Coccinellid Densities Research Articles

Insect diversity and population dynamics of natural enemies under sorghum–legume intercrops

The effect of intercropping sorghum with legumes on insect diversity and population dynamics of natural enemies was evaluated in the 2015/2016 cropping season at Botswana University of Agriculture and Natural Resources in Sebele, Gaborone. Sorghum monocrop, Sorghum bicolar (L) Moench, was intercropped with four commonly grown legumes, namely cowpea, Vigna unguiculata (L) Walp.; groundnut, Arachis hypogea L.; Bambara groundnut, Vigna subterranean (L.) Verdc; and chickpea, Cicer arietinum L. The study showed that intercropping significantly increased insect abundance, from 176.50 individuals on the monocrop to 438 individuals when sorghum was intercropped with cowpea being the highest among the intercrops. Similarly, species diversity significantly increased from 0.24 on monocrop to 0.54 when sorghum was intercropped with cowpea. There were more herbivores than predators, and the predominant insect herbivore found infesting sorghum was Melanaphis sacchari (Zehntner) (n = 2495), followed by Chilo partellus (Swinhoe) (n = 650). There was a significant difference in the level of parasitism between monocrop and intercrop systems. There were significantly more stemborer parasitoids found in the intercrops, ranging from 1 to 5%, compared to sorghum monocrop where no parasitism was observed. Predatory coccinellid density was not significantly influenced by intercropping but was by time of sampling. The results add to the body of knowledge indicating that intercropping significantly increases insect diversity and reduces the pressure of herbivores on crops in agroecosystems. Intercropping sorghum with legumes increased the number of biological control agents and reduced herbivore populations, and therefore can be recommended as a component of integrated pest management.

Effects of Organic Management on Predator Densities of Myzus persicae (Sulzer) During Transition to Organic Agriculture in Peach Fields in China

We studied the effects of organic management (OM) on densities of six predator species of green peach aphid (GPA), three coccinellid predators (Propylea japonica, Harmonia axyridis, Coccinella septempunctata), and three non-coccinellid predators (Chrysoperla sinica, Epistrophc baltcata, and Misumenops tricuspidatus) in five OM peach fields, compared and paired with five conventional management (CM) fields from the first year of OM in 2004–2009. Coccinellid and non-coccinellid predator densities were significantly higher on several sampling dates in OM fields than in CM fields. Coccinellid predator density was significantly lower in the first two years of OM than in the last three years in the OM fields. The density of non-coccinellid predators in the fourth year of OM was much greater than during the first year of OM, and there was a significant increase by the sixth year of OM compared to the first two years of OM. The leaf density index of GPA was significantly lower in the fifth and sixth year of OM than the first three years of OM in the OM peach fields. Our study suggests organic management can resume and increase predator densities of green peach aphid during transition to organic agriculture in peach fields.

Sugar feeding by coccinellids under field conditions: the effects of sugar sprays in soybean

Sucrose was applied weekly throughout the growing season at three US locations (South Dakota [SD], Maryland [MD], and Kentucky [KY]), and coccinellids and aphids (Aphis glycines Matsumura [Hemiptera: Aphididae]) were sampled 24 h later. Total coccinellid densities were 50–77% greater in sugar-sprayed soybean than in untreated plots. Coccinella septempuncata L., Hippodamia convergens Guerin-Meneville, and Harmonia axyridis Pallas were more abundant where sugar was applied. Coleomegilla maculata (DeGeer) was found in equally low numbers in all treatments. Aphid densities were similar in both treatments, and only reached economically threatening levels in SD. Coccinellids digested sugar meals within 1 h of consumption (measured using the cold anthrone test). Despite this narrow window of detection, field-collected coccinellids frequently tested positive for fructose. Under natural conditions, sugar is commonly ingested by coccinellids and sugar sprays increase coccinellid densities and their consumption of sugar. Sugar sprays did not enhance biological control of aphids in this experiment.

