Previous and Present Diets of Mite Predators Affect Antipredator Behaviour of Whitefly Prey

Predator diet is known to influence antipredator behaviour in prey. Yet, it is not clear how antipredator behaviour is affected by diet changes of the predator. We studied the effect of previous and present diet of a predatory mite Typhlodromips swirskii on the antipredator response of its prey, the whitefly Bemisia tabaci. An earlier study showed that adult female whiteflies that had experienced predators, had learned to avoid ovipositing on plants with predators whose previous and present diet consisted of whitefly eggs and immatures. Here, we investigate whether adult whiteflies also avoid plants with predators whose present and/or previous diet consisted of a non-whitefly food source. Adult whiteflies were found not to avoid plants with predators whose present diet consisted of pollen and whose previous diet had consisted of either pollen or whitefly eggs and larvae. They did avoid plants with predators whose present diet consisted of whiteflies and whose previous diet had consisted of pollen, but to a lesser extent than when previous and present diet consisted of whiteflies. In a choice experiment, whiteflies discriminated between plants with predators whose present diet consisted of whiteflies, but that differed in previous diet. Our results show that both previous and present diets of predators are important in eliciting antipredator behaviour.     

How predatory mites find plants with whitefly prey

We investigated the searching behaviour of two species of predatory mites, Typhlodromips swirskii (Athias-Henriot) and Euseius scutalis (Athias-Henriot), both known to feed on immature stages of the whitefly Bemisia tabaci Gennadius. When released in a greenhouse inside a circle of cucumber plants that were alternatingly clean or infested with immature whiteflies, the mites took several days to find plants. Both species were recaptured significantly more on plants with whiteflies. This suggests that the mites are able to discriminate between plants with and without whiteflies. The predators may either have been attracted to plants with whiteflies from a distance or arrested on plants with whiteflies. Typhlodromips swirskii that had previously fed on whitefly immatures on cucumber leaves were significantly attracted by volatiles from cucumber plants with whiteflies in a Y-tube olfactometer. This suggests that the mites use volatile cues to discriminate between infested and clean plants. However, this response waned rapidly; if predators, experienced as above, were starved for 3–4 h in absence of cucumber leaves, they no longer preferred volatiles of infested plants to clean plants. Furthermore, T. swirskii that had no experience with immature whiteflies on cucumber plants also did not prefer odours of infested plants to those of clean plants. Because the release experiment with this species in the greenhouse was done with inexperienced predators, this suggests that the aggregation of mites on plants with whiteflies was mainly caused by differential arrestment of mites on plants with prey and clean plants. For T. swirskii, this was in agreement with the finding that the fraction of predators on plants with prey increased with time to levels higher than 70%. A less clear trend was found for E. scutalis, for which the fraction of predators on plants with prey stabilized soon after release to levels from 54–70%. Hence, the predatory mites may find plants with prey by random searching, but they are subsequently arrested on these plants. An earlier study showed that 87% of all whiteflies released in a set-up as used here were recaptured within 1 day. Hence, the effectiveness with which predatory mites locate plants with whiteflies is low compared with that of their prey. We expect this to generate spatial patterns in the dynamics of predator and prey and this may have consequences for biological control of whiteflies with predatory mites.     

