Development and Reproduction of Ladybeetles (Coleoptera: Coccinellidae) on the Citrus Aphids Aphis spiraecola Patch and Toxoptera citricida (Kirkaldy) (Homoptera: Aphididae)

Seven species of Coccinellidae inhabiting citrus groves in Florida were evaluated for ability to develop and reproduce on the citrus aphids Toxoptera citricida (Kirkaldy) and Aphis spiraecola Patch. Choice tests performed with adults and larvae indicated that both aphid species were generally acceptable prey. Coccinella septempunctata L., Coleomegilla maculata fuscilabris (Mulsant), Coelophora inaequalis F., and Olla v-nigrum Mulsant were unable to complete development on either aphid. Hippodamia convergens Guerin larvae completed development on A. spiraecola with 68% survival; none survived on T. citricida. Only Cycloneda sanguinea (L.) and Harmonia axyridis Pallas completed development on both A. spiraecola (60 and 70% survival, respectively) and T. citricida (100 and 95% survival, respectively). Larval developmental time was shorter on T. citricida than on A. spiraecola, and resulting adults were heavier, differences being more pronounced in H. axyridis. Females of C. septempunctata, C. inaequalis, and O. v-nigrum produced viable eggs on T. citricida. O. v-nigrum did not produce eggs on A. spiraecola. Females of C. m. fuscilabris and H. axyridis produced no eggs on A. spiraecola and mostly infertile eggs on T. citricida. Female H. convergens laid twice as many eggs feeding on T. citricida as on A. spiraecola and egg viability was similar. C. sanguinea females laid similar numbers of eggs on both aphids, but eggs produced on A. spiraecola had higher fertility. Pollen added to the T. citricida diet temporarily improved the fertility of H. axyridis females, but not that of C. sanguinea females. C. sanguinea was judged the best candidate for augmentative biocontrol of T. citricida, the primary vector of citrus tristeza virus.     

Suitability of exotic and native lady beetle eggs (Coleoptera: Coccinellidae) for development of lady beetle larvae

Predation upon lady beetle (Coleoptera: Coccinellidae) eggs in the field is most often instances of egg cannibalism by larvae or adults while the majority of the remaining predation events upon coccinellid eggs is done by other species of Coccinellidae. Thus the recent introduction and establishment of Harmonia axyridis in the US could negatively affect native species of Coccinellidae via egg predation. However, little is known regarding the suitability of interspecific coccinellid eggs as a food source for larval development. In this study, it was found that native first or third instar Coleomegilla maculata and Olla v-nigrum larvae were incapable of surviving to the adult stage when provided solely exotic H. axyridis eggs. In stark contrast, H. axyridis larvae survived equally well when cannibalizing eggs or eating eggs of either native species. When C. maculata and O. v-nigrum were grouped as ‘native’ and compared with the exotic H. axyridis, more native eggs were attacked than exotic eggs and a higher percentage of eggs was attacked by H. axyridis larvae. Native and exotic larvae attacked a similar percentage of native eggs but native larvae attacked significantly fewer exotic eggs than did exotic larvae. These data suggest that H. axyridis may prey upon the eggs of these native species, when encountered in the field, compared with the likelihood of the native species preying upon H. axyridis eggs. Therefore, eggs of the native species C. maculata and O. v-nigrum will continue to be subjected to cannibalism and also to possible predation by other native species and the exotic H. axyridis.     

Liver-based artificial diets for the production of Orius laevigatus

Different meat- and liver-based artificialdiets were designed for the generalist predatorOrius laevigatus (Fieber) (Anthocoridae)and their suitability was compared to that ofits factitious food, Ephestia kuehniellaZeller (Pyralidae) eggs. The quality of thefood was measured by its ability to promotegrowth and oviposition of the insect. Nymphaldevelopment was slower on artificial diets thanon the control food, taking 15.0–15.9 days vs.14.3 days, respectively. Survival of nymphs fedartificial diets varied from 68.0–92.5%,compared with 96% for those fed E. kuehniella eggs. Adult weights were, however,not affected by diet. Fecundity of femalesprovided with liver diets was similar to orsomewhat lower than that of females fed Ephestia eggs. Oviposition rate and egg hatchwere similar on all diets tested. The resultssuggest that beef liver was the most importantcomponent of the diets tested, offering theessential nutrients to sustain growth andreproduction of O. laevigatus.Supplementing ingredients, like ground beef,egg yolk, sucrose and vitamin C can improve thenutritional value of the diet for O.laevigatus, but effects are rather small.Artificial diets containing liver and egg yolkas the main components may prove useful to makemass production of O. laevigatus andother heteropteran predators more cost effective.     

