Plant effects on prey choice by a vespid wasp, Polistes arizonensis

1. The effects of sunflower, Helianthus annuus , and groundcherry, Physalis pubescens , eaten by the tobacco budworm ( Heliothis virescens ), on predation by paper wasps ( Polistes arizonensis ) were examined.
2. Polistes arizonensis foragers took more caterpillars from H. annuus plants than P. pubescens in paired-choice tests.
3. They took longer to locate prey and apparently gave up searching faster on artificial plants mimicking P. pubescens than on artificial plants mimicking H. annuus .
4. In paired-choice tests for chemical effects, wasps chose more caterpillars within H. annuus odour than in P. pubescens odour.
5. They also chose more H. annuus -reared larvae than P. pubescens -reared larvae when they were presented without plants. Handling time was not affected.     

The parasitoidCotesia glomerata (Hymenoptera: Braconidae) discriminates between first and fifth larval instars of its hostPieris brassicae,on the basis of contact cues from frass,silk, and herbivore-damaged leaf tissue

Adult females of the larval parasitoidCotesia glomerata (L.) respond to chemical cues associated with feeding damage inflicted on cabbage plants by its host,Pieris brassicae (L.). The use of these infochemicals by the parasitoid during selection of the most suitable host instar was investigated. The parasitoid can successfully parasitize first-instar host larvae, while contacts with fifth-instar larvae are very risky since these caterpillars react to parasitization attempts by biting, spitting, and hitting, resulting in a high probability of the parasitoid being seriously injured or killed. Observations of the locomotor behavior of individual wasps on leaves with feeding damage inflicted by the first and the fifth larval instars and on host silk and frass showed that several cues affect the duration of searching by the parasitoids after reaching a leaf: cues on the margin of the feeding damage and cues in the host frass and silk. Whole frass, silk, and hexane extracts of frass obtained from first-instar elicited parasitoid's searching behavior significantly longer than frass, silk, and hexane extract of frass from the fifth instar. The results demonstrate thatC. glomerata can discriminate between first instars, which are more suitable hosts, and fifth instars ofP. brassicae without contacting the caterpillars, by exploiting instar-related cues.     

Shifts in developmental diet breadth of Lymantria xylina (Lepidoptera: Lymantriidae)

The moth Lymantria xylina Swinhoe (1903) (Lepidoptera: Lymantriidae) is a major defoliator of hardwood and fruit trees in Taiwan. Although the plants identified as host plants of L. xylina usually refer to plants used as food or as shelter, most of the host plant identifications have not considered the role of these hosts on larval development. This study investigated various instars feeding on different plants to assess the developmental diet breath of L. xylina. Forty-seven plant species, belonging to 25 families were used in feeding trials. Various bioassays, including first instar survival and long-term feeding trials, indicated the most suitable host plants for the different developmental stages. Results of the first instar survival trial indicated that first instars could survive only on 13 of the tested plant species. In addition, first instars could only successfully grow to pupa on seven of these 13 test plants species. To assess the developmental diet breath shifts of this moth, 38 plant species (excluding those nine plant species that the first instars did not feed upon) were fed to third and fifth instars in long-term feeding trials. Survival to pupa was noted on 12 and 13 test plant species for the third and fifth instars, respectively. In short, we found that the larvae performed differently when fed on various host plants and that the host plant range increased with the larval stage. Therefore, it is necessary to adjust the host plant range of this moth and to consider host plant breadth together with the developmental stages of caterpillars.     