几种弱选择性寄主蔬菜对烟粉虱的驱避作用

【目的】烟粉虱是茄果类蔬菜上的重要害虫,已对常用的化学农药产生了较强的抗药性。目前,利用非嗜好植物对烟粉虱的驱避作用和嗜好植物的诱集作用控制烟粉虱则受到越来越多的关注。【方法】选择芹菜、韭菜、茼蒿、香菜、葱、蒜等6种烟粉虱弱选择性寄主蔬菜,测定烟粉虱对供试蔬菜的嗅觉和视觉反应。在此基础上,筛选出非嗜性相对更强的3种蔬菜进行田间烟粉虱驱虫性测定。【结果】在室内寄主选择性测定中,烟粉虱对供试6种蔬菜的选择性均较小,其中对芹菜的选择率最低,韭菜次之,其余4种蔬菜的选择率为茼蒿香菜葱蒜;采用嗅觉选择性测定的方法测定烟粉虱对供试蔬菜的相对选择性,发现烟粉虱对芹菜的选择率最低(13.0%),韭菜次之(25.5%),其余各蔬菜的选择率大小为茼蒿(47.8%)香菜(40.2%)葱(38.5%)蒜(37.0%);烟粉虱对6种供试蔬菜颜色的选择性也存在明显的差异,其中,烟粉虱对芹菜和韭菜的选择率相对较低。在室内筛选的基础上,选择芹菜、韭菜、葱等3种蔬菜在辣椒田里进行间作驱虫实验,发现芹菜对田间辣椒上烟粉虱的驱避效果最好,驱避率达90.6%,韭菜次之(86.5%),葱的驱避效果一般。【结论】芹菜和韭菜对烟粉虱的驱避效果较好,该结论为烟粉虱的绿色防控提供了理论依据和技术支持。     

Phytoseiid predators suppress populations of Bemisia tabaci on cucumber plants with alternative food

Phytoseiids are known to attack whiteflies, but it is an open question whether they can be used for biological control of these pest insects. Preselection experiments in the laboratory showed that two out of five phytoseiid species tested, Euseius scutalis and Typhlodromips swirskii, stood out in terms of their ability to develop and reproduce on a diet of Bemisia tabaci immatures. In this paper, we show that both predators are able to suppress whitefly populations on isolated cucumber plants in a greenhouse. Predatory mites were released 2 weeks in advance of the release of B. tabaci. To enable their survival and promote their population growth, they were provided weekly with alternative food, that is, Typha sp. pollen. A few weeks after whitefly introduction, the numbers of adult whiteflies on plants with predators were consistently lower than on plants without predators, where B. tabaci populations grew exponentially. After 9 weeks, this amounted to a 16- to 21-fold difference in adult whitefly population size. This shows that the two phytoseiid species are promising biocontrol agents of B. tabaci on greenhouse cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.     

寄主挥发物、叶色在B型烟粉虱寄主选择中的作用

在室温条件下,研究B型烟粉虱Bemisia tabaci(Gennadius)对不同寄主植物和颜色的行为趋性。笼罩实验的结果显示,烟粉虱雌虫对共存的5种寄主植物偏好存在显著差异,总体上表现为对番茄的趋性最强(35·0%),甘蓝次之(27·7%),烟草和棉花再次之,辣椒最低(7·1%);且随着时间的延长,烟粉虱数量在番茄上逐渐增加,在甘蓝上呈下降趋势,在烟草、棉花和辣椒上变动幅度不大,但数量总体上仍是番茄(48·8%)>甘蓝(18·4%)>烟草、棉花>辣椒(3·4%)。但烟粉虱在不同寄主植物上的产卵量则表现为:甘蓝>番茄>棉花、烟草>辣椒;其中甘蓝和番茄上卵量分别占总卵量的56·8%和28·2%;而烟草、棉花和辣椒上的卵量均不到总卵量的6·0%。"Y"型嗅觉仪进一步测定表明:寄主植物番茄和甘蓝气味对烟粉虱具有显著引诱作用,且表现为番茄>甘蓝,辣椒不具引诱作用;烟粉虱对3种植物(番茄、甘蓝、辣椒)的叶片颜色均有显著趋性,选择率在75%左右,但在三者之间的趋性差异不明显;烟粉虱雌虫对黄色和绿色均具有显著趋性,且对黄色的趋性显著大于对绿色的趋性,但对红色无趋性。综合分析表明,在对寄主定向和定位过程中,B型烟粉虱的视觉和嗅觉均起作用,但在对同种颜色(绿色)的寄主进行选择和定位的过程中,嗅觉起主要作用,而对不同种颜色(红、黄、绿)的选择和定位时,其视觉起决定作用。     

