Weevil Preference Research Articles

Host selection behaviour of the banded pine weevil, Pissodes castaneus (Coleoptera: Curculionidae)

Abstract Pissodes castaneus represents an emerging pest species for Pinus spp. production in Latin America. This species attacks all the cultivated pine species in Patagonia Argentina causing wood damage and tree death. The objectives of this work were to describe the host preference behaviour of P. castaneus and the influence of wood damage by conspecifics on its host selection. In two‐choice bioassays, P. castaneus showed a feeding preference for Pinus contorta over P. ponderosa. However, percent weight gain when feeding on either species was similar. In other bioassays, P. castaneus spent more time in areas with twigs on which other conspecifics had recently fed, although they were able to successfully feed on twigs without previous damage. These results show that while P. castaneus can successfully colonize different pine species, P. contorta may be more susceptible to attack than P. ponderosa. Silvicultural management should be prioritized considering the weevil's preference for attacking damaged hosts.

Preference of Cosmopolites sordidus for fusarium wilt‐diseased banana plants

AbstractThe objective of this study was to understand the role of Cosmopolites sordidus in the dispersal of Fusarium oxysporum f. sp. cubense race 1 (Foc) and more specifically to determine whether C. sordidus is preferentially attracted to Foc‐contaminated banana plant material vs. Foc‐free material. The attraction of C. sordidus to healthy and Foc‐contaminated Gros Michel banana bulbs and pseudostems, as well as to pure cultures of Foc, was compared using four‐choice olfactometers. Males and females were studied separately. After storage in a dark room, weevils were placed in the central chamber of olfactometers. After 15 min, the orientation of each of the weevil was determined according to the food source located in each of the four peripheral chambers of the olfactometer. Overall, 560 olfactometer assays were carried out. Weevils were found to prefer Foc‐infected plant tissues. Weevil preference was not significantly affected by weevil sex. The attraction of C. sordidus to Foc‐contaminated plant material suggests that this insect could be important for the dissemination of Foc, especially in early stages of epidemics, when Foc‐infected plants are scarce.

Morphological and olfactory tree traits influence the susceptibility and suitability of the apple species Malus domestica and M. sylvestris to the florivorous weevil Anthonomus pomorum (Coleoptera: Curculionidae).

The florivorous apple blossom weevil, Anthonomus pomorum (Coleoptera: Curculionidae), is the most economically relevant insect pest of European apple orchards in early spring. Neither efficient monitoring nor ecologically sustainable management of this insect pest has yet been implemented. To identify heritable traits of apple trees that might influence the host selection of A. pomorum, we compared the susceptibility of apple tree species using infestation rates of the domesticated apple, Malus domestica (Rosaceae: Pyreae), and the European crab apple, M. sylvestris. We evaluated the suitability of the two apple species for A. pomorum by quantifying the mass of weevil offspring. Because volatile organic compounds (VOCs) emitted from flower buds of the domesticated apple have previously been suggested to mediate female weevil preference via olfactory cues, we conducted bioassay experiments with blossom buds of both apple species to explore the olfactory preference of adult weevils and, furthermore, identified the headspace VOCs of blossom buds of both apple species through GC-MS analysis. The infestation analysis showed that A. pomorum infested the native European crab apple more prevalently than the domesticated apple, which originated from Central Asia. The European crab apple also appeared to be better suited for weevil larval development than the domesticated apple, as weevils emerging from M. sylvestris had a higher body mass than those emerging from M. domestica. These field observations were supported by olfactory bioassays, which showed that A. pomorum significantly preferred the odor of M. sylvestris buds compared to the odor of M. domestica buds. The analysis of headspace VOCs indicated differences in the blossom bud volatiles separating several M. domestica individuals from M. sylvestris individuals. This knowledge might be employed in further studies to repel A. pomorum from M. domestica blossom buds.

