Parasitoid Activity Research Articles

A Study of Cactoblastis cactorum (Lepidoptera: Pyralidae) in its Native Range: Further Insights into Life Cycle, Larval Identification, Developmental Parameters, Natural Enemies, and Damage to the Host Plant Opuntia ficus-indica (Caryophyllales: Cactaceae)

Cactoblastis cactorum Berg (Lepidoptera: Pyralidae) has been extensively studied since its initial use as a biological control agent for invasive populations of Opuntia Mill. The moth is native to several South American countries including Argentina where the exotic Opuntia ficus-indica (L.) Mill. (Cactaceae) is grown as a commercial crop. Recently C. cactorum has attracted considerable attention following its non-intentional establishment in Florida, because it now threatens the highly diverse and economically important Opuntia taxa of the southern USA and Mexico. To elucidate several aspects of this system, we recorded phenological data and parasitoid activity from Argentina across an annual cycle. We reared several generations of moths to better document the life cycle, described several formerly unpublished larval stages and morphological characters, and compared developmental parameters from samples collected from different sites. We found that C. cactorum has 3 overlapping generations across a 9 mo growth period with winter quiescence at the larval VI instar or pupal stage. The most common natural enemy of larvae was the parasitoid Apanteles opuntiarum (Martinez and Berta) (Hymenoptera: Braconidae). Information is given on its development and percentages of parasitism throughout the year. No egg parasitoids were found in field-collected eggsticks or on experimental eggsticks. There were no significant differences between developmental stages and times of C. cactorum from Tucuman and Cordoba in Argentina. We found intermediate C. cactorum damage on low-density cultivated Opuntia, but much lower damage in commercial plantations with high densities of plants. Surprisingly, we found that a “black spot” fungal infection (Alternaria Nees) (Pleosporaceae) produced a higher level of damage in commercial plantations in Cordoba, as well as in natural settings in Tucuman

Pupal parasitoids for the biological control of Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae)

Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae), popularmente conhecida como broca da cana-de-açúcar, é a maior praga da cultura de cana de açúcar e é responsável por consideráveis danos econômicos. O manejo dessa praga é complexo devido ao alojamento no interior do colmo; quando imatura, cria galerias que enfraquecem as plantas, reduz a biomassa e a qualidade do suco da cana, e perdas na produtividade agrícola. O uso excessivo de inseticidas químicos propicia resistência dessas pragas, danos ao meio ambiente, à fauna e à flora e alto custo. Dessa forma, um componente imprescindível do manejo de pragas é o controle biológico. Todas as espécies animais e vegetais apresentam inimigos naturais (parasitoides, predadores, entomopatógenos) que atacam diversos estágios de desenvolvimento. Parasitoides representam uma importante ferramenta no controle biológico de pragas lepidópteras. O conhecimento da atividade do parasitoide pupal é importante para o desenvolvimento de estratégias de controle biológico para essa praga, a qual ocasiona perdas significativas. Portanto, este artigo usa dados publicados para destacar a importância e a eficácia dos parasitoides contra a pupa da broca da cana-de-açúcar.

Males and females evolve riskier traits in populations with eavesdropping parasitoids