Sweetpotato whitefly resistance to insecticides in Hawaii: Intra-island variation is related to insecticide use

Susceptibility to acephate, methomyl, and permethrin was determined with laboratory bioassays of field-collected adults from 15 populations of the B biotype of sweetpotato whitefly,Bemisia tabaci (Gennadius) (Homoptera:Aleyrodidae), from Hawaii. Comparisons at the LC₅₀ showed up to 24-fold resistance to acephate, 18-fold resistance to methomyl, and 4-fold resistance to permethrin. Analysis of variance showed significant intra-island variation in susceptibility to each insecticide, but no significant variation among islands. Insecticide use varied from 4 to 103 insecticide sprays per site per season. Acephate and methomyl were used more often than permethrin. The frequency of application and LC₅₀ for each insecticide were positively correlated across sites. These results suggest that local variation in insecticide use was a primary cause of variation in susceptibility. If local insecticide use is a key determinant of resistance, as our results suggest, growers can retard resistance development locally by reducing their own insecticide use.     

Thermotolerance and gene expression following heat stress in the whitefly Bemisia tabaci B and Q biotypes

The whitefly Bemisia tabaci (Gennadius) causes tremendous losses to agriculture by direct feeding on plants and by vectoring several families of plant viruses. The B. tabaci species complex comprises over 10 genetic groups (biotypes) that are well defined by DNA markers and biological characteristics. B and Q are amongst the most dominant and damaging biotypes, differing considerably in fecundity, host range, insecticide resistance, virus vectoriality, and the symbiotic bacteria they harbor. We used a spotted B. tabaci cDNA microarray to compare the expression patterns of 6000 ESTs of B and Q biotypes under standard 25 °C regime and heat stress at 40 °C. Overall, the number of genes affected by increasing temperature in the two biotypes was similar. Gene expression under 25 °C normal rearing temperature showed clear differences between the two biotypes: B exhibited higher expression of mitochondrial genes, and lower cytoskeleton, heat-shock and stress-related genes, compared to Q. Exposing B biotype whiteflies to heat stress was accompanied by rapid alteration of gene expression. For the first time, the results here present differences in gene expression between very closely related and sympatric B. tabaci biotypes, and suggest that these clear-cut differences are due to better adaptation of one biotype over another and might eventually lead to changes in the local and global distribution of both biotypes.     

Establishment of papaya banker plant system for parasitoid, Encarsia sophia (Hymenoptera: Aphilidae) against Bemisia tabaci (Hemiptera: Aleyrodidae) in greenhouse tomato production

The silverleaf whitefly, Bemisia tabaci biotype B (Gennadius) (Hemiptera: Aleyrodidae), is a key pest of tomato (Solanum lycopersicum L.) and other vegetable crops worldwide. To combat this pest, a non-crop banker plant system was evaluated that employs a parasitoid, Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae) with whitefly, Trialeurodes variabilis (Quaintance) (Hemiptera: Aleyrodidae), as an alternative host for rearing and dispersal of the parasitoid to the target pest. (a) Multi-choice and no-choice greenhouse experiments were conducted to determine host specificity of T. variabilis to papaya (Carica papaya L.) and three vegetable crops including tomato, green bean (Phaseolus vulgaris L.), and cabbage (Brassica oleracea L.). The result showed that papaya was an excellent non-crop banker plant for supporting the non-pest alternative host, T. variabilis, whose adults had a strong specificity to papaya plants for feeding and oviposition in both multi-choice and no-choice tests. (b) The dispersal ability of E. sophia was investigated from papaya banker plants to tomato and green bean plants infested with B. tabaci, as well as to papaya control plants infested with T. variabilis; and (c) the percent parasitism by E. sophia on T. variabilis reared on papaya plants and on B. tabaci infested on tomato plants was also evaluated. These data proved that E. sophia was able to disperse at least 14.5 m away from papaya plants to target tomato, bean or papaya control plants within 48–96 h. Furthermore, E. sophia was a strong parasitoid of both T. variabilis and B. tabaci. There was no significant difference in percent parasitism by E. sophia on T. variabilis (36.2–47.4%) infested on papaya plants or B. tabaci (29–45.9%) on tomato plants. Thus, a novel banker plant system for the potential management of B. tabaci was established using papaya as a non-crop banker plant to support a non-pest alternative host, T. variabilis for maintaining the parasitoid to control B. tabaci. The established banker plant system should provide growers with a new option for long-term control of B. tabaci in greenhouse vegetable production. Ongoing studies on the papaya banker plant system are being performed in commercial greenhouses.     

