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Convergent Lady Beetle Hippodamia convergens Guérin-Méneville (Insecta: Coleoptera: Coccinellidae)


Abstract and Figures

The convergent lady beetle, Hippodamia convergens Guérin- Méneville, is among the most common lady beetle species throughout North America and is an important natural enemy of aphids, scales, thrips, and other soft-bodied insects. It will also feed on pollen and nectar from flowers when prey is scarce. This species can be found in habitats ranging from grasslands, forests, agricultural fields, gardens, and natural parks. It is one of the few natural enemies that are currently wild-collected from mass aggregations for distribution to the pest control industry
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Convergent Lady Beetle Hippodamia convergens
Guérin-Méneville (Insecta: Coleoptera: Coccinellidae)1
Luis F. Aristizábal and Steven P. Arthurs2
1. This document is EENY592, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date June 2014.
Visit the EDIS website at http://edis.ifas.u.edu.
2. Luis Aristizábal, Entomology and Nematology Department; and Steven P. Arthurs, assistant professor, Mid-Florida Research and Education Center;
Entomology and Nematology Department, UF/IFAS Extension, Gainesville, FL 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services
only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status,
national origin, political opinions or aliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension oce.
U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County
Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.
e convergent lady beetle, Hippodamia convergens Guérin-
Méneville, is among the most common lady beetle species
throughout North America and is an important natural
enemy of aphids, scales, thrips, and other so-bodied
insects. It will also feed on pollen and nectar from owers
when prey is scarce. is species can be found in habitats
ranging from grasslands, forests, agricultural elds, gar-
dens, and natural parks. It is one of the few natural enemies
that are currently wild-collected from mass aggregations for
distribution to the pest control industry (Figure 1).
Convergent lady beetles are widespread throughout North
America (the United States, western Canada and Mexico)
and Central America, but only recorded from Colombia
in South America (Figure 2). In the United States, the
convergent lady beetle can be found from California to New
Jersey and Hawaii, with smaller populations in the eastern
states. In some areas, the convergent lady beetle, along with
other native species, may be displaced by the invasive Asian
multicolored ladybeetle, Harmonia axyridis (Pallas).
e adult is rounded and elongate-oval, averaging 7.8 mm
(0.3 inch) long for females and 5.8 mm (0.23 inch) long for
males. Adults are easily recognized by their bright red or
Figure 1. Mass of convergent lady beetles in Alamo Peak, Otero Co.,
Credits: Jerry Oldenettel
Figure 2. Reported geography distribution of the
Credits: Global Biodiversity Information Facility database
Convergent Lady Beetle Hippodamia convergens Guérin-Méneville (Insecta: Coleoptera: Coccinellidae)
orange elytra (hardened forewings) which usually have 12
black spots (6 on each elytron). e prothorax (area behind
the head) is black with a white border and two white,
converging lines, which give rise to the insect’s common
name. Marking on the elytra are variable, with some
individuals less spotted or spotless, but the white lines that
converge behind the head are common to all individuals.
e legs, head, and underside are black. e legs are short
with 3-segmented tarsi, and the antennae are short and
Clusters of yellow eggs are laid by the adult female beetle
in batches of 10-30 eggs on stems or leaves of plants where
abundant insect prey is present. Individual eggs are spindle-
shaped and 1-1.5 mm (≈1/20th inch) long and laid pointing
e larvae are black with orange spots on the prothorax
and abdomen and look like small alligators. Larvae develop
through four instars (stages), growing progressively larger
and more spotted with orange and reaching about 7 mm
(1/4 inch) before becoming a pupa. e pupa is hemi-
spherical and orange and black.
Figure 3. Newly emerged adult
Hippodamia convergens showing
typical body markings.
Credits: Luis F. Aristizábal, University of Florida
Figure 4. Eggs of
Hippodamia convergens (1 day old).
Credits: Luis F. Aristizábal, University of Florida
Figure 5. First instar larvae of
Hippodamia convergens.
