Recovery of a power plant cooling reservoir ecosystem from selenium bioaccumulation

Hyco Reservoir, a North Carolina power plant cooling impoundment, was impacted by selenium toxicity during the late 1970s. Selenium inputs via coal ash discharge resulted in bioaccumulation through the aquatic food chain which caused reproductive failure and population declines of bluegill, other Lepomis spp., largemouth bass, crappie, yellow perch, and sucker species. Following these declines, green sunfish, satinfin shiner, gizzard shad, eastern mosquitofish, and redbelly tilapia dominated the fish community. During 1990, the power plant converted to a dry fly ash handling system that reduced selenium loading into the reservoir. Construction costs for this system were approximately $48 million and annual operating costs have been approximately $1 million/year. Mean selenium concentrations in reservoir waters at the power plant discharge declined from 8.8 μg/l to 3.2 μg/l within one year of the system operation, and this decline was consistent with a priori mass balance modeling predictions. Depuration of selenium from sediments and tissues of plankton, benthos, and fish has been variable since the system operation. Significant selenium declines have occurred in tissues of aquatic organisms in the eight-year recovery period while little change has been observed in sediments. Recovery of the fish community has been rapid, particularly in areas upstream of the ash pond discharge, and confirmed population-level modeling predictions using a Leslie-matrix demographic model. Diversity of the fish community increased throughout the reservoir and species dominance shifted from a green sunfish and satinfin shiner-dominated system to a bluegill-dominated system within five years after the system operation. Increased bluegill and green sunfish hybridism also occurred during early recovery and coincided with a low abundance of spawning bluegill adults. Sport fisheries have re-developed for largemouth bass and crappie and strategies for managing the recovering fishery have included periodic stock assessments, creel surveys and harvest restrictions, prey fish stocking, and continued contaminant monitoring. This pollution abatement system has been successful in reducing selenium loading into the reservoir and prompting recovery of the aquatic ecosystem.     

Entrainment and impingement studies at two power plants on the Wabash River in Indiana

Fish entrainment and impingement studies were conducted at Cayuga and Wabash River generating Stations in 1987 and 1988, respectively. Concurrent river samplings were conducted upstream from the stations to assess adult fish and ichthyoplankton populations. The original 316(b) studies at these stations were conducted in 1976–1977 and concluded that the stations were having minimal adverse impact on the Wabash River fish community. The state regulatory agency did not agree with this interpretation and requested the subsequent 1987 and 1988 studies. The major issue at these once-through cooling power plants was the large water withdrawals at Cayuga and Wabash River Stations [1318 and 1096 cubic feet per second (cfs) maximum plant flows, respectively], in contrast to the relatively low average annual Wabash River flows (10,070 and 11,110 cfs, respectively). The close proximity of the stations (35 river miles apart) together with the high percentage of water withdrawn suggest that the potential risk of unacceptable impacts is high.The six-month impingement estimates for Cayuga and Wabash River Stations were 15,086 and 11,401 fish, respectively. Impingement catches at both stations were dominated by young-of-the-year (YOY) channel catfish and gizzard shad. In addition, small minnows (primarily bullhead minnow and emerald shiners) were commonly impinged at Cayuga Station. Minnows (predominantly spotfin shiner, bullhead minnow and emerald shiner) were also the dominant species in the river samplings upstream from the stations. In the entrainment samplings, an estimated 26,920,382 and 107,503,876 fish eggs and larvae were entrained each year at Cayuga and Wabash River Stations, respectively. Ictiobinae (buffaloes and carpsuckers) and Cyprinidae (minnows and shiners) were the dominant ichthyoplankton in the river. Approximately 3.5 and 23% of the total river ichthyoplankton were entrained at Cayuga and Wabash River Stations, respectively. Gizzard shad at Cayuga Station, and Ictiobinae and Cyprinidae at Wabash River Station (WRS) were the dominant taxa entrained by the stations. Unusually low river flows during the spring and summer of 1987 and 1988 provided worst-case conditions for entrainment and impingement at the stations. However, the relatively low impingement and entrainment numbers during these worst-case conditions indicated that these stations were not adversely affecting the Wabash River fish community.     