Predation and/or parasitism often limits the evolution of conspicuous male traits and female preferences because conspicuous traits can attract predators or parasites and it is costly for females to associate with males that attract predators or parasites. As a result, males and females in high-risk populations are expected to evolve safer mating behaviors compared to individuals from low-risk populations. We tested this antagonistic selection hypothesis in the field cricket Gryllus lineaticeps. Males produce chirped songs, and both female crickets and the eavesdropping parasitoid fly Ormia ochracea prefer faster chirp rates. The flies attack the field crickets late in the breeding season and parasitized crickets die. We used a common garden rearing design to test for evolved differences in songs and preferences between high- and low-risk populations. In contrast to predictions of the antagonistic selection hypothesis, males from high-risk populations produced faster (riskier) chirp rates and females preferred faster chirps. We suggest that late-season parasitism selects for increased investment in reproductive traits to maximize reproduction before the advent of parasitoid activity (“late-season parasitism hypothesis”), which would at least explain riskier female preferences and potentially riskier male songs in the high-risk populations. Predation and parasitism may thus have diverse and unexpected effects on the evolution of reproductive behavior, depending upon the temporal pattern of predator- or parasite-induced mortality. Mating signals are typically conspicuous and not only attract partners but also predators and parasites. Even the silent mating partner may experience predation or parasitism by associating with the signaler. Under these circumstances, it is commonly assumed that natural and sexual selection act in opposite directions, effectively limiting the evolution of conspicuous signals and preferences. We demonstrate that an eavesdropping parasitic fly caused the evolution of preferences, and potentially songs, in a field cricket in the opposite, more conspicuous, direction than predicted by antagonistic selection. We argue that the temporal pattern of parasitism in relation to the reproductive season likely causes this unexpected evolutionary pattern. We propose the late-season parasitism hypothesis as an alternative to the antagonistic selection hypothesis, which might better explain more conspicuous mating trait values in other species that experience seasonal predation or parasitism.

Nest site choice by the intertidal spider Desis formidabilis (Araneae: Desidae) and nest utilisation by its hymenopteran egg parasitoid

1. Echthrodesis lamorali Masner, 1968 is the only known parasitoid of the eggs of the intertidal rocky shore spider Desis formidabilis O.P. Cambridge 1890 and is endemic to a small area of South Africa.2. The abundance of spider nests and parasitoid presence were assessed in relation to their in‐ and between‐shore location at multiple sites within the distribution of E. lamorali along the Cape Peninsula (Western Cape, South Africa).3. Desis formidabilis nests were more abundant in the mid‐shore zone than higher up or lower down the shore. Spider population sizes also differed between collection sites, with higher numbers recorded on the cooler western coast of the peninsula.4. Evidence of parasitoid activity was recorded in 43.31% of the 127 nests and 13.85% of the 592 egg sacs they contained.5. Where parasitoids gained entry to a spider egg sac, oviposition took place into all of the eggs present.6. Incidence of wasp activity was positively correlated with spider nest concentration, not with height up the shore, suggesting that both the host and parasitoid are tolerant of salt‐water inundation.7. These results should assist managers of the Table Mountain National Park, in which the full distribution of E. lamorali falls, to better understand this component of rocky shore community dynamics.

Population dynamics and new record of larval parasitoids, Senometopia sp. and Winthemia sumatrensis (Townsend) (Diptera: Tachinidae) on banana skipper, Erionota torus Evans (Lepidoptera: Hesperiidae) from South Karnataka

Field study was conducted for two years (2014-16) to know the population dynamics of banana skipper, Erionota torus Evans (Lepidoptera: Hesperiidae) and its tachinid parasitoids, Senometopia sp., and Winthemia sumatrensis . The pooled data over the two years indicated that the skipper plant infestation ranged from 6.66 to 84.25 per cent and incidence started during the first fortnight of August (8.34 per cent incidence) when the crop was at broadleaf follower stage, and a gradual increase in the infestation level of skipper was observed with a peak activity (84.25 per cent incidence) during first fort night of January (Pre flowering period) and also extended to the flowering period (February to March). The pooled data over the years indicated the maximum incidence was recorded during pre flowering period with a mean infestation of 75.02 per cent followed by flowering period (45.67 per cent), broad leaf followers (29.58 per cent) and bunch period (1.66 per cent). Two tachinid parasitoids Senometopia sp., and W. sumatrensis were encountered during our two years study period. The larval parasitoids activity initiated from second fortnight of September (0.62 per cent) and reached its maximum population during second fortnight of November (7.25 per cent) and later parasitoid activity gradually declined till second fortnight of January (0.62 per cent). The maximum activity was noticed during pre flowering period with a mean of 3.27 per cent parasitization by Senometopia sp., and W. sumatrensis .

