Effects of trichomes on the behavior and distribution of Platyprepia virginalis caterpillars

Trichomes are an important physical resistance mechanism of plants, as they reduce insect herbivore movement, feeding, and digestion. However, we know little about how trichomes influence herbivore distributions and populations. We conducted laboratory and field experiments to evaluate the preferences of Platyprepia virginalis (Boisduval) (Lepidoptera: Arctiidae) caterpillars to natural and manipulated densities of trichomes on their primary food, Lupinus arboreus Sims (Fabaceae). We then conducted field surveys to determine whether variation in trichome density among lupine bushes affected caterpillar spatial distribution on the landscape. Platyprepia virginalis caterpillars preferred lupine leaves with fewer trichomes in choice and no‐choice experiments. In the field, caterpillar feeding damage was found more often on leaves with fewer trichomes. These preferences scaled up to the level of bushes in the landscape such that more caterpillars were found on bushes with lower trichome densities than on bushes with higher trichome densities. This is one of few studies to show the potential for trichome density to influence herbivore population size and distribution in a natural system at a landscape level. The results are consistent with trichomes functioning as a resistance mechanism with consequences for herbivore choice, performance, and distribution.     

Avian pest control in tea plantations of sub-Himalayan plains of Northeast India: Mixed-species foraging flock matters

This study reports on the biocontrol role birds play in caterpillar pest control of tea plantations of Northeast India. In this area large tracts of tea plantations have been extensively defoliated by the recent invasion of two forest-dwelling geometrid looper caterpillars, Hyposidra spp. and a lymantriid hairy caterpillar, Arctornis submarginata. This exacerbated tea herbivory by two resident pest caterpillars, Biston suppressaria and Eterusia magnifera. Currently there are no identified resident insect predators for any life stage of Hyposidra spp. and A. submarginata. Larvae of these pests drop from tea bushes using salivary thread, allowing caterpillars to escape from insect predators. The study identified 38 native insectivorous bird species in tea plantations, of which four species (Asian-pied starling, Chestnut-tailed starling, Jungle Myna, Red-vented Bulbul) could be potential control agents of looper and hairy caterpillar pests. These species had high population densities. Their cumulative abundances represented a major proportion of the total bird community during both the infested (86.44%) and non-infested phase (75.34%). They foraged in mixed-species flocks in both tea foliage and on the ground. This behavior is suited to capture foliage-living and dropped caterpillars that were flushed from tea bushes by foraging birds. Abundance and species richness of overall tea layer-foraging birds were higher in infested phase when compared to non-infested phase. The predation rate of four bird species of the foraging flock varied significantly. These results suggest that birds should be considered as important biological control agent of caterpillar pests of tea and considered in pest management plans.     

Host Plant Specialization and Species Turnover of Caterpillars Among Hosts in the Brazilian Cerrado

Decrease in the species composition similarity of herbivore assemblages with increasing phylogenetic distance between host plants is a widespread pattern. Here we used data for caterpillars in the Brazilian Cerrado to investigate how the similarity in caterpillar species composition decreases as the taxonomic level and genetic distance (GD) of their host plants increases. In addition, we elucidate the plant taxonomic level that provides the greatest contribution to turnover in the caterpillar species composition among host taxa. Adult Lepidoptera were reared from caterpillars collected from 52 plants over 13 yr in the same area, with each host plant sampled for 1 yr. Most species were specialists, with 66 percent of genus specialists among the nonsingleton species. The similarity in caterpillar species composition across plant taxa decreased from host species to genera, and from host genera to orders. Above this level, the similarity was consistently low. The GD between plants explained 82 percent of the variation in the similarity of caterpillar species composition. The contribution of caterpillar species turnover among host orders from the same superorder and among host superorders from the same subclass explained 70 percent of the caterpillar species richness as a whole. Our results lend support to the view that most tropical caterpillars are host specialists. Our findings further indicate that the number of orders and superorders of plants provide the greatest contribution to the total caterpillar richness compared with all of the other host taxonomic levels combined. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

A naturally occurring plant cysteine protease possesses remarkable toxicity against insect pests and synergizes Bacillus thuringiensis toxin

