Inbreeding and incompatibility in Trichogramma nr. brassicae: evidence and implications for quality control

Inbreeding effects and incompatibility relationships were examined in strains of the egg parasitoid Trichogramma nr brassicae (Hymenoptera: Trichogrammatidae) from southeastern Australia. Crosses between strains provided weak evidence of incompatibility in a few cases. However sex ratio in crosses within strains tended to be more female-biased than in crosses between strains. Inbreeding was imposed for four generations (F>0.59) of sib mating. The fitness of inbred strains was compared to that of outbred strains generated by crossing the inbred strains. No effects of inbreeding were found for any of the four female traits examined (fecundity, body length, head width and hind tibia length), indicating that T. nr. brassicae is not subjected to inbreeding depression. Inbreeding effects were also not found for male mating success as expected for the haploid sex. There were differences among strains for all traits apart from fecundity, indicating heritable variation. Strain differences for fitness measures were uncorrelated with wasp size. The potential use of inbreeding in the quality control of Trichogramma for mass-release is discussed. Inbreeding may be a useful tool in minimising the effects of laboratory adaptation, thereby extending the useful life of a strain.     

Host exploitation by parasitoids: local variations in foraging behaviour of females among populations of Trichogramma species

Using artificial patches of Ephestia kuehniella (Lepidoptera: Pyralidae) eggs, we compared two strains of Trichogramma cacoeciae Marchal and three strains of T. brassicae Bezdenko (Hymenoptera: Trichogrammatidae) for their strategies in colonizing hosts. The method by which females distribute their eggs among hosts was assessed either in terms of the average distance between parasitized hosts within a given patch, or of the average distance of attacks in discontinuous patches arranged in a circle.Within each strain, the traits increased as females aged; they vary among strains, their range of variations within T. cacoeciae falling within that of T. brassicae. Variations of both traits are correlated and strains can be easily classified according to their overall tendency to concentrate their attacks.The adaptive importance of the foraging behaviour of parasitoid insects suggests that differences reported here could reveal adaptive behavioural differentiations of natural populations in response to local variations in selective constraints, mainly those emanating from host diversity, abundance and distribution.

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Résumé Le mode de répartition des attaques parmi les hôtes est estimé par la distance moyenne entre les hôtes parasités dans une grande ooplaque homogène (500 hôtes) ou dans un système discontinu formé de six ooplaques de taille plus réduite (50 hôtes), régulièrement réparties sur un cercle.Pour chaque souche les deux caractères augmentent avec l'âge des femelles. Ils varient entre les souches, l'amplitude des variations au sein de l'espèce brassicae englobant celles observées chez cacoeciae.Les variations des deux caractères sont corrélées et les souches peuvent être classées suivant leur tendance plus ou moins marquée à concentrer leurs attaques.L'importance adaptative du comportement de colonisation des hôtes chez les insectes parasitoïdes laisse supposer que les différences constatées ici traduisent des différenciations locales des populations naturelles en réponse aux variations des contraintes sélectives, plus particulièrement celles qui sont liées à la diversité des hôtes, à leur abondance et à leur répartition.

     

Quality and environmental factors affecting Trichogramma brassicae efficiency under field conditions

Field parasitism of the egg parasitoid Trichogramma brassicae Bezdenko (Hymenoptera, Trichogrammatidae) (synonymous to T. maidis Pint. et Voegele) on Ostrinia nubilalis Hübner was compared to four single quality parameters (walking speed, fecundity on the factitious host Ephestia keuhniella Zeller, fecundity on the natural host O. nubilalis, and life span) previously measured in the laboratory and, a quality index calculated from three of the measured parameters. A single quality parameter (fecundity on E. keuhniella) and the calculated quality index showed a correlation to T. brassicae field parasitism, for different T. brassicae populations. The number of female Trichogramma released clearly influenced parasitism but not in the same proportion for all populations tested, reflecting that numbers released can only to some extent compensate for low quality in Trichogramma. Variation indegree hours above 18°C also influenced field parasitism. When incorporating degree hours to the quality index a significant correlation R²=0.56 (P=0.01) is obtained. In this work fecundity of T. brassicae on E. keuhniella can be as good an indicator for the potential field performance of T. brassicae, as the quality index which takes into account three quality parameters. Since environmental factors can obscure the potential performance of a population, i.e., one which under optimal laboratory conditions performs well, the quality index gives only a partial indication of how the released strains will perform in the field.     