Attraction of Sitophilus zeamais (Coleoptera: Curculionidae) to Four Host Plants

The maize weevil Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) is an important pest of stored grains, predominantly maize (Zea mays L.), wheat (Triticum L. spp.), rice (Oryza L. spp.), and sorghum (Sorghum bicolor [L.] Moench) (all Poaceae). Weevil infestations occur in the field and weevils are carried to the storage facility after harvest. Infestation also occurs in the grain storage facility. There is no effective field or storage trapping system for control. They are commonly parasitized by Pteromalidae Dalman (Hymenoptera: Chalcidoidea) spp. parasitoids in the Tropics; however, there is no biocontrol use of these Hymenoptera. Therefore, pesticide application and the development of resistant grain are the current control strategies; although, studies have indicated that odors associated with the grain upon which the weevils feed, mate, and oviposit are attractive to the weevil. Host plant produced volatiles and their associations with the maize weevil have not been investigated fully. To better understand the weevil's attraction to crop plants, a study was initiated to investigate the weevil's preference for immature host plants. Weevils that had been reared on 4 types of grain for several generations were presented immature plants of all 4 types of grains in choice tests to determine if they prefer grains of the host plant on which they had been reared. This research demonstrated that immature rice plants have the greatest attraction, and that previous feeding did not influence the weevil's host plant attraction. The isolation of key rice plant semiochemicals will be the focus in the development of an attractant for S. zeamais and may also prove effective for the control of Sitophilus oryzae (L.) (Coleoptera: Curculionidae).

Oviposition preference and offspring performance of Apoderus dimidiatus (Coleoptera: Atelabidae) between Rosa multiflora and Rubus ichangensis

AbstractLeaf‐rolling weevils (Coleoptera: Atelabidae) are considered to be specialists that oviposit only on one or two plant species. However, Apoderus dimidiatus can oviposit on at least five species. We aimed to determine whether A. dimidiatus females have different preferences for oviposition substrates, and whether differences in physical factors, nutrition and parasitism affected their choices. We observed the number of cradles, hatched larvae, pupae, emerging adults and parasitism rate during one breeding season. Weevils were given access to two host plant species, Rosa multiflora and Rubus ichangensis, and the leaf size and nutrient contents of the two plant species were investigated. We found that nutritional content, especially soluble carbohydrate, correlated with oviposition preference of weevils, and the more nutritious plant species, R. multiflora, was the preferred host in our experiment. Weevils can also use Ru. ichangensis and other plant species as hosts, likely to relieve the high parasitic pressure when laying eggs on a single host species.

Effects of methyl jasmonate on the concentration of volatile terpenes in tissues of Maritime pine and Monterey pine and its relation to pine weevil feeding

Understanding pine weevil [Hylobius abietis (L.)] feeding preferences and their relations to chemical defenses of pines may lead to improved protection of conifer seedlings across Europe and Asia. Previous studies showed reduced weevil damage in methyl jasmonate (MeJA) treated seedlings and that weevil preference for Monterey pine (Pinus radiata Ait.) or Maritime pine (Pinus pinaster D. Don) depended on feeding conditions. The present study explored whether volatile terpenes in plant tissues of control and MeJA-treated seedlings of these two pine species could explain differences in weevil feeding and seedling growth. Volatile terpenes of hexane extracts of needles and phloem were separated and identified by gas chromatography–mass spectrometry (GC–MS). The results confirmed that MeJA application reduced pine weevil feeding in both pine species, but the increase in resistance was not explained by any general change in the concentration of mono- and sesquiterpenes after MeJA application. MeJA effects on volatile terpenes differed between the two pine species. Responses to MeJA application were more intense in Monterey pine, for which total mono- and sesquiterpenes were induced and growth rates affected, even at the lowest concentration of MeJA (5 mM). In Maritime pine, seedling growth was affected only at the highest MeJA concentration (25 mM), and no effect was observed on total volatile terpenes. Contrasting effects of MeJA on key monoterpenes were also observed. In needles, the content of (−)-β-pinene, a monoterpene with deterrent properties against the pine weevil, increased in MeJA-treated seedlings of Monterey pine, but not in Maritime pine. In the phloem of Maritime pine, the MeJA treatment reduced the concentration of the pine weevil attractant (+)-α-pinene, whereas it was increased in Monterey pine. Altogether, results indicated that weevil preferences between the two species could be altered if resistance of seedlings were previously induced with MeJA. The differential inducibility of key volatile terpenes between the two pine species may be part of the explanation as to why pine weevil preferences to the two pine species differ between field and lab conditions.