When caterpillars feed on maize (Zea maize L.) lines with native resistance to several Lepidopteran pests, a defensive cysteine protease, Mir1-CP, rapidly accumulates at the wound site. Mir1-CP has been shown to inhibit caterpillar growth in vivo by attacking and permeabilizing the insect's peritrophic matrix (PM), a structure that surrounds the food bolus, assists in digestion and protects the midgut from microbes and toxins. PM permeabilization weakens the caterpillar defenses by facilitating the movement of other insecticidal proteins in the diet to the midgut microvilli and thereby enhancing their toxicity. To directly determine the toxicity of Mir1-CP, the purified recombinant enzyme was directly tested against four economically significant Lepidopteran pests in bioassays. Mir1-CP LC(50) values were 1.8, 3.6, 0.6, and 8.0 ppm for corn earworm, tobacco budworm, fall armyworm and southwestern corn borer, respectively. These values were the same order of magnitude as those determined for the Bacillus thuringiensis toxin Bt-CryIIA. In addition to being directly toxic to the larvae, 60 ppb Mir1-CP synergized sublethal concentrations of Bt-CryIIA in all four species. Permeabilization of the PM by Mir1-CP probably provides ready access to Bt-binding sites on the midgut microvilli and increases its activity. Consequently, Mir1-CP could be used for controlling caterpillar pests in maize using non-transgenic approaches and potentially could be used in other crops either singly or in combination with Bt-toxins.     

Response of natural populations of predators and parasitoids to artificially induced volatile emissions in maize plants (Zea mays L.)

1 In response to herbivore attack, maize plants (Zea mays L.) emit a specific blend of induced volatiles. Artificial damage and subsequent treatment of the damaged site with caterpillar regurgitant induces the same response. The induced volatile chemicals are known to be highly attractive to several parasitoids of herbivores in laboratory bioassays, but very limited information is available on how the plant odours affect entomophagous insects in the field. 2 Experiments were conducted to determine if induced maize volatiles attract parasitic and predatory insects under field conditions and whether they affect their spatial distribution. 3 In a preliminary field experiment with blue sticky traps near treated (damaged and treated with caterpillar regurgitant) and healthy plants, more entomophagous insects (total number of parasitic Hymenoptera, Anthocoridae and Syrphidae) were trapped near treated plants than near healthy plants. 4 In a second experiment, attraction to the induced volatiles was monitored with sticky traps placed next to treated and healthy maize plants in a regular maize field. No significant differences between the two treatments were found, but significantly more insects (parasitic wasps, thrips and anthocorid bugs) were trapped near to the top of plants than on traps placed near the mid‐stem. Displacement of these insect groups within the field seemed to occur principally over the canopy, but under severe weather conditions they travelled lower in the canopy. 5 In a third experiment, the effect of induced maize odours on the spatial distribution of predators and parasitoids was investigated by placing sticky traps at different distances from healthy and treated plants. The higher catches of parasitoids near treated plants and the increased presence of these insects on the downwind side of treated plants support the notion that herbivore‐induced maize odours attract natural enemies of maize pests in the field.     

Nuclear polyhedrosis virus as a biological control agent for Malacosoma americanum (Lepidoptera: Lasiocampidae)

In addition to damaging trees, the eastern tent caterpillar is implicated in early fetal loss and late‐term abortion in horses. In a field study, we evaluated the potential biological control of the caterpillar using eastern tent caterpillar nuclear polyhedrosis virus (ETNPV), a naturally occurring virus that is nearly species‐specific. Egg masses were hatched and second instar larvae were fed virus‐inoculated foliage to propagate the virus in vivo. Then, a viral pesticide was formulated at concentrations of 10⁴, 10⁶ and 10⁸ polyhedral inclusion bodies per ml. The pesticide was applied to foliage on which second, third and fourth instar caterpillars were feeding. When the majority of surviving larvae reached the sixth instar, colonies were collected and the surviving caterpillars counted. Mean numbers of surviving caterpillars per treatment were compared via 95% bootstrap confidence intervals. The data indicate second instar caterpillars were highly susceptible to the virus, but only at the highest concentration tested. Third instar caterpillars were also somewhat susceptible to high virus concentrations, while fourth instar caterpillars were fairly resistant. Our data provide the strongest evidence to date that ETNPV can be propagated, harvested and refined for formulation as a biological control agent for eastern tent caterpillar. Its use on this insect may be merited in circumstances where landowners and managers need to protect trees and horses.     