Comparative biology and life tables of Trichogramma evanescens and T. cacoeciae with Ephestia elutella as host at four constant temperatures

The age-specific fecundity of Trichogramma evanescens Westwood and T. cacoeciae Marchal (Hymenoptera: Trichogrammatidae) with Ephestia elutella (Hübner) (Lepidoptera: Pyralidae: Phycitinae) as host and the life span of the adults with and without hosts was determined at 20, 26, 30 and 35 °C and 75 ±5% r.h. in the laboratory. At 35 °C, no progeny emerged. The availability of hosts prolonged the longevity in both species. Longevity, percentage of parasitism, fecundity, and the intrinsic rate of natural increase were higher in T. evanescens than in T. cacoeciae. Trichogramma evanescens is expected to be more effective than T. cacoeciae for use in biological control of Ephestia spp., especially at low and high temperatures.     

SEX RATIO VARIATION IN A PARASITIC WASP II. DIALLEL CROSS

Sex ratio has been studied from many theoretical and empirical perspectives, but a general assumption in sex ratio research is that changes in sex ratio occur because of selection on sex ratio itself. I carried out a quantitative genetic experiment—a diallel cross among three strains—on a parasitic wasp, Muscidifurax raptor (Hymenoptera: Pteromalidae), to measure genetic variation for sex ratio. I also tested whether sex ratio may change as a consequence of selection on other life-history traits by estimating genetic covariances between sex ratio, fecundity, longevity, and development time. Most of the variation among strains could be accounted for by a maternal effect, likely caused by a microsporidian parasite that was transmitted through the West Germany (WG) strain. Genetic variation was small by comparison, but almost all traits were affected by dominance. The only significant additive genetic effect was for fecundity early in life. Upon crossing, all traits displayed heterosis: more female-biased sex ratio, greater fecundity, longer life, and faster development time. All life-history traits were correlated phenotypically, but the correlations were mainly the result of decreased performance in crosses with the WG strain that carried the microsporidian parasite. Dominance genetic correlations were also found between sex ratio, fecundity, and longevity. How the correlation between sex ratio and other life-history traits would affect sex ratio evolution depends upon the frequencies of sex-ratio genotypes within a population as well as the signs of the correlations, because sex ratio is under frequency-dependent selection whereas other traits are generally under directional selection. Although the results from crosses among laboratory populations should be approached with caution, the inbreeding depression (the difference between inbred and outcrossed progeny) found in M. raptor implies that the evolution of a female-biased sex ratio could be affected by selection for inbreeding avoidance.     

Comparative biology and life tables of Trichogramma cacoeciae,T. brassicae and T. evanescens (Hymenoptera: Trichogrammatidae) with Ephestia kuehniella and Cadra cautella (Lepidoptera: Pyralidae) as hosts at three constant temperatures

Egg parasitoids of the genus Trichogramma (Hym. Trichogrammatidae) have been successfully utilized for biocontrol of several Lepidopteran pests worldwide. Because of their low host specificity Trichogramma can be mass reared more easily in large numbers and on different natural and factitious hosts. Life table parameters were assessed for Trichogramma cacoeciae Marchall, T. evanescens Westwood and T. brassicae Bezdenko on Ephestia kuehniella Zeller and Cadra cautella Walker at three temperatures (20, 25 and 30°C) as the potential factitious hosts for mass rearing. Female longevity ranged between 9.77 and 2.56 days in our experiments. Fecundity ranged from 73 to 91 parasitized eggs in C. cautella and 76–109 parasitized eggs in E. kuehniella. T. brassicae exhibit similar values of the intrinsic rate of increase ratio (r _m) 0.5407 and 0.5478; the finite rates of increase (λ) were 1.717 and 1.7295 and the doubling times 1.28 and 1.26 at 25 and 30°C, respectively, in C. cautella. The mean duration of one generation (T) varied between 8.25 and 13.37 days for T. cacoeciae, 8.14 and 13.47 days for T. brassicae and 8.23 and 13.18 days for T. evanescens in C. cautella. Generation times for T. cacoeciae varied between 8.23 and 14.68 days, 8.28 and 14.37 days for T. brassicae, and 7.74 and 14.58 days for T. evanescens in E. kuehniella eggs. Both species (T. cacoeciae, T. brassicae) had the same intrinsic rate of increase (r _m; 0.5700 and 0.5704), finite rate of increase (λ; 1.7682, 1.7691) and doubling time (Dt, 1.21) at 30°C in E. kuehniella, respectively.     