Abiotic factors affecting Diachasmimorpha longicaudata (Hymenoptera: Braconidae) activity as a natural enemy of Ceratitis capitata (Diptera: Tephritidae) under semi‐natural conditions in the Mediterranean region

AbstractThe larval–pupal endoparasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) is currently the most commonly employed biological control agent against Tephritid fruit flies in the Americas. However, this parasitoid remains largely ignored and is not used in many regions, including the Mediterranean Basin. In this study, the potential of D. longicaudata as a biocontrol agent against the Mediterranean fruit fly (medfly) Ceratitis capitata (Diptera: Tephritidae) was addressed in an area of eastern Spain (the Valencian community). The parasitic activity of parasitoids and the effects of climatic conditions were evaluated throughout a 1‐year period in field‐cage experiments in which parasitoids were confined with apples artificially infested with medfly larvae. The following parameters were calculated and related statistically to several environmental conditions: the parasitism rate, the induced mortality and progeny sex ratio. The results show that D. longicaudata is able to parasitize medfly larvae throughout the year under semi‐natural conditions. Important fluctuations in the parasitism rate (from almost zero to 42%) and the induced mortality (from 6% to 80%) were partially influenced by climatic conditions. The parasitism rate increased with mean temperature and decreased with mean relative humidity, while the induced mortality decreased with minimum relative humidity. The optimal climatic conditions for the activity of the parasitoid were a mean temperature of 16–24°C combined with a relative humidity of 45%–60%. Overall, these results suggest that reduction in the medfly population due to D. longicaudata activity is feasible and provide information about the optimal time period for parasitoid release in the field. In conclusion, D. longicaudata has a significant potential to control C. capitata in the Mediterranean region.

Can Flowering Greencover Crops Promote Biological Control in German Vineyards?

Greencover crops are widely recommended to provide predators and parasitoids with floral resources for improved pest control. We studied parasitism and predation of European grapevine moth (Lobesia botrana) eggs and pupae as well as predatory mite abundances in an experimental vineyard with either one or two sowings of greencover crops compared to spontaneous vegetation. The co-occurrence between greencover flowering time and parasitoid activity differed greatly between the two study years. Parasitism was much higher when flowering and parasitoid activity coincided. While egg predation was enhanced by greencover crops, there were no significant benefits of greencover crops on parasitism of L. botrana eggs or pupae. Predatory mites did not show an as strong increase on grapevines in greencover crop plots as egg predation. Overall, our study demonstrates only limited pest control benefits of greencover crops. Given the strong within- and between year variation in natural enemy activity, studies across multiple years will be necessary to adequately describe the role of greencover crops for pest management and to identify the main predators of L. botrana eggs.

Olfactory host‐finding behaviour of Oulema melanopus (Coleoptera: Chrysomelidae) and its parasitoid, Tetrastichus julis (Hymenoptera: Eulophidae)

AbstractBehavioural responses to the host‐associated olfactory cues have not been completely understood for the cereal leaf beetle, Oulema melanopus, and its principal parasitoid, Tetrastichus julis. We, therefore, investigated the role of olfactory cues in the host‐finding behaviour of these species using olfactory bioassays. Behavioural responses of O. melanopus to odours emanating from intact host plants (wheat, oat, barley) vs. a clean‐air control were tested using multichoice and two‐choice bioassays. For T. julis, responses of naïve and experienced adult female wasps to odours associated with the faecal coat of O. melanopus larvae were measured under multichoice and two‐choice conditions. Our results indicate that olfactory cues are involved in the host‐finding behaviour of both O. melanopus and T. julis. Olfactory responses of O. melanopus were influenced by the sex of the beetle and the physiological stage of adults (reproductively active vs. in reproductive diapause). Females respond to olfactory cues in greater proportions than males, and reproductively active, overwintered adults show greater responsiveness than teneral adults in reproductive diapause. Behavioural responses to cues emanating from different crop species were different in multichoice bioassays but not in two‐choice bioassays. Further, we report for the first time that the olfactory cues associated with the faecal coat of O. melanopus evoke host‐finding behaviour of its parasitoid, T. julis. Naïve female wasps are more likely to use these cues to locate the potential host than experienced females. The results of this investigation provide insights into host finding by both the species and the nature of behavioural response brought about by olfactory stimuli, and the results can help to design strategies to improve parasitoid activity by enhancing the crop environment to generate cues for host finding and to manage O. melanopus populations.