Behavioral adaptations increase the value of enemy-free space for Heliothis subflexa,a specialist herbivore

We investigated the importance of specialized behaviors in the use of enemy-free space by comparing the host-use behavior of two closely related moths, Heliothis subflexa Guenee and H. virescens Fabricius. Heliothis subflexa is a specialist on plants in the genus Physalis, whereas H. virescens is an extreme generalist, feeding on plants in at least 14 families. Heliothis subflexa uses the inflated calyx surrounding Physalis fruits as enemy-free space, and field rates of parasitism for H. subflexa on Physalis are much lower than for H. virescens on tobacco and cotton, common hosts found in the same habitat as Physalis. If Physalis, architecture were solely responsible for H. subflexa's low rates of parasitism on Physalis, we predicted that H. virescens larvae experimentally induced to feed on Physalis would experience parasitism rates similar to those of H. subflexa. We found, however, that specialized host-use and host-acceptance behaviors are integral to the use of enemy-free space on Physalis and strongly augment the effects of the structural refuge. In laboratory assays, we found considerable differences between the larval behavior of the specialist. H. subflexa, and the generalist, H. virescens, and these contributed to H. subflexa's superior use of enemy-free space on Physalis. We tested the importance of these behavioral differences in the field by comparing parasitism of H. virescens on Physalis, H. virescens on tobacco, and H. subflexa on Physalis by Cardiochiles nigriceps Vierick, a specialist braconid parasitoid. For H. virescens, a threefold decrease in parasitism occurred when feeding on Physalis (mean parasitism +/- SEM = 13 +/- 4%) rather than tobacco (43 +/- 4%), a difference we attribute to the structural refuge provided by Physalis. However, parasitism of H. virescens on Physalis was more than ten times as great as that of H. subflexa on Pliv.salis (1 +/- 4%), supporting the hypothesis that specialized behaviors have a substantial impact on use of Physalis as enemy-free space. Behavioral adaptations may be central to the use of enemy-free space by phytophagous insects and may act as an important selective force in the evolution of dietary specialization.     

Effect of Heliothis subflexa herbivory on fruit abscission by Physalis species: the roles of mechanical damage and chemical factors

1. Insect oral secretions are important for the induction of a number of plant responses, but the relative role of mechanical damage in the induction of these responses is often not well understood. Damage from the frugivore Heliothis subflexa, a specialist on Physalis species, causes herbivore‐induced fruit abscission. In this field study, we examined the separate and combined effects of mechanical damage and H. subflexa oral secretions on Physalis fruit abscission. 2. To determine the relative role of mechanical and chemical factors, the following treatments were administered to fruit: (1) three levels of mechanical damage, (2) natural herbivore damage by control larvae and by larvae surgically treated to inhibit saliva secretion, and (3) injection of H.subflexa oral secretions and a water control. Abscission of mechanically damaged fruit with and without the addition of oral secretions was also compared. 3. Mechanical damage was sufficient to cause fruit abscission, and the addition of oral secretions to mechanically damaged fruit did not cause an increase in fruit abscission. Normal caterpillars and those treated to inhibit saliva secretion caused similar abscission rates. 4. Though most studies examining the effects of insect oral secretions on induced plant responses find these chemical stimuli to be important or essential, the results of the present study showed that oral secretions are not necessary for fruit abscission. Future work is needed to determine the relative importance of mechanical damage in herbivore‐induced plant responses in other systems.     

Effects of age and food source on secondary chemistry of larvae of Lymantria species (Lepidoptera: Lymantriidae)

Haemolymph and osmeterial secretions of caterpillars of Lymantria monacha (Linnaeus) and L. concolor Walker were analysed by gas chromatography/mass spectrometry for low molecular weight secondary metabolites. The similarities of their chemical compositions were determined by means of cluster analysis techniques in order to characterize possible chemical variations related to developmental stage or food of the larvae. For this purpose, two dissimilarity coefficients (Euclidean distances, Canberra metrics) and four clustering methods (UPGMA, WPGMA, WPGMC, single linkage) were combined. The patterns of secondary compounds obtained from the haemolymph and osmeterial secretions studied did not differ statistically significantly between two groups of L. monacha larvae fed with either larch, Larix decidua Mil., or Norway spruce, Picea abies (L.), indicating no relevant influence of plant chemistry. However, haemolymph of penultimate instar larvae of L. concolor fed on Rhododendron contained a mixture of compounds differing statistically significantly from that of last instar caterpillars. The total compositions of the corresponding gland secretions were statistically identical though the presence/amounts of individual compounds varied. This suggested that the haemolymph composition reflected changing physiological requirements of the successive instars, whereas the composition of the defensive mixtures remained comparatively constant, possibly due to a constant spectrum of potential enemies. A more pronounced age-dependence of larval chemistry was shown by a similar analysis of data from various developmental stages of L. dispar (Linnaeus) and one of its food plants. This analysis suggested plant composition affected the secondary chemistry of early larval instars of L. dispar. The results are discussed in terms of the roles of secondary metabolites in defence against natural enemies.     