Population dynamics of caterpillars on three cover crops before sowing cotton in Mato Grosso (Brazil)

Direct seeding mulch-based cropping systems under a preliminary cover crop such as millet are common in some areas of Brazil. Lepidopteran pests that damage cotton, soybean and maize crops can proliferate on cover crops, so preventive chemical treatments are necessary. Very little data is available on these pests on cover crops. This paper presents the dynamics of Spodoptera frugiperda, S. eridania, Mocis latipes and Diatraea saccharalis caterpillars monitored at Primavera do Leste, Mato Grosso state (Brazil) during the of 2005/2006 and 2006/2007 cropping seasons on four cover crops, i.e. finger millet (Eleusine coracana), pearl millet (Pennisetum glaucum), sorghum (Sorghum bicolor) and ruzigrass (Brachiaria ruziziensis). The pests were visually counted on plants within a 1 m2 transect (wooden frame). Caterpillars were reared to facilitate identification of collected species and parasitoids. Many S. frugiperda caterpillars were observed on millet in 2005, with a maximum of 37 caterpillars/m2. On sorghum, we found 30 caterpillars/m2, or 0.83 caterpillars/plant. The Diatraea borer attacked sorghum later than the other pests. M. latipes was also observed on millet. The millet cover crop had to be dried for at least 1 month before direct drilling the main cotton crop in order to impede S. frugiperda infestations on cotton plantlets, thus avoiding the need for substantial resowing. The comparative methodological aspects are discussed.     

昆虫种群动态时空回归预测方法及应用研究

根据昆虫种群内个体空间相互作用的特点,提出分析昆虫种群时空相关的三维相关图方法及种群动态预测的时空混合回归模型,对马尾松毛虫幼虫密切分布的预测采用了时空自回归加空趋势面的形式,预测的马尾松毛虫幼虫的平均密度和实测的平均密度在时空变化的趋势上是完全一致的,而且预测结果给出了马尾松毛虫的幼虫密度分布的图形形式,给防治决策提供了方便。     

Breeding success and lutein availability in great tit (Parus major)

The relationship among temporal variation in the availability of carotenoid-rich food, tissue carotenoid levels and breeding success are poorly known. We studied how diet quality and quantity affect the carotenoid profile and fledging success of great tit (Parus major) nestlings along a pollution gradient. We found declining seasonal trend in lutein concentration of caterpillars, which may be the explanation for the declining trend in nestlings' lutein concentration of plasma with season, despite the increase in caterpillar biomass. This may be because the biomass of most lutein-rich caterpillars (autumnal moths) decreased and less lutein-rich caterpillars (sawflies) increased during the breeding season. The temporal difference in occurrence of different caterpillar species means that peak lutein availability does not coincide with peak caterpillar abundance. However the positive association between total larval biomass and the number of great tit fledglings may suggest that fledging success depends more on total caterpillar availability than on lutein concentration of caterpillars.     

不同放牧强度下短花针茅荒漠草原植被的空间异质性

分析不同放牧强度下植物群落中物种的空间分布特征, 有助于阐明群落在放牧胁迫下的演替规律。该研究基于幂函数法则, 探讨了不同放牧强度下短花针茅(Stipa breviflora)荒漠草原群落植物的频率和空间异质性。结果表明: 不同放牧强度下物种空间分布与幂函数法则能很好地吻合; 不同物种空间异质性具有特异性, 随着放牧强度的增加, 提高群落空间异质性的物种分别由无芒隐子草(Cleistogenes songorica)、冷蒿(Artemisia frigida)、短花针茅、银灰旋花(Convolvulus ammannii)等多个物种逐渐转变为以无芒隐子草、短花针茅为主的少数物种, 同时, 物种空间异质性大于群落空间异质性的物种数逐渐减少。     

Does Manipulation by the Parasitoid Wasp Cotesia glomerata (L.) Cause Attachment Behaviour of Host Caterpillars on Cocoon Clusters?