The genetics of chutes and ladders: a community genetics approach to tritrophic interactions

Community genetics research has firmly established that intraspecific genetic variation in single populations can have large extended ecological consequences for populations and entire communities of organisms. Here, we sought to understand the bottom‐up effects of plant genetic variation on herbivore preference and performance, and the top–down control of predators on herbivores and their joint effects on plant fitness and evolution. Following three ecological genetics field experiments we detected heritable variation in plant traits that influenced both the preference and performance of a specialist weevil on Oenothera biennis. However, the weevil's preference and performance were not genetically correlated among O. biennis plant genotypes. Although predators and parasitoids were abundant, predators had no detectable effect on weevil performance because high egg and larval mortality was caused by non‐predatory factors such as intraspecific competition. Finally, neither the specialist weevil nor predators influenced plant fitness. Our results suggest that the focal tritrophic community studied here is primarily shaped by the bottom–up effects of plant genetic variation on herbivores, while top–down effects have no clear impacts on O. biennis fitness or evolution. We suggest that future studies should incorporate plant intraspecific genetic variation as a fundamental part of tritrophic interactions including their eco‐evolutionary dynamics.

Increased seed consumption by biological control weevil tempers positive CO2 effect on invasive plant (Centaurea diffusa) fitness

Predicted increases in atmospheric CO2 and temperature may benefit some invasive plants, increasing the need for effective invasive plant management. Biological control can be an effective means of managing invasive plants, but the anticipated range in responses of plant–insect interactions to climate change make it difficult to predict how effective biological control will be in the future. Field experiments that manipulate climate within biological control systems could improve predictive power, but are challenging to implement and therefore rare to date. Here, we show that free air CO2 enrichment in the field increased the fitness of Centaurea diffusa Lam., a problematic invader in much of the western United States. However, CO2 enrichment also increased the impact of the biological control agent Larinus minutus (Coleoptera: Curculionidae) on C. diffusa fitness. C. diffusa plants flowered earlier and seed heads developed faster with both elevated CO2 and increased temperature. Natural dispersal of L. minutus into the experimental plots provided a unique opportunity to examine weevil preference for and effects on C. diffusa grown under the different climate change treatments. Elevated CO2 increased both the proportion of seed heads infested by L. minutus and, correspondingly, the amount of seed removed by weevils. Warming had no detectable effect on weevil utilization of plants. Higher weevil densities on elevated CO2 plants reduced, but did not eliminate, the positive effects of CO2 on C. diffusa fitness. Correlations between plant development time and weevil infestation suggest that climate change increased weevil infestation by hastening plant phenology. Phenological mismatches are anticipated with climate change in many plant–insect systems, but in the case of L. minutus and C. diffusa in mixed-grass prairie, a better phenological match may make the biological control agent more effective as CO2 levels rise.

Herbivore pressure by weevils associated with flower color polymorphism in Geranium thunbergii (Geraniaceae)

Although floral herbivory has recently received increased attention as an important factor influencing plant reproduction, relatively little is known about how its frequency and intensity vary depending on traits of host plants. Here we report that herbivore pressure by a weevil, Zacladus geranii, is associated with a flower color polymorphism of Geranium thunbergii (Geraniaceae). Pink and white flower color morphs have been reported in G. thunbergii, and we found in a three-year field survey in multiple populations that, generally, adult weevils more preferentially visited white flowers than pink flowers. Consistently, we found more severe damage by weevil larvae in white flowers. Overall herbivore pressure for G. thunbergii varied strongly between populations, and the difference seems to be partly explained by the co-occurrence of a related plant species, Geranium yezoense, in a population, as weevils preferred it to both color morphs of G. thunbergii, thereby relaxing overall herbivore pressure for G. thunbergii. Nonetheless, despite such high variability, the preference of weevils for white morphs over pink morphs of G. thunbergii was found across multiple populations. We discuss possible mechanisms causing the association between flower color and herbivore preference as well as its evolutionary consequences.

Damage byNeochetinaWeevils (Coleoptera: Curculionidae) Induces Resistance inEichhornia crassipes(Commelinales: Pontederiaceae)

Induced resistance in invasive plants might influence herbivore performance or preference, and hamper herbivore-based biological control management. Specialist weevils Neochetina eichhorniae Hustache (Coleoptera: Curculionidae) and N. bruchi Warner (Coleoptera: Curculionidae) are two herbivores commonly used to control Eichhornia crassipes (Mart.) Solms (Commelinales: Pontederiaceae), a destructive and widespread invasive plant. However, we do not know whether Neochetina weevils induce resistance in E. crassipes. I report results from excised-leaf bioassay and whole-plant choice experiments testing adult weevil preference and performance in response to previous damage. I found that adult weevil damage induced resistance in E. crassipes, decreasing weevil performance, but simulated damage did not influence weevil performance in a comparable way. Simulated damage did, however, influence weevil preference. This study is the first test for induced resistance to Neochetina weevil herbivory in Eichhornia crassipes.