Modeling Environmental Influences in the Psyllaephagus bliteus (Hymenoptera: Encyrtidae)-Glycaspis brimblecombei (Hemiptera: Aphalaridae) Parasitoid-Host System.

Glycaspis brimblecombei Moore (Hemiptera: Aphalaridae) is an invasive psyllid introduced into the Mediterranean area, where it affects several species of Eucalyptus. Psyllaephagus bliteus Riek (Hymenoptera: Encyrtidae) is a specialized parasitoid of this psyllid that was accidentally introduced into Italy in 2011. We developed a model of this host-parasitoid system that accounts for the influence of environmental conditions on the G. brimblecombei population dynamics and P. bliteus parasitism rates in the natural ecosystem. The Lotka-Volterra-based model predicts non-constant host growth and parasitoid mortality rates in association with variation in environmental conditions. The model was tested by analyzing sampling data collected in Naples in 2011 (before the parasitoid was present) and defining several environmental patterns, termed Temperature-Rain or T-R patterns, which correspond to the host growth rate. A mean value of the host growth rate was assigned to each T-R pattern, as well as a variation of the parasitoid mortality rate based on temperature thresholds. The proposed model was applied in simulation tests related to T-R patterns carried out with a data series sampled between June 2014 and July 2015 in five Italian sites located in Campania, Lazio, Sicily, and Sardinia regions. The simulation results showed that the proposed model provides an accurate approximation of population trends, although oscillation details may not be apparent. Results predict a 64% reduction in G. brimblecombei population density owing to P. bliteus parasitoid activity. Our results are discussed with respect to features of the host-parasitoid interaction that could be exploited in future biological control programs.

Parasitism on seed predators overcomes the detrimental effects of defoliation on plant fitness in a tritrophic system

It is widely recognised that the interaction between plants and herbivores cannot be completely understood if the natural enemies of the latter are not included. Most studies looking at the effects of herbivores and their enemies on plant fitness only consider one herbivore species or guild; however, plants in nature usually face the attack of more than one herbivore guild simultaneously and these herbivores may have a non-additive effect on the attraction with bodyguards and plant fitness. In this study, we asked whether folivory affects the activity of parasitoids on seed predators and whether this effect cascades down to plant fitness. We assessed these questions in a tritrophic system: the plant Ruellia nudiflora, its pre-dispersal seed predators and the parasitoids of the latter. Plants were submitted to either 50 % artificial defoliation or no defoliation (control). The number of seeds, fruit production and parasitoid incidence was assessed periodically in both sets of plants. Parasitoids indirectly and positively affected seed number, while defoliation had a direct negative effect on the number of seeds and an indirect negative effect on parasitoid incidence. However, the combined effect of defoliation and seed predation increased the indirect positive effect of the parasitoids on seed production, which overcame the negative effects of defoliation.

Phenology of Asian Citrus Psyllid (Hemiptera: Liviidae), With Special Reference to Biological Control by Tamarixia radiata , in the Residential Landscape of Southern California.

Since its discovery in 2008, the pestiferous Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), has become widely established in residential citrus trees throughout southern California. In 2011, Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae), a host-specific parasitoid of D. citri , sourced from Punjab Pakistan, was introduced into California as part of a classical biological program aimed at suppressing D. citri populations in urban areas. Despite these release efforts, little is known about the population dynamics of D. citri in urban citrus or the efficacy of T. radiata in controlling psyllid populations in urban-grown citrus. To address this shortcoming, the population phenology of D. citri was monitored biweekly for 2-3 yr on five different host plants (Rutaceae) at 11 residential sites across Riverside and Los Angeles Counties in southern California. Citrus flush growth patterns and parasitoid activity levels were also assessed. Urban D. citri populations were present year round at each site, with highest densities occurring over July through November. Temperature was an important indicator of overall D. citri densities with positive correlations across all life stages. Regularly flushing lime trees consistently supported the highest densities of psyllid eggs and nymphs, while equally vigorous flushing curry leaf plants supported the highest adult densities. While T. radiata activity was detected at all sites, average year-round percent parasitism was low throughout the study, averaging <5% in 2012, 2013, and 2014.