316(b) and Quad Cities Station,Commonwealth Edison Company

Quad Cities Station is a 1630 MW_e dual reactor facility located on the Upper Mississippi River approximately 30 miles north of Davenport, Iowa and Rock Island, Illinois. As designed, the Station utilizes river water at the rate of 2270 cfs in an open-cycle mode of operation. From the 316(b) perspective, numerous agencies and intervenors expressed major concern regarding the potential adverse impacts of open-cycle entrainment and impingement effects on the River’s highly valued and diverse fishery. As a result, the fishery has been monitored continuously since 1971 through field surveys directed at measurements of community composition and relative abundance, as well as fish impingement surveys of the Station’s intake. From 1972 to 1983 the Station operated in a closed-cycle or partial closed-cycle mode.Regulatory relief and intervenor approval for open-cycle operation were not granted until 1984, following several years of intensive studies directed at entrainment/impingement and methods to reduce impingement. Beginning in 1978, the freshwater drum was selected as the indicator species most likely to manifest changes in population characteristics potentially resulting from open-cycle operation. Population levels (numbers and biomass), growth, fecundity, sex ratios and survival were all monitored to determine if compensatory responses occurred within the population following increases in impingement under open-cycle operation. Included in the agreement that allowed the return to open-cycle operation was a commitment to construct and operate a fish production facility to mitigate for potential impacts.After 14 years of monitoring under open-cycle operation, there have been no measurable changes in the local fishery and, specifically, none within the freshwater drum population. Naturally occurring environmental conditions have more profound influences on this dynamic and resilient fishery than operation of a large generation facility. Station operation is relatively constant from year to year and impingement monitoring may actually be the most accurate monitoring activity. Fluctuations in annual impingement projections are reflections of conditions within the river and the fishery’s response to them. Increases or decreases in fish numbers impinged at the Station in any given year are primarily due to fluctuations in the fishery and the effects of existing environmental variables and not to Station operation. The fishery fluctuations are reflections of conditions within the river and the fishery’s response to them.     

硅藻群落指示的近50年来大理西湖湖泊生态系统演变规律

近年来,增强的人类活动使得云南部分湖泊生态系统发生退化,由草型清水态向藻型浊水态转变.全球变化背景下,了解湖泊生态系统演变规律是进行有效管理的前提,具有重要的科学意义.本研究以云南大理州小型浅水湖泊西湖为例,通过对沉积物硅藻群落和理化指标的分析,探讨了20世纪60年代中期以来大理西湖环境演变历程.结果表明,大理西湖生态系统在近50年发生了明显的稳态转换,以2000年为节点,硅藻群落从2000年前偏好贫营养环境的底栖附生种Cocconeis placentula、Staurosira construens、Gomphonema angustum和Achnanthidium minutissimum为优势种的状态,逐渐演替为偏好中营养环境的底栖附生硅藻Encyonopsis microcephala和Navicula cryptocephala及偏好富营养环境的浮游硅藻Cyclotella atomus、Cyclotella meneghiniana、Stephanodiscus hantzschii和Aulacoseira granulata为主导的状态.时间序列的主成分分析表明,硅藻群落主要响应了营养的变化.冗余分析结果也证实营养盐富集是大理西湖硅藻群落长期演化的主要驱动因素.本文论述了近50年来大理西湖流域气候变化和开发活动（农业围垦、化肥施用、畜牧养殖和渔业养殖等）促使湖泊营养盐持续积累,浮游藻类大量繁殖,湖泊内部生产力显著提高,湖泊生态系统逐渐向藻型浊水态转变的演化特征.     

Factors influencing mercury accumulation in three species of forage fish from Caddo Lake, Texas, USA

Most studies that have examined mercury (Hg) contamination of fish have focused on game species feeding near the top of the food web, while studies that examine forage fish that feed near the base of the food web are rare. We conducted a survey of Hg contamination in three species of forage fish, brook silverside (Labidesthes sicculus), threadfin shad (Dorosoma petenense) and gizzard shad (Dorosoma cepedianum), from Caddo Lake, Texas, USA and found species-specific differences in Hg concentrations. We examined total length, age, trophic position (determined using δ15N), and growth rate of forage fish as factors that could have influenced within-and between-species differences in Hg concentration. Total length and age were the best predictors of within-species differences in Hg concentration. Between-species differences in Hg concentrations were most strongly influenced by trophic position.     