Negative dietary effects of Colorado potato beetle eggs for the larvae of native and introduced ladybird beetles

Aphidophagous ladybird beetles (Coleoptera: Coccinellidae) are attracted to and feed heavily on aphids, but many species will also feed opportunistically on other prey that they encounter. In potatoes (Solanum tuberosum L.) in Washington State, USA, coccinellids feed on both green peach aphids (“GPA,” Myzus persicae Sulzer) and eggs of the Colorado potato beetle (“CPB,” Leptinotarsa decemlineata Say). The guild of aphidophagous ladybirds includes two native species, Hippodamia convergens Guérin-Méneville and Coccinella transversoguttata Brown. Recently, an introduced species, Coccinella septempunctata L., has invaded and apparently displaced its native congener. A second exotic, Harmonia axyridis Pallas, has colonized the area and is becoming more abundant. We compared larval development of each species on a monotypic diet of GPA, a monotypic diet of CPB eggs, or a mixed diet of both GPA and CPB eggs. Our goal was to answer two questions: (1) do larvae of the four ladybird species benefit from including CPB eggs in their diet and (2) do the four ladybird species differ in their ability to utilize CPB eggs as prey? No larva of any species completed development on a pure diet of CPB eggs, and survivorship was highest for all species when they fed on a pure diet of GPA. One native species, H. convergens, and one exotic species, H. axyridis, exhibited significantly lower survivorship on a mixed diet of both CPB eggs and GPA, compared to a pure GPA diet; H. axyridis also took longer to develop from egg to adult when both prey were provided. Survivorship of the two Coccinella spp. was not altered by the inclusion of CPB eggs with GPA, although CPB eggs lengthened the development time of C. transversoguttata. Adult size was not consistently affected by diet for any of the coccinellids. Overall, no ladybird species benefited from the inclusion of potato beetle eggs in its diet. The two Coccinella species responded similarly to the inclusion of CPB eggs, and so we would not expect any difference in the success of coccinellid larval development in potato fields following the replacement of C. transversoguttata by C. septempunctata. Hippodamia convergens and H. axyridis, the two species whose survivorship was depressed by combining CPB egg and aphid prey, were also the two species that consumed the greatest number of CPB eggs during successful larval development. A comparison of total egg consumption by each species cohort suggested that displacement of the other species by H. axyridis would not alter CPB biological control, because the higher per capita feeding rate by H. axyridis larvae compensated for individuals’ greater mortality risk on a diet including CPB eggs.     

Suitability of pollen sources for the development and reproduction of Coleomegilla maculata (Coleoptera: Coccinellidae) under simulated drought conditions

Laboratory experiments compared the nutritive value of various pollen sources for the development of Coleomegilla maculata DeGeer under conditions of continuous water availability and simulated drought. When water was continuously available, larval survival was not different from 100% on diets of frozen eggs of Ephestia kuehniella Zeller, corn pollen, sorghum pollen, or pulverized bee pollen, whereas survival of larvae was significantly reduced on the latter three diets in the simulated drought treatment. Pollen of cultivated sunflower, Helianthus annus L., proved fatal to both larvae and adults; its surface structure caused clumping and accumulation on the insect cuticle that led to death from exhaustion/desiccation in petri dishes. The Ephestia egg diet yielded shorter developmental times and heavier adult weights than any pollen diet in both treatments. The drought treatment increased developmental time on all diets with a significant treatment–diet interaction. Drought reduced the adult weight of females on the sorghum pollen diet, and that of both sexes on the bee pollen diet, again with a significant treatment–diet interaction. Initial water content was highest in corn pollen (36.8%), followed by Ephestia eggs (29.2%), sorghum pollen (25.3%), sunflower pollen (8.7%), and bee pollen (4.6%), but did not appear correlated with C. maculata larval survival on pollen sources under drought conditions. Reproductive adult females that received corn or sorghum pollen as a supplement to Ephestia eggs did not differ in fecundity or fertility from those fed only Ephestia eggs.     