Sex Allocation by a Parasitoid Wasp (Hymenoptera: Ichneumonidae) to Different Host Species: A Question for the Mechanism of Host Size Estimation

Sex allocation by the polyphagous solitary pupal parasitoid wasp Pimpla luctuosa Smith to a small host species, Galleria mellonella (L.), and a large host species, Mamestra brassicae L., was investigated to test whether female wasps responded to hosts of different sizes across different host species. In the experiments, both host species were presented to each test female wasp. Primary and secondary sex ratio experiments revealed that female wasps laid more female eggs in larger pupae of each host species, indicating that female wasps recognized size differences within host species. The wasp sex ratio (male ratio) from M. brassicae, however, was much higher than that expected on the basis of the sex ratio curve from different-sized G. mellonella. Larger hosts of each host species yielded larger wasps, indicating that the host size estimation by female wasps across different host species was incomplete or was not simple. These results suggested that P. luctuosa evaluated host size not only by physical measures such as dimension but also by other unknown measures. A possible explanation for the adaptiveness of different sex ratio responses by Pimpla luctuosa to different host species was discussed.     

Effects of host age on parasitism and progeny allocation in Trichogrammatidae

The impact of host age on the number of hosts killed, survival of progeny, progeny allocation, and sex allocation was examined for several Trichogrammatidae (Hymenoptera) species in laboratory choice tests. Individual female parasitoids were provided with young, medium-aged and old eggs of one of three lepidopterous host species: Trichoplusia ni (Hübner) (Noctuidae), Pieris rapae (L.) (Pieridae), or Plutella xylostella (L.) (Plutellidae). Trichogrammatid species behaved as gregarious parasitoids with the first two host species, and as solitary parasitoids with eggs of the smaller latter one. They mostly preferred young eggs of T. ni, but did not discriminate among P. rapae eggs of different ages, and often preferred young or medium-aged P. xylostella eggs over old eggs. Survival of progeny did not vary constantly with host age, although it was often very low in P. rapae eggs of any age. Clutch size frequently decreased with host age in both T. ni and P. rapae. Offspring sex ratio did not change with age of T. ni and P. rapae eggs, and rarely did so in P. xylostella eggs. In regard to host age, the results with T. ni are the ones which are the most in agreement with optimal foraging theoretical predictions, as clutch size was the highest in preferred younger eggs.     

Scope for genetic enhancement of the parasitisation potential of four native strains of Trichogrammatoidea sp. nr. lutea Girault (Hymenoptera: Trichogrammatidae) in Kenya

In response to emerging interest in commercial mass production of Trichogramma for Helicoverpa armigera biocontrol in eastern Africa, laboratory experiments were undertaken to assess the scope for genetic enhancement of the parasitisation potential of native strains of the local common trichogrammatid species, Trichogrammatoidea sp. nr. lutea. Four promising strains (ex-Kilifi – Kilifi District, ex-Kwa Chai – Kibwezi District, ex-Rarieda – Bondo District and ex-Ebuhayi, Kakamega District) were tested for cross-mating in reciprocal combinations with focus on fecundity and progeny female ratio. While all the crosses resulted in F1 progeny of both sexes, significant differences were observed between homogamic and reciprocal heterogamic crosses in fecundity, progeny production, proportion of female progeny and adult longevity. Among all the crosses, the cross between ex-Rarieda strain females and ex-Kilifi strain males resulted in progeny that was significantly superior in fecundity and progeny female ratio. Conversely, Kilifi strain females crossed to males from ex-Rarieda strain gave rise to progeny with relatively low fecundity and female ratio. There were significant differences between homogamic crosses and most reciprocal heterogamic crosses in the major biological attributes. Genotypic and phenotypic variance-covariance matrices generated for six life-history traits showed high positive correlations for most traits in both inbred (P<0.05) and reciprocal heterogamic crosses (P<0.05 and P<0.001). Fecundity and number of female offspring were the most important factors in the heterogamic crosses. The results confirmed the scope for genetic enhancement through inter-strain crossing for improving the field impact potential of T. sp. nr. lutea being targeted for commercial mass production.     

