Ovipositional Synergists and Artificial Diets for Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae)

We studied ovipositional synergists and artificial diets for rearing Trichogramma australicum. Artificial "diet A" included 40% haemolymph of Helicoverpa armigera (Hübner) final instar larvae, 30% of a 10% malt solution in deionised water, 20% chicken egg yolk and 10% Neisenheimer's salt solution with 76 units Penicillin and 76 units Streptomycin/ml diet. Artificial "diet B" was identical except Grace's insect medium® replaced Neisenheimer's salt solution. the number of T. australicum larvae in artificial eggs filled with diet A and diet B was not significantly different (P > 0.05). Significantly fewer (P < 0.05) larvae developed to pupae and adults in artificial eggs filled with diet A. Quantity and quality of artificial diet affected the mortality of T. australicum larvae reared in vitro. Ovipositional synergists included 10% gelatine solution, 10% polyvinyl alcohol solution or 1% agar solution in deionised water. Synergist test-solutions were individually smeared on the external surface of artificial eggs (hemispherical depressions in plastic membrane). Eggs laid and number of T. australicum larvae produced were significantly higher in artificial eggs smeared with gelatine than artificial eggs smeared with polyvinyl alcohol, agar or non-smeared (control) eggs.     

Oviposition Behaviour and Reproductive Performance of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) Reared in Artificial Diet

Biotypes of Trichogramma australicum were reared on artificial diet "A", Helicoverpa armigera (Hübner) (natural host) eggs and Sitotroga cerealella (Olivier) (factitious host) eggs. We evaluated the quality of these biotypes by comparing their oviposition behaviour and reproductive performance on H. armigera eggs. Female T. australicum reared in vitro accepted H. armigera eggs for oviposition and displayed similar behavioural components of oviposition to females reared on natural hosts. However, handling time during oviposition in H. armigera eggs by females from in vitro rearing was significantly longer than handling time of females reared on the natural host because the females needed a significantly longer time for host feeding. In vitro reared females produced significantly more progeny and parasitised more H. armigera eggs than the females reared on S. cerealella. Improvements to the artificial diet for T. australicum may reduce handling time of the in vitro reared females and increase the female population. These improvements may include changes in nutrient content and size of the artificial eggs.     

Biology of Campoletis chlorideae (Uchida) (Hym., Ichneumonidae) developing in Bt-treated, Bt-resistant Helicoverpa armigera (Hübner) (Lep., Noctuidae) larvae

Abstract:  Life history parameters in two generations of endoparasitoid Campoletis chlorideae (Uchida) were examined using Bacillus thuringiensis (Bt)-resistant Helicoverpa armigera (Hübner) larvae feeding on B. thuringiensis toxin Cry1Ac. In the laboratory, Bt toxin was fed to Bt-resistant host larvae continuously in case of Bt treatment and only before or after the host larvae were parasitized in Bt–P and P–Bt treatments, respectively. C. chlorideae pupae developed faster in Bt treatment than non-Bt treatment. The shortened pupal stage duration was mainly because of the feeding of host larvae on Bt-diet before being parasitized. Body length of adult male C. chlorideae developed inside Bt-treated Bt-resistant (Bt–Bt) H. armigera larvae significantly decreased, especially in host larvae feeding on Bt-diet after being parasitized. However, survival, pupal mortality and adult longevity of C. chlorideae were almost unaffected in Bt-resistant H. armigera larvae feeding on Bt-toxin. Furthermore, Bt-treated host larvae had the same effect on the F₁ progeny of C. chlorideae as the previous generation, and there was no significant difference between generations. This experiment suggests that there is very limited effect on the life history parameters in two generations of C. chlorideae parasitizing Bt–Bt H. armigera larvae. But both generations of C. chlorideae are affected when Bt-resistant H. armigera larvae fed on Bt toxin for different durations.     