Mercury contamination and accumulation in sediments of the East China Sea

Mercury (Hg) concentrations in sediment samples collected from the inner and middle shelves of the East China Sea (ECS) were analyzed to evaluate Hg contamination levels and to calculate Hg sedimentation rates and total accumulation in the ECS. The range of Hg concentrations in surface sediments of the inner shelf was 26.5–47.6 ng/g, and that for the middle shelf was 4.1–13.9 ng/g. Hg concentrations correlated well with organic carbon contents but varied inversely with sediment grain size. Enrichment factors indicated that the whole inner shelf and a small portion of the middle shelf were slightly contaminated by Hg. Hg accumulation rates in the ECS ranged between 0.42–48.7 ng/(cm2·yr), with higher values observed in the inner shelf. Total Hg accumulation in the calculated area (accounting for 80% of the ECS continental shelf area) ranged from 25 to 30 tons/yr; approximately 51% and 17% of the accumulated Hg mass was deposited in the Yangtze estuarine zone and the inner shelf, respectively.     

The ‘I see you’ prey–predator signal of Apis cerana is innate

An ‘I see you’ (ISY) prey–predator signal can co-evolve when such a signal benefits both prey and predator. The prey benefits if, by producing the signal, the predator is likely to break off an attack. The predator benefits if it is informed by the signal that the prey is aware of its presence and can break off what is likely to be an unsuccessful and potentially costly hunt. Because the signal and response co-evolve in two species, the behaviour underlying an ISY signal is expected to have a strong genetic component and cannot be entirely learned. An example of an ISY signal is the ‘shimmering’ behaviour performed by Asian hive bee workers in the presence of their predator Vespa velutina. To test the prediction that bee–hornet signalling is heritable, we let honey bee workers of two species emerge in an incubator so that they had never been exposed to V. velutina. In Apis cerana, the shimmering response developed 48 h post-emergence, was strong after 72 h and increased further over 2 weeks. In contrast, A. mellifera, which has evolved in the absence of Asian hornets, did not produce the shimmering signal. In control tests, A. cerana workers exposed to a non-threatening butterfly did not respond with the shimmering signal.     

Weather-driven changes in population density determine wing dimorphism in a bush-cricket species

Long-winged (macropterous) individuals that are capable of flight in predominantly short-winged (flightless) species can considerably affect population dynamics and range expansion. Understanding the triggers that determine macropterism is crucial for understanding whether the dispersal ability of species allows them to shift their distributions through fragmented landscapes or in response to climate change. From 2002 to 2009, we studied population densities and wing dimorphism (macroptery) of Metrioptera roeselii, on 62 plots in central Germany. In the first step, we used a generalized linear mixed-effects model to assess the variables that influence macroptery. Macroptery rates are strongly positively correlated with bush-cricket abundance and not with vegetation structure and habitat moisture. Populations with macropters had significantly higher densities than those without. In the second step, we analysed the relationship between population densities and several mesoclimate/weather parameters. Densities were positively correlated with warm and dry weather conditions during hatching time in April, and previous year weather is less important than present year weather. In the light of the ongoing range expansion of M. roeselii in large parts of Europe, our results support the hypothesis that at high latitudes macropterism and range expansion are indirectly caused by weather-driven changes in population densities.     

Unpacking multi-trophic herbivore-grass-endophyte interactions: feedbacks across different scales in vegetation responses to Soay sheep herbivory

Grazing can induce changes in both plant productivity and nutritional quality, which may subsequently influence herbivore carrying capacity. While research on Soay sheep (Ovis aries L.) dynamics on Hirta Island in the St. Kilda archipelago has elucidated the complexity of population drivers, including parasites, the role of herbivore-generated feedbacks as an intrinsic regulating factor remains unclear. The sheep lack large predators and every 3–9 years undergo population crashes (overcompensatory mortality). We investigated the effects of grazing on (1) sward productivity and (2) quality (toxicity) of the primary forage species, red fescue (Festuca rubra L.), which is highly infected by an alkaloid-synthesizing fungal endophyte. Grazing had a negative impact on both forage quantity and quality. At higher sheep densities, impacts on sward growth were magnified, resulting in a nonlinear relationship with plant productivity. Simultaneously, endophyte hyphal load (and by inference, toxicity) peaked close to the time of a crash. A greenhouse experiment showed that alkaloid concentration in F. rubra increased in response to artificial defoliation. We conclude that at high sheep densities, grazing-mediated reductions in productivity, together with sustained alkaloid production, are likely to influence sheep dynamics. Future research should consider the interactive effects of forage toxicity, quantity, and nutritional content.     