Parasitism of aphid embryos by Aphidius smithi: some effects of extremely small host size

Embryos of the pea aphid, Acyrthosiphon pisum (Harris), were successfully parasitized by Aphidius smithi Sharma & Subba Rao while still inside their mother. Parasites from embryos were much smaller, laid fewer eggs, but survived as long as their counterparts that had developed in adult viviparous aphids. Lifetime fecundity was positively correlated with wasp size, as measured by dry weight at the time of death. A. smithi females produced the same offspring sex ratio at eclosion on both host classes, although emergence was significantly lower from mummified adult aphids than from embryos. The data are discussed with regard to progeny and sex allocation decisions by solitary hymenopterous parasites. It is suggested that, in A. smithi, the decision to lay a fertilized or unfertilized egg is influenced by the host's overall size, rather than by the size and quality of a smaller target area inside the host, such as embryos.     

Reproductive barriers between populations of the cereal rust mite <Emphasis Type="Italic">Abacarus hystrix</Emphasis> confirm their host specialization

Recent studies have shown that certain host populations of the cereal rust mite Abacarus hystrix are highly specialized in their host use and it is likely that reproductive isolation exists between them. Here I verified this expectation by testing for reproductive barriers between ryegrass and quackgrass populations of A. hystrix. I performed reciprocal crosses between individuals from both populations and observed results of crosses. Leaves of the three grass species, ryegrass, quackgrass and wheat, were used as mating arenas. I used two criteria to determine reproductive barriers between strains: the proportion of female progeny and viability of progeny. If studied populations of this haplodiploid species are reproductively isolated a male-biased sex ratio and/or hybrid progeny of reduced viability would be expected. I found that in the presence of quackgrass and ryegrass pre-zygotic barriers between studied populations exists. On wheat I observed asymmetry in reproductive barriers. Between females from quackgrass and males from ryegrass a pre-zygotic barrier existed (only males obtained). However, the opposite reciprocal cross (females from ryegrass and males from quackgrass) produced progeny of both sexes. A male-biased sex ratio and low adult emergence suggests that post-zygotic mechanisms acted here. Low viability of progeny obtained from crosses in which females from ryegrass were engaged suggests that the origin of the female nymph acted as a predictor of hybrid inviability. The pattern of sterility observed in the cereal rust mite indicates that in the presence of three hosts (ryegrass, quackgrass and wheat) pre- and post-zygotic reproductive barriers between quackgrass and ryegrass populations of this mite exist. In addition to host fidelity (which acts as pre-zygotic barrier) there are post-zygotic barriers to gene flow.     

Are egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) promising biological control agents for regulating the invasive Box tree pyralid,Cydalima perspectalis (Lepidoptera: Crambidae)?

The Box tree pyralid, Cydalima perspectalis Walker (Lepidoptera: Crambidae), is an invasive species in Europe, not yet regulated by natural enemies. It is highly destructive to ornamental and native Buxus due to defoliation by larval feeding. The ability of eight Trichogramma species (T. brassicae Bezdenko, T. bourarachae Pintureau & Babault, T. cacoeciae Marchal, T. cordubensis Vargas & Cabello, T. dendrolimi Matsumura, T. evanescens Westwood, T. nerudai Pintureau & Gerding and T. pintoi Voegele) to parasitise and locate eggs of C. perspectalis was assessed in the laboratory. In direct observation tests, all species started to examine and oviposit into exposed eggs. Resulting egg parasitism was low and ranged between 4% and 20% for most of the parasitoid species after three days of exposure. Only T. dendrolimi parasitised significantly more host eggs with parasitism rates above 40%. On average, two to three progeny emerged from one host egg and the resulting sex ratio was female-biased, indicating suitability of the target host for progeny production. In subsequent cage tests on potted Buxus plants, again T. dendrolimi was the most efficient species in locating host eggs on foliage. We conclude that C. perspectalis eggs are attractive to various Trichogramma species. T. pintoi had the highest number of egg encounters and active females. T. dendrolimi females were most able to locate host eggs and to oviposit and produce successfully on them. Nonetheless, further study is needed to clarify the suspected role of potentially egg defensive mechanisms that may impede higher parasitisation in C. perspectalis.     