Influence of rearing hosts on host size acceptance by Trichogramma australicum

We investigated the acceptance of different sized host models by Trichogramma australicum in the laboratory. We used isoline cultures of T. australicum reared in hosts of different sizes. Helicoverpa armigera represent relatively large hosts, and those of Sitotroga cerealella are small, termed the Ha and Sc biotypes, respectively. Five sizes of glass beads were tested for acceptance: diameter 0.5, 0.75, 1.0, 1.5 and 2.0 mm. The acceptance of a host model was determined by persistent attempted drilling of a glass bead by a female. The relationship between host egg size and number of eggs laid by a female was also investigated. We used three sizes of artificial egg (diameter 0.75, 1.00, and 1.50 mm of hemispherical cupules) each containing artificial diet. Ha biotype wasps accepted host models in the range 0.75--1.50 mm dia. (vol. 0.166--1.325 l), whereas those of the Sc biotype accepted host models in the range 0.50--1.00 mm dia. (vol. 0.05--0.393 l). This evidence suggests a lineal (possibly genetic) influence to host size acceptance for T. australicum, dependent on the size of the host in which the wasp has been reared. Also T. australicum lay fewer eggs in smaller artificial eggs than in larger ones. The role of host size in host acceptance and number of eggs delivered, and its implications, is discussed.     

Effects of physiological condition and experience on oviposition behaviour of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) on eggs of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

We produced an ethogram for and investigated effects of physiological condition and experience on oviposition behaviour for Trichogramma australicum on Helicoverpa armigera eggs. The data, coupled with the ethogram, have enabled the establishment of standard behavioural categories which can be used to assess acceptability of H. armigera eggs to T. australicum reared in vitro or in eggs of other species. Physiological and experiential conditions were investigated using females of three different ages (0–24, 24–48 and 48–72 h old), two types of sexual states (mated and unmated) and two types of ovipositional experience (naive and experienced). Durations of host finding, host examination, and post-ovipositional re-examination were reduced by oviposition experience and were shorter in younger females (0–48 h old). Oviposition experience reduces the duration of the drilling and percentage of females host-feeding. Being mated and young reduces the host examination time in subsequent oviposition bouts. Only ovipositionally inexperienced females host-feed before oviposition and host-fed more frequently than experienced individuals after oviposition. Host-feeding needs consideration for optimal culture.     

Host-dependent differences in prey acquisition between populations of a kleptoparasitic spider Argyrodes kumadai (Araneae: Theridiidae)

Abstract.  1. A kleptoparasitic spider, Argyrodes kumadai , is known to use phylogenetically unrelated host species in different regions – Cyrtophora moluccensis (Araneidae) in south-west Japan and Agelena silvatica (Agelenidae) in north-east Japan. The work reported here examined whether differences in host characters affect prey acquisition of A. kumadai .
2. Field surveys showed that prey-biomass capture rate of Argyrodes was significantly higher in populations parasitising Cyrtophora than in populations parasitising Agelena . Although Argyrodes appeared to catch fewer prey within Cyrtophora webs, they were able to feed upon substantially larger prey.
3. Differences in prey-biomass capture rate were found to reflect differences in host traits rather than regional differences in potential prey availability. Individuals in populations parasitising Cyrtophora were observed to acquire prey via a number of foraging tactics that included stealing wrapped food bundles, feeding upon prey remains and, in the case of large prey items, feeding together with the host. In contrast, individuals in populations parasitising Agelena were only ever observed to feed upon small prey items ignored by its host.
4. This variability in prey acquisition between kleptoparasite populations reflected different opportunities for feeding within their respective host webs – opportunities that were primarily determined by the foraging behaviour of the host. One key trait associated with host foraging behaviour was host-web structure, namely the presence/absence of a retreat.     

Experience acquisition by Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae)

We investigated experience acquisition (alpha-conditioning) by females of the parasitoid Trichogramma australicum using host eggs of the noctuid moth Helicoverpa armigera (Hübner). We compared the acceptance of a host egg by females with different levels of ovipositional experience. The level of experience was designated using the standard oviposition sequence: (1) host contact (C); (2) host examination (E); (3) drilling (D); (4) full insertion (FI); and (5) oviposition (O). Each treatment consisted of a single experience level, but together these consituted a qualitative behavioural continuum of oviposition experience from naive (N) to experienced wasps. We found that host experience by adult T. australicum females can modify their behaviour. Mean duration of host finding was: N = C > E = D > FI = O. Mean duration of host examination and full insertion were: N = C > E = D = FI = O. Drilling was constant for all experience levels. Experience in drilling of the chorion during the previous host-exposure process represents a critical experience for a female and results in efficient handling and more ready acceptance of a subsequently encountered host egg.     