Leaf growth signals the onset of effective plant resistance against Hessian fly larvae

For plant resistance that is induced rather than constitutive, the precise timing of a sequence of events must be considered (i.e., initial detection of the insect by the plant's surveillance systems, up-regulation of signaling and defense pathways, achievement of effective levels of defense, and finally down-regulation of signaling and defense). Here, we provide a timeline for the interaction between resistant wheat ( Triticum aestivum L.) (Poaceae) and the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). To create this timeline, we measured the daily growth of the third, fourth, and fifth leaves of susceptible and resistant plants. Because each leaf had a different spatial relationship to the site of larval attack (i.e., the sheath epidermal cells of the third leaf) and a different pattern of growth relative to the 3–5 days that larvae attacked resistant plants, we learned different things from each leaf. The third leaf shows how quickly responses of susceptible and resistant plants diverge (i.e., 36–60 h after initial larval attack). The fourth leaf shows that, for both susceptible and resistant plants, negative effects of larval attack extend beyond the third leaf. These negative effects are more severe for susceptible plants, but even in resistant plants continue for several days after larvae have died. The fifth leaf is interesting because it shows how rapidly the resistant plant recovers from larval attack. Thus, 204–348 h after initial attack, a time when the fourth leaf of resistant plants is showing reduced growth and the fifth leaf of susceptible plants is showing zero growth, the fifth leaf of resistant plants shows a small increase in growth. Grasses with resistance gene-mediated resistance may have a two-fold strategy, using resistance mechanisms to stop Hessian fly larvae from further attack and tolerance mechanisms to protect resources for future plant growth.     

Field observations of oviposition by a specialist herbivore on plant parts and plant species unsuitable as larval food

Where a female places her eggs can have a major impact on the fitness of her offspring, especially for insects in which the winged adults are far more mobile than the neonates. Larvae of Heliothis subflexa (Guenee) (Lepidoptera: Noctuidae), a specialist moth phylogenetically nested within a generalist clade, feed only on fruit of some Physalis species. Field observations of the oviposition behavior of H. subflexa revealed that 1) females laid most of their eggs on leaves of the Physalis plant, despite the larvae's frugivorous diet, and 2) females laid nearly 20% of the eggs on nonhost plant species. Most eggs oviposited on nonhosts were placed close to the host plant-88% were within 15 cm of the Physalis plant. However, in a study of neonate movement, we found that a distance of 2 cm from the hatch site to the host plant significantly decreased the ability of neonates to establish on the host plant. The estimated fitness cost, quantified as reduced neonate survival, for females ovipositing on nonhosts is 8-17%. Many ecological and evolutionary factors could result in oviposition on less suitable host parts and on nonhosts. One possibility is that specialization on Physalis has recently evolved in H. subflexa, and females have not fully optimized their oviposition behavior. However, the fitness cost of oviposition on nonhosts may be balanced by fitness benefits of such behavior, such as faster decision-making and reduced predation.     

Understanding gregariousness in a larval Lepidopteran: the roles of host plant, predation, and microclimate