Coccinellids, Aphids, and Pollen in Diversified Vegetable Fields with Transgenic and Isoline Cultivars

The influence of concurrent introduction of three transgenic vegetable cultivars on seasonal dynamics of coccinellids and their food, aphids and pollen, was examined within diversified farm systems practicing insect pest management in northeastern US agroecosystems. The transgenic cultivars used included sweet corn, potato, and winter squash, expressing Cry1(A)b, Cry3A, and plant viral coat proteins that target Lepidoptera, Coleoptera, and aphid-transmitted viruses, respectively. Transgenic systems reduced insecticides by 25%. Weekly differences in coccinellid density between transgenic and isoline crops were rare and transitory, governed by timing of at-planting or foliar insecticide use patterns; however cumulative frequencies for three of the six coccinellid species differed between transgenic and isoline crops. At a multicrop, farm systems level, seasonal dynamics of the coccinellids and aphids tracked dynamics in the sweet corn, which far surpassed the other crops in abundance of coccinellids and pollen, and harbored consistently higher aphid densities. Although these results warrant further study, the patterns suggest that diversified transgenic vegetable crops under current commercial management demonstrated transitory conservation of coccinellids, and that integration with selective insecticides or other IPM tactics could increase this potential.

Contrasting effects of natural habitat loss on generalist and specialist aphid natural enemies

The greater susceptibility of higher trophic levels to habitat loss has been demonstrated to disrupt important trophic interactions such as consumer control of prey populations. This pattern is predicted to break down for generalist species that can use matrix habitats, yet empirical studies comparing generalist and specialist enemy pressure in response to natural habitat loss are lacking. Here we examined the effects of landscape simplification resulting from habitat conversion to agriculture on nettles, Urtica dioica, their specialized aphid herbivore, Microlophium carnosum, and associated natural enemies that varied broadly in their degree of specialization. Both nettles and their specialized aphid herbivore were significantly more abundant in complex than simple landscapes. Different enemy groups showed contrasting responses. Aphid specialists (parasitic wasps and cecidomyiid midges) reached higher densities in complex than simple landscapes, and this effect was primarily related to shifts in local resource abundance (i.e. nettle aphid densities). In contrast, densities of generalists (coccinellid beetles and spiders) were significantly higher in simple landscapes, presumably due to spillover of generalists from surrounding cropland habitats. Natural enemy-prey ratios did not differ significantly across landscape types for specialist groups but were significantly higher in simple than complex landscapes for generalist groups, suggesting that enemy pressure on nettle aphids likely increases with landscape simplification. This was supported by our finding that aphid population growth rates were lower in simple than complex landscapes, and declined significantly with increasing coccinellid densities. Thus, in marked contrast to previous work, our results suggest that natural habitat loss may augment rather than disrupt consumer–prey interactions, and this will depend greatly on the degree of specialization of functionally dominant natural enemies.

Contrasting effects of natural habitat loss on generalist and specialist aphid natural enemies

The greater susceptibility of higher trophic levels to habitat loss has been demonstrated to disrupt important trophic interactions such as consumer control of prey populations. This pattern is predicted to break down for generalist species that can use matrix habitats, yet empirical studies comparing generalist and specialist enemy pressure in response to natural habitat loss are lacking. Here we examined the effects of landscape simplification resulting from habitat conversion to agriculture on nettles, Urtica dioica, their specialized aphid herbivore, Microlophium carnosum, and associated natural enemies that varied broadly in their degree of specialization. Both nettles and their specialized aphid herbivore were significantly more abundant in complex than simple landscapes. Different enemy groups showed contrasting responses. Aphid specialists (parasitic wasps and cecidomyiid midges) reached higher densities in complex than simple landscapes, and this effect was primarily related to shifts in local resource abundance (i.e. nettle aphid densities). In contrast, densities of generalists (coccinellid beetles and spiders) were significantly higher in simple landscapes, presumably due to spillover of generalists from surrounding cropland habitats. Natural enemy‐prey ratios did not differ significantly across landscape types for specialist groups but were significantly higher in simple than complex landscapes for generalist groups, suggesting that enemy pressure on nettle aphids likely increases with landscape simplification. This was supported by our finding that aphid population growth rates were lower in simple than complex landscapes, and declined significantly with increasing coccinellid densities. Thus, in marked contrast to previous work, our results suggest that natural habitat loss may augment rather than disrupt consumer–prey interactions, and this will depend greatly on the degree of specialization of functionally dominant natural enemies.