Effect of sorghum resistant to Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae) on oviposition and development of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract Helicoverpa armigera oviposition preference for, and larval development on sorghum hybrids with differing resistance to sorghum midge, Stenodiplosis sorghicola , were investigated. When H. armigera larvae were fed seed of resistant and susceptible hybrids in the laboratory there were no differences in larval and pupal sizes or the rate of development. The same result was recorded when larvae fed on panicles on plants in a glasshouse. On some sampling occasions, significantly more eggs were laid on panicles of resistant hybrids in the field. This occurred when plants were in plots and also in a mixed planting. Midge-resistance status did not affect levels of egg parasitism. In a field study using recombinant inbred lines between a midge-resistant and a midge-susceptible line, no relationship was found between level of resistance and oviposition of H. armigera . We conclude that, although midge-resistant hybrids are sometimes preferred for oviposition by H. armigera, the resistance per se does not determine this preference. Egg survival, larval survival, development and resultant damage are not significantly affected by the midge-resistance status of the host.     

Potential novel hosts for the lily leaf beetle Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae) in eastern North America

Abstract.  1. Introduced insects often incorporate native plants into their diets and might be expected to show a predilection for novel hosts that are phylogenetically related to their normal hosts. The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), is an introduced pest of cultivated lilies. Oviposition behaviour, larval behaviour, and development of L. lilii was examined on a range of potential host plants, as well as on the normal host, Asiatic hybrid lilies Lilium sp.
2. Neonate larval feeding behaviour was quantified on 15 food plant species: 10 from the Liliales, three from the Asparagales and two eudicots. Larvae fed plants closely related to the genus Lilium were more likely to initiate feeding, less likely to abandon their food leaf, and consumed more leaf area.
3. In no-choice tests, females oviposited on the novel hosts Lilium philadelphicum , Medeola virginiana , Clintonia borealis , Streptopus amplexifolius , and Polygonatum biflorum ; however, all but L. philadelphicum received very few eggs. Non- Lilium novel hosts were not used for oviposition when presented along with Asiatic lilies in choice tests.
4. A single individual was reared to the adult stage on the novel host S. amplexifolius . Several larvae survived to the pupal stage on M. virginiana , although no adults emerged from those pupae. Larvae reared on the native wood lily L. philadelphicum performed equally well or better than on the Asiatic cultivar.
5. Our results indicate that the lily leaf beetle poses a threat to native Liliaceae. Several native Lilium species, including L. philadelphicum , are threatened or endangered in certain jurisdictions throughout their range; these species should be monitored closely for colonisation by the beetle.     

Growth and respiration of embryos and larvae of the rabbittish Siganus randalli (Pisces, Siganidae)

Growth and respiration of larval rabbitfish from Guam were examined. Larvae were reared from eggs in 2- to 10-ton tanks and were fed rotifers, Anemia , and artificial feed in succession as development proceeded through metamorphosis. Growth in length was rapid during the 12 h after hatching, then slowed until the larvae began to feed. The yolk sac was usually absorbed by 36 h after hatching. Rates of respiration of larvae and eggs were determined with a dissolved oxygen electrode at various times through development. Larval metabolism increased steadily during the embryonic stages culminating in a metabolic burst immediately after hatching. Respiration rates remained relatively stable from shortly after hatching until the onset of exogenous feeding, after which respiration rates increased with larval size. The respiration rates of post-yolk-sac larvae scaled isometrically with larval dry mass. Daily growth of feeding larvae was 27 to 28% of larval dry mass.     

Oviposition preference and larval performance of monarch butterflies (Danaus plexippus) on two invasive swallow-wort species

The potential of two invasive herbaceous vines Vincetoxicum nigrum (L.) Moench and Vincetoxicum rossicum (Kleopow) Barbar. (Asclepiadaceae) to reduce monarch butterfly (Danaus plexippus L.) (Lepidoptera: Nymphalidae, Danainae) populations was investigated by evaluating oviposition selection in adult monarch butterflies and larval feeding preference in choice tests comparing the native host plant of monarch butterflies, Asclepias syriaca L. (Asclepiadaceae) and the two non‐indigenous Vincetoxicum species. In both choice and no‐choice tests, no eggs were oviposited on either of the two Vincetoxicum species whereas over 66 eggs per female were oviposited on A. syriaca plants. All first instar larvae allowed to feed on A. syriaca for 48 h survived while a significantly lower proportion survived on V. rossicum (44%) and V. nigrum (14%). Mean weight of larvae that did survive on the Vincetoxicum species was significantly lower than the mean weight of larvae that fed on A. syriaca. The mean weight of surviving larvae, however, did not differ between the two Vincetoxicum species. The mean proportion of leaves consumed by larvae feeding on A. syriaca was significantly greater than the mean proportion of leaves consumed by larvae feeding on either Vincetoxicum species. Findings from this research indicate that V. rossicum and V. nigrum are not viable hosts of monarch butterflies and are likely to pose little direct threat to their populations as oviposition sinks. The ability of these highly aggressive plants, however, to out‐compete and displace the native host of monarchs, A. syriaca, may pose a more serious threat. The potential of monarch populations to adapt to the two Vincetoxicum species as host plants over the long‐term is discussed.     