Abstract.  1. Many moth and butterfly larvae are gregarious early in development, but become solitary in late instars. This ontogenetic variation in behaviour is probably the result of temporal changes in the costs and benefits associated with gregariousness. This study provides observational and experimental evidence that, in one particular moth species, a series of different ecological factors influence larval behaviour at different times during development.
2. Field observations show that young caterpillars of the limocodid Doratifera casta form large aggregations while foraging, but that mature larvae are largely solitary.
3. A field experiment revealed that individual first to third instar larvae in larger groups develop more rapidly, but that group size had no detectable influence on survival. The developmental advantage associated with gregariousness is affected by host plant species, but not by predator exclusion, suggesting that group living in these cryptic early instar larvae promotes feeding facilitation, but does not provide individuals with protection from natural enemies.
4. Laboratory experiments revealed that aposematic fourth instar caterpillars in large groups were less likely to be attacked by a generalist insect predator than those in small groups.
5. Field observations provided no evidence that group living affects body temperature, suggesting that microclimatic factors do not favour gregariousness in this species.
6. It is concluded that gregariousness in D. casta confers at least two different advantages on larvae at different stages early in development, but that these advantages disappear, or are outweighed by costs associated with intraspecific competition, in final instars.     

Patterns and mechanisms of growth of fifth-instar Manduca sexta caterpillars following exposure to low- or high-protein food during early instars.

For many insect herbivores, variation in protein availability is a pervasive part of the environment. I explore how variable protein availability affects growth rates of fifth-instar Manduca sexta caterpillars and how growth is related to behavior and physiology. Groups of larvae were reared on low- or high-protein artificial diets (5.9% and 17.7% casein by dry weight, respectively) and then transferred in the fifth instar to the same or opposite diet. During or after the 24-h period following transfer, I measured growth rate, consumption rate, growth efficiency, midgut proteolytic activity, and masses of midgut contents and tissues. Fifth-instar caterpillars reared in earlier instars on high-protein diet grew about 20% more rapidly over 24 h than did caterpillars reared on low-protein diet. This growth pattern appears to be caused by differences in consumption and growth efficiency: caterpillars reared on high protein consumed more food, and used it more efficiently, than did caterpillars reared on low-protein diet. Over the short term (24 h), in contrast, fifth instars that received low-protein diet grew as rapidly as caterpillars that received high-protein diet. Increased (compensatory) consumption appears to be the primary mechanism by which caterpillars consuming low-protein food maintained growth rates.     

Functional response of Picromerus bidens: effects of host plant

Abstract:  The influence of three solanaceous plants (tomato, sweet pepper and eggplant) on the functional response of the predatory bug Picromerus bidens to densities of fourth-instar larvae of the beet armyworm Spodoptera exigua was assessed. Logistic regression indicated a type II functional response on all host plants. Over all prey densities, P. bidens killed significantly fewer fourth instars of S. exigua on tomato than on sweet pepper or eggplant (1.96 ± 0.17 vs. 4.37 ± 0.19 and 3.90 ± 0.15 larvae per predator per 24 h respectively). A higher theoretical maximum predation rate was estimated on sweet pepper (11.1 prey larvae per day) and eggplant (7.4) than on tomato (5.4). The mean number of prey killed per day by P. bidens females ranged from 0.78 at a density of one prey on tomato to 8.45 at a density of 24 prey on sweet pepper. The data indicated that the estimates of handling time ( T _h) and attack rate ( a ) were highly affected by host plant. Based on asymptotic 95% confidence intervals, a lower attack coefficient was found on tomato (0.02 h⁻¹) than on sweet pepper or eggplant (0.07 and 0.11 h⁻¹ respectively). On the other hand, handling times were significantly longer on tomato (4.42 h) and eggplant (3.23 h) than on sweet pepper (2.15 h). This laboratory study suggests that plant characteristics influence the ability of P. bidens to respond to changes in prey density.     

