Impact of oilseed rape expressing the insecticidal cysteine protease inhibitor oryzacystatin on the beneficial predator Harmonia axyridis (multicoloured Asian ladybeetle)

Insect-resistant transgenic plants have been suggested to have deleterious effects on beneficial predators through transmission of the transgene product by the pest to the predator. To test this hypothesis, effects of oilseed rape expressing the cysteine protease inhibitor oryzacystatin-1 (OC-1) on the predatory ladybird Harmonia axyridis were investigated using diamondback moth Plutella xylostella as the pest species. As expected, oilseed rape expressing OC-1 had no effects on either development or survival of the pest, which utilizes serine digestive proteases. Immunoassays confirmed accumulation of the transgene product in pest larval tissues at levels of up to 3 ng per gut. Characterization of proteolytic digestive enzymes of H. axyridis demonstrated that larvae and adults utilize cysteine and aspartic proteases; the former activity was completely inhibited by oryzacystatin in vitro. However, when H. axyridis larvae consumed prey reared on OC-1 expressing plants over their entire life cycle, no significant effects upon survival or overall development were observed. The inhibitor initially stimulated development, with a shortening of the developmental period of the second instar by 27% (P < 0.0001) accompanied by a 36% increase in weight of second instar larvae (P = 0.007). OC-1 had no detrimental effects on reproductive fitness of adult H. axyridis. Interestingly there was a significant increase in consumption of OC-1 dosed prey. The results show that prey reared on transgenic plants expressing a protein which inhibited ladybird digestive enzymes in vitro had no effects in vivo; the ladybird was able to up-regulate digestive proteases in response to the inhibitor.     

Potential for intraguild predation and competition among predatory Coccinellidae and Chrysopidae

In a laboratory study two coccinellid species, Coleomegilla maculata (DeGeer) and Harmonia axyridis Pallas, completed preimaginal development on lacewing eggs, Chrysoperla carnea Stephens or pea aphids, Acyrthosiphon pisum (Harris) in similar times. Preimaginal survival on C. carnea eggs was similar to survival on A. pisum for all stages of C. maculata and H. axyridis. Coccinellid adults that developed on C. carnea eggs were smaller than adults reared on A. pisum. Coccinella septempunctata L. did not complete preimaginal development on C. carnea eggs. Chrysoperla carnea preimaginal developmental time was approximately 20 days when fed either C. maculata eggs or A. pisum. Chrysoperla carnea fed C. maculata eggs developed into smaller adults, compared to adults reared as larvae on A. pisum, Ostrinia nubilalis (Hübner) eggs, or A. pisum alternated daily with O. nubilalis eggs. C. carnea did not complete preimaginal development on H. axyridis eggs. Cannibalism occurred more frequently between C. carnea third instars than between C. maculata fourth instars. When a C. carnea third instar was paired with a C. maculata fourth instar, more C. maculata were preyed upon by C. carnea, regardless of the herbivorous prey density. In the field these two predator species may negatively affect each other and reduce their suppression of pest densities.     

Temperature-dependent development of Chilocorus bipustulatus (Coleoptera: Coccinellidae)

The effect of temperature on development and survival of Chilocorus bipustulatus L. (Coleoptera: Coccinellidae), a predator of many scale insects, was studied under laboratory conditions. The duration of development of egg, first, second, third, and fourth larval instars, pupa, and preovioposition period at seven constant temperatures (15, 17.5, 20, 25, 30, 32.5, and 35°C) was measured. Development time decreased significantly with increasing temperature within the range 15-30°C. Survival was higher at medium temperatures (17.5-30(ο)C) in comparison with that at more extreme temperature regimens (15 and >30(ο)C). Egg and first larval instars were the stages where C. bipustulatus suffered the highest mortality levels at all temperatures. The highest survival was recorded when experimental individuals were older than the third larval instar. Thermal requirements of development (developmental thresholds, thermal constant, optimum temperature) of C. bipustulatus were estimated with application of linear and one nonlinear models (Logan I). Upper and lower developmental thresholds ranged between 35.2-37.9 and 11.1-13.0°C, respectively. The optimum temperature for development (where maximum rate of development occurs) was estimated at between 33.6 and 34.7°C. The thermal constant for total development was estimated 474.7 degree-days.     