番茄是烟青虫的寄主植物吗？

长期以来,国内有关文献一直将番茄列为烟青虫Helicoverpa assulta的寄主植物,但田间调查结果往往与此矛盾,本研究的目的是阐明番茄是否为烟青虫的寄主植物。室内试验表明,虽然烟青虫成虫在盆栽番茄植株上产卵较多,但无论是用番茄离体嫩叶还是用盆栽植株饲养,初孵幼虫绝大部分在1龄死亡,平均存活时间很短,不会对番茄造成有经济意义的危害;即使用番茄青果饲养的3龄幼虫也不能活到6龄。根据人工饲料饲养结果估测,番茄苷对初孵幼虫的致死中浓度LC₅₀为0.0744%,叶和青果中报道的番茄苷含量已接近或超过此水平,这是幼虫不能存活的主要原因之一。田间调查也表明,烟青虫并不危害番茄。因此,番茄不是烟青虫的寄主植物。文献中的记载很可能是将棉铃虫误判为烟青虫。     

取食不同食物对小菜蛾幼虫肠道细菌多样性的影响

【目的】植食性昆虫肠道细菌的组成与其食物密切相关。本研究旨在探究小菜蛾Plutella xylostella幼虫肠道细菌多样性与其取食食物之间的关系以及它们之间相互适应的过程。【方法】本研究选取小菜蛾人工饲料品系(S)及其转寄主到结球甘蓝Brassica oleracea var. capitata、结球白菜Brassica rapa subsp. pekinensis和花椰菜Brassica olerocea var. botrytis饲养后第1代(分别为G1C, G1CC和G1WC)和第3代(分别为G3C, G3CC和G3WC)的4龄幼虫,提取小菜蛾肠道细菌基因组DNA,利用Illumina MiSeq二代高通量测序技术,分析其肠道细菌多样性和丰度。【结果】α多样性指数分析发现,取食不同食物的小菜蛾4龄幼虫肠道细菌多样性高低顺序为G1WC>G1CC>S>G1C。在菌群组成上,以人工饲料为食的S样品肠道细菌主要由厚壁菌门(Firmicutes)组成,转寄主植物后的G1C, G1CC和G1WC肠道中厚壁菌门(Firmicutes)相对丰度显著下降,G1C和G1CC小菜蛾肠道中变形菌门(Proteobacteria)相对丰度显著上升成为优势菌群,G1WC肠道中拟杆菌门(Bacteroidetes)成为优势菌群。在寄主植物上连续饲养3代后,与第1代相比,小菜蛾肠道细菌α多样性指数没有显著性改变,但在结球甘蓝和结球白菜上小菜蛾肠道菌群结构却发生了变化,相比G1C,G3C肠道中芽孢杆菌目(Bacillales)的相对丰度显著下降;相比G1CC, G3CC肠道中放线菌门(Proteobacteria)、芽单胞菌门(Gemmatimonadetes)和硝化螺旋菌门(Nitrospirae)的相对丰度均显著上升。【结论】取食人工饲料和不同寄主植物的小菜蛾幼虫肠道细菌多样性和群落构成存在显著差异,寄主植物对小菜蛾肠道微生物的结构组成具有重要的影响,且小菜蛾肠道微生物对寄主植物可能存在一个长期适应的过程。本研究为进一步探讨影响小菜蛾肠道细菌变化的因素,以及后续研究肠道细菌与寄主植物之间的互作奠定了良好的基础。     

THE PARASITOID,Cotesia flavipes (CAMERON) (HYMENOPTERA: BRACONIDAE), INFLUENCES FOOD CONSUMPTION AND UTILIZATION BY LARVAL Diatraea saccharalis (F.) (LEPIDOPTERA: CRAMBIDAE)

