及优化防治策略等具有一定的指导意义.     

Effects of Pieris host species on life history parameters in a solitary specialist and gregarious generalist parasitoid (Cotesia species)

Host specificity and host selection by insect parasitoids are hypothesized to be correlated with suitability of the hosts for parasitoid development. The present study investigates the correlation between host suitability and earlier studied host-finding behaviour of two closely related braconid larval parasitoid species, the generalist Cotesia glomerata (L.) and the specialist C. rubecula (Marshall) (Hymenoptera: Braconidae). We compared the capability of both parasitoid species to parasitize and develop in three Pieris host species, i.e. P. brassicae (L.), P. rapae (L.) and P. napi (L.) (Lepidoptera: Pieridae). In laboratory experiments, we measured the effect of host species on fitness parameters such as survival, development, sex ratio and size of parasitoid progeny. The results show that C. glomerata is capable of developing in the three host species, with significant differences in parasitoid survival, clutch size and adult weight among Pieris species. The host range for development was more restricted for C. rubecula. Although C. rubecula is physiologically able to develop in P. brassicae larvae, parasitoid fitness is negatively affected by this host species, compared to its most regular host, P. rapae. A comparison of the present data on host suitability with earlier studies on host-searching behaviour suggests that the host-foraging behaviour of both parasitoid species not only leads to selection of the most suitable host species for parasitoid development, but also plays a significant role in shaping parasitoid host range.     

Vestiges of an ancestral host plant: preference and performance in the butterfly Polygonia faunus and its sister species P. c‐album

1. In the study of the evolution of insect–host plant interactions, important information is provided by host ranking correspondences among female preference, offspring preference, and offspring performance. Here, we contrast such patterns in two polyphagous sister species in the butterfly family Nymphalidae, the Nearctic Polygonia faunus, and the Palearctic P. c‐album. 2. These two species have similar host ranges, but according to the literature P. faunus does not use the ancestral host plant clade – the ‘urticalean rosids’. Comparisons of the species can thus test the effects of a change in insect–plant associations over a long time scale. Cage experiments confirmed that P. faunus females avoid laying eggs on Urtica dioica (the preferred host of P. c‐album), instead preferring Salix, Betula, and Ribes. 3. However, newly hatched larvae of both species readily accept and grow well on U. dioica, supporting the general theory that evolutionary changes in host range are initiated through shifts in female host preferences, whereas larvae are more conservative and also can retain the capacity to perform well on ancestral hosts over long time spans. 4. Similar rankings of host plants among female preference, offspring preference, and offspring performance were observed in P. c‐album but not in P. faunus. This is probably a result of vestiges of larval adaptations to the lost ancestral host taxon in the latter species. 5. Female and larval preferences seem to be largely free to evolve independently, and consequently larval preferences warrant more attention.     

Oviposition vs. offspring fitness in Aphidius colemani parasitizing different aphid species

We measured the acceptance and suitability of four aphid species [Aphis gossypii Glover, Myzus persicae (Sulzer), Rhopalosiphum padi (L.), and Schizaphis graminum (Rondani)] (Homoptera: Aphididae) for the parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae). Female parasitoids parasitized fewer R. padi than the other three aphid species, and fewer offspring successfully completed development in R. padi than in the other three host species. Sex ratios of emerging adults were more male‐biased from R. padi than from the other three aphid species, suggesting that R. padi is a poor quality host for this population of A. colemani. Ovipositing A. colemani encountered R. padi at a slower rate, spent more time handling R. padi, and parasitoid offspring died at a higher rate in R. padi compared to A. gossypii. Our results show that oviposition behavior and offspring performance are correlated. In each experiment, we tested the effect of the host species in which the parasitoids developed (parental host) on the number of hosts attacked, the proportion of each host species accepted for oviposition and the survival of progeny. Parental host affected maternal body size and, through its effect on body size, the rate of encounter with hosts. Other than this, parental host species did not affect parasitism.     

Relative host plant species use by the lantana biological control agent Aconophora compressa (Membracidae) across its native and introduced ranges