甜菜夜蛾对不同寄主植物的产卵和取食选择

为了探讨甜菜夜蛾Spodoptera exigua对不同寄主植物的产卵选择及成虫产卵选择与幼虫取食选择间的关联度, 本研究选取玉米、豇豆、甘蓝、黄瓜、棉花、辣椒和番茄7种植物进行了选择性和非选择性实验研究, 并采用Y型嗅觉仪测定了成虫对其中3种寄主植物及其挥发物抽提物的趋性。结果表明：在田间非选择性实验中, 甜菜夜蛾在不同寄主植物上的落卵量依次为：玉米>辣椒>棉花>黄瓜、豇豆、番茄>甘蓝。Y型嗅觉仪的行为测定表明, 雌成虫对玉米及其挥发物抽提物的趋性最强, 黄瓜次之, 对甘蓝的趋性最弱, 这与雌虫的产卵选择性一致。不同龄期甜菜夜蛾幼虫对寄主植物的取食选择性有所不同, 且随观测时间的延长有所改变;低龄幼虫对豇豆、玉米和黄瓜的选择性较强, 对甘蓝、番茄、辣椒和棉花的取食选择性则较弱, 高龄幼虫对辣椒也具有较强的选择性;5龄幼虫对寄主植物的选择性不如低龄幼虫明显。结果显示, 甜菜夜蛾对不同寄主植物的产卵选择性显著不同, 植物抽提物在雌成虫的产卵选择中具有重要作用, 甜菜夜蛾对寄主植物的产卵选择性和幼虫取食选择性并不一致。     

Determinants of predation on phytophagous insects: the importance of diet breadth

To evaluate the role of predation in the evolution of diet specialization and to determine the effectiveness of various larval defenses, we offered lepidopteran larvae to colonies of the tropical ant Paraponera clavata. We recorded behavioral and physical characteristics of prey items and used log-linear models to analyze their importance as deterrents to predation by P. clavata. The most important determinant of probability of prey rejection by P. clavata was a prey's diet breadth; specialists were rejected by the ants significantly more than generalists. Other less important, but significant, predictors of prey rejection included ontogeny, morphology and chemistry. Late instar caterpillars were rejected more frequently than early instars, hairy caterpillars were rejected more frequently than caterpillars with other morphologies, and one caterpillar species with an unpalatable extract was rejected more frequently than two species with palatable extracts.     

Dropping behaviour of larvae of aphidophagous ladybirds and its effects on incidence of intraguild predation: interactions between the intraguild prey, Adalia bipunctata (L.) and Coccinella septempunctata (L.), and the intraguild predator, Harmonia axyridis Pallas

Abstract.  1. Two experiments were performed in the laboratory to assess the behaviour of dropping from a host plant as a defence against intraguild predation in aphidophagous ladybird larvae.
2. In the first experiment, encounters were observed on bean plants between fourth instars of the intraguild predator species, Harmonia axyridis , and first instars of two other ladybird species, Adalia bipunctata (L.) and Coccinella septempunctata (L.). The percentages of first instars of the latter two species that dropped from the plant in response to attack differed dramatically, with 47.5% of C. septempunctata first instars dropping vs. 0% of A. bipunctata .
3. In the second experiment, first instars of A. bipunctata or C. septempunctata and a fourth instar of H. axyridis were allowed to forage together on bean plants for 3 h. During this time, 44.3% of C. septempunctata larvae dropped from the plant, but less than 2% of A. bipunctata larvae did so. In contrast, 95.0% of A. bipunctata larvae fell victim to intraguild predation by H. axyridis vs. only 54.5% of C. septempunctata larvae.
4. The significance of dropping behaviour of ladybird larvae as a defence against intraguild predation, and the relationship of dropping behaviour to species-specific habitat affinity of ladybirds, is discussed.     

The influence of food plant dispersion on caterpillar searching success

Abstract. 1. Collards (Brassica oleracea L.) grown in clumps were more difficult for unstarved, early instar cabbage white caterpillars (Pieris rapae L.) to find than collards spaced at regular intervals, although total plant densities were identical.
2. Early instar, unstarved larvae are less mobile than later instar larvae (our data) or starved larvae (Jones' 1977 data).
3. Starved larvae and late instar larvae tend to find plants more readily than do unstarved or younger larvae.
4. We contend that larval mobility governs the success of searching caterpillars and their sensitivity to variations in plant dispersion.
5. Our results show that the dispersion of targets can influence searching success even though target density is constant. This means that the degree of clumping in host plants is capable of influencing their availability to herbivores.     