Thermal acclimation of interactions: differential responses to temperature change alter predator-prey relationship

Different species respond differently to environmental change so that species interactions cannot be predicted from single-species performance curves. We tested the hypothesis that interspecific difference in the capacity for thermal acclimation modulates predator-prey interactions. Acclimation of locomotor performance in a predator (Australian bass, Macquaria novemaculeata) was qualitatively different to that of its prey (eastern mosquitofish, Gambusia holbrooki). Warm (25°C) acclimated bass made more attacks than cold (15°C) acclimated fish regardless of acute test temperatures (10-30°C), and greater frequency of attacks was associated with increased prey capture success. However, the number of attacks declined at the highest test temperature (30°C). Interestingly, escape speeds of mosquitofish during predation trials were greater than burst speeds measured in a swimming arena, whereas attack speeds of bass were lower than burst speeds. As a result, escape speeds of mosquitofish were greater at warm temperatures (25°C and 30°C) than attack speeds of bass. The decline in the number of attacks and the increase in escape speed of prey means that predation pressure decreases at high temperatures. We show that differential thermal responses affect species interactions even at temperatures that are within thermal tolerance ranges. This thermal sensitivity of predator-prey interactions can be a mechanism by which global warming affects ecological communities.     

Prey Selection by the Lady Beetle Harmonia axyridis: The Influence of Prey Mobility and Prey Species

The influence of prey mobility and species on prey selection by the coccinellid Harmonia axyridis Pallas was determined under laboratory conditions for two prey species, Hyaliodes vitripennis (Say) and Tetranychus urticae Koch. Prey selection was influenced by prey mobility. In the presence of active prey, the coccinellid selected T. urticae while in presence of immobilized prey, H. vitripennis was preferred. Harmonia axyridis searching time was longer in the presence of active H. vitripennis than in the presence of active T. urticae. Moreover, the coccinellid capture rate was lower for active H. vitripennis caused by effective defensive mechanisms. Prey suitability was affected by prey mobility and species. Immobilized H. vitripennis were the most profitable prey, i.e. induced a shorter developmental time and no mortality. However, active H. vitripennis were not a suitable food source for H. axyridis. Our results suggested that three factors are involved in prey selection by H. axyridis: (i) prey mobility; (ii) prey defensive mechanisms; and (iii) prey species.     

Asymmetric reproductive interference between specialist and generalist predatory ladybirds

1.?Closely related species often differ greatly in the quality and breadth of resources exploited, but the actual mechanisms causing these differences are poorly understood. Because in the laboratory specialized species often survive and perform as well or better on host species that are never utilized in nature, negative ecological interactions restricting host range must exist. Here, we focused on reproductive interference, which has been theoretically predicted to drive niche separation between closely related species with overlapping mating signals. 2.?We examined the interspecific sexual interactions in relation to ecological specialization and generalization in two sibling ladybird species, Harmonia yedoensis and Harmonia axyridis. Harmonia yedoensis is a specialist predator that preys only on pine aphids, which are highly elusive prey for ladybird hatchlings, whereas H.?axyridis is a generalist predator with a broad prey and habitat range. 3.?We experimentally showed that conspecific sperm fertilized the vast majority of eggs regardless of mating order (i.e. conspecific sperm precedence) when a female of H.?yedoensis or H.?axyridis mated with both a conspecific and a heterospecific male. Moreover, we demonstrated that mating opportunities of H.?yedoensis females strongly decreased as heterospecific density increased relative to conspecific density. In contrast, in H.?axyridis, female mating success was high regardless of conspecific or heterospecific density. 4.?Our results suggest that the generalist H.?axyridis should be dominant to the specialist H.?yedoensis in terms of reproductive interference. Our results support the hypothesis that asymmetric reproductive interference from the dominant species may force the non-dominant species to become a specialist predator that exclusively utilizes less preferred prey in nature.     