Credits: Luis F. Aristizábal, University of Florida
Figure 6. Second instar larvae of
Hippodamia convergens.
Credits: Luis F. Aristizábal, University of Florida
Figure 7. Third instar larvae of
Hippodamia convergens.
Credits: Luis F. Aristizábal, University of Florida
Convergent Lady Beetle Hippodamia convergens Guérin-Méneville (Insecta: Coleoptera: Coccinellidae)
Seasonal Biology
Convergent lady beetle is a bivoltine species, with two
generations per year (spring and fall) over much of its
range. ere may be additional generations in the South;
the life cycle in Florida has not been reported. During the
summer and winter when temperatures are too high or
low, and during periods when food sources are insucient
for reproduction, adult convergent lady beetles enter into
reproductive diapause. During these periods, adults may
aggregate under tree branches or under rocks.
e abundance of food plays an important role in their
fecundity. Before laying eggs (ovipositing), the female
needs to consume an adequate source of carbohydrates and
proteins. If food is plentiful, the pre-oviposition is about 5
days aer mating (Figure 10); if food is in short supply, the
female may wait several days or weeks before starting to
oviposit. e adults can eat honeydew, nectar, and pollen
when prey is scarce; however, females must consume aphids
or other live prey to reproduce. Each well-fed female may
lay 200 or more eggs during her life. e developmental
period (egg to adult) for convergent lady beetles measured
in our laboratory under conditions of 25°C, 80% relative
humidity and 16 hours daylight is about 21 days (averaging
3.5 days for egg stage, 2.6 days for rst instar, 2.7 days for
second instar, 2.1 days for third instar, 3.8 days fourth instar
and 5.4 days for the pupa).
Predatory Behavior
Convergent lady beetle larvae are active predators and
begin searching for small insects soon aer they hatch from
the egg. In some cases, the unhatched eggs are eaten by the
rst larvae to emerge. Visual, olfactory, and chemical cues,
including pheromones and honeydew secreted by aphids,
may be used to locate prey. Larger larvae are voracious
feeders and may consume between 30 and 50 aphids per
day. When food is scarce, Hippodamia convergens can
become cannibalistic.
is lady beetle is an important natural biological control
agent for aphid pests found on cotton, potato, corn, peach,
melon, cabbage, and other crops. Reported prey include
the Russian wheat aphid, Diuraphis noxia (Nordvilko), the
corn leaf aphid, Rhopalosiphum maidis (Fitch), the bird
cherry oat aphid, Rhopalosiphum padi (L.), the tobacco
aphid, Myzus nicotianae (Blackman), and the pea aphid,
Acyrthosiphon pisum (Harris). Eggs and larvae of other
small insects, such as potato psyllids, Bactericera cockerelli
(Sulc), and asparagus beetles, Crioceris asparagi (L.), are
reported as prey items.
Recently some citrus producers in Florida have released
large numbers of commercially obtained convergent lady
beetles from California against the Asian citrus psyllid
Diaphorina citri (Kuwayama), vector of the causal agent of
Figure 8. Fourth instar larvae of
Hippodamia convergens.
Credits: Luis F. Aristizábal, University of Florida
Figure 9. Pupa of
Hippodamia convergens.
Credits: Luis F. Aristizábal, University of Florida
Figure 10. Ovariole development of
Hippodamia convergens fed
aphids at 25° C.