Some parasitoid wasps appear to control the behaviour of their hosts. However, altered behaviours of parasitised hosts are not necessarily caused by parasitoids but are sometimes the result of traumatic side effects of parasitism. However, it was difficult for us to discriminate the cause of host's behaviours between manipulation by parasitoids and traumatic side effects. Larvae of the parasitoid wasp Cotesia glomerata form cocoon clusters after egression from the parasitised host caterpillar Pieris brassicae . Following parasitoid egression, host caterpillars survive for several days and remain near the cocoon clusters. These caterpillars may repel solitary pteromalid hyperparasitoid wasps, Trichomalopsis apanteloctena , that attempt to parasitise fresh C. glomerata pupae. We allowed hyperparasitoids to attack cocoon clusters in the field and laboratory and then assessed the costs and benefits to C. glomerata of attachment by the parasitised caterpillars. The eclosion success of C. glomerata in cocoon clusters with attached caterpillars was higher than that in clusters without attached caterpillars in both field and laboratory experiments. This difference was attributed to shorter hyperparasitoid visits to cocoon clusters with attached host caterpillars. However, large cluster size was potentially costly for host attachment, because the duration of host caterpillar attachment decreased with increasing numbers of C. glomerata per caterpillar. This trade-off may be related to shortages of fat body resources, which are shared between the development of wasp larvae and the survival of host caterpillars. Therefore, we concluded that caterpillar attachment satisfied some requirements of host manipulation by C. glomerata .     

Comparison of midgut bacterial diversity in tropical caterpillars (Lepidoptera: Saturniidae) fed on different diets

As primary consumers of foliage, caterpillars play essential roles in shaping the trophic structure of tropical forests. The caterpillar midgut is specialized in plant tissue processing; its pH is exceptionally alkaline and contains high concentrations of toxic compounds derived from the ingested plant material (secondary compounds or allelochemicals) and from the insect itself. The midgut, therefore, represents an extreme environment for microbial life. Isolates from different bacterial taxa have been recovered from caterpillar midguts, but little is known about the impact of these microorganisms on caterpillar biology. Our long-term goals are to identify midgut symbionts and to investigate their functions. As a first step, different diet formulations were evaluated for rearing two species of tropical saturniid caterpillars. Using the polymerase chain reaction (PCR) with primers hybridizing broadly to sequences from the bacterial domain, 16S rRNA gene libraries were constructed with midgut DNA extracted from caterpillars reared on different diets. Amplified rDNA restriction analysis indicated that bacterial sequences recovered from the midguts of caterpillars fed on foliage were more diverse than those from caterpillars fed on artificial diet. Sequences related to Methylobacterium sp., Bradyrhizobium sp., and Propionibacterium sp. were detected in all caterpillar libraries regardless of diet, but were not detected in a library constructed from the diet itself. Furthermore, libraries constructed with DNA recovered from surface-sterilized eggs indicated potential for vertical transmission of midgut symbionts. Taken together, these results suggest that microorganisms associated with the tropical caterpillar midgut may engage in symbiotic interactions with these ecologically important insects.     

The Effects of an entomopathogenic fungus, Beauveria bassiana (balsamo) vuillemin (hyphomycetes), on Prostephanus truncatus (horn) (Col.: Bostrichidae), Sitophilus zeamais motschulsky (Col.: Curculionidae), and grain losses in stored maize in the Benin Republic

A fungal entomopathogen, Beauveria bassiana, was used to treat maize ears placed in traditional grain stores against Prostephanus truncatus in a field experiment conducted from September 1997 to March 1998 in the Benin Republic, West Africa. Treatments included oil-based spray with and without conidia, maize stored with and without the husk, and stores with and without artificial infestation. Additional treated ears kept in insect-proof cages under field conditions were sampled weekly and exposed to insects to estimate the virulence and persistence of the pathogen during the storage season. P. truncatus densities were significantly lower in treatments that included conidia, although densities were high in all artificially infested treatments and grain losses were severe. The effect of the pathogen was modeled with an exponential decay function and incorporated in a published P. truncatus simulation model. The effects of hypothetical pathogens with different virulence and persistence characteristics were evaluated in terms of insect density and percentage grain loss.     