A field screening of pomegranate cultivars for resistance to the carob moth, Ectomyelois ceratoniae, and compatibility with its larval parasitoids

The use of resistant cultivars could be an efficient pest management strategy against the carob moth Ectomyelois ceratoniae in pomegranate orchards. To identify possible resistant pomegranate cultivars, fruit infestation with E. ceratoniae larvae as well as the incidence of their parasitoids were monitored on 19 pomegranate cultivars in Isfahan, Iran. There were significant differences between cultivars in terms of larval infestation of fruits and the parasitoid activity on them. The cultivars S-Sefid-Saveh and Malas-Esfahan were the most resistant cultivars with 10% ± 0.9% and 15% ± 2.4% infestations, respectively. The most susceptible cultivars were D-hamomi-Pishva, Shahpar-Pishva and G-shahpar-Varamin with 80% ± 2%, 80% ± 0.88% and 79% ± 0.7% infestation, respectively. Parasitism rate was significantly different between cultivars as well, but this was not related to the cultivars resistance. Three parasitoid species, Apanteles myeloenta, Venturia canescens and Bracon hebetor, were collected and identified from the pest larvae, and A. myeloenta was the most abundant species. The highest rate of parasitism (6.8% ± 0.4%) was observed on the G-Shahpar-Varamin, which was the only cultivar from which all the parasitoid species were collected.

Native and introduced range surveys for egg parasitoids of Agrilus auroguttatus, an invasive pest of native oaks in California

The invasive goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), has caused extensive mortality to indigenous oaks in southern California. This woodborer is native to southern Arizona where low population densities may, in part, be due to the presence of co-evolved natural enemies. Surveys were conducted in Arizona and California from June to August 2013 by deploying sentinel egg masses in an attempt to attract, collect and identify potential egg parasitoids of this beetle that could be used for a classical biological control programme in California. In total, 18,052 A. auroguttatus eggs were deployed throughout the native and introduced range. Parasitoids did not attack any eggs deployed in Arizona or California. The inability to detect egg parasitoids could be explained by the following: (1) host-specific egg parasitoids of A. auroguttatus do not exist, (2) surveying time did not coincide with peak activity of egg parasitoids or (3) surveying methods were insufficient at detecting egg parasitoids.

Neochrysocharis okazakii(Hymenoptera: Eulophidae) as a Major Parasitoid Wasp of Stone Leek Leaf MinerLiriomyza chinensis(Diptera: Agromyzidae) in Central Vietnam

Liriomyza chinensisis a major pest of Welsh onionAllium fistulosumin Asia but little is known about the abundance of its natural enemies. A field survey was made to explore the major parasitoids ofL. chinensisleaf miner in central Vietnam. An eulophid parasitoid,Neochrysocharis okazakii,comprised more than 95% of parasitoids reared from leaf miner larvae collected in the onion field and 98.3% of leaf miner parasitoids found during searches of onion plants. The mean number of femaleN. okazakiion plants was greater in onion fields with a higher density ofL. chinensis, and, during searches, a greater proportion ofN. okazakiiwas found on onion with moreL. chinensismines, suggesting density-dependent parasitoid aggregation. Melanized dead larvae ofL. chinensiswere more frequently found in onion fields with more parasitoids, demonstrating that melanized leaf miners are a good indicator of parasitoid activity. Mean instant rate of host encounter byN. okazakiiin the field was estimated at 0.077, and the likelihood of a parasitoid finding a host increased with host density. Taken together, these results show thatN. okazakiiis the major parasitoid ofL. chinensis. Usefulness of this parasitoid in stone leek leaf miner management is discussed.