Credits: Steven Arthurs, University of Florida
Convergent Lady Beetle Hippodamia convergens Guérin-Méneville (Insecta: Coleoptera: Coccinellidae)
the devastating Huanglongbing or citrus greening disease
and the citrus aphid, Aphis spiraecola (Patch). However,
there is currently little information on ecacy of this
predator against the psyllid or other pests in citrus groves in
Natural Enemies
Generalist predators such as large big-eyed bugs, Geocoris
bullatus (Say), and damsel bugs, Nabis alternatus (Parshley),
are reported as natural enemies of convergent lady beetle
eggs. e braconid wasp Dinocampus (=Perilitus) coccinel-
lae (Schrank) has been found parasitizing convergent lady
beetles (Figure 11). Some microsporidian diseases (primi-
tive fungi) have also been recovered from eld-collected
specimens. e microsporidian Nosema hippodamiae is
thought to cause chronic and sublethal eects, such as
reduced fecundity and survival of adults. Many birds are
predators of ladybeetles as well. However, the red color
with black spots on the elytra may play a role as warning
coloration, and ladybeetles with spots, such as Hippodamia
convergens, tend to be eaten less frequently than unspotted
Use as a Biological Control Agent
Although convergent lady beetles are generally a solitary
species, they exhibit periodic aggregation behaviors. is
phenomenon is displayed when large numbers of adults
from the fall generation migrate to cooler mountain regions
to overwinter. During the following spring season, these
adults migrate back to agricultural elds, grasslands and
other rural areas in search of aphids and places to lay their
eggs. is aggregation behavior is typical of Hippodamia
convergens but not generally observed in other lady beetle
species except for Harmonia axyridis, which aggregates in
e most famous large aggregations of this species occur in
the Sierra Nevada Mountains of California. Each year, large
quantities of beetles are collected from these overwintering
sites and put into refrigerated storage before being pack-
aged and distributed to growers and garden outlets. Most
companies package and distribute convergent ladybeetles
in quantities ranging from 1,500 to 72,000 adults for use
against aphids, mites, whiteies, thrips, and mealybugs,
with recommended release rates around 1,500 adults per
500 square feet or 70,000 adults per acre.
e tradition of using this species as a form of natural pest
control has continued, despite reports that eld-collected
beetles may harbor parasites and pathogens that may be
inadvertently released along with the beetles. Moreover,
since most wild-collected beetles overwinter while repro-
ductively immature (ovaries are not yet developed) and
have a natural tendency to disperse away from release sites,
their eectiveness as biological control agents for gardeners
and organic crops production is not guaranteed.
Figure 11.
Hippodamia convergens second instar larvae feeding on
melon aphid.
Credits: Luis F. Aristizábal, University of Florida
Figure 12. Larva of a parasitic wasp (probably Dinocampus
coccinellae) recovered from
Hippodamia convergens.
Credits: Steven Arthurs, University of Florida
Figure 13. Release of
Hippodamia convergens on rose plants.
Credits: Luis F. Aristizábal, University of Florida
Convergent Lady Beetle Hippodamia convergens Guérin-Méneville (Insecta: Coleoptera: Coccinellidae)
Selected References
Bjørnson S. 2008. Natural enemies of the convergent lady
beetle, Hippodamia convergens Guérin-Méneville: eir
inadvertent importation and potential signicance for
augmentative biological control. Biological Control 44:
Darby A, Raymond B, Douglas A. 2003. e olfactory
response of coccinellids to aphids on plants. Entomologia
Experimentalis et Applicata 95: 113-117.
Dolenska M, Nedved O, Vesely P, Tesarova M, Fuchs R.
2009. What constitutes optical warning signals of ladybirds
(Coleoptera: Coccinellidae) towards bird predators: colour,
pattern or general look? Biological Journal of the Linnaen
Society 98: 234-242.
Eigenbrode SD, White C, Rohde M, Simon CJ. 1998.
Behavior and eectiveness of adult Hippodamia convergens
(Coleoptera: Coccinellidae) as a predator of Acyrthosiphon
pisum (Homoptera: Aphididae) on a wax mutant of Pisum
sativum. Environmental Entomology 27: 902-909.
Jamal E, Brown G. 2001. Orientation of Hippodamia
convergens (Coleoptera: Coccinellidae) larvae to volatile
chemicals associated with Myzus nicotianae (Homoptera:
Aphididae). Environmental Entomology 30: 1012-1016.