Sublethal effects of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes) on the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) under laboratory conditions

Sublethal effects were evaluated in subsequent generations of whiteflies Bemisia tabaci (Gennadius) arising from parental generations exposed in the four nymphal stages to the fungus Beauveria bassiana (Balsamo) Vuillemin. Examples of such effects include impaired fertility, production of malformations or external variations, and reduced survival of later generations. Malformations of the head, legs, wings or abdomen were not observed in adults derived from treated nymphs, nor were negative effects observed in the fecundity and fertility of the descendants of the whiteflies treated with the fungus. However, moulting problems were observed in insects descended from B. bassiana-treated whiteflies. This is the first time that such effects have been reported, with almost 30% of imagos resulting from treated nymphs unable to detach completely from the exuvia. A gradual reduction in mortality rates between subsequent generations was observed. The importance of these results is discussed in the light of findings from other studies into the effects of entomopathogenic fungi on pest insects.     

Herbivore response to vegetational diversity: spatial interaction of resources and natural enemies

Vegetational diversity in agricultural systems is predicted to reduce herbivore populations, but we observed the opposite effect: higher nymph population densities of a functionally monophagous herbivore, the squash bug, Anasa tristis (Hemiptera: Coreidae) in a vegetationally diverse squash-bean-corn polyculture than in a squash monoculture. We examined spatial and temporal aspects of squash bug and predator populations in relation to vegetational diversity. Average colonization, oviposition, and mortality rates for the herbivore were similar in monocultures and polycultures. In the polyculture, however, we found that squash bugs eggs were highly aggregated on plants on the outer edges of plots. Predation was also lower on plants near the edges, allowing the large aggregations of eggs found in the polyculture to escape predation and ultimately produce more squash bugs. Spatial interactions between herbivores and natural enemies may underlie some of the general effects of vegetational diversity on herbivores.     

Characterization and distribution of esterase electromorphs in the whitefly,Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae)

Esterase profiles were examined for over 40 populations of the whitefly,Bemisia tabaci, obtained from native and cultivated plant hosts worldwide. Twelve unique electromorphs were identified from distinct populations concentrated largely in Central America, Africa, and India. One electromorph, type B, has recently been proposed as a separate species,Bemisia argentifolii, and has recently spread throughout much of the world. When considered with evidence from mating studies and the ability to induce phytotoxic disorders (squash silverleaf disorder), our data suggest that the single taxonBemisia tabaci may actually represent a species complex.     

Development of Encarsia bimaculata (Heraty and Polaszek) (Hymenoptera: Aphelinidae) in Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) nymphs

Encarsia bimaculata was recently described from India as a potentially useful parasitoid of Bemisia tabaci. Its developmental biology was studied in the laboratory at 25–30 °C and 70–75% RH. Results showed that E. bimaculata is a solitary, arrhenotokous, heteronomous, autoparasitoid. Mated females laid eggs internally in B. tabaci nymphs that developed as primary parasitoids. Males developed as hyperparasitoids, either in females of their own species or in other primary aphelinid parasitoids. Superparasitism was common under cage conditions. Both sexes have an egg, three larval instars, prepupal, and pupal stages. Development from egg to adult took 12.70 ± 2.10 days for females and 14.48 ± 2.60 days for males. Individual B. tabaci nymphs were examined for E. bimaculata parasitization using three isozymes: esterase, malate dehydrogenase, and xanthine dehydrogenase. All three isozymes showed differential banding patterns that identified E. bimaculata parasitized or unparasitized B. tabaci nymphs.     