Apical Thickening of Epicarp is Responsible for Embryo Protection in Acorns of Quercus Variabilis

The present study explored the evolutionary role of epicarp thickness ofQ. variabilisacorns as a defensive mechanism against weevil infestation. Our results, based on two years' study, suggested that length and fresh mass of insect-damaged acorns were not different from those of intact ones, but width did differ. About 2, 18, and 79% of oviposition sites are distributed at the apical end, middle part, and basal end of acorns, respectively. About 5, 49, and 55% of eggs or larvae are infested at the apical end, middle part, and basal end, respectively. Similarly, about 10, 43, and 45% of emergence holes are found at the apical end, middle part, and basal end. Epicarp thickness varied among the three parts of acorns and was significantly negatively correlated with the appearance percentage of oviposition sites, infestation sites, and emergence sites, respectively. However, secondary metabolites and nutrition reserve showed no close correlation with the appearance percentage of oviposition sites, infestation sites, and emergence sites. Acorns with emergence holes at the apical end exhibited significantly lower seedling emergence and survival rates. Therefore, variation in epicarp thickness in individual acorns may be responsible for the weevil's preference for oviposition, infestation, and emergence, and acts as an alternative and important strategy protecting acorn embryos from pre-dispersal larval damage.

Spatial distribution of colonizing Listronotus maculicollis populations: implications for targeted management and host preference

AbstractWe characterized the spatio‐temporal distribution of emerging overwintered adult Listronotus maculicollis populations colonizing golf course fairways with Spatial Analyses by Distance IndicEs (SADIE) with the goal to better target management tactics and to test assumptions for weevil preference for annual bluegrass (Poa annua). Adults randomly colonized and moved throughout fairways. However, cumulative captures were significantly aggregated along fairway edges closest to overwintering sites demonstrating progressive movement through the edges. Spatial association analyses suggest that the spatial patterns of cumulative captures of adults rather than weekly patterns were strongly associated with larvae, indicating that the adults enter fairways from the edges and deposit eggs over the course of several weeks. We did not observe an effect of host species on the distribution of either adult or larval L. maculicollis which leads us to question traditional assumptions of host preference for short mown P. annua. Instead, we propose that the aggregated distribution of larvae is generated by a low encounter rate of short mown hosts, rather than preference for species or cultivar. This study indicates that caution need to be applied when using preference‐performance criteria in host preference studies. Future behavioural studies need to address the contributions of encounter rate and host species on L. maculicollis host selection and oviposition.

INFLUENCE OF SPRING FROST AND BLOSSOM WEEVIL DAMAGE ON STRAWBERRY YIELD FORMATION

Depending on the year, strawberry blossoms are damaged by blossom weevil and spring frost. Both damages depend largely on the cultivars, its time of flowering and frost tolerance of blossoms, or blossom weevil preference of cultivar and temperatures before and during flowering. Cv. 'Senga Sengana' was chosen for the study because it has been extensively grown in northern European countries for a long time and in all cultivar evaluation trials in Estonia it has been used as a control. Data were gathered over the eight years period (1999-2007). The data from 'Senga Sengana' were compared to the data obtained from 14 strawberry cultivars on blossom weevil damage in 2005 and 2006 and on spring frost damage in 2006. The results reveal the blossom weevil preference of cultivars. Blossom weevil prefers cv. 'Venta' most of all, cv. 'Sega Sengana' gets less damage. The damage of blossom weevil is most severe in years when average temperatures in May are over 10°C and there are no severe spring frosts. The damage of blossom weevil is extensive in years when the number of blossoms is low (with 'Senga Sengana' in 2003) 'Senga Sengana', being a late cultivar, does not suffer much from spring frosts. Over the nine-year test period only in two years (2002 and 2004) its blossoms had remarkable damage from spring frosts. In 2006 cultivars 'Gerida' and 'Wega' suffered most from spring frosts. With cv. 'Gerida' the damage rate was high partly due to low number of blossoms.