Sentinel eggs underestimate rates of parasitism of the exotic brown marmorated stink bug, Halyomorpha halys

Native to eastern Asia, the brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), has become a serious invasive pest in North America. Consequently, accurate assessment of parasitism rates under field conditions is critical for determining baseline parasitism rates of native egg parasitoids on BMSB, and for future evaluations of native or exotic parasitoid biological control release strategies and impacts. BMSB sentinel (laboratory-laid) egg masses have typically been used for this purpose, even though they could be providing misleading estimates of parasitoid activity. Accordingly, we compared the use of BMSB sentinel (laboratory-laid) and wild (naturally field-laid) egg masses in 2012 and 2013 to examine rates of parasitism and the parasitoid community composition of indigenous egg parasitoids in outdoor ornamental nurseries. Wild egg masses consistently had higher rates of parasitism than sentinel egg masses. In 2012, wild egg masses had a mean percent parasitism of 28.4% compared to 4.6% in sentinel egg masses, while in 2013 the difference between the two methods increased even further with a mean percent parasitism of 55.3% in wild egg masses compared to 0.8% in sentinel eggs. Furthermore, we found greater total numbers of parasitoids (889, 42) and greater species richness (seven, five), when using wild egg masses compared to sentinel egg masses, respectively. While sentinel egg masses provide a rapid and convenient way to assess the presence of natural enemies, our findings indicate that using sentinel egg masses could dramatically underestimate actual rates of parasitism and provide inaccurate estimates of parasitoid community composition. Future studies should address potential mechanisms underlying these patterns such as lack of certain host cues required by parasitoids in sentinel compared to wild egg masses.

Insect attraction to herbivore-induced beech volatiles under different forest management regimes.

Insect herbivore enemies such as parasitoids and predators are important in controlling herbivore pests. From agricultural systems we know that land-use intensification can negatively impact biological control as an important ecosystem service. The aim of our study was to investigate the importance of management regime for natural enemy pressure and biological control possibilities in forests dominated by European beech. We hypothesize that the volatile blend released from herbivore-infested beech trees functions as a signal, attracting parasitoids and herbivore enemies. Furthermore, we hypothesize that forest management regime influences the composition of species attracted by these herbivore-induced beech volatiles. We installed flight-interception traps next to Lymantria dispar caterpillar-infested young beech trees releasing herbivore-induced volatiles and next to non-infested control trees. Significantly more parasitoids were captured next to caterpillar-infested trees compared to non-infested controls, irrespective of forest type. However, the composition of the trophic guilds in the traps did vary in response to forest management regime. While the proportion of chewing insects was highest in non-managed forests, the proportion of sucking insects peaked in forests with low management and of parasitoids in young, highly managed, forest stands. Neither the number of naturally occurring beech saplings nor herbivory levels in the proximity of our experiment affected the abundance and diversity of parasitoids caught. Our data show that herbivore-induced beech volatiles attract herbivore enemies under field conditions. They further suggest that differences in the structural complexity of forests as a consequence of management regime only play a minor role in parasitoid activity and thus in indirect tree defense.

Occurrence of Parasitoid, Leiophron Sp. (Hymenoptera: Braconidae), on Adults of Helopeltis antonii Signoret in Cashew

Helopeltis antonii is a major pest of cashew, cocoa, neem, guava and pepper in the old world tropics. Survey for parasites identified a parasitoid, Leiophron sp. (Hymenoptera: Braconidae), on adults of H. antonii. The parasitism was low (1.3%), of which 59.4% was observed during the month of June. Size of the parasitoid larvae was 3.66 ± 0.11mm in length, and 1.31±0.03mm in breadth. Pre-pupation period was 1.75±0.22 days. Copulation was observed between parasitized H. antonii males and females indicating, that, mating was not affected by parasitism. Parasitoid activity showed significant positive correlation (r = 0.62; P = 0.05) with rainfall. Parasitism provided by this parasitoid certainly warrants further investigation on biological control of this economically important pest.

Responses of cereal aphids and their parasitic wasps to landscape complexity.