Overwintering of the egg parasitoid Trichogramma brassicae in Northern Switzerland

As part of a general risk assessment study weinvestigated the overwintering abilities ofTrichogramma brassicae Bezd. (Hym.: Trichogrammatidae) in Northern Switzerland. Eggs of six host species parasitized by T. brassicae were exposed under outdoor conditions every two weeksbetween 26 September and 7 November 1998. Wefound that T. brassicae is able tooverwinter successfully on six lepidopteranspecies in the families Tortricidae, Noctuidae,Plutellidae, Pyralidae and Crambidae. Between75 and 100% emergence was observed in thefollowing spring for all of the six tested hostspecies exposed on 26 September. On laterexposure dates, spring emergence decreasedsignificantly and no development of T. brassicae offspring occurred from host eggsparasitized on 7 November.Emergence of T. brassicae from eggs ofEphestia kuehniella Zeller parasitized atweekly intervals in autumn 1999 occurred in thesame year until the end of October if the eggswere parasitized by 10 September. All offspringfrom eggs that were parasitized from 17September onwards went into diapause. Springemergence of T. brassicae adults wasobserved between end of April and beginning ofMay both in 1999 and 2000. Fecundity of T.brassicae females that overwintered on E.kuehniella was not significantly different fromthe fecundity of control females that werereared without diapause under optimalconditions at 25 °C. Our resultsdemonstrate that the egg parasitoid T.brassicae is able to overwinter successfullyin Northern Switzerland and has the potentialto establish in Switzerland. As a result,potential non-target effects are not locallyrestricted but may occur on a largegeographical scale.     

Effect of cold storage of adult Trichogramma brassicae,T. cacoeciae and T. evanescens (Hym.: Trichogrammatidae)

Abstract

Trichogramma cacoeciae Marchall, T. brassicae Bezdenko and T. evanescens Westwood could be useful in biological control programmes of agricultural insect pest. The possibility of storing adult Trighogramma species at low temperatures, and the effect of such storage on the quality of the parasitoids and its fecundity were studied. Trighogramma cacoeciae, T. brassicae and T. evanescens adults were stored for 1, 2, 3, 4 and 5 days at 4 ± 1°C in a refrigerator, 60 – 70%RH and full darkness. Storage at 4 ± 1°C reduced fecundity and longevity of female parasitoids.     

The Response Specificity of <Emphasis Type="Italic">Trichogramma</Emphasis> Egg Parasitoids towards Infochemicals during Host Location

Parasitoids are confronted with many different infochemicals of their hosts and food plants during host selection. Here, we investigated the effect of kairomones from the adult host Pieris brassicae and of cues present on Brussels sprout plants infested by P. brassicae eggs on the behavioral response of the egg parasitoid Trichogramma evanescens. Additionally, we tested whether the parasitoid’s acceptance of P. brassicae eggs changes with different host ages. The wasps did not discriminate between olfactory cues from mated and virgin females or between mated females and males of P. brassicae. T. evanescens randomly climbed on the butterflies, showing a phoretic behavior without any preference for a certain sex. The parasitoid was arrested on leaf parts next to 1-day-old host egg masses. This arrestment might be due to cues deposited during oviposition. The wasps parasitized host eggs up to 3 days old equally well. Our results were compared with former studies on responses by T .brassicae showing that T. evanescens makes less use of infochemicals from P. brassicae than T. brassicae.     

Influence of host size on oviposition behaviour and fitness of Elachertus cacoeciae attacking a low-density population of spruce budworm Choristoneura fumiferana larvae

1. Oviposition behaviour and host size ? fitness relationships of a gregarious, idiobiont ectoparasitoid, Elachertus cacoeciae (Howard) (Hymenoptera: Eulophidae), were studied by implanting one fourth‐, fifth‐, and sixth‐instar spruce budworm Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) larva per tree in a stand where the density of the wild C. fumiferana population was low. 2. Development time of E. cacoeciae larvae was quickest on fifth‐instar C. fumiferana larvae, which were the preferred hosts for oviposition. 3. Brood sex ratio (proportion of females) was related positively to increasing C. fumiferana instar, indicating that more females were laid on larger hosts. 4. Parasitoid offspring size increased with increasing C. fumiferana instar and decreased with increasing brood size on smaller hosts. Female but not male size was related positively to increasing brood sex ratio (proportion of females). 5. Under laboratory conditions, parasitoid longevity was related positively to parasitoid size and realised lifetime fecundity, and clutch size was related positively to host size. 6. These results suggest that selection of intermediate‐sized C. fumiferana larvae may be adaptive for E. cacoeciae.     

