Increased damage by western flower thrips Frankliniella occidentalis in chrysanthemum intercropped with subterranean clover

Suppressive effects of intercropping on Frankliniella occidentalis (Pergande) infestations have been reported in several crops. However, this study demonstrates that in year-round chrysanthemum, Dendranthema grandiflora Tzvelev, undersowing with subterranean clover, Trifolium subterraneum L., results in an increased thrips feeding damage. In a pot experiment, performed with chrysanthemum plants (cultivars Reagan and Tiger) grown with or without subterranean clover, significantly more leaves with silver and growth damage were found in the chrysanthemum plants with subterranean clover in comparison with the monocropped chrysanthemum plants. Similarly, the degree of deformation of leaf perimeter and leaf surface was higher in the top leaves of the intercropped chrysanthemum plant. In the soil experiment (only performed with Tiger and plants were grown in the soil in the greenhouse) intercropped chrysanthemum plants suffered a higher feeding damage as well. Analysis of the relation between silver or growth damage and the thrips pressure demonstrates that at similar thrips pressure in the intercropped chrysanthemum plants suffered significantly more damage. The higher thrips pressure in the intercropped chrysanthemum only explains the differences in damage partly. Changes in the reaction of chrysanthemum plants to thrips feeding or in the behaviour of the thrips, mediated by the presence of the non-host crop, are discussed. Our explanation is that chrysanthemum plants grown with clover are more susceptible to thrips feeding than monocropped plants. We conclude that undersowing with clover does not contribute to reduce damage by F. occidentalis in year-round chrysanthemum. Also, the influence of crop diversification on a pest cannot be foreseen until the specific characteristics of each individual crop – pest system are studied.     

Effects of undersown clover on host-plant selection by Thrips tabaci adults in leek

The suppressive effects of undersown clover on Thrips tabaci Lindeman infestation in leek is known but not the stages in thrips population dynamics that are affected by intercropping and the mechanisms involved. Colonization or settling of adult onion thrips (T. tabaci) in monocropped leek (Allium porrum L.) and in leek intercropped with strawberry clover (Trifolium fragiferum L.) was studied in two potted plant experiments. Potted leek plants with and without undersown clover were placed for a short period (2 and 5 days) in monocropped or intercropped field plots when high thrips infestation was expected. Thrips adults were counted on all leaves and in the shaft during this observation period. Thrips populations were monitored weekly in the field plots throughout the entire growing season.In both potted plant experiments, there were consistently fewer thrips adults on intercropped leek plants than on monocropped plants. The plant growth parameters – number of leaves and stem diameter – were similar in all treatments and thus did not explain differences in thrips adults. Natural enemies were absent on both leek and clover, and thus cannot explain the differences in adult thrips numbers. Furthermore, no adults of T. tabaci were found on the clover in the potted plant experiment and only very few in the field experiment. Thus it was concluded that strawberry clover was not an effective trap crop for thrips.In the second potted plant experiment, clover was removed just before the leek plants were introduced to the field, thus eliminating direct physical, visual and olfactory interference by clover. After the undersown clover was removed, the leek plants harboured only one-third of the number of thrips adults, as compared to the monocropped plants. This study supports the notion that there are subtle links between intercropping and plant quality, and indicates that host-plant quality is an underlying cause of the reduction in adult thrips numbers in leek/clover intercropping.     

Cover crop, rye residue and in-furrow treatment effects on thrips

Abstract:  Thrips and thrips damage to cotton and peanut plants were compared in plots with in-furrow treatments of aldicarb, phorate and diammonium phosphate (DAP) fertilizer under two tillage regimes with a winter cover of crimson clover and under different levels of rye residue ground cover. Adult and larval thrips numbers were significantly lower in cotton plots following winter crimson clover cultivation compared with no-cover plots in all 3 years. Thrips numbers did not differ with respect to the in-furrow treatments in the clover plots, but in the no-cover plots, they were significantly higher in the untreated control and DAP treatments compared with the aldicarb treatment. Thrips damage was higher in the no-cover than the clover plots except in the aldicarb treatments. Within the cover crop plots, thrips damage was highest in the control and phorate treatments and similar in the DAP and aldicarb treatments. There was an inverse relationship between the amount of rye residue ground cover and thrips density and thrips damage in cotton and peanuts. There was also an inverse relationship between the density of rye residue and damage to peanuts from Bunyaviridae tospovirus. Cotton yield was reduced in the cover crop plots and was not measured in the rye residue and peanut plots. These results suggest that ground cover alone decreases thrips numbers and thrips damage in both cotton and peanuts and that a winter crimson clover cover and an in-furrow treatment of DAP enhanced plant protection from thrips in cotton.     