Experimental Treatment Threshold for the Cotton Aphid (Homoptera: Aphididae) Using Natural Enemies in Arkansas Cotton

The potential of an experimental threshold for reducing the number of insecticide applications for control of the cotton aphid, Aphis gossypii Glover, was demonstrated in cotton. A 3-yr field study at Clarkedale, AR, compared the current economic threshold for the cotton aphid to an experimental threshold that incorporates predaceous coccinellids, aphid parasitoids and the aphid fungus, Neozygites fresenii (Nowakowski) Batko. Treatments consisted of untreated plots, conventional treatment threshold plots, experimental threshold plots, and a fungicide treatment designed to disrupt aphid fungus epizootics. This fungicide treatment failed to influence fungal epizootics, so data for these plots were removed. Twice weekly, aphids were counted on 20 plants per plot and predators were counted using a dislodgment method. An application of 0.033 kg ai/ha of imidacloprid was made when aphids reached treatment level according to conventional or experimental threshold levels. Insecticide applications were triggered by the conventional threshold on 18 and 28 June 1999, on 28 June and 3 July 2000, and on 7 and 12 July 2001. The experimental threshold called for applications on 28 June 1999, 3 July 2000, and 19 July 2001. Aphid densities peaked in untreated plots at 142, 76, and 27 aphids per leaf and in treated plots at 49, 34, and 29 in 1999, 2000 and 2001, respectively. Larval coccinellid densities in untreated plots peaked at 9.0, 3.7, and 0.6 larvae per row-m and in treated plots 3.0, 1.4, and 0.5 in 1999, 2000 and 2001, respectively. Adult coccinellid densities peaked in untreated plots at 3.0, 2.7, and 0.5 adults/row-m and in treated plots at 0.8, 2.1, and 0.5 in 1999, 2000, and 2001, respectively. During each year, an epizootic of N. fresenii caused a rapid decrease in aphid numbers in mid to late July, eliminating the need for additional treatments. In 1999, significantly lower yield of lint occurred in the untreated plots than in conventional or experimental plots. No significant yield differences among treatments occurred in 2000 or 2001. Use of the experimental threshold delayed the initial insecticide application by 1 wk and eliminated one insecticide application on the experimental plots whereas maintaining cotton yields.

Species diversity, abundance, and phenology of aphid natural enemies on spring wheats resistant and susceptible to Russian wheat aphid

The species composition, relativeabundance, and seasonal dynamics of selectednatural enemies of cereal aphids were monitoredin spring wheat fields in Moscow, Idaho in 1997and 1998. Trials also examined the potentialimpact of resistance to Russian wheat aphid(RWA), Diuraphis noxia (Mordvilko)(Homoptera: Aphididae) in wheat, on aphidbiological control agents. Natural enemypopulations were monitored on two springwheats: D. noxia susceptible variety`Centennial' and resistant genotype `IDO488'. Field plots were artificially infested withadult D. noxia, and sampled for cerealaphids and parasitoids weekly. Coccinellidpredators were monitored once in 1997 and twicein 1998. The coccinellids Hippodamiaconvergens Guerin, Coccinellaseptempunctata L., C. transversoguttataBrown and C. trifasciata Mulsant weredetected. No significant differences in adultor immature coccinellid densities were observedbetween the D. noxia resistant andsusceptible genotypes. During both years, themost abundant primary hymenopteran parasitoidswere Diaeretiella rapae (M'Intosh), Aphidius ervi Haliday, A. avenaphis(Fitch), and Lysiphlebus testaceipes(Cresson), Aphelinus varipes (Foerster),Aphidius colemani Viereck, Aphidiuspicipes (Nees), Aphidius sp., Monoctonus washingtonensis Pike & Stary, Praon gallicum Stary, Praon occidentaleBaker, and Praon sp. were also detected. Numbers of both D. noxia and D.rapae were significantly greater on Centennialthan on IDO488 in both years. When all speciesof cereal aphids and parasitoids areconsidered, the total percentage parasitism wasnot significantly different between thegenotypes. There was no interaction betweenD. noxia resistance and the populationdensity of the predators or parasitoidsmonitored. These results suggest that the D. noxia resistant line had no adverse impacton natural enemies under the conditions ofthese field experiments.