Impact of avian and arthropod predation on lepidopteran caterpillar densities and plant productivity in an ephemeral agroecosystem

Abstract.  1. Most studies evaluating the combined impact of spiders and other predators on herbivore densities in agroecosystems have focused primarily on their trophic connections with invertebrate predators (e.g. carabids, chrysopids); however linkages among spiders and vertebrate predators may also help structure the population dynamics of insect herbivores. A field experiment was conducted to examine the impact of avian and spider predation on lepidopteran caterpillar densities and plant productivity within a Brassica agroecosystem.
2. Arthropod abundance, leaf-chewing damage, and final plant productivity associated with broccoli, Brassica oleracea L. (var. italica ), were recorded for four treatments: (1) bird present but spiders removed; (2) both birds and spiders present; (3) birds excluded, spiders present; and (4) birds and spiders both excluded.
3. Densities of Artogeia rapae L. (Lepidoptera: Pieridae) and Trichoplusia ni Hübner (Lepidoptera: Noctuidae) large caterpillars and post feeding stages were reduced significantly by bird predation. The abundance of large caterpillars was also reduced on spider-inhabited plants during early plant growth; however the assemblage of birds and spiders did not suppress caterpillar densities more significantly than either predator alone.
4. Plants protected by birds, spiders, and birds plus spiders sustained less folivory attributable to leaf chewing caterpillars than check plants. Plant productivity was also greater for predator-protected plants than check plants.
5. Although spiders and parasitoids were responsible for some of the mortality inflicted upon lepidopteran caterpillars, it was concluded that in this study system, birds are the most important natural enemies of folivores.     

Functional response of the predators Podisus maculiventris (Say) and Podisus nigrispinus (Dallas) (Het., Pentatomidae) to the beet armyworm, Spodoptera exigua (Hübner) (Lep., Noctuidae): ef fect of temperature

Predation abilities of Podisus maculiventris and Podisus nigrispinus on caterpillars of the beet armyworm, Spodoptera exigua (Hübner), were compared at three different temperatures (18, 23 and 27°C) by performing functional response tests. In both species, predation capacity was a function of temperature and prey density: more prey were captured as temperature and number of prey offered increased. Results indicated that type II and III functional responses provided the best fit to the data obtained for P. nigrispinus at 18 and 23°C, and at 27°C, respectively. However, the data for P. maculiventris showed a better fit to type II at 18°C and to type III at higher temperatures. In both pentatomids the handling time decreased with increasing temperature. At higher temperatures, P. nigrispinus demonstrated greater predation rates than P. maculiventris . The implications of these findings for the control of caterpillar pests in glasshouses are discussed.     

Garotenoids and colouration of poplar hawkmoth caterpillars (Laothoe populi)

Carotcnoids and chlorophylls a and b were extracted from final instar caterpillars of the poplar hawkmoth ( Laothoe populi ) and the eyed hawkmoth ( Smerinthus ocellata ), as well as from their food plants. Both species of caterpillar absorb the two chlorophylls and the carotenoids lutein, cis -lutein and β-carotene in the gut and deposit lutein and cis -lutein in the integument. It is the lutein, together with pterobilin, that is largely responsible for the colour of the insect: yellow-green poplar hawkmoth caterpillars have more lutein in the integument than dull green ones which in turn have more than white ones. Yellow-green and dull green caterpillars both sequester lutein and cis -lutein in the gut wall, but the yellow-greens translocate more of these pigments to the integument than the dull greens. The white caterpillars absorb very little lutein and cis -lutein into the gut, and so they have much less also in the integument. The mechanism by which the reflected light perceived by the caterpillar is translated into differential absorption of pigment by the gut and deposition in the integument is not known.     

Effect of pine foliage damage on the incidence of larval diapause in the pine caterpillar Dendrolimus punctatus (Lepidoptera: Lasiocampidae)