Behavioural traits mediating effects of two plant-ants on their specific myrmecophyte host

Summary. Symbiotic ant species vary in their effects on the same host plant, and some ant species are exploiters. These can destabilise the interaction. The behavioural repertoire of ant associates should be important in determining their effects on the host. We examined several traits of foraging behaviour of two ant species associated with the African understorey tree Leonardoxa africana africana – the protective mutualist Petalomyrmex phylax and the parasite Cataulacus mckeyi – to examine the mechanistic basis of the difference in their effects on the plant. These two ant species displayed significant differences not only in activity rhythms, P. phylax patrolling leaves day and night while C. mckeyi was strictly diurnal, but also in their predatory behaviour (P. phylax killed more herbivores) and recruitment dynamics (C. mckeyi recruited at a lower level). For all traits examined, C. mckeyi expressed behaviours reflecting an opportunistic exploitation of the nectar produced by the host plant, whereas those displayed by P. phylax contribute to conferring effective protection of the host plant. Our results suggest that prey capture may be important as a source of food for Petalomyrmex, in addition to its function in increasing plant-provided resources through protection.Received 27 August 2004; revised 11 November 2004; accepted 16 November 2004.     

Nesting behavior and nest site selection in monk parakeets (Myiopsitta monachus) in the Pantanal of Brazil

We examined nesting behavior in monk parakeets (Myiopsitta monachus) in their native habitat in the Brazilian Pantanal. Unique among parrots, monk parakeets build communal nest structures that contain many cavities, each belonging to an individual pair. We studied 41 parakeet colonies that had 104 nest structures. We hypothesized that nest structures would be located in trees providing the greatest support and protection from predators and inclement weather, and that nest sites and nest cavities would differ from random locations with respect to tree characteristics, location of houses, and presence of jabiru stork (Jabiru mycteria) nests, as suggested anecdotally by other authors. Fewer than half of the colonies were close (<350 m) to houses. There was a strong association with jabiru storks; 21 of 23 stork nests had monk parakeet nest cavities attached, accounting for 51% of parakeet colonies. Of the 21 jabiru-associated colonies, 6 had additional parakeet structures and 15 had only the jabiru-attached parakeet structure. Monk parakeet colonies associated with jabiru nests had significantly more nesting cavities than did monospecific monk parakeet colonies, due mainly to those attached directly to the jabiru nest. In jabiru-associated colonies, parakeet nest structures were located higher and in taller trees than in monospecific colonies. There was no difference in trunk diameters of parakeet nesting trees with or without jabirus. Although we tabulated 24 tree species as nest trees, nearest-neighbor trees, or matched-point trees, only 6 species were used for nesting. When compared to matched points, monk parakeet structures were preferentially located in piuva (Tabebuia spp.) and mandovi trees (Sterculia apetela). Parakeet structures were in taller trees with thicker trunk diameters than matched points. Most nest cavities (71%) faced in a northerly direction (northwest to northeast), away from cold southerly winds. Choice of a nest site and orientation appears to reflect structural, weather, and predator constraints. Thick, tall trees with stout branches provided stable sites for their large nest structures, which are known to collapse because of their own weight and strong winds. Nesting with jabirus confers structural advantages (they could attach many nests to the bottom of the jabiru nest, potentially gaining benefits from social facilitation), early warning, and predator defense.     

Influences of plant species on life history traits of Cotesia rubecula (Hymenoptera: Braconidae) and its host Pieris rapae (Lepidotera: Pieridae)

The relative suitability of four plants was studied for larvae of Pieris rapae L. and its parasitoid Cotesia rubecula (Marshall). For unparasitized P. rapae, pupal dry weight and egg-pupa growth rate were higher on cabbage, radish and nasturtium than on Indian hedge mustard. Larval developmental rate and size were greatest for C. rubecula when its host was feeding on nasturtium. Wasp survival was not affected by the host insect/plant combination in which the parasitoid developed. These results indicate that the plant on which host larvae feed is an important factor in development of the parasitoid.     