Coccinellids in Cotton: Population Response to Pesticide Application and Feeding Response to Cotton Aphids (Homoptera: Aphididae)

Four treatments were evaluated during 1997 and 1998 to determine the effects of pesticides on coccinellid densities: (1) untreated control, (2) foliar applications of a systemic insecticide, imidacloprid (Provado 1.6 F), when spray thresholds of aphid numbers were exceeded in all plots, (3) weekly foliar applications of a fungicide, chlorothalonil (Bravo 720), and (4) weekly foliar applications of imidacloprid (Provado 1.6 F). The coccinellids observed in Georgia cotton during the study included Hippodamia convergens Guerin-Meneville, Scymnus spp., Harmonia axyri- dis (Pallas), Coccinella septempunctata L., and Coleomegilla maculata (Mulsant). During 1997, H. convergens and Scymnus spp. comprised 75 and 15%, respectively, of all coccinellids observed during the study. During 1998, Scymnus spp. comprised 44% of all coccinellids, and H. convergens comprised 33%. Coccinellid population densities closely tracked those of cotton aphids during both years. Cotton aphid and coccinellid densities were greatest in the chlorothalonil treatment during both years of the study. In functional feeding response experiments, fourth-instar and adult Scynmus creperus exhibited a type II functional response to A. gossypii density under laboratory conditions. Fourth instars exhibited a higher search rate and shorter handling time than adult S. creperus. Collectively, coccinellids are a valuable component of the cotton aphid's natural enemy complex.

Maintenance of ladybeetle diversity across a heterogeneous African agricultural/savanna land mosaic

The importance of agricultural land for maintaining indigenous biodiversity is an important contemporary issue. A large agricultural estate in Swaziland, which is a mosaic of citrus orchards, exotic tree windbreaks, indigenous riparian vegetation and savanna was investigated. The distribution of larval and adult coccinellids within the habitat types, and the relative influences of temperature, relative humidity, ground insolation and prey presence was assessed over a 2-year period. The highest coccinellid densities and species richness occurred within the orchards. Riparian habitats on the boundaries of the estate were closer to the orchard habitat in species composition than was the natural savanna. Not surprisingly, the presence/absence of prey was the most important variable which determined coccinellid distribution and density in the agricultural landscape. Relative humidity, temperature and ground insolation had no significant effect on coccinellid densities. Some species, such as the exotic Cheilomenes lunata, and the indigenous Scynmus sp. and Nephus sp. were widely dispersed and occurred in all habitats, while the economically important but exotic species, Rodolia cardinalis was only within the citrus orchards. Overall, the coccinellid assemblage was not a good indicator of habitat type. Nevertheless, a variety of habitat types (i.e. a heterogenous landscape) appear to be essential for the survival of most coccinellids. Indeed, the heterogeneous agricultural and natural land mosaic provides maximum plant diversity and hence coccinellid diversity, thus increasing the potential for natural control of pest prey species in the orchards, while at the same time maximizing survival of indigenous coccinellids.

Mortality of Coccinellid (Coleoptera: Coccinellidae) Larvae and Pupae When Prey Become Scarce

Coccinellid larvae are known to prey upon conspecific and heterospecific eggs, larvae, prepupae, and pupae. This behavior may depend on both the aggregation and intensive search of potential cannibals and predators near aphid colonies and the disappearance of aphids before coccinellid larvae have completed their development. We examined how coccinellid density and prey availability influence cannibalism and interspecific predation of larvae and pupae of 4 species of coccinellids. We determined whether coccinellid mortality and dispersal were density-dependent when prey become scarce, and estimated the leaving rates of Coleomegilla maculata (DeGeer), Adalia bipunctata (L.), and Hippodamia convergens (Guerin) larvae from plants with aphids and plants without aphids. Our results show that larval and pupal cannibalism and interspecific predation occur more frequently when aphid populations crash, but we found no evidence of coccinellid density-dependent mortality or density-dependent larval dispersal among species. However, A. bipunctata and H. convergens were significantly more aggressive and more likely to leave a plant without aphids than was C. maculata. These results suggest that the decision to stay on a plant is not strongly aphid- or pollen-mediated for C. maculata, but the decision to stay or leave does appear to be aphid-mediated for H. convergens and to some extent A. bipunctata. Whether a coccinellid larva stays or leaves and its tendency to cannibalize can affect larval and pupal survival and the population dynamics of each species.