A comparative study on effects of normal versus elevated temperatures during preimaginal and young adult period on body weight and fat body content of mature Coccinella septempunctata and Harmonia axyridis (Coleoptera: Coccinellidae)

Two climate chamber experiments were performed to simulate the effects of global warming on life table parameters of coccinellids. We investigated the effects of two daily temperature profiles during preimaginal development (larval and pupal) and the young adult period (first 10 d) on body weight and fat body content of adult Coccinella septempunctata L. and Harmonia axyridis (Pallas) fed English grain aphids [Sitobion avenae (F.)] ad libitum: 1) normal, i.e., current daily temperatures in central Europe (T0: mean, 17.8°C; maximum, 21.8°C; minimum, 13.4°C) and 2) increased by 3K (T3: mean, 20.8°C; maximum, 25.5°C; minimum, 15.7°C). The first experiment was performed at the same temperatures (T0 or T3) during both periods to establish the responses of the two species to temperature. The second was conducted to identify the period (preimaginal or adult) in which the responses occurred and to confirm the results of the first experiment. Compared with normal temperatures (T0), elevated temperatures (T3) resulted in significant decreases in preimaginal development time and increases in aphid consumption rates in both species. C. septempunctata (10-d-old adults) had the highest weights when reared at T3, H. axyridis at T0. C. septempunctata was significantly heavier than H. axyridis in most cases, particularly in females. The body fat content of C. septempunctata was higher than that of H. axyridis at T0 and T3 temperatures. At T3 temperatures, fat accumulation in C. septempunctata increased, whereas that in H. axyridis remained relatively low. Body weight and fat body content of 10-d-old adults of both species seemed to be determined by temperature conditions during preimaginal development.     

Relationships Between Attack and Escape Rates, Cannibalism, and Intraguild Predation in Larvae of Two Predatory Ladybirds

We compared incidences of cannibalism and intraguild (IG) predation (IGP) and quantified attack and escape rates—mechanisms which possibly account for the difference in incidences of these interactions—in laboratory experiments with Harmonia axyridis and Coccinella septempunctata. There was a tendency for H. axyridis to act as an IG predator and C. septempunctata as an IG prey. Cannibalism was also often observed in both species. The incidences of both IGP and cannibalism were different between the species. The average attack rates of C. septempunctata were less than 20%, but those of the more aggressive H. axyridis exceeded 50%. Larvae of both species attacked conspecifics and heterospecifics H. axyridis larvae successfully escaped when attacked by both conspecifics and by heterospecifics, while larvae of C. septempunctata escaped from attacks of conspecifics but not from those of heterospecifics. Thus the aggressive behavior of H. axyridis, in particular, of the third and fourth instars, negatively affects the larval survival of C. septempunctata. It may contribute to the dominance of H. axyridis in ladybird assemblages and its displacement of other ladybird species in several places in the world.     

Comparative use of Mindarus abietinus (Homoptera: Aphididae) by two coccinellids (Coleoptera: Coccinellidae), the native Anatis mali and the exotic Harmonia axyridis, in a Christmas tree plantation

The exotic coccinellid Harmonia axyridis (Pallas) recently expanded its range into eastern Canada and elsewhere in North America. We hypothesized that this coccinellid should be less well adapted to the prey Mindarus abietinus Koch. on balsam fir trees than the native coccinellid Anatis mali (Say), which evolved in close association with aphids on conifers in North America. We compared, under field conditions, prey use by both species by collecting data on their synchrony with M. abietinus, their prey searching and predation behaviors, life stage distribution in fir canopy, and their overall reproductive success in this system. The seasonal life cycle of A. mali was better synchronized with that of M. abietinus compared with that of H. axyridis. In spring, A. mali adults appeared nearly 2 wk earlier on trees than H. axyridis and were active predators of the aphid fundatrices. A. mali oviposition thus began before the aphid population started to grow, and its larvae were most active during peak aphid colonies. Behavioral observations showed that both adults and larvae of the native A. mali searched for prey more actively than those of H. axyridis. Distribution of life stages also showed that eggs and pupae had different distributions on trees and that the adult-to-adult net reproductive rate of A. mali was three times higher than that of H. axyridis. Thus, the native A. mali was better adapted than H. axyridis to prey on M. abietinus, possibly because it evolved for a much longer period of time with this prey in conifer habitats.     