Joudrey P, Bjørnson S. 2007. Eects of an unidentied
microsporidium on the convergent lady beetle, Hippodamia
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used for biological control. Journal of Invertebrate Pathology
Katsarou I, Margaritopoulos J, Tsitsipis J, Perdikis D, Zarpas
K. 2005. Eect of temperature on development, growth
and feeding of Coccinella septempunctata and Hippodamia
convergens reared on the tobacco aphid, Myzus persicae
nicotianae. Biocontrol 50: 565-588.
Michaud J, Qureshi J. 2006. Reproductive diapause in
Hippodamia convergens (Coleoptera: Coccinellidae) and its
life history consequences. Biological Control 39: 193-200.
Purandare S, Tenhumberg B. 2012. Inuence of aphid
honeydew on the foraging behaviour of Hippodamia
convergens larvae. Ecological Entomology 37: 184-192.
Qureshi JA, Stansly PA. 2011. ree homopteran pests of
citrus as prey for the convergent lady beetle: suitability and
preference. Environmental Entomology 40:1503-10.
Rodriguez SC, Miller JC. 1995. Life history traits in Hippo-
damia convergens (Coleoptera: Coccinellidae) aer selec-
tion for fast development. Biological Control 5: 389-396.
Saito T, Bjørnson S. 2006. Horizontal transmission of
a microsporidium from the convergent lady beetle,
Hippodamia convergens Guérin-Méneville (Coleoptera:
Coccinellidae), to three coccinellid species of Nova Scotia.
Biological Control 39: 427-433.
Saito T, Bjørnson S. 2013. e convergent lady beetle,
Hippodamia convergens Guérin-Méneville and its endo-
parasitoid Dinocampus coccinellae (Schrank): the eect
of a microsporidium on parasitoid development and host
preference. Journal of Invertebrate Pathology 113:18-25.
Seagraves MP. 2009. Lady beetle oviposition behavior in
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Sluss R. 1968. Behavioral and anatomical responses of the
convergent lady beetle to parasitism by Perilitus coccinellae
(Schrank) (Hymenoptera: Braconidae). Journal of Inverte-
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biotic resistance by native generalist predators slow lady
beetle invasions? Biological Control 63: 79-86.
Wells ML, McPherson RM. 1999. Population dynamics
of three coccinellids in ue-cured tobacco and functional
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Environmental Entomology 28: 768-773.
Full-text available
Urban community gardens provide habitat for biodiversity within urban landscapes. Beneficial insects, those that provide important ecosystem services like pollination and pest control, are among the many inhabitants of these green spaces. Garden management and the composition of the urban matrix in which they are embedded can affect not only the abundance and species richness of beneficial insects but also their community composition and functional traits. During 2014 and 2015 (June to September), we collected ladybird beetles (Coleoptera: Coccinellidae) in 19 community gardens in three counties of the California Central Coast. We examined the effects of garden- and landscape-level characteristics on ladybird community composition and functional traits. Out of the 19 species collected, only 3 were non-native to California (3 were not identified to species). Similarities in ladybird species composition were not driven by geographic distance between gardens, which suggest that beetles in these landscapes are not experiencing dispersal limitation. Instead, three landscape-level environmental variables and seven garden-scale ones correlated with changes in community composition. Even though we perceive cities as highly disturbed low-quality landscapes, our results suggest that highly mobile arthropods such as ladybird beetles, may not perceive the urban matrix as a barrier to movement and that urban gardens can be inhabited by native species with different sizes, diet breadths and diets. Nevertheless, our results also suggest garden specific management practices, such as altering ground cover, can affect the taxonomic and functional composition of ladybird beetles with potential implications to their ecosystem services.