A behavioural study to help clarify how undersowing with clover affects host-plant selection by pest insects of brassica crops

Laboratory and field-cage tests were done to determine how undersowing brassica plants (Brassica oleraceae L. and B. rapa L.) (Cruciferae) with subterranean clover (Trifolium subterraneum L.) (Papilionaceae) affected host-plant selection by eight pest insect species of brassica crops. The pest species tested were Pieris rapae (Lepidoptera: Pieridae) (the small white butterfly), Pieris brassicae (Lepidoptera: Pieridae) (the large white butterfly), Delia radicum (Diptera: Anthomyiidae) (the cabbage root fly), Phaedon cochleariae (Coleoptera: Chrysomelidae) (the mustard beetle), Plutella xylostella (Lepidoptera: Yponomeutidae) (the diamond-back moth), Evergestis forficalis (Lepidoptera: Pyralidae) (the garden-pebble moth), Mamestra brassicae (Lepidoptera: Noctuidae) (the cabbage moth) and Brevicoryne brassicae (Hemiptera: Aphididae) (the cabbage aphid). In all tests, except two in which the brassica plants were about three times as high as the clover background, 39%–100% fewer of the pest insect stage monitored were found on host plants presented in clover than on those presented in bare soil. Contrary to claims supporting the ‘enemies hypothesis’, differences in colonization alone appeared sufficient to account for the lower numbers of insects found when host plants are undersown with clover. To be effective in reducing plant colonization, the clover must cover 50%, and preferably more, of the vertical profile of the crop plants. As clover used as an undersown crop often has to be cut to make it less competitive with the main brassica crop, temporal aspects of the condition of the clover during critical periods of pest activity need to be recorded carefully before concluding that undersowing does not produce the effect desired against certain pest species under field conditions. The effective clover barrier is like any other treatment, if it is not present at the appropriate time it cannot be expected to reduce pest insect numbers.     

Population dynamics and integrated pest management of Thrips tabaci on leek under field conditions in northwest Italy

Thrips tabaci Lindeman (Thysanoptera: Thripidae) is a major pest of leek, Allium porrum L. (Alliaceae), in Piedmont, northwest Italy, and to control its infestation the leek crop is sprayed intensively with insecticides during the summer period. In order to find the most efficient and environment‐friendly method of thrips control, research was conducted on six commercial farms during 2005–2006 to assess thrips population composition and infestation levels, and in an experimental field during 2005–2007. Biological and chemical control were compared during 2005–2006, whereas integrated pest management was adopted during 2007. During the growing season, thrips and natural enemy populations were monitored at 14‐day intervals by beating plants; new leaves of plants were also visually inspected for thrips‐feeding symptoms. Furthermore, in the experimental field at harvest‐time, the level of thrips injury to plants was assigned to one of five classes, depending on the percentage of leaf area damaged. Over 99% of phytophagous adult thrips found were male and female T. tabaci. Infestations were very variable in the crops surveyed, partly due to broad‐spectrum chemical treatments against the leek pests, which often failed to control thrips. In general, populations peaked in September, when they reached the maximum mean values ranging between 1.7 and 33.1 thrips per plant. At harvest, none of the surveyed farms experienced quality losses due to thrips injuries. In the experimental field during 2005–2006, the mean number of thrips per plant was greater in the chemical than in the biological control treatment, even though damage indices showed no significant differences between the two treatments. Predatory thrips of the genus Aeolothrips (Thysanoptera: Thripidae) and predatory bugs of the genus Orius (Heteroptera: Anthocoridae), mostly Orius majusculus Reuter, were particularly abundant during 2007, supporting the importance of management with selective insecticides to encourage natural colonization by predators.     