Fish survival on fine mesh traveling screens

The survival of fish impinged on 1-mm mesh Ristroph-type traveling screens was evaluated at Somerset Station, a 625-MW coal-fired electric generating station located on the south shore of Lake Ontario. Somerset Station was designed and built with an offshore intake, discharge and fish return system. Survival testing was conducted over a 4-year period that included all four seasons. Test fish were diverted from the fish return and held for 96 h for observation. Following observation, a specially constructed screening table was used to differentiate test fish that typically would have been impinged on a standard 9.5-mm mesh screen from smaller individuals that typically would be entrained. Twenty-eight species were tested, and collections were dominated by five species: alewife, emerald shiner, gizzard shad, rainbow smelt, and spottail shiner. Survival rates commonly approached or exceeded 80%, and were influenced by species, fish size or life stage, season and fish condition. Results are interpreted in terms of survival rates demonstrated elsewhere for entrained fish and fish impinged on alternative traveling screen technologies.     

东湖生态学研究慨况

以长江中下游流域具代表性的武汉东湖为基地对其生态学进行了长期的观测和系统研究．详细地阐述了氮、磷在水体中分布、转移及积累,浮游植物的演替,浮游植物初级生产力及其对鱼产潜力的估算,浮游动物现存量和生产量,有机碎屑在生态系统中的功能和鱼类放养对生态系统的下行效应等     

Giant honeybees (Apis dorsata) mob wasps away from the nest by directed visual patterns

The open nesting behaviour of giant honeybees (Apis dorsata) accounts for the evolution of a series of defence strategies to protect the colonies from predation. In particular, the concerted action of shimmering behaviour is known to effectively confuse and repel predators. In shimmering, bees on the nest surface flip their abdomens in a highly coordinated manner to generate Mexican wave-like patterns. The paper documents a further-going capacity of this kind of collective defence: the visual patterns of shimmering waves align regarding their directional characteristics with the projected flight manoeuvres of the wasps when preying in front of the bees’ nest. The honeybees take here advantage of a threefold asymmetry intrinsic to the prey–predator interaction: (a) the visual patterns of shimmering turn faster than the wasps on their flight path, (b) they “follow” the wasps more persistently (up to 100 ms) than the wasps “follow” the shimmering patterns (up to 40 ms) and (c) the shimmering patterns align with the wasps’ flight in all directions at the same strength, whereas the wasps have some preference for horizontal correspondence. The findings give evidence that shimmering honeybees utilize directional alignment to enforce their repelling power against preying wasps. This phenomenon can be identified as predator driving which is generally associated with mobbing behaviour (particularly known in selfish herds of vertebrate species), which is, until now, not reported in insects.     

三峡库区内陆腹地典型水库型湖泊中DOM吸收光谱特征

溶解性有机质(DOM)是湖泊生态系统重要组成部分,其性质和结构决定了其在污染物(例如汞)环境行为中扮演着重要角色.本研究选取三峡库区内陆腹地典型水库型湖泊——长寿湖,采用吸收光谱表征方法,通过1年时间对DOM地球化学变化规律进行了定性定量分析,并结合汞观测数据,讨论了DOM对不同形态汞浓度的影响.结果表明,和1月相比,长寿湖4~11月DOC差异性低于CDOM,4~11月间差异性不显著.有色组分变化是解释DOM季节性变化的重要原因.DOM中主要生色团仍然来自于大分子量的芳香性组分.而CDOM三波长模型可较好对DOC的年际观测进行反演.同时,SUVA254和S275~295季节性变化特征较明显,1月芳香性和分子量均最小,4月上升.与其他类型湖泊相比,长寿湖水体DOM芳香性和分子量大小均低于森林湖泊,但高于高原湖泊.周边生态系统和土地利用类型对湖泊DOM差异影响明显.另外,SUVA254和DOC与各形态Hg无明显相关性,但水体生色组分和分子量大小是控制溶解态和活性汞的重要因素;而湖区甲基汞变化可能与湖泊初级生产力导致的有机质富集和迁移关系密切.     