Interactive influence of biotic and abiotic cues on the plasticity of preferred body temperatures in a predator–prey system

The ability to modify phenotypes in response to heterogeneity of the thermal environment represents an important component of an ectotherm's non-genetic adaptive capacity. Despite considerable attention being dedicated to the study of thermally-induced developmental plasticity, whether or not interspecific interactions shape the plastic response in both a predator and its prey remains unknown. We tested several predictions about the joint influence of predator/prey scents and thermal conditions on the plasticity of preferred body temperatures (T (p)) in both actors of this interaction, using a dragonfly nymphs-newt larvae system. Dragonfly nymphs (Aeshna cyanea) and newt eggs (Ichthyosaura alpestris) were subjected to fluctuating cold and warm thermal regimes (7-12 and 12-22°C, respectively) and the presence/absence of a predator or prey chemical cues. Preferred body temperatures were measured in an aquatic thermal gradient (5-33°C) over a 24-h period. Newt T (p) increased with developmental temperature irrespective of the presence/absence of predator cues. In dragonflies, thermal reaction norms for T (p) were affected by the interaction between temperature and prey cues. Specifically, the presence of newt scents in cold regime lowered dragonfly T (p). We concluded that predator-prey interactions influenced thermally-induced plasticity of T (p) but not in a reciprocal fashion. The occurrence of frequency-dependent thermal plasticity may have broad implications for predator-prey population dynamics, the evolution of thermal biology traits, and the consequences of sustaining climate change within ecological communities.     

Effects of plant gross morphology on predator searching behaviour

Plant morphology influences insect predators' abilities to capture prey and control pest populations. Several mechanisms for this effect of plants on predator foraging have been proposed. In particular, it is often claimed that increased complexity of plant structures may increase search time and reduce foraging success. Using time-lapse photography we recorded search paths, and compared the total path lengths, percentages of plants searched, and path tortuosity of adult multicolored Asian lady beetles (Harmonia axyridis Pallas) and green lacewing larvae (Chrysoperla carnea Stephens) foraging for pea aphids (Acyrthosiphon pisum Harris) on pea near-isolines (Pisum sativum L.) that differed in shape. We found that H. axyridis searched leafy morphologies less thoroughly than those with more branches, while C. carnea larvae search paths did not differ on any of the pea morphologies. In addition, the ability of H. axyridis to attach to plants and maneuver was increased on morphologies with many branches and edges, while C. carnea was able to attach to all morphologies. Both species, however, had significantly reduced predation success on inverted leaf surfaces. We conclude that undersides of leaves, far from the leaf margin, may serve as partial prey refugia. In addition, we find increased plant branching or an increase in other morphological features which provide predator attachment points may promote foraging success.     

Voracity and feeding preferences of two aphidophagous coccinellids on Aphis citricola and Tetranychus urticae

Voracity and feeding preferences of adult Coccinella septempunctata L. and Harmonia axyridis Pallas (Coleoptera: Coccinellidae, tribe Coccinellini) were evaluated in the laboratory on a common prey, the spirea aphid, Aphis citricola van der Goot (Homoptera: Aphididae), and on the twospotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), a prey previously unrecorded for these two predators. The experiments were carried out in the laboratory on apple saplings (Malus domestica Borkhausen). Adult males and females of H. axyridis consumed significantly more mites than adults of C. septempunctata. For H. axyridis, males consumed 41.3 spider mites in 24 h and females 48.4, whereas for C. septempunctata males consumed 14.1 prey and females 15.2. The consumption of spirea aphids by the males was similar for the two species. Consumption by the females was significantly greater for H. axyridis (46.5) than for C. septempunctata (22.2). The two coccinellids showed a significant preference for A. citricola in the presence of T. urticae. This preference was more pronounced for C. septempunctata. The total number of prey consumed and the percentage of exploited biomass decreased significantly for C. septempunctata and stayed relatively constant for H. axyridis as the number of mites increased in the prey ratio. Our results suggest that T. urticae is only an alternative prey for both predators, and that H. axyridis should be more efficient than C. septempunctata in a prey assemblage with aphids and mites.     