Leaf toughness changes the effectiveness of larval aggregation in the butterfly Byasa alcinous bradanus (Lepidoptera: Papilionidae)

Two subspecies of the papilionid butterfly Byasa alcinous , B. a. bradanus and B. a. alcinous , have varying degrees of larval aggregation. Early instar larvae of ssp. bradanus always occur in aggregations. To determine the functions of larval aggregation in this subspecies, we examined the effects of leaf toughness on larval performance when caterpillars were reared alone and in aggregations. Newly hatched larvae were reared either individually or in groups of 10 and were fed either tough or tender leaves of Aristolochia debilis . When fed tough leaves, more gregarious larvae survived the first instar. This difference between solitary and aggregated larvae did not occur when caterpillars were fed soft leaves. The effects of aggregation on larval weight and duration were not significant between leaf-toughness treatments. Larval aggregation of B. a. bradanus improves larval survivorship in early instars that use host plants with tough leaves.     

马尾松毛虫过氧化氢酶及过氧化物酶与耐药性的关系

马尾松毛虫Dendrolimus punctatus幼虫体内存在着过氧化氢酶(CAT)和过氧化物酶(POD)。4龄幼虫的CAT和POD活力较大,其次是6龄幼虫,5龄幼虫的CAT和POD活力较4龄和6龄幼虫低。醚菊酯(etofenprox)处理后,在兴奋期(30 min),CAT和POD活力水平上升。4龄和6龄幼虫在抑制期(50 min以后),CAT和POD活力呈波动式上升,接近死亡时下降。5龄幼虫的CAT和POD活力呈波动式上升,接近死亡时下降。5龄幼虫的CAT在抑制期保持比正常虫体高的活力。结果表明,马尾松毛虫4龄、5龄和6龄幼虫与耐药性存在一定的相关性,研制酶的抑制剂具有实用意义。根据毒力测定结果,马尾松毛虫幼虫对醚菊酯的耐药力,5龄是4龄的1.43倍,6龄是4龄的1.72倍。因此,药物防治的合理时期应掌握在4龄以前较适宜。     

Gamma irradiation as a quarantine treatment for apples infested by codling moth (Lep., Tortricidae)

Abstract: Effects of gamma radiation on the fifth instar codling moth, Cydia pomonella (L.), larvae were examined. Mature larvae were exposed to a series of gamma radiation doses ranging from 50 to 250 Gy and survival to pupae and adults was examined. The results showed that pupation and adult emergence decreased with increasing radiation dose. The results also showed that diapausing larvae were more sensitive to irradiation treatment than non-diapausing larvae, and females were more sensitive than males. A dose of 150 Gy reduced adult emergence to less than 2% in non-diapausing larvae, while a dose of 200 Gy completely prevented it. Furthermore, none of the emerging moths exposed to a dose of 150 Gy were females; at 100 Gy dose, the percentage of females was less than 14%. Irradiating larvae in apple fruit in a small-scale laboratory experiment produced similar results. Tests in which >100 000 larvae (in the fifth instar) were irradiated in an artificial rearing medium with a dose of 200 Gy resulted in no adult emergence. Similar results were also obtained when >32 000 larvae in the same stage were exposed in apple fruit to the same dose. The results indicate that the use of ionizing radiation as a quarantine treatment for codling moth infested fruits is feasible and requires a relatively low dose.     

The myth of “minima” and “maxima”, the species of Physalis in the Indian Subcontinent

The status of the names, Physalis minima L. and P. maxima Mill. (Solanaceae), and their alleged presence on the Indian subcontinent are discussed. The issues of nativity and identity of Linnaean Physalis minima are long-debated while the use of the name P. maxima Mill. and its report from India are recent. The available evidence indicates that the name “P. minima L.” is misapplied to two different elements, viz., P. angulata L. and P. lagascae Roem. & Schult. The name Physalis minima L. may be rejected as nomen confusum, for which the paper provides the primary information. As on today, it is submerged under the synonymy of P. angulata L. The correct name for the widely known P. minima is P. lagascae. The name “P. maxima Mill.” applied to the escape and naturalized weed in the Indian subcontinent and elsewhere is to be substituted by P. pruinosa L., a name misapplied to P. grisea (Waterf.) M. Martínez.