THE COMPETITION BETWEEN BARLEY AND CERTAIN WEEDS UNDER CONTROLLED CONDITIONS

One of the commonest agricultural practices in Britain is the undersowing of barley and other corn crops with clover as a preparation for a clover ley after the corn crop has been reaped. The effect of the clover growing among the corn, where manuring (especially with nitrogen) is made as favourable as possible for the corn crop, is not clear. If nitrogen is deficient, it is well known that clover can furnish nitrogen for the corn, but where the supply is ample, the clover may act as a competitive crop.
When barley and clover were planted together, with abundance of water and nutrients for both, it was found that the presence of even a small number of barley plants reduced the growth of the clover by over 50%, but that an increase in the density of the barley did not increase the effect. The presence of the clover reduced the barley crop by an amount which tended to get less as the density of the barley was increased. In a sparse crop of barley, increase in clover density reduced the growth of barley very little, while that of the clover was again found to be little more than half what was obtained when this plant was grown alone.
There is no evidence of any specific effect of the roots of the one plant on the other. In the circumstances of these experiments it would seem that, far from the clover supplying nitrogen to the barley, it tends to steal some of that which would otherwise be available to the latter, when they are grown together.     

The effect of undersowing cabbage with white clover on thrips infestation and flight activity

In 2001-2003, the levels of infestation of thrips in cabbage monocrops and cabbage/white clover intercrops were compared. The flight activity of thrips was monitored using blue sticky traps and white water traps to obtain a better understanding of population dynamics of thrips. Plant samples were taken to record the number of thrips on cabbage. Over the years of observations, the highest number of thrips was collected in blue sticky traps on cabbage undersown with white clover. In the period from 15th June to 5th July 2001, the number of thrips collected in blue sticky traps in the monocropped cultivation and intercrops with white clover was on similar low levels. Next, the number suddenly increased to 372 thrips/trap in monocropped cultivation and 509 thrips/trap in the intercropped cultivation. During the period of the highest peak of thrips activity, which was on 17th July, there were 650 thrips/trap and nearly the same number was noticed for both types of cultivations. After this period, until the end of vegetation, the greater number of thrips was noticed for the traps placed in the intercrops. Additionally, in 2001 the thrips were collected in white water traps. Using this type of traps, 480 total thrips/trap were collected in the monocropped cultivation and 819/thrips/trap in the intercrops during the whole vegetation season. The percentage participation of Thrips tabaci Lind. caught in white water traps was 24.4% in the monocropped cultivation and 15.4% in the intercrops. In 2002, during the period from the middle of June to the third decade of July, significantly higher number of thrips was collected in blue sticky traps placed in the cabbage with white clover. The number of thrips collected during the period of the mass flights, which means in the first decade of July was over twice as many thrips in the traps placed in the intercropped cultivation (1316 thrips/trap) as in the monocropped cultivation (589 thrips/trap). In 2003, during the whole vegetation period, the number of thrips collected in blue sticky traps placed on the plots where cabbage was cultivated with white clover was evidently higher. In this year two peaks of the thrips flight activity were recorded: the first on 16th July and the second on 5th August. On both occassions, the number of thrips collected in blue sticky traps placed in the intercropped cultivations was about twice as high as in the monoculture cultivation. In 2001-2003, the thrips feeding on cabbage in the monocropped and intercropped cultivations were observed mainly in July and once again in August. The number of thrips on cabbage was low, only in 2002 this number was higher. In 2001, the number of thrips on cabbage in both types of cultivations was on similar level. The highest number of thrips was observed during the peak of thrips flight activity, which was in the middle of July. In years 2002-2003, despite the higher number of thrips collected in blue sticky traps placed in the intercropped cultivations, the number of pests collected from the cabbage undersown with white clover was lower than in the monocropped cultivation. In 2002, the period of the most intensive occurrence of thrips on cabbage was overlapping with the period of mass flight activity of thrips. During this period, a little higher number of thrips was noticed on cabbage in the intercropped cultivation (3.4 thrips/plant) than in the monocropped cultivation (3.2 thrips/plant). In 2003, the highest number of thrips on cabbage in both types of cultivations was noticed before the first significant peak of thrips flight activity. Whereas in the first decade of August, when the same high number of thrips collected in blue sticky traps was again noticed, no increase in the number of thrips feeding on cabbage was observed in both type of cultivations. Over all years of observations, despite the higher number of thrips collected in blue sticky traps in the intercropped cultivation, this number was always lower on the cabbage undersown with white clover. The most dominant species in both cultivations was Thrips tabaci Lind. Its percentage participation in the collected material was 83.1% in the monocropped cultivation and 76.6% in the intercropped cultivation.     