The reproductive strategy of the gregarious parasitoid,Pteromalus puparum (Hymenoptera: Pteromalidae)

Summary Host size of Pteromalus puparum, a gregarious pupal parasitoid, shows a wide inter- and intraspecific variation. Experiments were made to study the regulation of the number and sex ratio of progeny per host by the parasitoid. The parasitoid could discriminate inter- and intraspecific size differences of the host and regulate the number of eggs according to the host size when a single female attacked the host. The sex ratio of progeny (proportion males) was about 0.1. The number of progeny laid by the female agreed with the energetically most efficient number og eggs in order to maximize total weight of progeny per host but not with the reproductively most efficient number of eggs to maximize the total fecundity of the progeny. The parasitoid laid smaller number of eggs in a half buried host, but the number was much larger than a half of those in a fully exposed host. When more than one female attacked a single host, the number and sex ratio of progeny per host increased with the number of females attacking the host, but the number of progeny per female decreased. The change of the sex ratio agreed with the prediction of the local mate competition model.     

<Emphasis Type="Italic">Wolbachia</Emphasis>-induced cytoplasmic incompatibility in Japanese populations of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae)

Intracellular bacteria of the genus Wolbachia (alpha Proteobacteria) induce cytoplasmic incompatibility (CI) in many arthropod species, including spider mites, but not all Wolbachia cause CI. In spider mites CI becomes apparent by a reduced egg hatchability and a lower daughter:son ratio: CI in haplodiploid organisms in general was expected to produce all-male offspring or a male-biased sex ratio without any death of eggs. In a previous study of Japanese populations of Tetranychus urticae, two out of three green-form populations tested were infected with non-CI Wolbachia strains, whereas none of six red-form populations harbored Wolbachia. As the survey of Wolbachia infection in T. urticae is still fragmentary in Japan, we checked Wolbachia infection in thirty green-form populations and 29 red-form populations collected from a wide range of Japanese islands. For Wolbachia-infected populations, we tested the effects of Wolbachia on the reproductive traits and determined the phylogenetic relationships of the different strains of Wolbachia. All but one green-form populations were infected with Wolbachia and all strains belonged to the subgroup Ori when the wsp gene was used to determine the phylogenetic relationships of different strains of Wolbachia. Six out of 29 red-form populations harbored Wolbachia and the infected strains belonged to the subgroups Ori and Bugs. Twenty-four of 29 infected green-form populations and five of six infected red-form populations induced CI among the hosts. Thus, CI-Wolbachia strains are widespread in Japan, and no geographical trend was observed in the CI-Wolbachia. Although three red-form populations harbored other intracellular bacteria Cardinium, they did not affect host reproduction.     

Are indigenous strains of Trichogramma sp. (Hym., Trichogrammatidae) better candidates for biological control of lepidopterous pests of the olive tree?

Strains of the egg parasitoid, Trichogramma, indigenous in olive groves in the Mediterranean region (T. bourarachae Pintureau & Babault, T. cacoeciae Marchal, T. cordubensis Vargas & Cabello, T. euproctidis Girault, T. nerudai Pintureau & Gerding, T. oleae Voegelé & Pointel) as well as commercially available strains (T. brassicae Bezdenko, T. cacoeciae, T. evanescens Westwood), were assessed in laboratory and semi-field experiments for their attributes as biological control agents for use against lepidopterous olive pests like the olive moth (Prays oleae Bern.) and the jasmine moth (Palpita unionalis Hübn.). In a choice test, an Egyptian strain of T. cordubensis parasitized significantly more olive and jasmine moth eggs than those of the rearing host Sitotroga cerealella Olivier. This strain was also most efficient in finding eggs of the target pests on olive foliage and on potted olive trees. Survival and fecundity of a Tunisian strain of T. bourarachae was not affected when exposed to hot (35°C) and arid (< 40% relative humidity) conditions in comparison to the mild standard of 25°C and 70% relative humidity. It was concluded that indigenous strains collected from olive groves were more effective against the target pests and more tolerant to arid conditions than commercially available parasitoid species, indicating that biological control agents should preferably be isolated from the relevant pest/crop system.