The pine caterpillar Dendrolimus punctatus (Walker) with a larval facultative diapause is one of the most destructive insect pests of the pine tree Pinus massoniana in China. The larvae feeding on pine trees with different damage levels were studied to determine the induction of diapause under both laboratory and field conditions. Developmental duration of larvae before the third instar was the longest when fed with 75%–90% damaged needles, followed by 25%–40% damaged needles and intact pine needles, whereas mortalities did not differ among different treatments under the conditions of 25° and critical photoperiod 13.5:10.5 L:D. At 25°, no diapause was induced under 15:9 L:D, whereas 100% diapause occurred under 12:12 L:D regardless of the levels of needle damage. Incidences of larvae entering diapause when they were fed with intact, 25%–40% and 75%–90% damaged pine needles were 51.7%, 70.8% and 81% under 13.5:10.5 L:D, respectively. Similar results were obtained in the field experiment. Incidence of diapause was significantly different among the pine needle damage levels of pine trees when the photoperiod was close to the critical day length, indicating that the effect of host plants on diapause induction was dependent on the range of photoperiod. The content of amino acid and sugar decreased and tannin increased in pine needles after feeding by the pine caterpillars, suggesting that changed levels of nutrients in damaged needles or a particular substance emitted by damaged pine trees was perhaps involved in the diapause induction of the pine caterpillar.     

Monitoring and modeling of field infestation and damage by the maize ear borer Mussidia nigrivenella (Lepidoptera: Pyralidae) in Benin, West Africa

In many countries in West Africa, the pyralid ear borer Mussidia nigrivenella Ragonot occasionally causes severe damage to pre- and postharvest maize. Between 1992 and 1995, the distribution of and damage caused by M. nigrivenella were studied in Benin using survey data and an on-station field experiment. The borer was distributed across the whole country, and at maturity an average 25% of the ears sampled in maize fields were infested. Damage levels varied with agro-ecological zones and were highest in the Guinea Savannas. However, borer-related yield losses were comparatively low. Three applications of cypermethrin over the growing season did not provide sufficient control in the on-station field experiment. A model was developed to estimate maize losses caused by M. nigrivenella, using the percentage of infested ears, which explained 93% of the variance. Extrapolation of field data indicated a 25% yield loss once a 100% infestation of maize ears was reached. For surveys in maize fields the model is a valid tool for a rapid assessment of crop losses caused by M. nigrivenella.     

Traditional Regulation of Edible Caterpillar Exploitation in the Kopa Area of Mpika District in Northern Zambia

The Traditional Ecological Knowledge (TEK) of the Bisa people of northern Zambia on species, life cycles and host plants of the caterpillars they exploit for food and for household income generation, and the traditional control of caterpillar harvesting, were investigated through a household survey. The accessed indigenous knowledge on caterpillar biology was validated through a forest survey, caterpillar collections and identifications. Eight species of caterpillars were harvested from the surrounding miombo woodlands. Their life systems and host plants were well understood by members of local communities and this knoweldge was communicated amongst them orally. Popular commercial species were Gynanisa maya Strand and Gonimbrasia zambesina Walker. Over 20 miombo tree species hosted the two species but the mean numbers of the caterpillars on Julbernadia paniculata Troupin were significantly larger than those on other host plants (p < 0.05), indicating that J. paniculata was probably the main host plant of the two species. Traditional regulation of caterpillar harvesting involved: (i) monitoring for edible caterpillar development and abundance and for changes in caterpillar habitats, (ii) protection of host plants and moth eggs against late bush fires, through use of traditional fire technology, and (iii) temporal restriction of edible caterpillar harvesting. The possibility of the Zambian Government promoting caterpillar harvesting as an economic incentive to the Bisa people to conserve both this renewable edible caterpillar natural resource and their environment is discussed.     

Orientation and Dispersal Patterns of the Eastern Tent Caterpillar, <Emphasis Type="Italic">Malacosoma americanum</Emphasis> F. (<Emphasis Type="Italic">Lepidoptera: Lasiocampidae</Emphasis>)

Larvae of the eastern tent caterpillar, Malacosoma americanum, undergo density-dependent dispersal in response to depleted resources. Because these caterpillars have recently been implicated in abortions of pregnant mares (equine Mare Reproductive Loss Syndrome, or MRLS), there is increased interest in managing caterpillar populations, potentially through manipulation of caterpillar dispersal behavior. Consequently, we investigated dispersal patterns of food-deprived eastern tent caterpillars in artificial arenas with respect to distance, direction, and response to visual stimuli. Distance traveled is influenced by time of day, and is strongly correlated with time elapsed. Movement is non-random, and correlates closely with the position of the sun. The pattern is more pronounced with foraging third instars than with penultimate fifth instars. Visual cues appear important in caterpillar orientation, and caterpillars are responsive to vertically oriented, black objects.