Parasitoids exploit host insects for food and other resources; they alter host development and physiology to optimize conditions to favor parasitoid development. Parasitoids influence their hosts by injecting eggs, along with a variety of substances, including venoms, polydnaviruses, ovarian fluids, and other maternal factors, into hosts. These factors induce profound changes in hosts, such as behavior, metabolism, endocrine events, and immune defense. Because endoparasitoids develop and consume tissues from within their hosts, it is reasonable to suggest that internal parasitization would also influence host food consumption and metabolism. We report on the effects of parasitism by Cotesia flavipes on the food consumption and utilization of its host, Diatraea saccharalis. Cotesia flavipes reduces the host food consumption, but parasitized larvae considered a unit with their parasitoid's attained the same final weight as the nonparasitized larvae. Nutritional indices, midgut activities of carbohydrases, and trypsin of parasitized and nonparasitized D. saccharalis were assessed. Parasitized larvae had reduced relative food consumption, metabolic and growth rates, coupled with higher efficiency for conversion of the digested, but not ingested, food into body mass. Parasitism also affected food flux through the gut and protein contents in the midgut of parasitized larvae. The activity of α‐amylase and trehalase in parasitized host was enhanced in the first day after parasitism relative to control larvae. Saccharase activity remained unchanged during larval development. Trypsin activity was reduced from the fifth to ninth day after parasitism. We argue on the mechanisms involved in host food processing after parasitism.     

Development of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) in Helicoverpa (Lepidoptera: Noctuidae) host eggs

Abstract Morphological studies of development of the egg parasitoid Trichogramma australicum Girault in the cotton bollworm, Helicoverpa armigera (Hübner), were conducted to provide benchmarks for assessing developmental rates in both natural hosts and artificial diets. Observations of living embryos and histological sections show that embryos proceed rapidly through cleavage and blastoderm formation and show a characteristic pinching or rotation 8 h after deposition. Eggs progressively increase in volume, primarily by increasing in diameter at the widest point. At 29 ± 1°C the duration of the egg stage is 22−24 h, the larval stage 27 h, the prepupal stage 50−52 h, and pupa 85 h. Larvae undergo dramatic shape changes as they ingest food but do not show signs of larval moults, reinforcing observations that there is only one larval instar. Criteria for staging the embryonic and postembryonic development in natural hosts will be used for future studies aimed at developing and refining artificial diets for Trichogramma.     

Limiting the success of stem borers (Prodoxus quinquepunctellus) in yuccas: indirect effects of ants, aphids, and fruit position

Abstract.  1. Although the moth–yucca mutualism is often studied as a pairwise interaction, yucca plants are also the sole host for a variety of other visitors. One of these additional visitors is a stem-boring moth, Prodoxus quinquepunctellus.
2. In this study, it is shown how the reproductive success of Prodoxus indirectly depends on the interactions between yuccas and their pollinators ( Tegeticula , Prodoxidae) as well as the indirect effects of ants and aphids.
3. Aggressive wood ants foraging on yuccas will attack adult Prodoxus moths while attempting to oviposit. This reduces the number of eggs laid in yucca stalks, leading to fewer larvae feeding in the stalks.
4. Once in the stalk, the survival of Prodoxus eggs/larvae depends upon the rate at which the flowering stalks dry out during fruit maturation. Portions of the stalk above the highest fruit dry out quickly and survivorship approaches zero in these dry sections, while larvae in green sections of the flowering stalk have significantly higher survival rates. The presence of aphids feeding on the stalk slows down the rate of stalk drying and could lead to increased survival of Prodoxus larvae.
5. Overall, ants have strong indirect effects on P. quinquepunctellus by controlling how many eggs are laid in the stalk and by influencing the distribution of aphids. However, it is primarily the presence and position of the fruit that can affect larval survivorship, and fruit position is a function of pollinator visits and resource limitation. These complex interactions illustrate the importance of studying the yucca–moth mutualism in a community context.     

Chemical signals mediating interactions betweenGaleruca tanaceti L. (Coleoptera, Chrysomelidae) and its egg parasitoidOomyzus galerucivorus (Hedqvits) (Hymenoptera, Eulophidae)

Chemical signals mediating interactions betweenGaleruca tanaceti and its egg parasitoidOomyzus galerucivorus (Hymenoptera, Eulophidae) were studied. Neither odor of gravid females ofG. tanaceti nor volatiles of their feces were attractive to the parasitoid. However, the presence of the beetles’ feces on a substrate arrested the parasitoid and elicited frequent antennal drumming. Thus, feces may contain a kairomone important for host finding. Odors of damaged and undamaged host plants had no effect on the parasitoids.O. galerucivorus did not detect its host eggs at close range but encountered them by chance. Neither the structure nor the dark color of the egg surface play a key role in host recognition, but chemicals of the extrachorion which could be isolated by dichloromethane. Fractionation of the dichloromethane extract by TLC revealed a single active fraction which induced host recognition behavior. Since the eggs ofG. tanaceti contain anthraquinones and anthrones which are active as feeding deterrents against predators, we hypothesized that reproductive success ofO. galerucivorus is due to sequestration of these protective compounds. However, GC-MS analyses revealed that there was no transfer of them from the host egg into the adult parasitoid.     