Interactions between the fungal pathogen Beauveria bassiana and three species of coccinellid: Harmonia axyridis, Coccinella septempunctata and Adalia bipunctata

Harmonia axyridis is a predatory coccinellid, native to central and eastern Asia. It has been available in many countries for use as a biological control agent of pest aphids and scale insects. In many of these countries, including the USA, H. axyridis has established. It is now considered an invasive alien species for a number of reasons, including its impact on functional biodiversity. Beauveria bassiana is known to be a natural mortality agent of overwintering coccinellids and is a potential candidate for the biological control of H. axyridis. In this paper we compare the susceptibility of three species of coccinellid, H. axyridis (cultures derived from Japan and UK), Coccinella septempunctata and Adalia bipunctata to infection by B. bassiana (commercial strain GHA) after exposure at three doses (10⁵, 10⁷, 10⁹ conidia ml⁻¹). The two subpopulations of H. axyridis (Japan and UK) were more resistant to B. bassiana infection than either A. bipunctata or C. septempunctata. This is exemplified by the median lethal doses at 10 days post-inoculation (LD₅₀) of 10^6.2, 10^6.0, 10^8.3, 10^9.6 conidia ml⁻¹ for A. bipunctata, C. septempunctata, H. axyridis (Japan) and H. axyridis (UK), respectively. Only doses of 10⁹ conidia ml⁻¹ resulted in mortality of H. axyridis, in contrast, 80% of C. septempunctata and 70% of A. bipunctata exposed to 10⁷ conidia ml⁻¹ of B. bassiana succumbed to infection. The fecundity (cumulative mean egg production over 10 days) of A. bipunctata and H. axyridis (UK) was also assessed. The fecundity of C. septempunctata could not be assessed because this species requires diapause prior to the onset of reproduction and these studies were on beetles that had recently eclosed (2–8 weeks). Harmonia axyridis (Japan) produced no eggs in most treatments including the control and so was excluded from analysis. High dose (10⁹ conidia ml⁻¹) inoculation reduced the fecundity of A. bipunctata to zero but egg production was similar for individuals inoculated with doses of 10⁵, 10⁷ conidia ml⁻¹ and control individuals. In contrast, all doses of B. basssiana reduced H. axyridis (UK) egg production dramatically. We discuss these results in relation to the potential for control of H. axyridis using B. bassiana.     

Influence of diet on life table parameters of <Emphasis Type="Italic">Iphiseius degenerans</Emphasis> (Acari: Phytoseiidae)

Studies on the reproduction, longevity and life table parameters of Iphiseius degenerans (Berlese) were carried out under laboratory conditions of 25 ± 1 °C, 75 ± 5% RH and 16L:8D h. As food sources for the predatory mite, Ricinus communis L. pollen, all stages of the spider mite Tetranychus urticae Koch, Frankliniella occidentalis (Pergande) larvae, and Ephestia kuehniella Zeller eggs were selected. All diets were accepted as food by the adult mites. Female longevity ranged from 29.5 to 42.4 days, the highest value was recorded on a diet of Ephestia eggs. The highest percentage of females escaping the experimental arena was observed on the diet consisting of thrips larvae. The highest oviposition rate (1.9 eggs/female.day) was recorded when the predator was fed on spider mites on an artificial substrate. For other diets, oviposition rates ranged from 1.0 to 1.3 eggs/female.day. The intrinsic rate of natural increase (r _m) of I. degenerans varied between 0.015 and 0.142 females/female.day. The diet consisting of castor bean pollen resulted in the highest population growth whereas the diet on spider mites brushed off onto a bean leaf arena resulted in the slowest population growth. This can be explained by the inability of the predator to cope with the webbing of T. urticae, and the high escape rate of the progeny when reared on spider mites. The percentage of females in the offspring ranged from 40 to 73%.This revised version was published online in May 2005 with a corrected cover date.     