Relationship between onion thrips (Thrips tabaci) and Stemphylium vesicarium in the development of Stemphylium leaf blight in onion

Stemphylium leaf blight caused by Stemphylium vesicarium and onion thrips (Thrips tabaci) are two common causes of leaf damage in onion production. Onion thrips is known to interact synergistically with pathogens to exacerbate plant disease. However, the potential relationship between onion thrips and Stemphylium leaf blight is unknown. In a series of controlled laboratory and field trials, the relationship between thrips feeding and movement on the development and severity of Stemphylium leaf blight were examined. In laboratory assays, onions (“Avalon” and “Ailsa Craig”) with varying levels of thrips feeding damage were inoculated with S. vesicarium. Pathogen colonisation and leaf dieback were measured after 2 weeks. In pathogen transfer assays, thrips were exposed to S. vesicarium conidia, transferred to onion and leaf disease development was monitored. In field trials, insecticide use was examined as a potential indirect means to reduce Stemphylium leaf blight disease and pathogen colonisation by reducing thrips damage. Results from laboratory trials revealed that a reduction in thrips feeding decreased S. vesicarium colonisation of onion leaves by 2.3–2.9 times, and decreased leaf dieback by 40–50%. Additionally, onion thrips were capable of transferring S. vesicarium conidia to onion plants (albeit at a low frequency of 2–14% of plants inoculated). In field trials, the symptoms and colonisation of Stemphylium leaf blight were reduced by 27 and 17%, respectively with the use of insecticide to control thrips. These results suggest that onion thrips may play a significant role in the development of Stemphylium leaf blight, and thrips control may reduce disease in commercial onion fields.     

Biotic resistance limits the invasiveness of the western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae), in Florida

The spread of the western flower thrips, Frankliniella occidentalis (Pergande), has resulted in the world‐wide destabilization of established integrated pest management programs for many crops. It is hypothesized that frequent exposure to insecticides in intensive agriculture selected for resistant populations, which allowed invasive populations in the eastern USA to overcome biotic resistance from the native community of species. Research conducted in Florida to understand the role of biotic factors in limiting the abundance of the western flower thrips is reviewed. Orius spp. (Hemiptera: Anthocoridae) are effective predators that suppress populations of thrips on crop and non‐crop hosts in southern and northern Florida. Orius are more effective predators of the western flower thrips than the native flower thrips, F. tritici (Fitch) and F. bispinosa (Morgan). The native species are competitors of the western flower thrips. Excessive fertilization and the use of broad‐spectrum insecticides in crop fields further enhances populations of the western flower thrips. Interactions with native species clearly limit the abundance of western flower thrips in Florida, but populations are abundant in fertilized crop fields where application of insecticides excludes predators and competitor species.     

The impact of a parasitic nematode, Thripinema fuscum, on the feeding behavior and vector competence of Frankliniella fusca

Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) is the predominant thrips species found inhabiting and reproducing in peanut, Arachis hypogaea L. (Fabaceae), and is one of at least seven thrips species reported to transmit Tomato spotted wilt virus (TSWV). The entomogenous nematode Thripinema fuscum Tipping & Nguyen (Tylenchida: Allantonematidae), a natural enemy of F. fusca , parasitizes larval and adult populations under field conditions. All known Thripinema species render the host female thrips sterile and have the potential to suppress pest populations to near extinction. As a result, secondary spread of TSWV in peanut is reduced. Reduction of the virus under field conditions may also be due to lower transmission rates caused by parasite-induced alterations in host feeding behavior. Therefore, the feeding rates of healthy and parasitized F. fusca male and female cohorts on leaf discs were recorded daily for 10 days and digital images were subjected to image analysis and viral transmission rates were compared daily using double antibody sandwich enzyme-linked immunosorbent assay. Thripinema fuscum reduced the feeding of female F. fusca by nearly 65%, and the ability of females to transmit TSWV by 50%. Potential mechanisms underlying the parasite-induced alterations in feeding behavior and transmission are discussed. Parasitism by T. fuscum significantly reduced male longevity, but female longevity was not affected. These results provide further evidence that T. fuscum aids in regulating viruliferous F. fusca pest populations and suggests its potential as a biological control agent for inoculative release in peanut.     