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Larval coccinellids are thought to exhibit random search behavior but recent work has suggested that closer analysis of search paths could reveal more olfaction-driven behavior than previously realized. To test this idea, the use of volatile chemical cues by larvae of the coccinellid Hippodamia convergens Guérin-Méneville in searching for prey tobacco aphids, Myzus nicotianae Blackman, were studied. Larvae (second, third, and fourth instars) were exposed to three volatile sources; aphids alone, aphids on tobacco leaves and tobacco leaves previously exposed to aphids. Larvae were placed in an arena and their search path traced onto a grid then divided into seven different components relating approach angles and velocities at various time intervals. In general, older larvae were more efficient at searching than were younger ones. Older larvae had lower approach angles and higher approach velocities associated with treatments than did younger larvae. Different search behavior components responded differently to the various treatments but in most cases significant effects attributable to olfactory cues were obtained. The results support the potential use of olfactory cues by these larvae and suggest that a more extensive set of analyses and treatments should be conducted.
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Adult females of the coccinellid predator Hippodamia convergens (Say) spent more time walking and less time grooming on a line of peas, Pisum sativum L., that has reduced waxbloom on all parts of the plant (due to the mutation wel) compared with a near-isogenic sister line with normal waxbloom. H. convergens walking was distributed over all parts of the low-wax plants, whereas on normal-wax plants walking occurred mostly on stems and the edges of leaves and stipules. The beetles were able to generate 30 times the adhesive traction force on leaf surfaces of low-wax plants compared with normal-wax plants. In cage studies, H. convergens (4 adults per plant) were more effective at reducing population growth of pea aphid, Acyrthosiphon pisum (Harris), on low-wax plants than on normal-wax plants, but only at initial aphid densities of 10 aphids per plant. At higher initial densities (20 and 40 aphids per plant), differential impact of H. convergens was not observed or disappeared after 4-5 d. The results indicate that reduced waxbloom in peas could improve the effectiveness ofH. convergens on peas at low prey densities.
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Most ladybirds (Coleoptera: Coccinellidae) possess chemical protection against predators and signal its presence by less or more conspicuous coloration, which can be considered as a warning. Most ladybirds possess a dotted pattern, althougn the number, shape, and size of the spots, as well as their colour, varies considerably. Almost all ladybirds have a characteristic general appearance (body shape). We considered these traits to be used in ladybird recognition by avian predators. In the present study, we compared the reactions of avian predators (Parus major) caught in the wild, to four differently coloured ladybird beetles (Coccinella septempunctata, Exochomus quadripustulatus, Subcoccinella vigintiquatuorpunctata, and Cynegetis impunctata) and two artificial modifications of C. septempunctata; the first was deprived of their elytral spotted pattern by painting it brown, the other had their elytra removed (i.e. altering their general ladybird appearance). Ladybirds with a spotted pattern were attacked less frequently than unspotted ones. Ladybirds with removed elytra were attacked much more often than any ladybird with a preserved general appearance. The results obtained in the present study suggest the high importance of the spotted pattern as well as general appearance in the ladybird recognition process. Additional experiments with naïve birds (hand-reared P. major) demonstrated the innateness of the aversion to two differently spotted ladybird species (C. septempunctata and Scymnus frontalis). © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 234–242.
1. Environmental cues associated with prey are known to increase predator foraging efficiency. Ladybird larvae are major predators of aphids. The sugary excretion of aphids (honeydew) has been proposed to serve as a prey-associated cue for ladybird larvae. 2. Ladybird larvae are regularly found on the ground moving between plants or after falling off plants. The use of prey-associated cues would be particularly beneficial for ladybird larvae on the ground in that such cues would help them to decide which plants to climb because aphids are patchily distributed within as well as amongst plants and, as a result, many plants are either not infested with aphids or do not host an aphid species of high nutritional value for ladybird larvae. 3. Laboratory experiments with larvae of Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) were carried out to explore whether honeydew accumulated on the ground is used as a foraging cue. The study also investigated whether, if honeydew is a foraging cue, larvae show differential responses to honeydew of high-quality prey Acyrthosiphon pisum Harris compared with that of low-quality prey Aphis fabae Scopoli (both: Homoptera: Aphididae). 4. Hippodamia convergens larvae stayed longer in areas containing honeydew but did not engage in longer bouts of searching. Furthermore, larvae did not distinguish between honeydew from high- and low-quality aphid prey.