The effect of temperature on development and fecundityof Scymnus levaillanti

Development and fecundity of Scymnus levaillanti(Mulsant) were recorded at fiveconstant temperatures ranging from 15 to 35 ± 1 °C in 5 °C increments, 60 ± 5% RHand 16 h of artificial light (5000 Lux). Developmentaltime (egg to adult) of S. levaillantisignificantly decreased with increasing temperatures,ranging from 63.9 days at 15 °C to 11.1 days at35 °C. Development from egg to adult required305.2 DD above a developmental threshold estimated as11.7 °C. Oviposition periods lasted 86.5, 76.1,47.2, and 31.5 days at 20, 25, 30 and 35 °C,respectively. No eggs were deposited at 15 °C.Higher temperatures resulted in shorter generationtimes (T_O) and in decreased net reproductiverates (R_O) of the coccinellid. S.levaillanti kept at 30 °C produced 0.151females/female/day, the highest per capita rate ofpopulation growth (r_m). The `functional response'of larvae and adults of S. levaillanti matcheswell that described by Holling (1959) as Type 2.Daily number of eggs deposited by females increased toa plateau with increasing prey density. Resultsobtained here provide information about the biology ofS. levaillanti, and its feeding capacityindicates that it may act as an important control agent.     

Functional response ofCurinus coeruleus (Col.: Coccinellidae) toHeteropsylla cubana (Hom.: Psyllidae) on artificial and natural substrates

Laboratory measurements of the functional response of adultCurinus coeruleus (Mulsant) to nymphs ofHeteropsylla cubana Crawford on filter paper and on leaves of different host plants showed a significant effect of these different substrates on nymph consumption at several different densities. Moreover, this effect may be explained by the influence of the substrate on the search rate of the predator. Host plants tested includedLeucaena leucocephala (Lam) de Witt,L. diversifolia (Schlecht.) Benth. andL. pallida Britton and Rose. Results obtained may be relevant to plant-protection research programs involving the integration of biological control with host-plant resistance.      

Development of Encarsia bimaculata (Heraty and Polaszek) (Hymenoptera: Aphelinidae) in Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) nymphs

Encarsia bimaculata was recently described from India as a potentially useful parasitoid of Bemisia tabaci. Its developmental biology was studied in the laboratory at 25–30 °C and 70–75% RH. Results showed that E. bimaculata is a solitary, arrhenotokous, heteronomous, autoparasitoid. Mated females laid eggs internally in B. tabaci nymphs that developed as primary parasitoids. Males developed as hyperparasitoids, either in females of their own species or in other primary aphelinid parasitoids. Superparasitism was common under cage conditions. Both sexes have an egg, three larval instars, prepupal, and pupal stages. Development from egg to adult took 12.70 ± 2.10 days for females and 14.48 ± 2.60 days for males. Individual B. tabaci nymphs were examined for E. bimaculata parasitization using three isozymes: esterase, malate dehydrogenase, and xanthine dehydrogenase. All three isozymes showed differential banding patterns that identified E. bimaculata parasitized or unparasitized B. tabaci nymphs.     

Life history of the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Kenya

We conducted laboratory and field experiments to elucidate the life history of Ixodiphagus hookeri, a parasitoid of the ixodid tick Amblyomma variegatum in Western Kenya. Ixodiphagus hookeri females oviposited in unfed host nymphs as well as engorged nymphs, but rarely in engorged larvae. While I. hookeri developed to adults in engorged nymphs, the eggs laid in unfed nymphs disappeared within 2 days after oviposition. As temperature increased, development time of I. hookeri from oviposition to adult emergence in engorged nymphs decreased from 46 days at 23 °C to 35 days at 28 °C, and their immature survival in engorged nymphs decreased from 67% at 23 °C to 22% at 28 °C. No parasitoid adult emerged from hosts at 30 °C. Individual hosts parasitized by single females produced 42–53 adult wasps, 73% of which were females. As a typical pro-ovigenic species, I. hookeri females had an average of 84 mature eggs at emergence and lived only for a few days. When laboratory-reared, unfed nymphs of A. variegatum were attached to cattle for 4–9 days in subsistence farmers’ fields in Western Kenya, 25% of the engorged nymphs and 4% of the unfed nymphs on cattle were parasitized by I. hookeri, demonstrating that I. hookeri females search for and oviposit in A. variegatum nymphs on cattle. Unlike other strains of I. hookeri that overwinter as eggs in unfed nymphs, I. hookeri could continuously reproduce throughout the year in Western Kenya.     