Interpopulation variation in predator foraging behaviour promotes the evolutionary divergence of prey

Despite intensive investigation of the role of predation on evolutionary processes, few studies have questioned the possibility of the evolutionary divergence of prey populations in response to interpopulation variation in predator foraging behaviour. In an interaction between a seed-predatory insect, the camellia weevil (Curculio camelliae), and its host plant, the Japanese camellia (Camellia japonica), I tested whether the evolutionary differentiation of the plant's defensive trait, pericarp thickness, was related to the interpopulation variation in the foraging behaviour of female weevils. I found that the preference of weevils for the plant fruit based on pericarp thickness varied across 13 populations in Japan. Importantly, variation in weevil behaviour explained interpopulation variation in pericarp thickness and the direction/strength of natural selection on the trait. Overall, I show that adaptive foraging of predators can result in the evolutionary divergence of predator-prey interactions.

Chemically Mediated Host-Plant Selection by the Milfoil Weevil: A Freshwater Insect–Plant Interaction

The milfoil weevil Euhrychiopsis lecontei is a specialist aquatic herbivore that feeds, oviposits, and mates on the invasive freshwater macrophyte Myriophyllum spicatum. We characterized the weevil's preference for M. spicatum, and through bioassay-driven fractionation, isolated and identified two chemicals released by M. spicatum that attract E. lecontei. Mass spectrometry and nuclear magnetic resonance spectroscopy were used to identify the attractive compounds as glycerol and uracil. Dose-response curves for glycerol and uracil indicated that weevil preference increased as sample concentration increased. Weevils were attracted to a crude sample of M. spicatum-released chemicals from 0.17 to 17 mg/l, to glycerol from 18 to 1800 microM (0.0017-0.17 mg/l), and to uracil from 0.015 to 15 microM (0.00014-1.4 mg/l). Although glycerol and uracil are ubiquitous, weevils are likely responding to high concentrations that are released as a result of the rapid growth of M. spicatum. Uracil concentration was greater in the exudates of M. spicatum than other Myriophyllum spp. E. lecontei was attracted to glycerol at a concentration similar to that at which terrestrial insects are attracted to sugar alcohols. This is the first example of a freshwater specialist insect being attracted to chemicals released by its host plant. Analysis of the water milfoil-weevil interaction provides further understanding as to how insects locate their host plants in aquatic systems.

Evolution of the Host Plant Associations of the <I>Anthonomus grandis</I> Species Group (Coleoptera: Curculionidae): Phylogenetic Tests of Various Hypotheses

A phylogenetic analysis was conducted of the Anthonomus grandis species group (Coleoptera: Curculionidae) and used to test various hypotheses concerning the evolution of these weevil species with their host plants. Phylogenetic analysis indicated that the five species of the A. grandis species group comprise two major clades. In the first clade, A. grandis Boheman is the sister taxon of A. hunteri Burke & Cate and A. mallyi Jones & Burke, and the second clade contains A. townsendi Jones & Burke and A. palmeri Jones & Burke. The proposed weevil phylogeny and knowledge of host associations strongly support the hypothesis that the genus Hampea (Malvales: Malvaceae), and not cotton ( Gossypium), is the original host plant genus of the A. grandis species group. Comparison of the phylogeny of the A. grandis group with that of a previously published phylogeny of Hampea showed little congruence, suggesting that the species of weevils are associated with Hampea as a result of host shifts and colonization processes, as opposed to co-speciation or coevolution (parallel cladogenesis). Mapping habitat associations and geographic distributions onto the phylogeny of the A. grandis group indicate that weevil preference for general habitat type (montane versus lowland habitats) and geographic proximity of species of Hampea were probably the principal factors responsible for observed associations of the weevils with their respective host plants. Possible characteristics of the A. grandis group, which may favor colonization as opposed to cospeciation processes in the association of its host plants, are discussed in light of these results.