Increased lipid accumulation but not reduced metabolism explains improved starvation tolerance in cold-acclimated arthropod predators

Predatory arthropods are used for biological control in greenhouses, but there is increasing interest to extend their use to the outdoor environment where temperatures are typically lower. Acclimation at low temperature increases the ability of ectotherms to cope with subsequent more extreme cold, but may involve costs or benefits to other performance traits. A recent study in mesostigmatid mites (Gaeolaelaps aculeifer) showed that starvation tolerance was improved following a period of cold exposure. However, the physiological mechanisms that underlie improved starvation tolerance following cold exposure were not investigated. To examine whether cold acclimation would also improve starvation tolerance in an insect, we repeated the starvation study in another arthropod predator, the pirate bug Orius majusculus, as well as in G. aculeifer. Before tests, the two species were acclimated at 10, 15, or 20 °C for 7 (G. aculeifer) or 16 (O. majusculus) days. We then analyzed the effects of thermal exposure on body composition, consumption, and basal metabolic rate in both species. Our results confirmed that exposure to low temperature improves starvation tolerance in these arthropod predators. Body composition analyses revealed that both species had accumulated larger lipid stores during exposure to colder temperature, which at least in part can explain the larger starvation tolerance following cold exposure. In contrast, consumption and basal metabolic rate were not changed by thermal acclimation. Our study indicates that predatory arthropods exposed to cold increase their physiological robustness and ability to endure environmental challenges, including low temperature and low prey availability.     

上海淀山湖水环境容量评估

淀山湖是上海市重要的饮用水源保护区和生态涵养区.近10年来水质富营养化程度急剧增加,藻类水华频发,对上海饮用水源地水质安全构成了巨大威胁.为水污染控制和水质改善提供科学依据,利用已有评估模型评估了不同水质目标情景下淀山湖对COD、TN 和TP的最大容量,结果表明,在保持现状水质条件下,COD、TN和TP的环境容量分别为47213,8337.7,476.3t/a;水质控制目标为II类时,其环境容量分别为46325,1191.1,59.5t/a;水质目标为III类时,环境容量分别为68547,2382.2,119.1t/a.为IV类水质目标时,TN、TP的环境容量分别为3573.3,238.2t/a.     

Social spiders of the genus Anelosimus occur in wetter, more productive environments than non-social species

Latitude, rainfall, and productivity have been shown to influence social organisation and level of sociality in arthropods on large geographic scales. Social spiders form permanent group-living societies where they cooperate in brood care, web maintenance, and foraging. Sociality has evolved independently in a number of unrelated spider genera and may reflect convergent evolutionary responses to common environmental drivers. The genus Anelosimus contains a third of approximately 25 described permanently social spider species, eight to nine species that all occur in the Americas. To test for environmental correlates of sociality in Anelosimus across the Americas, we used logistic regression to detect effects of annual rainfall, productivity, and precipitation seasonality on the relative likelihood of occurrence of social and non-social Anelosimus spiders. Our analyses show that social species tend to occur at higher annual rainfall and productivity than non-social species, supporting the hypothesised effects of these environmental variables on the geographical distribution of social species. We did not find support for the hypothesis that permanently social species occur in areas with low precipitation seasonality. High annual precipitation and, to less extent, high productivity favour the occurrence of permanently group-living Anelosimus spiders relative to subsocial and solitary species. These results are partially consistent with previous findings for the Old World spider genus Stegodyphus, where a link between high habitat productivity and sociality was also found. Unlike Anelosimus, however, Stegodyphus typically occur in dry habitats negating a general importance of high precipitation for sociality. Sociality in spiders thus seems to be strongly linked to productivity, probably reflecting the need for relatively high availability of large prey to sustain social colonies.     

Ecological consistency across space: a synthesis of the ecological aspects of Dromiciops gliroides in Argentina and Chile