Influence of diet and photoperiod on development and reproduction of European populations of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

The current study examines the effect of photoperiod (16:08 or 12:12 h L:D) and diet (eggs of Ephestia kuehniella Zeller (Lepidoptera: Phycitidae) or the pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae)) on the development and reproduction of the multicoloured Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). A long-term laboratory population of H. axyridis (since 1998) and a melanic and non-melanic population originating from field collected individuals of H. axyridis in Belgium were used in this study. Long day conditions (16 h photoperiod) shortened development of the field populations with 2–3 days when compared with short day conditions (12 h photoperiod). Oviposition in the field populations was delayed by 1–3 months when reared at a 12 h photoperiod. Dissections indicated that the females were in reproductive diapause. As compared with live pea aphids, a diet consisting of E. kuehniella eggs yielded heavier adult body weights (up to 12%) and increased the number of egg laying days (by 45–169%) for both field populations at a 16 h photoperiod and lengthened adult life span (by 45–92%) under both light regimens. The morph types differed in their response to the foods offered in terms of developmental rate, pre-oviposition period and number of oviposition days. The laboratory and field strains responded differentially to regimens of food and photoperiod. The study indicated a greater nutritional plasticity of the non-melanic morphs which may offer them a competitive advantage that may in part explain the predominance of non-melanic morphs in newly colonized areas.     

Food consumption and utilisation by larvae of two coccinellid predators, Scymnus levaillanti and Cycloneda sanguinea, on cotton aphid, Aphis gossypii

This study was carried out under laboratory conditions at various temperatures to compare food consumption and efficiency of conversion of food to body mass for larvae of two coccinellid predators, Scymnus levaillanti Mulsant (Coleoptera: Coccinellidae) and Cycloneda sanguinea (L.) (Coleoptera: Coccinellidae), which differ in body size and feeding method. The consumption rate of each larval stage of both species increased with increasing temperature. The consumption rate for total development (from egg hatch to pupation) of S. levaillanti was found to be 22.9 aphids per day at 30°C. It was much higher for C. sanguinea (975.1 aphids per day at 25°C and 1066 aphids per day at 30°C). The larger species, C. sanguinea was more voracious at each temperature than the smaller species, S. levaillanti. The larvae of S. levaillanti, employing pre-oral digestion, were more efficient in converting food to body mass than larvae of C. sanguinea, which used chewing and sucking. The fourth instars of both species were less efficient in converting food to body mass than were their first three instars. It was concluded that body size and feeding method of coccinellid predators play an important role in food consumption and efficiency of conversion of food to body mass.     

Oviposition in Cryptolaemus montrouzieri stimulated by wax filaments of its prey

The oviposition responses of Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) to the soft scale Eupulvinaria hydrangeae (Steinweden) (Homoptera: Coccidae) and to the mealybug Planococcus citri (Risso) (Homoptera: Pseudococcidae) have been compared in the laboratory. The females delay oviposition and withhold mature eggs in their lateral oviducts in the absence of wax filaments produced by the prey (only present in the ovisac of E. hydrangeae, present in all stages of P. citri). Contact chemical cues perceived by females when probing the wax filaments with their mouthparts are the signals inducing the search for oviposition sites. The second step is under the control of the ovipositor by which females locate confined sites to lay eggs. This oviposition behaviour could have a considerable impact on the prey exploitation strategy of this important biocontrol agent and might help to understand its apparent ineffectiveness in situations of low prey density.     