Selection on offspring size varies within and among families in relation to host nutritional quality

Life history theory often assumes a positive relationship between offspring size and fitness, although the strength and form of this relationship is expected to vary with environmental conditions. In arthropods, surprisingly few studies have examined the influence of larval environment on the offspring size–fitness relation. In phytophagous insects, the few studies that have examined variation in larval host plants have found a negative correlation between host plant nutritional quality and the strength of selection favoring larger offspring size, suggesting that this pattern might be general. I present experimental evidence for such a relationship in a population of the moth Rothschildia lebeau feeding on its three primary host plant species. Unlike previous studies, I consider the effect of offspring size on growth and survival at two levels, both among families and among siblings within families. Neonate caterpillar mass had a significant effect on growth and survival. The effect on growth, however, was weak, resulted primarily from variation among families, and did not differ among host plant diets. The effect on survival was stronger and varied among host plant diets, among families, and within families on different host plants in a manner that was generally consistent with the hypothesized negative correlation between host plant nutritional quality and the strength of selection favoring larger offspring size. Overall, results suggest that the consequences of variation in offspring size for survival within and among families are host plant-dependent in this system.     

Within-patch foraging behaviour of the aphid parasitoidAphidius funebris: plant architecture, host behaviour, and individual variation

The influence of plant architecture, host colony size, and host colony structure on the foraging behaviour of the aphid parasitoidAphidius funebris Mackauer (Hymenoptera: Aphidiidae) was investigated using a factorial experimental design. The factorial design involved releasing individual parasitoid females in aphid colonies consisting of either 10 or 20 individuals ofUroleucon jaceae L. (Homoptera: Aphididae) of either only larval instar L3 or a mixture of host instars, both on unmanipulated plants and on plants that had all leaves adjacent to the colony removed. Interactions between the parasitoid and its host were recorded until the parasitoid had left the plant. The time females spent on the host plant and the number of eggs laid varied greatly among females. Host colony size significantly affected patch residence time and the number of contacts between parasitoids and aphids. Plant architecture influenced the time-budget of the parasitoids which used leaves adjacent to the aphid colony for attacking aphids. Female oviposition rate was higher on unmanipulated plants than on manipulated plants. No further significant treatment effects on patch residence time, the number of contacts, attacks or ovipositions were found. Oviposition success ofA. funebris was influenced by instar-specific host behaviour. Several rules-of-thumb proposed by foraging theory did not account for parasitoid patch-leaving behaviour.     

Parasitoid wasp affects metabolism of cockroach host to favor food preservation for its offspring

Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey to provide a food supply for their offspring. We have examined the effects of the venom of the parasitoid wasp Ampulex compressa on the metabolism of its cockroach prey. This wasp stings into the brain of the cockroach causing hypokinesia. We first established that larval development, from egg laying to pupation, lasts about 8 days. During this period, the metabolism of the stung cockroach slows down, as measured by a decrease in oxygen consumption. Similar decreases in oxygen consumption occurred after pharmacologically induced paralysis or after removing descending input from the head ganglia by severing the neck connectives. However, neither of these two groups of cockroaches survived more than six days, while 90% of stung cockroaches survived at least this long. In addition, cockroaches with severed neck connectives lost significantly more body mass, mainly due to dehydration. Hence, the sting of A. compressa not only renders the cockroach prey helplessly submissive, but also changes its metabolism to sustain more nutrients for the developing larva. This metabolic manipulation is subtler than the complete removal of descending input from the head ganglia, since it leaves some physiological processes, such as water retention, intact.     

How do Pieris rapae search for Brassicaceae host plants?

Pieris rapae curucivora Boisduval is a major cause of damage to important Brassicaceae vegetable crops. The method of host landing plant selection by adult females was investigated by covering cabbage (host) and lettuce (non-host) plants to block visual and/or olfactory signals, and also by using volatile extracts of both plants.