Predaceous Behavior and Life History of Odontopharynx longicaudata (Diplogasterida)

The behavior of a California isolate of the predaceous nematode, Odontopharynx longicaudata de Man, was studied in water agar culture. When feeding on an Acrobeloides sp. the predator completed its life cycle in 13 to 14 days at 25 C. Optimum temperature for reproduction of the predator was 25 C, few individuals survived at 10 C, and 30 C was lethal. Males were necessary for reproduction, and at 25 C the sex ratio was about 1:1. All postembryonic stages were voracious feeders. A single female predator consumed 30 individuals of another Acrobeloides sp. in 1.5 days. Juveniles must feed in order to complete their development. Three modes of feeding were observed depending on the prey selected. A high degree of prey selectivity occurred; 6 of 17 nematode prey species were readily consumed by the predator, but there was little or no feeding on the remaining 11 species. Predation percentage varied with prey species. Consumption of Anguina pacificae and the two Acrobeloides spp. was almost 100%, consumption of A. amsinckiae, Pratylenchus vulnus, and Trichodorus sp. was 70-78%. Difference in final predator population densities was obtained after feeding on the two species of Acrobeloides. Final predator population densities increased linearly with increasing inoculum levels of the first Acrobeloides sp.     

异色瓢虫对与本土蚜虫共存的外来扶桑绵粉蚧的搜寻和捕食行为

【目的】外来入侵物种作为猎物可能影响本土广谱捕食者的搜寻和捕食行为。本研究旨在揭示异色瓢虫Harmonia axyridis对与本土豌豆修尾蚜Megoura japonica混合发生的外来入侵扶桑绵粉蚧Phenacoccus solenopsis的搜寻和捕食行为。【方法】试验前对异色瓢虫设两个饲喂猎物种类处理：用扶桑绵粉蚧连续饲养3代以上(前期饲喂粉蚧的瓢虫)和用豌豆修尾蚜连续饲养3代以上(前期饲喂蚜虫的瓢虫)。在盆栽蚕豆Vicia faba苗上随机选一片叶接扶桑绵粉蚧3龄若虫和3或4日龄豌豆修尾蚜若蚜,在总猎物数量20-30头(具体数量随机确定)范围内随机组配两种猎物数量使粉蚧占比从5.6%至83.3%不等,待猎物在叶片上稳定后接入1头饥饿24 h的异色瓢虫4龄幼虫,连续观察2 h,统计异色瓢虫首次捕食是否选择粉蚧、捕食的粉蚧数量占总捕食猎物数量的比例、搜索用时占总搜捕用时的比例以及处理粉蚧用时占总搜捕用时的比例;以扶桑绵粉蚧在猎物斑块中的比例和饲喂猎物种类处理为自变量因素,用回归模型拟合其对异色瓢虫搜寻和捕食行为等观测变量的影响。【结果】异色瓢虫4龄幼虫首次捕食选择粉蚧概率随粉蚧比例增大而增大,粉蚧比例每增大10%,首次捕食粉蚧概率增大77.2%,而且此概率不受此前饲喂猎物种类的影响。捕食的粉蚧数量占比与粉蚧比例的关系受饲喂猎物种类的影响：粉蚧比例每增加10%,前期饲喂粉蚧的瓢虫捕食的粉蚧数量占比增大137%,而前期饲喂蚜虫的瓢虫捕食的粉蚧数量占比增大60%。异色瓢虫搜索用时比例受粉蚧比例的影响,但不受饲喂猎物种类的影响：粉蚧比例每增加10%,搜索用时比例增大13%;前期饲喂粉蚧的瓢虫搜索用时比例略低于前期饲喂蚜虫的瓢虫(降低7%)。异色瓢虫处理粉蚧用时比例受粉蚧比例的影响,但不受饲喂猎物种类的影响：粉蚧比例每增加10%,处理粉蚧用时比例增大41%。【结论】本研究结果说明在遭遇外来入侵扶桑绵粉蚧与本土蚜虫共存的猎物斑块时,异色瓢虫对粉蚧的捕食选择依赖于其相对比例,依赖程度因此前取食粉蚧而增强。     

Temperature-dependent development of the predatory mite <Emphasis Type="Italic">Cheyletus malaccensis</Emphasis> (Acari: Cheyletidae)