Evaluation of the nematodes Steinernema feltiae and Thripinema nicklewoodi as biological control agents of western flower thrips Frankliniella occidentalis infesting chrysanthemum

In greenhouse studies, we evaluated a commercial formulation of the entomopathogenic nematode Steinernema feltiae and the inoculative release of the thrips-parasitic nematode Thripinema nicklewoodi against western flower thrips (WFT), Frankliniella occidentalis Pergande infesting potted chrysanthemums. Foliar sprays of S. feltiae applied at 1.25-2.5×10³ IJ mL^-1 and 1000 - 2000 L ha^-1 at 3-day intervals alone (targeting feeding stages) or in combination with soil applications (simultaneously treating non-feeding stages in the soil at the same rates) decreased but did not provide adequate control of thrips in flowering plants artificially infested with a dense population. Similar nematode treatments applied for four to five applications at 6-day intervals in two batches of initially clean chrysanthemums failed to prevent unacceptable damage to flowers and leaves from a dense natural infestation within the greenhouse. Although some IJ survived up to 48 h within flowers and flower buds, few nematode-infected thrips (larvae and adults) were recovered. In studies with T. nicklewoodi (which is not amenable for mass production), the inoculative releases of two parasitized hosts per plant enabled the nematode to become established within existing WFT populations under greenhouse conditions. However, relatively poor transmission and slow speed of kill (nematode primarily suppresses populations through host sterilization) prevented low level inoculations being effective over a single crop cycle. Further studies showed that transmission of T. nicklewoodi persisted for nine host generations, infected up to 83% of adult thrips and provided long-term suppression of discrete caged populations, but only after uneconomically high thrips densities had been reached.     

Effect of lime,phosphorus and mycorrhizal fungi on growth,nodulation and nitrogen fixation by white clover (Trifolium repens) grown in UK hill soils

Summary The responses of white clover (cv NZ Grasslands Huia grown in four UK hill soil types) to additions of lime and P, to inoculation with Rhizobium and mycorrhizal fungi, and to differences in soil water status were assessed in pot and field experiments. With a deep peat soil in pots, shoot production, nodulation and N fixation by clover were increased by 160, 130 and 85% respectively following inoculation with mycorrhiza, but in the field, despite a doubling of root infection, there was no response in growth. On a brown earth soil in the field inoculation with one endophyte (Glomus mosseae L1) out of four tested depressed production of white clover shoots by 42% but enhanced that of leeks (Allium porrum) by 50%; the others were without effect. With dry peaty podzol and brown earth soils in pots, clover shoot production was highest with added P when a water holding capacity of 80% was maintained, but roots from the latter had only 2.6 compared to 68 nodules per plant from the former. Further work is required to explain poor nodulation in the brown earth soils.     

Evaluation of sampling methodology for determining the population dynamics of onion thrips (Thysanoptera: Thripidae) in Ontario onion fields

Onion thrips, Thrips tabaci Lindeman, are an economic pest of alliums worldwide. In Ontario onion-growing regions, seasonal abundance and population trends of onion thrips are not well known. The objectives of this research were to investigate onion thrips population dynamics by using both white sticky traps and plant counts, to gain insight into flight height, and to determine the genus and sex of thrips fauna present in monitored fields. Adult thrips were captured on white sticky traps placed in two commercial onion fields in the Thedford-Grand Bend Marsh region as early as mid-May in 2001, 2002, and 2003. Thrips were not recorded on onion plants in these fields until late June and early July. A comparison of sticky trap captures to plant counts revealed a strong, positive correlation, indicating that sticky traps, which consistently detected thrips earlier than plant counts, could be used instead of plant counts early in the season to monitor onion thrips populations. Pole traps placed in onion and an adjacent soybean, Glycine max (L.) Merr., field revealed that regardless of crop type, most thrips were captured 0.7-0.95 m above the soil surface. During this study, 70% of 137,000 thrips captured on sticky traps and 89% of 1,482 thrips captured in pan traps were female onion thrips. No male onion thrips were identified in this study: most of the remaining thrips were Frankliniella spp.     