Combining Ability for Maize Weevil Preference of Maize Grain

Maize weevil (Sitophilus zeamais Motschulsky) can cause severe grain damage in maize (Zea mays L.). Knowledge of inheritance of weevils' preference would be helpful in designing breeding strategies to develop more tolerant/resistant cultivars. This study was conducted to estimate general (GCA) and specific combining ability (SCA) for weevil preference/nonpreference. We used a 10‐parent diallel cross in 1992 (Griffmg's Method 3, Model 1). In 1993, due to insufficient seeds for some crosses, two eight‐parent diallels (Griffing's Method 4, Model 1) were evaluated for GCA and SCA for maize weevil preference of maize grain. The two eight‐parent diailels were subsets of the original 10‐parent diallel. Second generation grain samples (100 g per plot) from F1 crosses grown in the field were evaluated for maize weevil preference during 96‐d (1992 experiment) and 108‐d (1993 experiments) periods in the laboratory. The GCA, SCA, and reciprocal mean squares from the 10‐parent diallel results from 1992 were significant. Both GCA and SCA were important in the analysis of the Subset 1 eight‐parent diallel combined across years, whereas only GCA was significant in the Subset 2 eight‐parent diallel combined across 1992 and 1993 data. Positive effects indicated non‐preference and negative effects, preference of grain. Common parent means and GCA effects showed that L108 transmitted the most nonpreference and Mo17, the least nonpreference to its hybrids. In the 1992 data, significant positive GCA effects were detected in L108, L605, and L654; and significant negative GCA effects in B73, Mo17, L329, L729, and L266. Mol7 had a significant positive maternal effect (11.6), whereas B73 had significant negative maternal effect (−11.93). The single cross Mo17♀ × B73♂ would possess more nonpreference than its reciprocal cross. Combined across years, analyses of two eight‐parent diallel subsets of the original 10‐parent diallel indicated GCA was more important than SCA in inheritance of preference/nonpreference.

Mechanisms of resistance to the red sunflower seed weevil in sunflower accessions

In the northern Great Plains of North America, internal seed feeding by larvae of the red sunflower seed weevil, Smicronyx fulvus LeConte, causes economic damage to sunflower, Helianthus annuus L. Our purpose was to identify sunflower germplasm with resistance to the red sunflower seed weevil and to determine mechanisms of resistance. In 1986, 300 sunflower accessions were evaluated for the percentage of seed damaged by red sunflower seed weevil larvae. In 1987, six accessions selected on the basis of the 1986 results were evaluated for resistance to the red sunflower seed weevil. The selected accessions had flowering dates comparable to the susceptible check. The percentage of seeds with exit holes (emerged and successfully developed larvae), with larvae (unemerged larvae remaining in the seed), with inclusive damage (total percentage of seeds with exit holes or larvae), and with adult feeding or oviposition scars was used to test for larval antibiosis and adult preference. Larval antibiosis was detected in accessions 251465, 175730, 170407 and 170408 which had significantly higher percentages of seeds with larvae than did the susceptible check. The percentages of seeds with larvae and with inclusive damage were positively correlated with adult feeding or oviposition scars. Therefore, in the accessions tested, larval infestations appeared to be at least partially determined by adult red sunflower seed weevil preference.

Root disturbance of common ash, Fraxinus excelsior (Oleaceae), leads to reduced foliar toughness and increased feeding by a folivorous weevil, Stereonychus fraxini (Coleoptera, Curculionidae)

Abstract. Bioassays were carried out to examine differences in the feeding of a folivorous weevil, Stereonychus fraxini De Geer, on leaves from ash saplings with undamaged roots, and those with damaged roots. Beetles ate significantly more of the leaves of root‐damaged saplings in a choice experiment. A separate study of the effect of root damage on leaf toughness was carried out on a second group of ash saplings. Saplings with damaged roots had less tough leaves than control saplings. Decreased leaf toughness in hypothesized as a mechanism to explain the preference of weevils for leaves from damaged trees. Both chemical and physical changes may occur in the tissues of ash trees in response to environmental stress such as drought and root damage. Root damage caused by agricultural disturbance is hypothesized as a mechanism making mature ash trees in hedgerow ecosystems more susceptible to insect herbivores.

Chemosensory responses of cowpea weevil,Callosobruchus chinensis to an aquatic weed, water hyacinth,Eichhornia crassipes (Mart) Solms

The behavioral responses of cowpea weevil,Callosobruchus chinensis to the leaf extracts of the aquatic weed, water hyacinth,Eichhornia crassipes (Mart) Solms. was evaluated by three different methods. The petroleum ether-soluble fraction ofE. crassipes induced high weevil attraction in all methods employed. The olfactometer assay provided a reading on weevil chemosensory responses, whereas the free-choice tests measured response and preference of weevils to the untreated or extract-treated food grain of their choice over a longer period. The extracts were also presented under no choice test conditions to assay them for the presence of oviposition stimulants. In all these methods the extracts of water hyacinth evoked a quick directional response. Another interesting feature is that the extract, besides producing attraction, also caused mortality of the insects.