The effect of temperature on the development of immature stages of the predator Cheyletus malaccensis Oudemans, produced by either fertilized or virgin females, was studied at 17.5, 20, 25, 30, 32.5, and 35°C, 80 ± 5% relative humidity, in complete darkness, and fed Tyrophagus putrescentiae (Schrank). The population maintained at 15°C failed to reproduce. The thermal data obtained were used for the estimation of the thermal requirements (developmental thresholds, thermal constant, optimum temperature) of this predator by a linear and nonlinear model (Logan type I model). Upper and lower developmental thresholds ranged between 37.4–37.8 and 11.6–12.0°C, respectively. Optimum temperature for development was estimated at between 33.1 and 33.5°C. The thermal constant ranged between 238.1 and 312.5 degree-days. Based on the data of the total pre-imaginal period, immatures’ survival peaked at 25°C. Arrhenotokous parthenogenesis (haplodiploidy) is confirmed in the species: virgin females always produce males, whereas fertilized females give rise to offspring of both sexes. Survival of the immature stages and offspring sex ratio were not significantly influenced by temperature.     

Nutritional plasticity of the predatory ladybeetle Harmonia axyridis (Coleoptera: Coccinellidae): comparison between natural and substitution prey

The predatory coccinellid Harmonia axyridis is a polyphagous species, efficient at controlling certain aphid species and already commercialized in Europe for that purpose. The complete development of this predator can be accomplished using the aphid Acyrthosiphon pisum or Ephestia kuehniella eggs as substitution prey. Biochemical analyses were conducted on the proteins, lipids, and carbohydrates of these two different prey species. E. kuehniella eggs were 2 times richer in amino acids than A. pisum adults (12% of the fresh weight vs. 6%). E. kuehniella eggs were 3 times richer in lipids than the aphids but, on the contrary, the aphids were 1.5 times richer in glycogen. The impact of these two kinds of food on the body composition of the coccinellid was evaluated to appreciate the degree of nutritional plasticity of the coccinellid. The composition of the coccinellids feeding either on E. kuehniella eggs or on aphids was compared for amino acid, fatty acid and glycogen contents, revealing a good capability of H. axyridis to develop on foods that are very different in their biochemical composition. Nevertheless, when fed on aphids, the crude protein content of the predator was reduced and the lipid content decreased by a factor of two, with a change in amino and fatty acid patterns. Some biological parameters, such as larval mortality, adult weight, and fecundity, were modified according to the food eaten.     

Temperature-related development and population parameters for Typhlodromus pyri (Acari: Phytoseiidae) found in Oregon vineyards

The beneficial mite Typhlodromus pyri is a key predator of grapevine rust mite Calepitrimerus vitis in Pacific coastal vineyards. Rust mite feeding has been associated with damage such as stunted, deformed shoot growth and reductions in fruit yield. The life history traits of T. pyri were assessed at seven constant temperatures (12.5, 15, 17.5, 20, 25, 30 and 35 °C) to determine population parameters providing data to better predict biological control of C. vitis populations by T. pyri in vineyards. Successful development from the egg to adult stage was observed at temperatures ranging from 15 to 30 °C. Constant exposure to 12.5 and 35 °C resulted in 100 % mortality in immature T. pyri. Developmental times, fecundity and longevity were highest at 25 °C. The estimated minimum and maximum developmental thresholds were 7.24 and 42.56 °C, respectively. Intrinsic rate of increase (r ( m )) was positive from 15 to 30 °C indicating population growth within this range of temperatures. Net reproductive rate and intrinsic rate of increase were greatest at 25 °C. These developmental parameters can be used to estimate population growth, determine seasonal phenology and aid in conservation management of T. pyri. Results presented in this study will aid in evaluating the effectiveness of T. pyri as a key biological control agent of C. vitis during different periods of the growing season in Pacific Northwest vineyards.     