Aconophora compressa Walker (Hemiptera: Membracidae) was released in 1995 against the weed lantana in Australia, and is now found on multiple host plant species. The intensity and regularity at which A. compressa uses different host species was quantified in its introduced Australian range and also its native Mexican range. In Australia, host plants fell into three statistically defined categories, as indicated by the relative rates and intensities at which they were used in the field. Fiddlewood (Citharexylum spinosum L.: Verbenaceae) was used much more regularly and at higher densities than any other host sampled, and alone made up the first group. The second group, lantana (Lantana camara L.: Verbenaceae; pink variety) and geisha girl (Duranta erecta L.: Verbenaceae), were used less regularly and at much lower densities than fiddlewood. The third group, Sheena’s gold (another variety of D. erecta), jacaranda (Jacaranda mimosifolia D. Don: Bignoniaceae) and myoporum (Myoporum acuminatum R. Br.: Myoporaceae), were used infrequently and at even lower densities. In Mexico, the insect was found at relatively low densities on all hosts relative to those in Australia. Densities were highest on L. urticifolia, D. erecta and Tecoma stans (L.) Juss. ex Kunth (Bignoniaceae), which were used at similar rates to one another. It was found also on a few other verbenaceous and non-verbenaceous host species but at even lower densities. The relative rate at which Citharexylum spp. and L. urticifolia were used could not be assessed in Mexico because A. compressa was found on only one plant of each species in areas where these host species co-occurred. The low rate at which A. compressa occurred on fiddlewood in Mexico is likely to be an artefact of the short-term nature of the surveys or differences in the suites of Citharexylum and Lantana species available there. These results provide further incentive to insist on structured and quantified surveys of non-target host use in the native range of potential biological control agents prior to host testing studies in quarantine.     

Host plant evaluation behaviour of Bemisia tabaci and its modification by external or internal uptake of imidacloprid

The behaviour of adult Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) was observed on leaves of cotton, Gossypium hirsutum L., to study the process of host plant evaluation. Seven distinct behavioural elements were identified and recorded for a period of 20 min after initial contact with leaves. The behaviour of the whiteflies was observed on untreated leaves or on leaves treated with either foliar or systemically applied imidacloprid. Thus, contact with imidacloprid by whiteflies was either via the external cuticle or by ingestion, allowing determination of the effect of uptake route on host evaluation behaviour. Analysis of behavioural sequences and comparison of latencies, frequencies and durations of elements of behaviour between treatments revealed that host evaluation behaviour was similar on untreated and foliar treated leaves, but markedly different on those treated systemically. After their first probe, whiteflies on systemically treated leaves were much more active, spending significantly greater time walking and dabbing the labium tip onto the leaf surface. There was also a 50% reduction in the total time spent probing into systemically treated leaves, compared to the other treatments. This effect was the result of a shorter mean probe duration, and no effect of treatment was found on the frequency of probing. Pre-oviposition behaviour was significantly more common on the systemically treated leaves, although the number of eggs laid was similar on all treatments. These results also show that the host evaluation phase of adult female B. tabaci was dominated by probing. The behavioural sequence that leads to probing was affected significantly by imidacloprid when ingested, but not by direct contact with this compound on the leaf surface. The wider implications for the mechanisms of whitefly–host plant interactions are discussed.     

Suitability of the maize weevil and angoumois grain moth as hosts for the parasitoidsAnisopteromalus calandrae andPteromalus cerealellae

Two parasitoids,Pteromalus cerealellae (Ashmead) andAnisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), were compared for their ability to parasitize two important internally-developing insect pests of stored maize (Zea mays L.). Parasitism byP. cerealellae was greater on Angoumois grain moth,Sitotroga cerealella (Olivier), than on maize weevil,Sitophilus zeamais Motschulsky, in no-choice experiments.Anisopteromalus calandrae parasitized more maize weevils than didP. cerealellae. The former parasitoid parasitized only a few Angoumois grain moths successfully in maize, but parasitized many in wheat if the hosts were younger than 3 weeks old. Thus, both host age and type of grain affect suitability for parasitism. The effects of parental host (species on which the female developed) and experimental host (species exposed to parasitism) on parasitism rate ofP. cerealellae were tested in a host-switching experiment. Parasitism by parasitoids reared on maize weevils was 23% lower than that of parasitoids reared on Angoumois grain moth. This effect was independent of which host the filial generation of parasitoids was tested on. However, the experimental host species had a much greater effect on parasitoid fecundity than the parental host species. Female progeny had smaller body sizes when emerging from maize weevil than from Angoumois grain moth, which may explain the parental host effect on fecundity. There was also a slight intergenerational effect of host species on parasitoid body size.     

Host plant recognition in monophagous weevils: Specialization ofCeutorhynchus inaffectatus to glucosinolates from its host plantHesperis matronalis

Several aphid honeydews were incorporated into sucrose solutions and presented to hop aphids, Phorodon humuli (Schrank), as artificial diets in free-choice bioassays. Small additions of honeydew collected from two species of aphid feeding on hop, Humulus lupulus L., arrested the searching behavior of the hop aphid and appeared to stimulate prolonged periods of ingestion. This effect was more dependent on the host plant honeydew source than the species of aphid that produced the honeydew. Aphid honeydews collected from plants other than hop (non-hosts to P. humuli) contained hop aphid phagostimulants that were less effective. Our results indicate that analysis of aphid honeydew could help describe chemical cues involved in the recognition of appropriate host plants by aphid species.