Dromiciops gliroides is an arboreal marsupial found in the temperate forests of South America (36–43 °S). This species is the sole extant representative of the order Microbiotheria, and is a key seed disperser of many native plant species, including the keystone mistletoe Tristerix corymbosus. Here, we synthesized the current knowledge on the ecological aspects of this species, and compared the available information from Argentina and Chile. Population density (23?±?2 (mean ± SE) individual/ha) and home range (1.6?±?0.6?ha) appear to be relatively similar across a marked ecological gradient in the mainland, but lower densities (7?±?2 individual/ha) and smaller home ranges (0.26?±?0.04?ha) were detected at island sites. We detected regional variation in body condition in Chile, but there were no significant differences across a wider E-W gradient. Movement patterns fit a random walk model; such behavior might have important consequences in shaping plant’s spatial patterns. Although our data suggest that D. gliroides is more tolerant to habitat disturbance than previously thought, its incapability to disperse across non-forested areas suggests that the rapid rate of habitat loss and fragmentation that characterizes southern temperate forests likely poses a serious threat to this species. These ecological similarities are surprising given that forests studied receive dramatically different rainfall and correspond to distinct forest types. The evidence synthetized here dispels some of the myths about this species but also stresses the need for more comprehensive ecological studies across its distribution range.     

From repulsion to attraction: species- and spatial context-dependent threat sensitive response of the spider mite Tetranychus urticae to predatory mite cues

Prey perceiving predation risk commonly change their behavior to avoid predation. However, antipredator strategies are costly. Therefore, according to the threat-sensitive predator avoidance hypothesis, prey should match the intensity of their antipredator behaviors to the degree of threat, which may depend on the predator species and the spatial context. We assessed threat sensitivity of the two-spotted spider mite, Tetranychus urticae, to the cues of three predatory mites, Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius andersoni, posing different degrees of risk in two spatial contexts. We first conducted a no-choice test measuring oviposition and activity of T. urticae exposed to chemical traces of predators or traces plus predator eggs. Then, we tested the site preference of T. urticae in choice tests, using artificial cages and leaves. In the no-choice test, T. urticae deposited their first egg later in the presence of cues of P. persimilis than of the other two predators and cue absence, indicating interspecific threat-sensitivity. T. urticae laid also fewer eggs in the presence of cues of P. persimilis and A. andersoni than of N. californicus and cue absence. In the artificial cage test, the spider mites preferred the site with predator traces, whereas in the leaf test, they preferentially resided on leaves without traces. We argue that in a nonplant environment, chemical predator traces do not indicate a risk for T. urticae, and instead, these traces function as indirect habitat cues. The spider mites were attracted to these cues because they associated them with the existence of a nearby host plant.     

Are linear habitats in agrarian landscapes source areas of beneficial or pest rodents?

This study tested the hypotheses that populations of the montane vole Microtus montanus (a potential pest species) and deer mouse Peromyscus maniculatus (a potential beneficial species) in linear habitats will be (i) positively related to the type of vegetation (abundance and diversity of vascular plants) within and adjacent to those habitats; and (ii) correlated with population changes and productivity (reproductive performance, recruitment, and survival) in nearby apple (Malus domestica) orchards. Population dynamics of M. montanus and P. maniculatus were measured by intensive live-trapping from 2003 to 2006 in replicated hedgerows, riparian strips, and nearby orchards, in southern British Columbia, Canada. Hedgerows were borders between orchards, orchards and old fields, as well as orchards and natural forest. Contrary to hypothesis (i), M. montanus and P. maniculatus populations were not positively related to vegetation type within linear habitats and their adjacent crop and non-crop areas. Mean abundance and diversity of vegetation attributes were similar among linear habitats. Hypothesis (ii) was not supported for M. montanus populations in linear habitats since they did not correlate with population changes in nearby apple orchards, during a peak year in abundance. Populations of P. maniculatus were similar in abundance and other demographic variables among the linear habitats and apple orchards, and hence hypothesis (ii) was supported for this species.     

Interactions of host-plant resistance in cotton with predators and parasites

Results from no-choice field and greenhouse studies established an inverse relationship between plant trichome density in cotton and the level of successful attacks on Heliothis zea (Boddie) eggs by the parasite, Trichogramma pretiosum (Riley) and the predator, Chrysopa rufilabris (Burmeister). Thus, plant damage from H. zea can be reduced on glabrous cotton phenotypes due to antixenosis and increased entomophage effectiveness compared to hirsute and pilose phenotypes. Studies by other scientists which demonstrate interactions of natural enemies with host-plant resistance in cotton are also discussed. Symbiotic relationships between the host-plant and its associated predator/parasitoid complex may significantly influence the expression of host-plant resistance in cotton. Scientists involved in programs for development of host-plant resistant cultivars are encouraged to utilize sources of resistance which increase effectiveness of key natural enemies of the major pest species.