Intraguild predation behaviour of ladybirds in semi-field experiments explains invasion success of Harmonia axyridis

Harmonia axyridis has been introduced as a biological control agent in Europe and the USA. Since its introduction, it has established and spread, and it is now regarded as an invasive alien species. It has been suggested that intraguild predation is especially important for the invasion success of H. axyridis. The aim of this study was to compare the intraguild predation behaviour of three ladybird species (Coccinella septempunctata, Adalia bipunctata, and H. axyridis). Predation behaviour was investigated in semi-field experiments on small lime trees (Tilia platyphyllos). Two fourth-instar larvae placed on a tree rarely made contact during 3-hour observations. When placed together on a single leaf in 23%-43% of the observations at least one contact was made. Of those contacts 0%-27% resulted in an attack. Harmonia axyridis attacked mostly heterospecifics, while A. bipunctata and C. septempunctata attacked heterospecifics as often as conspecifics. In comparison with A. bipunctata and C. septempunctata, H. axyridis was the most successful intraguild predator as it won 86% and 44% of heterospecific battles against A. bipunctata and C. septempunctata respectively, whilst A. bipunctata won none of the heterospecific battles and C. septempunctata won only the heterospecific battles against A. bipunctata. Coccinella septempunctata dropped from a leaf earlier and more often than the other two species but was in some cases able to return to the tree, especially under cloudy conditions. The frequency with which a species dropped did not depend on the species the larva was paired with. The results of these semi-field experiments confirm that H. axyridis is a strong intraguild predator as a consequence of its aggressiveness and good defence against predation from heterospecific species. The fact that H. axyridis is such a strong intraguild predator helps to explain its successful establishment as invasive alien species in Europe and the USA.     

Effect of temperature and relative humidity on the development and fecundity of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae)

The spotted stemborer, Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), is one of the most important insect pests attacking maize and sorghum in Ethiopia. Recent studies have indicated that the pest is spreading to new locations where it was not reported before. In the current study, laboratory investigations were carried out to determine the combined effect of different levels of relative humidity and temperature regimes on the development and fecundity of C. partellus, as these physical factors are known to play an important role in the life cycle of insects and adaptability to local climate. Developmental time, longevity, potential fecundity and realized fecundity of C. partellus were measured under controlled conditions. Three temperature regimes (22°C, 26°C and 30°C) and three relative humidity levels (40%, 60% and 80%) were tested. It was found that temperature, relative humidity (RH) and their interaction significantly affected the developmental time, adult longevity, potential fecundity and realized fecundity of the pest. Developmental time was inversely related to temperature. Mean duration of C. partellus life cycle was 70.2 days at 22°C and 80% RH, whereas it took only 26.5 days to complete its life cycle at 30°C and 40% RH. Male and female longevity were similar in most cases. The adult life span ranged between 6.9-11.1 days at 22°C and 3.1-7.2 days at 30°C for different levels of relative humidity. The most suitable conditions for C. partellus development and fecundity were 26-30°C temperatures regimes and 60-80% RH levels.     

Temperature and diet effects on immature development of predatory mite Typhlodromus athenas Swirski and Ragusa (Acari: Phyotseiidae)

Temperature and food quality both can influence growth rates and developmental time of herbivorous insects and mites. Typhlodromus athenas Swirski and Ragusa is an indigenous mite in the Mediterranean region and data on its temperature dependent development are lacking. In the current study, temperature-dependent development and survival of T. athenas immature stages were evaluated on eggs and all stages of Tetranychus urticae Koch, as well as on almond (Prunus amygdalis Batsch) pollen, under seven constant temperatures ranging from 15 to 35°C, 65% RH, and a photoperiod of 16:8 (L:D) h. On both diets survival was considerably high at all temperatures. The longest developmental period of immature stages was recorded at 15°C, whereas the shortest was at 30°C. Female immatures on almond pollen had shorter developmental time compared to that on twospotted spider mites. Food had a significant effect on female total developmental time at temperatures lower than 25°C. The lower developmental thresholds, estimated by a linear model, for egg-to-adult of females and males fed on pollen were 8.60 and 8.77°C, respectively, whereas on T. urticae they were 10.15 and 10.62°C, respectively. Higher values of tmin for total development were estimated by a nonlinear model (Lactin-2), and ranged from 10.21°C for both females and males on almond, to 11.07 for females and 10.78°C for males on prey. Moreover, this model estimated optimal and lethal temperatures accurately. The results of this study indicate that T. athenas appears better adapted to higher temperatures that occur in the Mediterranean region and may be a useful biological control agent.