Assessment of legume and nonlegume ground covers on Coleoptera: Coccinellidae density for low-input pecan management

AbstractAn annual legume cover crop was evaluated in pecan orchards to increase coccinellids that would reduce pecan aphids. Treatments were a ‘Dixie’ crimson clover and hairy vetch mixture and a grass sod. Coccinellids were abundant on the legume ground covers, but coccinellid density in the tree canopy was rarely affected by ground cover treatment. There were substantial differences between the coccinellid species collected from the legumes and from the trees. In Oklahoma, Olla v-nigrum (Mulsant) and Cycloneda munda (Say) were the main species in the trees, while Hippodamia convergens Guerin, Coccinella septempunctata L, and Coleomegilla maculata lengi Timberlake were dominant species in the legumes. In Georgia, Harmonia axyridis (Pallas) was the dominant species in the trees, and C. septempunctata in the legumes. Pecan aphids at two Oklahoma sites usually were not affected by cover crop treatment, but at the Georgia site, early-season aphids frequently were lower with a legume cover crop than with a grass sod. The accumulated effect of all aphid predators and parasitoids attracted to the legume aphids may have reduced the density of the pecan aphid.

Sequential sampling for adult coccinellids in wheat

AbstractAdult aphidophagous coccinellids are important predators of cereal aphids in wheat in the Great Plains of the United States for which sampling methods are needed to facilitate improved management. An equation relating the mean number of adult coccinellids per m2 in a wheat field to its variance was obtained using Taylor's power law. A sequential sampling procedure was developed to estimate the number of adult coccinellids per m2 with constant average statistical precision (standard error/mean). The procedure was constructed by an equation relating the number of adult coccinellids per m2 to the number of adult coccinellids per minute of counting incorporating into the Taylor's power law relationship. The procedure involves conducting a series of 1‐min counts while walking through a field at a constant velocity of 10 m per minute. After each 1‐min count sequential sampling stop‐lines are consulted to determine if the specified level of precision has been achieved. Two methods, a statistical procedure and comparison with independent data, were used to assess the consistency with which the specified level of precision was achieved by the procedure. Results indicated that observed precision was close to that specified by the user over a wide range of adult coccinellid density.

Estimating Populations of Aphidophagous Coccinellidae (Coleoptera) in Winter Wheat

Coccinellids are important natural enemies of aphid pests in wheat, Triticum aestivum em Thell, in the Great Plains of the United States. Coccinellid community development in wheat fields is unpredictable; therefore, precise, efficient sampling methods for coccinellids are needed for use in integrated pest management research and decision making. Our objectives were to compare removal sampling with quadrat sampling for estimating population density of adult and larval coccinellids in winter wheat, and to determine if timed count sampling and sweepnet sampling were useful for estimating adult and larval coccinellid densities. Removal sampling accurately estimated population density for adults of most species but consistently underestimated larval density. Timed count samples and sweepnet samples were significantly correlated with absolute density of both larval and adult coccinellids. Regression models were developed to convert estimates of relative to estimates of absolute population density. Depending on sampling method and life stage, models included the number of tillers per 0.3 m, wheat plant growth stage, plant height, and the number of aphids per tiller as variables; R 2 values ranged from 0.89 to 0.93. Sweepnet sampling was more precise per unit of effort than timed count, quadrat, or removal sampling for estimating adult coccinellid density. Removal sampling (removing all coccinellids seen during 2 successive 15-min searches from each of 9 plots (25 m 2 ) was the least efficient method.