The intensification of agriculture has caused a decline in the complexity of agricultural landscapes because of the expansion of arable lands and the removal of natural habitats. These landscape changes, which have substantial effects on natural enemies (e.g., parasitoids) and on biological control services, have received considerable attention recently. In the current study, we analyzed the effects of landscape complexity on cereal aphids and their parasitic wasps in 24 sites during a period of 3 yr. In total, 11 primary parasitoid species and 6 hyperparasitoid species, comprising 5,220 individuals, were collected in our experiments. With the exception of two primary parasitic wasps (Trioxys asiaticus Telenga and Toxares sp.) and one hyperparasitic wasp (Dendrocerus carpenteri [Curtis]), most species were sensitive to landscape complexity after > or = 1 yr. Species diversity, primary parasitism, and hyperparasitism increased with increasing landscape complexity. However, the relationship between the population density of active primary parasitoids (effective primary parasitoids) and landscape complexity was indicated by a quadratic function, not a linear function. The effective population density of primary parasitoids was maximal (2.04 individuals per 100 wheat stems) if the percentage of noncrop habitat was 38%. The hypothesis that landscape complexity may enhance the activity or higher diversity of primary parasitoids and hyperparasitoids was well-supported by our study. However, the hyperparasitoids had a more sensitive response to landscape complexity than the primary parasitoids. Further studies should aim to enhance the biological pest control of primary parasitoids and suppress hyperparasitoids by habitat manipulation. This technique could be used effectively for pest management in mosaic landscapes through habitat rearrangement and reorganization.

Effects of landscape complexity and habitat management on stemborer colonization, parasitism and damage to maize

Lepidopteran stemborers are a serious constraint to efficient production of maize in sub-Saharan Africa. One of the most effective ways of managing these pests is through a habitat management system called push–pull. Landscape complexity has been shown to enhance biological control of insect pests, and therefore may influence effectiveness of habitat management systems designed to control pests. We studied the relative importance of the push–pull cropping system as a local effect and proportional cover of grassland as a landscape effect on (i) stemborer population density and damage to maize, and (ii) parasitism and mortality of stemborer life stages in western Kenya. We found a significant interactive effect between cropping system and grassland cover on abundance of stemborer larvae and pupa, and a near significant interactive effect of these variables on rates of egg parasitism. Cropping system had the largest effect on larval and pupal abundance in more complex landscapes, whereas it affected egg parasitism most strongly in the simplest landscapes. Grasslands appeared to primarily function as a source for the pests, rather than for natural enemies. However, sites from landscapes with a larger range of grassland cover need to be studied to fully explore the combined effects of cropping system and landscape complexity on pest control in this system. The push–pull cropping system significantly suppressed stemborer colonization of the maize and enhanced activity of stemborer parasitoids, with significant reductions in crop damage and increase in grain yield.

Kairomonal effect of host body washing on the egg parasitoid Trichogramma brasiliensis (Ashmead) (Hymenoptera: Trichogrammatidae).

Bioassay with hexane extracts of male and female whole body wash of host insects viz ., Earias vittella and Spodoptera litura with Trichogramma brasiliensis revealed their kairomonal activities. Whole body extracts of male and female moths were analysed separately by gas chromatography for determining their hydrocarbon profile, which showed the presence of straight chain saturated hydrocarbons ranging from C 8 to C 35 . The concentration of these hydrocarbons ranged from 0.02 µg/g to 2579 µg/g of insect extract. Both the host insects showed variation in number and concentration of these chemicals, which were responsible for influencing the parasitoid activity, parasitism and emergence. The foraging activity of the parasitoid as indicated by parasitoid activity index (PAI) was highest (12.00) in S. litura male body extract at concentration C 4 (1000 ppm) followed by (10.83) in E. vittella female body extract at C 5 (10,000 ppm) by T. brasiliensis . Maximum percentage parasitism of (45.55) and emergence (12.50) was observed at concentration C 4 in S. litura male body extract followed by E. vittella female body extract. Highest overall response was recorded in egg cards treated with whole body wash of male and female of S. litura and E. vittella , respectively, which may be attributed to the presence of more number of favourable saturated hydrocarbons viz .; heneicosane, tricosane, pentacosane, hexacosane, octacosane, and nonacosane, as revealed by GC. These favourable hydrocarbons at appropriate concentration of body extract of E. vittella female and S. litura male could be used for enhancing parasitization by T. brasiliensis .