Interactions between the parasitoid wasp Dinocampus coccinellae and two species of coccinellid from Japan and Britain

The establishment, spread and increase of the invasive coccinellid Harmonia axyridis Pallas in North America and Britain have coincided with declines in native ladybirds. In Britain, this pattern was predicted soon after H. axyridis was first recorded. However, predictions of the impact that H. axyridis may have on the parasites, parasitoids and pathogens of native coccinellids have been less certain, largely because of uncertainty over whether H. axyridis would become an alternate host for such agents. Dinocampus coccinellae (Schrank) is a braconid parasitoid of ladybirds of the sub-family Coccinellinae. In Japan, this wasp uses both Coccinella septempunctata brucki Mulsant and H. axyridis as hosts, but successfully parasitizes a higher proportion of the former species. Data are here presented that indicate the same is true in Britain, but to a greater extent. This study investigates the interactions of D. coccinellae with C. septempunctata L. and H. axyridis from Japan and Britain. We show that coccinellid activity affects encounter rates with the wasp, with H. axyridis being more active than C. septempunctata in the tests. Escalation rates from investigation to ovipositional attack were higher for C. septempunctata than H. axyridis for both Japanese and British wasps. Wasp emergence was higher, relative to ovipositional attack, from C. septempunctata than from H. axyridis. Wasps did not discriminate between Japanese and British ladybirds of the same species. British wasp eclosion rates were higher from Japanese than from British H. axyridis. We consider both the effect D. coccinellae may have on H. axyridis population demography, and the effect H. axyridis may have on D. coccinellae in Europe.     

Pollen as an alternative food for Harmonia axyridis

The current study examines the potential of the multicoloured Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) to use pollen as a food to sustain development and reproduction in the absence of insect prey. Three populations of H. axyridis were used in this study: a long-term laboratory population (since 1998) and a melanic and non-melanic population originating from field collected individuals in Belgium. The insects were allowed to develop and reproduce on frozen eggs of Ephestia kuehniella Zeller (Lepidoptera: Phycitidae), frozen moist bee pollen or an even mixture of the two. Females of the field population offered the mixed diet initiated oviposition sooner than those fed only E. kuehniella eggs, but other developmental and reproductive traits were similar on these diets. A diet of pollen alone allowed 35–48% of the larvae of the field population of H. axyridis to successfully reach adulthood. However, developmental time for these individuals was prolonged by 31–49% and adult body weight was reduced by 37–68%, compared to individuals offered the diets containing E. kuehniella eggs. When fed exclusively on pollen in their larval and adult life, about 40% of the adult females of either field population were able to produce a small number of viable eggs. The laboratory and field strains differed in their response to diet for a number of developmental and reproductive traits. The exploitation of pollen and other plant foods at times when insect prey is scarce, may offer a further competitive advantage to the non-indigenous coccinellid H. axyridis over native European predatory lady beetles that share the same niche and are less capable of using pollen as an alternative food.     

Influence of diet on growth,food retention time,and gill ventilation rate of nymphs of Cloeon sp. (Ephemeroptera: Baetidae)

Early instar nymphs of the mayfly, Cloeon sp. were kept on an algal or a detrital diet at 20 ± 1 °C in the laboratory. A control group was not given any food. Nymphs kept on algae showed significantly (P = 0.001) higher growth both in terms of length and biomass than for those kept on detritus. None of the nymphs given algae or detritus died during the experiment, and 40 per cent of those fed algae and 20 per cent fed detritus reached maturity by the termination of the experiment. Food retention time as well as gill ventilation rate of nymphs feeding on algae were significantly (P = 0.001) higher than those feeding on detritus. It is probable that these two factors largely enabled the nymphs to survive as well as to grow and reach maturity, though relatively slowly, solely on a detrital diet. However, algae was clearly shown to be a superior food resource for Cloeon sp. nymphs.     

