Genetic Variability, Population Differentiation, and Correlations for Thermal Tolerance Indices in the Minute Wasp, Trichogramma cacoeciae

Temperature is a main driver of the ecology and evolution of ectotherms. In particular, the ability to move at sub-lethal low temperatures can be described through three thermal tolerance indices—critical thermal minimum (CTmin), chill coma temperature (CCT), and activity recovery (AR). Although these indices have proven relevant for inter-specific comparisons, little is known about their intraspecific variability as well as possible genetic correlations between them. We thus investigated these two topics (intraspecific variability and genetic correlations between thermal tolerance indices) using the minute wasp, Trichogramma cacoeciae. Strains from T. cacoeciae were sampled across three geographic regions in France—two bioclimatic zones along a sharp altitudinal cline in a Mediterranean context (meso-Mediterranean at low elevations and supra-Mediterranean at higher elevations) and a more northwestern area characterized by continental or mountainous climates. Our results evidenced a significant effect of both the longitude and the severity of the cold during winter months on CCT. Results were however counter-intuitive since the strains from the two bioclimatic zones characterized by more severe winters (northwestern area and supra-Mediterranean) exhibited opposite patterns. In addition, a strong positive correlation was observed between CCT and CTmin. Neither strain differentiation nor the covariations between traits seem to be linked with the molecular diversity observed on the part of the mitochondrial marker COI.

Development and reproduction of Trichogramma cacoeciae Marchal, 1927 (Hymenoptera: Trichogrammatidae) on Cydia pomonella (Linnaeus, 1758) (Lepidoptera: Tortricidae) eggs

The effects of temperature treatments (15, 20, 25, 30, 35 ±1ºC), parasite age, host age, and availability of food on the development and reproduction of the egg parasite Trichogramma cacoeciae on Cydia pomonella eggs, were examined. The results showed that temperature had a profound effect on the mean number of parasitized eggs/females and the survival of immatures to the adult stage. Parasitization was highest on the 1st day after emergence, gradually decreasing for the next 2-10 days (depending on the temperature); it reached a peak at 25±1 ºC. The results also showed an inverse relationship between temperature, developmental time and mean adult longevity; the rate of development increased and longevity decreased with increasing temperature. The availability of food (honey) increased the parasitization rate, and the younger the host (C. pomonella eggs), the more susceptible it was to parasitization.

Lethal and sublethal effects of ten insecticides, used in date palm production in Saudi Arabia, on the parasitoid Trichogramma cacoeciae

Lethal and sublethal effects of ten insecticides commonly used in date palm production in Saudi Arabia were assessed in the laboratory against adults of Trichogramma cacoeciae, an important egg parasitoid of the dried fruit moth Ephestia calidella. Bioassays were conducted according to the standard protocol of the International Organization for Biological Control IOBC/WPRS/Working Group ‘Pesticides and Beneficial Organisms’. Our results showed that cypermethrin, deltamethrin, malathion, phenthoate, methomyl, and carbosulfan were moderately harmful (IOBC Class 3) to the parasitoid. The botanical insecticides azadirachtin and matrine were moderately harmful (IOBC Class 3) and slightly harmful (IOBC Class 2), respectively. The insect growth regulator pyriproxyfen was slightly harmful, whereas bistrifluron was harmless (IOBC Class 1). Regarding sublethal effects, the parasitism ratios compared to control were reduced by pyriproxyfen and azadirachtin to 49.0% and 58.0%, respectively; hence they are classified as slightly harmful insecticides (IOBC Class 2). Bistrifluron and matrine were harmless (IOBC Class 1) as parasitism ratios were reduced by 9.2% and 27.6%, respectively. Longevity of adults exposed to bistrifluron and matrine (3.6 and 3.3 days, respectively) and to pyriproxyfen and azadirachtin (1.7 and 1.3 days, respectively) was significantly lower than that in control (4.67 days). In semi-field tests, residues of most insecticides on leaves of tomato, a common host plant of lepidopteran pests parasitized by T. cacoeciae, were considered moderately harmful to harmful based on parasitoid mortality at 24 h post-treatment whereas they were slightly harmful at 7 and 14 days post-treatment

Trichogramma cacoeciae as a biological control agent of the tomato pinworm Tuta absoluta in Northeastern Tunisia

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is considered as key pest attacking tomato in Tunisia and in many other countries around the world. In order to investigate the efficacy of Trichogramma cacoeciae (Marchal) (Hymenoptera: Trichogrammatidae) for biological control of this pest in Northeastern Tunisia, releases were performed in open field conditions. T. cacoeciae showed a good efficacy on reducing the number of T. absoluta eggs and larvae when releasing 30 adults/plant in plots covered with insect-proof netting in May 2012. The results showed that this parasitoid may be a promising agent for T. absoluta biological control in Tunisia.