Interactions with native species often influence whether exotic species will become invasive. The lady beetles Coccinella septempunctata and Harmonia axyridis are broadly successful invaders, but they have failed to fully establish in some parts of western North America. One possibility is that the locally-abundant, generalist predatory bugs Nabis alternatus and Geocoris bullatus resist invasion by acting as intraguild predators. We investigated the relative likelihoods of (1) the invasive lady beetles falling prey to the native generalist bugs compared to two native lady beetles, Hippodamia convergens and Coccinella transversoguttata, and (2) the relative likelihood of these exotic vs. native lady beetles committing reciprocal intraguild predation and consuming the two native predatory bugs. A series of predation trials demonstrated that C. septempunctata exhibited similar susceptibility to predation by Nabis and Geocoris, and a similar likelihood to commit reciprocal intraguild predation on the two bugs, relative to its native congener C. transversoguttata. In contrast, among all species tested, the exotic species H. axyridis was the least susceptible to intraguild predation by the bugs and was the most likely to consume Nabis and Geocoris. Altogether, these results suggest that native predatory bugs would have similar effects on the native and exotic Coccinella species, conferring no particular harm or advantage to C. septempunctata during its invasion. However, H. axyridis enjoyed advantages over the native bugs by being a rare victim but common perpetrator of intraguild predation; all else being equal, this would tend to favor replacement of native species by H. axyridis.
The development of larval Perilitus coccinellae in the hemocoel of male Hippodamia convergens is described. Especial emphasis is placed upon the development of the trophic cells which originate from the dissociation of the parasite's embryonic membrane.Some aspects of the response of male beetles to parasitism by P. coccinellae are considered. The influence of parasitism on the feeding and respiration rates of the beetles is described. These was no effect on the mating behavior or testicular morphology in parasitized beetles. Two types of lesions are described from the fat body of host beetles: (1) those ascribed to the activity of the P. coccinellae larvae, and (2) those ascribed to the activity of the parasitic cells.Microsporidian infections were found in 10–20% of the P. coccinellae and in about 50% of the H. convergens. The lesions caused by the microsporidian infections in beetles are described including neoplasms in the midgut epithelium and in Malpighian tubules. The influence of the microsporidioses of both H. convergens and P. coccinellae on the development of the wasp are discussed.
Individuals of the convergent lady beetle Hippodamia convergens Guérin-Méneville, selected for a fast developmental rate (intensely selected line) through five generations, were assessed for unintended selective effects on adult weight and longevity, survivorship, food consumption, fecundity, and population growth parameters. Beetles from an intensely selected line were compared with beetles from a moderately selected line and field-collected wild types. After selection, survivorship from first instar to adult emergence at 18, 22, and 26°C was improved by 9.4, 8.5, and 22.2%, respectively, in the intensely selected line. Selection of individuals for fast development did not affect adult weight (19.6 mg), fecundity (344 eggs), longevity (53 days), nor third-fourth instar consumption of aphids (106 mg of pea aphids). Also, the intrinsic rate of increase (rm) and number of beetle generations per year were calculated for the intensely selected line, the moderately selected line, and wild-type beetles. The rm was higher for the intensely (0.099) than for the moderately selected line (0.091) and wild type (0.092). A degree-day model demonstrated that the intensely selected line may complete 3.9 and 5.3 generations in Corvallis and Hermiston, Oregon, respectively. The moderately selected line and wild-type populations would only complete 3.4 and 3.2 generations in Corvallis, respectively, and 4.6 and 4.5 generations in Hermiston, respectively.