Estimating Aphidophagous Coccinellid Populations in Alfalfa

Precise yet time-efficient sampling methods for coccinellids would be useful in integrated pest management (IPM) research and decision-making in alfalfa. We compared quadrat sampling, removal sampling, counting coccinellids for a constant amount of time while walking slowly through a field (timed counts), and sweepnet sampling for estimating adult and larval coccinellid density in alfalfa. Removal sampling gave biased estimates of density of adultColeomegilla maculataDegeer, but gave acceptable estimates of density of adults of other species. Regression models were developed to convert relative population estimates of adult and larval coccinellids obtained by sweepnet and timed count sampling to absolute population estimates (number per m2). For adults, plant height was included in the best regression models for converting sweepnet catch and timed counts to population density. For larvae, plant growth stage was included in the best regression model for converting sweepnet catch to density. The number of aphids per 10 sweeps was included in the model for converting timed counts of larvae to density; however, this model was of little value because it explained only 13% of the variation in the relationship between timed counts and population density. Coefficients of determination of regression models for estimating adult density from timed count and sweepnet sampling were 0.90 and 0.93, respectively. The model for converting sweepnet catch of larvae had a coefficient of determination of 0.71. In terms of statistical precision achieved per unit time spent sampling, a 25-sweep sample was the most efficient sample unit for estimating adult density. A double 12-min removal sample was most efficient for sampling larvae, but this method gave biased estimates of larval density, and overall, sweepnet sampling was better.

Beneficial role of corn leaf aphid, Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae), in maintaining Hippodamia spp. (Coleoptera: Coccinellidae) in grain sorghum

The significance of corn leaf aphid, Rhopalosiphum maidis (Fitch), as a food source for the natural enemies of greenbug, Schizaphis graminum (Rondani), was determined in the Texas High Plains sorghum agroecosystem. The most abundant coccinellid species were Hippodamia convergens (Guerin-Meneville) and H. sinuata (Mulsant). Neither coccinellid species showed any preference for either greenbug or corn leaf aphid in replicated choice predation tests. Corn leaf aphid and coccinellid densities increased at similar rates in the early season during both 1982 and 1983. Regression analyses suggested that variation in corn leaf aphid and greenbug densities significantly contribute to the variation in coccinellid densities. Furthermore, corn leaf aphid and coccinellid densities were significantly and positively correlated prior to sorghum panicle emergence. However, after panicle emergence only greenbug and coccinellid densities were highly correlated, reflecting a change in coccinellid food source from primarily corn leaf aphids to greenbugs. The ability of coccinellids to regulate greenbug densities may be largely dependent on the abundance of corn leaf aphids as a food source during early season crop growth.

EFFECTS OF VARIOUS FACTORS ON THE LOCAL DISTRIBUTION AND DENSITY OF COCCINELLID ADULTS ON CORN (COLEOPTERA: COCCINELLIDAE)

AbstractThe adult densities of Hippodamia tredecimpunctata tibialis (Say), Coccinella novemnotata Hbst., and Coccinella transversoguttata richardsoni Brown, on corn fluctuated in July and August and reached their maxima at pollination, whereas the density of Coleomegilla maculata lengi Timberlake fluctuated much less. C. maculata, H. tredecimpunctata, and C. transversoguttata were more numerous on plants with a liver diet applied to their foliage than on untreated plants. H. tredecimpunctata, C. novemnotata, and C. transversoguttata were less numerous on plants that had their tassels removed and produced no pollen than on intact plants. C. maculata, H. tredecimpunctata, and C. transversoguttata were more numerous on plants exposed to the maximum amount of sunshine than on plants that were shaded for part of each day. H. tredecimpunctata was more numerous on plants situated at low elevation than at high elevation, whereas C. transversoguttata was more numerous at high than at low elevation. C. maculata and H. tredecimpunctata were more numerous on plants near the middle of a corn field than on plants at the perimeter of a field adjacent to buckwheat, whereas C. novemnotata and C. transversoguttata were most numerous on plants near the perimeter. Two-species associations of C. maculata and H. tredecimpunctata, C. novemnotata and H. tredecimpunctata, C. novemnotata and C. transversoguttata, and C. novemnotata and H. tredecimpunctata occurred on individual plants. Plant density and time of planting affected coccinellid density. Adult density was greatest at a plant density of 3.2 plants per square metre and adults were more numerous on early than on late planted corn.