Evaluation of biorational insecticides and DNA barcoding as tools to improve insect pest management in lablab bean (Lablab purpureus) in Bangladesh

Lablab bean (Lablab purpureus) is a popular vegetable crop in Bangladesh, but farmers growing this crop experience significant losses to insect pests despite heavy reliance on conventional insecticides. We conducted field studies to improve pest management in lablab bean by testing biorational insecticides as alternatives to conventional insecticides for the control of pod borers (Maruca vitrata) and aphids (Aphis craccivora), and characterizing flower-inhabiting thrips as an emerging pest in this crop. In field experiments, spinosad was the most promising biorational we tested, suppressing pod-boring caterpillars more effectively than thiamethoxam or quinalphos. In contrast, azadirachtin (neem) did not significantly suppress any of the insect pests we measured, although target aphid populations were generally low at our research site. Using DNA barcoding at the coxI locus combined with morphological identification, we found eight thrips taxa inhabiting lablab bean flowers, dominated by Megalurothrips usitatus and M. distalis/peculiaris. A preliminary regression analysis indicated that these flower-inhabiting thrips reduced lablab bean yield. Our results suggest that spinosad may be useful within lablab bean IPM programs, and that these programs will likely need to incorporate tactics against thrips to effectively protect yield. Finally, we found that DNA barcoding was a valuable tool for pest identification in an understudied crop and region, but that to reach its full potential will require an investment in more comprehensive reference libraries.     

How much pollen can thrips destroy?

ABSTRACT. 1. A laboratory technique for measuring the number of pollen grains consumed by thrips is described.
2. Thrips imaginis Bagnall and Thrips obscuratus (Crawford) (Thripidae) were studied particularly on pollen of the kiwifruit Actinidia deliciosa (A. Chevalier) Liang & Ferguson in New Zealand, and Echium plantagineum L. in Australia.
3. Mean daily feeding rates (in grains per thrips per day) ranged from 29 to 843, with an individual rate as high as 1626 for T.imaginis larvae II on E. plantagineum.
4. The time taken to feed on a single grain was proportional to grain volume, and decreased with temperature.
5. Daily feeding rates were significantly different between pollens, and were higher for smaller grains. The total volume of pollen contents consumed and the total time spent ingesting this volume per thrips per day may be constant with respect to pollen species.
6. Daily feeding rates were equivalent to 0.2–0.7% of the average total pollen production of a flower per thrips per day.
7. Extrapolation of the daily feeding rates suggests that pollen damage by thrips could sometimes be reducing crop yield or plant fitness.     

Field estimation of variation in host plant use between local populations of pea aphids from two crops

Abstract. 1. In a reciprocal transplant experiment on pea aphids (Acyrthosiphon pisum (Harris)), the relative performance of clones collected from nearby alfalfa and red clover fields was tested by allowing clonal replicates to develop on both crops under field conditions.
2. Populations from alfalfa and red clover differed in relative survivorship and probabilities of reproduction on the two crops. Clones had significantly higher performance on the crop from which they were collected (the 'home' crop) than they did on the other crop.
3. Evidence is presented that previous experience on these host plants cannot account for the increased probability of reproduction observed on the 'home' crop. Thus, the differences between these two populations in their relative performance on alfalfa and clover are likely to be genetically based.
4. These results illustrate that local adaptation to different host plants can occur within small geographical areas, despite the high probability that migrants are exchanged between nearby fields of the two crops.
5. Experimental designs of the type described here permit estimation of patterns of genetic variation within and between insect populations. When applied to pest species, such designs will facilitate the study of evolution in agricultural systems.     