Biology of <Emphasis Type="Italic">Dermacentor silvarum</Emphasis> (Acari: Ixodidae) under laboratory conditions

The minimum life cycle of Dermacentor silvarum Olenev had a mean duration of 87.5 days (range 74–102 days) under laboratory conditions [(27±1 °C), 70% RH, 6 L: 18 D]. The mean time in (days) for the different stages of its cycle was as follows: incubation period of eggs was 15.3 days; prefeeding, feeding and premoulting periods of larvae and nymphs averaged 5.5, 4.0 and 7.3 days, and 5.2, 5.0 and 14.6 days, respectively; prefeeding, feeding, preoviposition and oviposition periods of female adults lasted for 7.8, 4.5, 4.3 and 14.0 days, respectively. There existed a highly significant correlation between engorged body weight of females and egg masses laid (r = 0.9877, p<0.001). The reproductive efficiency index (REI) and reproductive fitness index (RFI) in females were 11.09 and 9.58, respectively. No relationship between nymphal engorged body weight and resultant sexes was observed. Delayed feeding and non-oviposition (in June and July) existed in females, and low temperature (−10 °C) treatment for 45 days could terminate oviposition diapause. However, the egg masses laid by post-diapause females were significantly smaller than those laid by females engorged in March, April and May.     

Ladybird population dynamics in potato: comparison of native species with an invasive species, Harmonia axyridis

Following the detection of the harlequin ladybird, Harmonia axyridis, in 2003 in potato crops in Belgium, a study was carried out between 2004 and 2006 on the phenology of this species compared to native species in potato. The results confirmed the success of H. axyridis, with high population levels in 2004 and 2005. In 2006, aphid populations were very low and no H. axyridis larvae were sampled in potato, but the indigenous species Coccinella septempunctata and Propylea quatuordecimpunctata were detected. A species by species comparison of the date of first larvae detection, the larvae population peak, and the difference between this peak and the aphid population peak was performed. Results showed a clear correlation between C. septempunctata and P. quatuordecimpunctata and potato aphids, with a delay of 3.5 and 6.5 days between the aphid and ladybird population peaks for the two native species. H. axyridis arrived 7–8 days after the two indigenous species and the larval peak population occurred 15.8 days after the aphid population peak. This meant that H. axyridis had to complete its larval development with very low aphid populations or even with no aphids at all. The reason for its late arrival and the possible food resources used by H. axyridis larvae are discussed.     

Life table and predation of Oligota pygmaea (Coleoptera: Staphylinidae) a major predator of the red spider mite, Oligonychus coffeae (Acarina: Tetranychidae) infesting tea

The staphylinid beetle, Oligota pygmaea (Solier) is an important predator of the red spider mite, Oligonychus coffeae (Nietner) infesting tea. Biology, life table and predatory efficiency of O. pygmaea were studied under laboratory conditions. Duration of developmental stages of O. pygmaea was 3.2, 5.7 and 12.5 d for eggs, larvae and pupae, respectively with an average of 23.0 d from egg to adult emergence. After a mean preovipostion period of 2.9 d, each female laid an average of 400.5 eggs in its life span. Adult O. pygmaea lived for an average of 54.1 d. Adult females lived for a longer period of 58.8 d compared to the longevity of 49.4 d of adult male. Studies revealed that its life table characterized by an intrinsic rate of natural population increase (r) of 0.118 d, net reproductive rates (R_o) of 243.693 eggs/female, gross reproduction rate (Σm_x) of 245.313 eggs/female, generation time (T) of 46.575 d, doubling time (DT) of 5.874 d and finite rate of increase (λ) of 1.125 d. Seasonal abundance of O. pygmaea and its prey, O. coffeae was monitored by sampling 25 tea leaves randomly from each experimental block grown under the prevailing field conditions. O. pygmaea showed a typical pattern of population dynamics with a peak during January to March and low incidence during June to September. Peak in the population of O. pygmaea coincided with the abundance of O. coffeae in the tea fields. Weather factors such as high temperature, low relative humidity and low sunshine hours adversely affected the populations of O. pygmaea. The first to third instar larvae of O. pygmaea consumed 31.0–133.2 eggs of mites per day. Third instar larva of O. pygmaea consumed an average of 133.2 eggs, 46.4 hexapod larvae, 39.6 nymphs and 11.4 adults per day. Adult females consumed more number of red spider mites compared to the males.