Convergent lady beetles, Hippodamia convergens Guérin-Méneville are host to the braconid endoparasitoid, Dinocampus coccinellae (Schrank) and the microsporidian pathogen, Tubulinosema hippodamiae. The interrelationship between the endoparasitoid and the pathogen in H. convergens adults under laboratory conditions were examined by quantifying the effect of microsporidiosis on D. coccinellae development and host preference. Uninfected wasps were provided either uninfected or T. hippodamiae-infected beetles as hosts and the development of their progeny was observed over 30 days. The duration of endoparasitoid development from egg deposition in the host until adult eclosion for D. coccinellae did not differ significantly, regardless of the infection status of the host beetle. All wasp progeny that developed within, and emerged from, T. hippodamiae-infected beetles were infected with the microsporidian pathogen (n =48; 100% transmission). Infected D. coccinellae adults were also provided either uninfected or T. hippodamiae- infected host beetles so that the development of their progeny could be assessed over 30 days. Endoparasitoid development did not differ significantly; however, a significantly greater proportion of beetles stung by microsporidia-infected wasps did not contain an endoparasitoid larva when dissected at the end of the 30-day trial when compared to those stung by uninfected wasps. This suggests that the pathogen may reduce wasp fecundity or egg viability. Examination of paraffin-embedded D. coccinellae adult tissues revealed an extensive microsporidian infection throughout all major organs and tissues with exception of the ovary. During host choice trials, uninfected and microsporidia-infected D. coccinellae adults pursued, took an ovipositional stance, and attacked uninfected beetles more often than microsporidia-infected hosts but these observations did not differ significantly (P > 0.05).
The seasonal abundance of 3 species of coccinellids was observed on flue-cured tobacco, Nicotiana tabacum L., during 1997 and 1998 in Tift County, GA. The most abundant coccinellid during both seasons was the convergent lady beetle, Hippodamia convergens Guérin-Méneville, which was present from mid-May, when tobacco aphids, Myzus nicotianae Blackman, colonized the crop, until late July when sampling ended. The sevenspotted lady beetle, Coccinella septempunctata L., and the multicolored Asian lady beetle, Harmonia axyridis (Pallas), were also observed. C. septempunctata was most abundant early in the season and maintained low population levels during June and July. Conversely, H. axyridis was absent in tobacco until late May and remained abundant until sampling was discontinued. Populations of H. convergens, H. axyridis, and C. septempunctata were linearly related to tobacco aphid populations during 1998. In functional response experiments, 4th-instar larvae and adult H. convergens exhibited a type II functional response to aphid density. Fourth-instar larvae had a higher search rate and a longer handling time than adult H. convergens. Two other coccinellid species were observed at low population densities on flue-cured tobacco, Coleomegilla maculata (Mulsant) and Cycloneda munda (Say). Collectively, coccinellids may be important biological control agents of tobacco aphids on Georgia flue-cured tobacco.
Convergent lady beetles, Hippodamia convergens Guérin-Méneville, are a popular choice for aphid control in North America. An unidentified microsporidium was found in H. convergens adults that were purchased from a commercial insectary in 2004. This study examined egg cannibalism and egg predation as a means of horizontal transmission of the unidentified microsporidium among H. convergens larvae and three coccinellid species found in Nova Scotia: Coccinella septempunctata (seven-spotted lady beetle), C. trifasciata perplexa (three-banded lady beetle), and Harmonia axyridis (multicolored Asian lady beetle). The microsporidium was transmitted with 100% efficiency when first instars fed on microsporidia-infected eggs. Mean spore count data from smear preparations of infected beetles suggest that the infection was as heavy in C. trifasciata perplexa (a native coccinellid) (11.2 ± 0.96 spores/100 μm2) as it was in H. convergens (the natural host) (12.8 ± 1.16) but lighter in the introduced species C. septempunctata (7.5 ± 0.65) and H. axyridis (0.8 ± 0.11). For all of the beetle species examined, larval development was significantly longer for microsporidia-infected individuals than for their uninfected cohorts. The microsporidium had no effect on larval mortality. Based on the results of this study, field-collected H. convergens should be examined for microsporidia and uninfected individuals should be used to rear individuals for release in biological control programs. However, this is unlikely to happen because H. convergens are relatively easy and inexpensive to collect from their overwintering sites for redistribution.