Effects of intercropping white cabbage with clovers on pest infestation and yield

During two consecutive years the effects of intercropping fresh market white cabbage with two species of clover on pest populations and yield were studied. White cabbage cv. Minicole was intercropped withTrifolium repens (white clover) andTrifolium subterraneum (subterranean clover) as compared to the monocrop. During the season observations were made on pest population developments, especially ofMamestra brassicae L. (cabbage moth),Brevicoryne brassicae L. (cabbage aphid),Delia brassicae L. (cabbage root fly), and evaluation of caterpillar feeding injury. At harvest the yield in quantity and quality was determined to be able to assess the gross financial result. Intercropping effects in terms of suppression of oviposition and larval populations of various pests were found. Although no pesticides were used and competition reduced the weight, the quality of the intercropped cabbages lead to a better financial result compared to the monocropped cabbage crop. The results are discussed in the perspective of the practical implications in the context of IPM.     

Comparison of two populations of Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) as candidates for biological control of the invasive weed Schinus terebinthifolia (Sapindales: Anacardiaceae)

Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae) (hereafter Schinus), is one of the worst invasive species in Florida and Hawaii. The thrips Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae) is being considered as a potential biological control agent of Schinus. Two populations of this thrips were collected in the weed's native range; one from central-east Brazil (Ouro Preto thrips) and a second from north-east Brazil (Salvador thrips). Temperature requirements, adult fecundity and impact on different plant haplotypes by P. ichini were examined in the laboratory. Complete development of thrips from both populations occurred at temperatures ranging from 20 to 30°C. Two approaches were used to model the predicted distributions of the thrips populations in the USA: the physiological model (NAPPFAST) based on cold tolerance and the ecological niche model based on climatic variables (MaxEnt). The physiological model predicted that both populations of P. ichini may establish in similar areas of the USA, overlapping with the distribution of Schinus. However, the niche model predicted that only the Ouro Preto thrips could establish in the USA. The difference in model predictions suggests an apparent preadaptation of the Salvador thrips to lower temperatures than those experienced at the locations they were collected in Brazil. The Ouro Preto thrips had similar fecundity on two Florida Schinus haplotypes, whereas lower fecundity on haplotype A was found for the Salvador thrips. Based on these results, the Ouro Preto population may be better adapted to the climatic conditions and plant haplotypes found in Florida. Moreover, greenhouse studies indicated that Schinus growth was greatly reduced by thrips feeding, which may result in lower weed reproduction and densities in the field.     

Olfactory responses of western flower thrips (Frankliniella occidentalis) populations to a non‐pheromone lure

Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest of horticultural crops worldwide. The search for alternative pest management techniques has resulted in increasing interest in the use of kairomones and other behaviour‐modifying chemicals to mitigate the impact of this pest. In this study, we determined whether the origin of populations, feeding history, and/or genotype influence the response of WFT to the thrips kairomone lure methyl isonicotinate (MI) in a Y‐tube olfactometer study. Four New Zealand thrips populations were tested: (1) from a commercial glasshouse capsicum crop, (2) from a long‐established laboratory colony (>222 generations) kept on chrysanthemums, (3) from a laboratory colony (6–9 generations) kept on French dwarf beans, and (4) thought to be a separate cryptic non‐pest species from outdoor yellow tree lupins, Lupinus arboreus Sims (Fabaceae). In the laboratory tests, significantly more WFT from all four populations chose the MI‐laden arm of a Y‐tube olfactometer when it contained 1 μl methyl isonicotinate (61.3–73.2%) compared with the blank no‐odour arm. No differences in response to MI were found between the two laboratory and the one glasshouse WFT populations. Both laboratory populations and the greenhouse population belonged to the ‘glasshouse pest’ genotype of WFT. However, the cryptic non‐pest WFT genotype responded more strongly to MI than any of the other populations, although the response was only significantly stronger than that of the long‐established laboratory population. Significant differences were also found among populations in the average time taken for thrips to make a choice to enter either arm of the Y‐tube olfactometer, with the cryptic non‐pest lupin genotype taking the shortest time, followed by thrips from the capsicum glasshouse. The results are discussed with respect to the variability in olfactory perception and olfactory behaviour within a species and the relevance to the use of such a kairomone lure in pest management programmes.