Aerial dispersal and host plant selection by neonate Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae)

Abstract.  1. Neonate evergreen bagworms, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae), disperse by dropping on a strand of silk, termed silking , and ballooning on the wind. Larvae construct silken bags with fragments of plant foliage. This species is highly polyphagous, feeding on more than 125 species of woody plants of 45 families. The larvae commonly infests juniper ( Juniperus spp.) and arborvitae ( Thuja spp.), but rarely feed on deciduous hosts such as maples. The hypothesis is proposed that polyphagy in T. ephemeraeformis is maintained by variation among larvae in dispersal behaviour, and time constraints on the opportunity to disperse, but patterns of host species preference result from a predisposition for larvae to settle on arborvitae and juniper but disperse from other hosts.
2. Consistent with that hypothesis, laboratory experiments revealed: (a) starved larvae varied in their tendency to disperse from paper leaf models; (b) starved larvae readily silked only during their first day; (c) larvae became increasingly sedentary the longer they were exposed to plant foliage; (d) when provided with several opportunities to silk, larvae became sedentary after exposure to arborvitae foliage, but repeatedly silked after exposure to maple ( Acer species) foliage or paper; and (e) larvae were less inclined to silk from foliage of arborvitae than from maple.
3. Field experiments supported the hypothesis by demonstrating that: (a) neonates tended to disperse from maple leaves while larvae older than 1 day tended to settle and remain; and (b) neonates were less likely to disperse from arborvitae and juniper trees than from maples.     

Ants as egg predators of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Australian cotton crops

Abstract Helicoverpa armigera is a major pest of Australian cotton crops. To assess the impact of ant predation on H. armigera populations, the behaviour of four common ant taxa was observed in cotton crops in northern New South Wales over the 1999−2000 and 2001−02 seasons. Areas of cotton were artificially stocked with H. armigera eggs prior to observation. Pheidole spp. were the most frequently observed ants within the crop canopy in 1999−2000 and took the most H. armigera eggs. Iridomyrmex spp. were more frequently observed than Pheidole spp. in 2001−02 and also took some H. armigera eggs. Neither Paratrechina spp. nor Rhytidoponera metallica (Smith) took any H. armigera eggs, although both were seen in the crop canopy. Irrigation, cultivation and insecticide application disrupted foraging ants and limited their impact on H. armigera populations.     

A comparison of the host preference of monarch butterflies (Danaus plexippus) for milkweed (Asclepias syriaca) over dog-strangler vine (Vincetoxicum rossicum)

Observations in the field indicate that monarch butterflies will oviposit on dog‐strangler vine, an invasive introduced species in the same family as milkweed (Asclepias spp.), the principal larval host of monarchs. The potential impact of this behaviour depends on the strength of the preference of monarch adults to oviposit on these two hosts and the relative ability of larvae to survive on each. We determined the preference for milkweed vs. dog‐strangler vine of ovipositing adults and first instar larvae in choice and no‐choice tests. We also compared the ability of larvae to consume, develop, and survive on either host. In the presence of both hosts, adults exhibited a strong preference to oviposit on milkweed over dog‐strangler vine (mean 80.7 eggs compared to 0.4 eggs over 48 h, respectively). In the absence of milkweed, adults ceased oviposition (mean 0.9 eggs in 48 h), but resumed oviposition when the dog‐strangler vine was replaced with milkweed (mean 99.1 eggs in 48 h). Given a choice between hosts over 24 h, 92% of larvae moved to milkweed leaves and consumed 3.94 cm² of milkweed leaves compared to 2% of larvae that moved to dog‐strangler vine and consumed negligible amounts of leaf material (0.01 cm²). Without a choice, larvae on dog‐strangler vine never consumed more than mean 0.02 cm² larva^?1 in a 24‐h period, did not develop beyond the first instar, and died within 96 h. We obtained no data in support of an effect of the presence of dog‐strangler vine on monarch butterfly populations.